ABSTRACT. An artificial neural-network-based subgrid-scale model, which is capable of predicting turbulent flows at untrained Reynolds numbers and on untrained grid resolution is developed. Providing the grid-scale strain-rate tensor alone as an input leads the model to predict a subgrid-scale stress tensor aligns with the strain-rate tensor, and the model performs similarly to the dynamic Smagorinsky model. On the other hand, providing the resolved stress tensor as an input in addition to the strain-rate tensor is found to significantly improve the prediction of the subgrid-scale stress and dissipation, thereby the accuracy and stability of the solution. In an attempt to apply the neural-network-based model trained for turbulent flows with a limited range of the Reynolds number and grid resolution to turbulent flows at untrained conditions on untrained grid resolution, special attention is given to the normalization of the input and output tensors. It is found that successful generalization of the model to turbulence for various untrained conditions and resolution is possible if distributions of the normalized inputs and outputs of the neural-network remain unchanged as the Reynolds number and grid resolution vary. In a posteriori tests of the forced and the decaying homogeneous isotropic turbulence and turbulent channel flows, the developed neural-network model is found to predict turbulence statistics more accurately, maintain the numerical stability without ad-hoc stabilization such as clipping of the excessive backscatter, and to be computationally more efficient than the algebraic dynamic SGS models.

ABSTRACT. Side jet thrust vector control has been widely used in high-speed aero-vehicles such as missiles for quick maneuverability and control during flight. These side jets operate at sonic speeds and interact with the incoming high speed flow to create a complex flow-field over the missile. We use Jatayu, which is an in-house parallel RANS solver, to study the physics of different missile flight and control parameter variation on these complex interactions. The full missile body in 3-D has been modeled on a hybrid mesh for the study. The computed results have been compared with the experiments from the literature, and a very good match has been obtained. The side jets aid in quick maneuvering of the missile by generating lateral acceleration, which has been quantified by calculating aerodynamic coefficients such as the coefficient of normal force and the nominal pitching moment coefficient. Using this data, we study the effect of the side jets on missile trajectory during different flight conditions and demonstrate that the SST k-$\omega$ model with compressibility correction can solve such complex supersonic flows, which will be of interest to CFD practitioners.

ABSTRACT. Granular and particle-laden flows appear in many industrial processes and natural hazards. The discrete nature of the constituent solid particles allows different interaction mechanisms with the neighbor particles to form flow-dependent mesoscopic structure as new transport mechanisms, like how eddies take part in turbulent flow processes. We shall present experimental evidence of these mesoscopic structure and how particle-based simulation assist the development of a rheology law for such a yield-type non-Newtonian material. We then present a regularized CFD solver to confirm the crucial role of the mesoscopic transport mechanism in capturing the unique flow phenomenon and how simulations help to advance the flow modeling.

ABSTRACT. The current study investigates the flow and sound field modifications caused by suction-blowing excitation (SBE) on a NACA0012 airfoil. The project aims to comprehend the effect of the excitation strip’s position on an airfoil’s flow and sound field. The flow approaches the airfoil at a 5o angle of attack and a Reynolds number (Re) of 5000. Solving the unsteady, two-dimensional compressible Navier-Stokes equations yield the flow and sound field with a direct numerical simlutation (DNS) approach. Flow and sound fields are also examined for stimulation on both surfaces versus excitation solely on the upper surface. Following that, the position of the excitation strip is adjusted, and the effect on the sound field is thoroughly investigated. When the SBE is applied at the trailing edge, the aerodynamic forces do not change significantly, but the sound field exhibits directivity bias. The sound intensity increases when the excitation strip is placed near the leading edge compared to the no-excitation condition. The aeroacoustic sound has been quantified using proper orthogonal decomposition

ABSTRACT. Numerical analysis of transonic flow in an idealized clean cavity is presented. The clean weapon bays are modelled as a rectangular M219 cavity having a length-to-depth ratio (L/D) of 5 with no door configuration. When the internal weapon bay is exposed to free-stream conditions, a highly unsteady flow field is encountered over and inside the weapon bay, instigating pressure fluctuations which may cause unsteady loads to surrounding structures, leading to increase in the noise. A numerical investigation of unsteady flow fields inside the weapon bays is conducted using time-accurate compressible viscous flow solvers on structured meshes. The Unsteady Reynolds-Averaged Navier Stokes (URANS) solver is applied to simulate the cavity flow and results are compared with the experimental results available in the literature. Further, the results from two commercial flow solvers viz., STARCCM+ and ANSYS FLUENT software are also compared with the experimental values. It is observed that flow unsteadiness inside the cavity is mainly due to detaching and reattaching process of the shear layer. The pressure history at a monitoring point inside the cavity is recorded to measure the unsteady field fluctuations. This data is used to find the spectral content of the pressure signal using the Fast Fourier Transform (FFT).

ABSTRACT. Computational Fluid Dynamics (CFD) is widely used across industries to solve various engineering and science problems. CFD modeling involves multiple knowledge-intensive processes such as mathematical formulation of physics and boundary conditions, geometry creation, meshing of the geometry, pre-processing, simulation, and analysis of the simulated results. As a result, the creation of an accurate CFD model becomes difficult and time-consuming for a novice CFD user. We provide a solution to this problem through CFD Guidance System (CGS) and enable a beginner to carry out a CFD modeling and simulation quickly and accurately using available CFD software.

The knowledge gap is divided into two parts, namely, semantic knowledge and tacit knowledge. Semantic knowledge is the knowledge of fluid mechanics (FM), numeric, and CFD software and code while the tacit knowledge involves user expertise. Semantic knowledge is captured in Ontologies, Knowledge Elements (KE), logics and rules whereas tacit knowledge is captured through empirical model and machine-learned model (ML). The proposed solution is realized on TCS-PREMAP and is internally called TCS Intelligent CFD Expert (TICE). The CGS helps the user in creating CFD models, carries out simulation of the created model using OpenFOAM and Ansys Fluent CFD software automatically. The simulated result is post-processed by CGS as per the set objective and a comprehensive report is generated. This report contains details of geometry, mesh, modeling details, and the simulated results.

ABSTRACT. Wind energy is a viable alternative to conventional fossil fuels, and vertical axis wind turbines (VAWTs) are gaining popularity because of their versatility and power density (power produced per unit area of land used) compared to horizontal axis wind turbines (HAWTs). In the present study, the authors utilize the less expensive reduced order modeling technique of the Actuator Line (ALM) to model the VAWTs via modifying an open-source solver Xcompat3D. The extensive validation study compares the wake characteristics and the power coefficient with the available experimental and computational results. Further, to assess the performance of the wind turbine farms, the cluster of three turbines has been utilized to optimize their separation distance (in streamwise and transverse directions) when placed in an in-line configuration. The results suggest that the optimum performance of the three-clustered turbine is obtained when the turbines are separated by 2.5 times the cylinder diameter in the transverse direction and 0.34 times the cylinder diameter in the streamwise direction. In other cases, a reduction in the combined performance is observed.

ABSTRACT. In current world scenario, wind flow studies of urban environment is getting importance primarily due to its direct relevance with the urban pollution dispersion, urban temperature studies, disease dispersion rate as well as in planning for energy efficient buildings. Hence, among various urban issues and its CFD based scientific simulations, the one which is getting more attention is wind flow over the individual urban buildings and streets as this forms the first as well as primary level of comport to the dwelling population. Any such CFD studies has many practical challenges especially when the simulation need to reflect the real time flow situation of micro scale urban region. In line with this, this article primarily explores the CFD wind flow simulations of part of Bangalore region at micro scale level.

ABSTRACT. A comprehensive understanding of wake interactions of wind turbines is essential for improving the power production of wind farms by minimizing wake losses and reducing fatigue loads on the turbines. These wake losses are sensitive to changes in the wind flow direction and yaw misalignment of the wind turbines. The present study simulates the effect of different degrees of yaw misalignment (γ = 0˚, 15˚, 30˚ and 45˚) and different directions of wind flow (ϕ = 0˚, 30˚, 45˚, and 60˚) on a 24-turbine wind farm. A detailed analysis of the time-averaged streamwise velocity and turbulence intensity is carried out to understand the impact of ϕ and γ on the wind farm performance. The results show that the wind farm wake losses are dependent on the yaw misalignment and the wind flow direction in complex and counter-intuitive ways.

ABSTRACT. Since growing students spend a lot of time at school, the ventilation performance of the classroom has a great influence on students' health and learning ability. Air ventilation performance for indoor air quality in school classrooms has emerged as an important social issue due to the increase in the number of days of continuous high concentrations of particulate matter. In the present study, numerical simulation is introduced to optimal design of air ventilation system, which can improve air ventilation performance inside school classrooms. The indoor airflow is mainly controlled by supply and return diffusers installed on the ceiling or the floor of the classrooms. Air ventilation performance is analyzed in detail using the results of numerical simulation, including streamlines, temperature and the age of air.

ABSTRACT. Most of the line replacement units for all aircrafts used in India are imported from abroad. CSIR-CMERI has developed a 2-inch pressure-reducing and shutoff valve suitable for the environmental control system of small aircraft like SARAS. The PRSOV consists of three separate valves namely, a solenoid valve, a main valve, and a relief valve for datum setting. In the present study, the design and analysis of pressure-reducing and shutoff valves operating in the range of 30 psi to 125 psi are discussed in detail. The structural analysis including vibration along with flow simulations was performed using ANSYS. It is found from experiments performed at room temperature that the designed valve performs well for the designed pressure range within the acceptable limit.

ABSTRACT. Large-eddy simulations (LES) of the flow in a wind farm sited on heterogeneously surface roughness are performed. The LES use a high-order numerical framework with a state-of-the-art subgrid-scale model and wind turbines modelled by a standard thrusting actuator-disk model. Compared to the flow in a wind farm sited on a homogeneously rough surface, the change in surface roughness affects the first and second order turbulent statistics. Different velocity deficits are constructed based on various definitions of ``upstream'' velocity. The study considers two such velocity deficit definitions and analyzes their implications for analytical modeling of these velocity deficits.

ABSTRACT. For a number of decades numerous efforts have been put in understanding the exhaust plume behavior. Such a flow physics can be observed in powered missiles and rockets, while the plume structure has an effect on the stability and performance of missiles itself, it also affects the body, such as an aircraft from which the missile has been fired, coming in its wake. Ingestion of the exhaust plume by the air intakes is one such example, in which the performance of the engine can get severely affected if the temperature of the ingested gases are higher than the acceptable value. All these and numerous other reasons call for an in-depth analysis of plume, which in itself has a complicated flow physics. Several aerodynamic complexities arises due to the fact that these exhaust jets are highly under-expanded which means the nozzle has not been able to expand the flow to match the ambient condition, and the pressure at the exit of the nozzle is higher than the ambient pressure. This gives rise to complex phenomenon like shock diamonds, Mach disc, barrel shocks. Apart from the complexities within the plume, the plume induced shock interacts with the boundary layer and this causes a shock induced separation which further adds to the complexity of the problem. The whole plume structure can be divided into three regions, namely a near field, a transition and a far-field region. The near field region can be further classified as an inviscid core and a viscous mixing layer. All the viscous phenomenon like mixing and reactions occur in the viscous mixing layer region. Furthermore at the exit of the nozzle, appears a Prandtl-Meyer expansion fan, which is typical for under-expanded jets (for over-expanded nozzle shock appears at the nozzle exit, in order to match the ambient condition), as the flow needs to be accelerated and pressure has to be reduced to match the ambient condition. These waves get reflected from the plume boundary in the form of compression waves and result in the formation of barrel shock, which, if strong, result in the formation of a normal shock at the center line, called as a Mach disc. This phenomenon is repeated downstream and result in the formation of shock diamonds which becomes weaker with enhanced mixing. Since experimental analysis provides us with limited data, in order to get a complete understanding of a flow involving such complexities numerical modelling is required and hence choice of the turbulence model becomes very important as it is already well established that specific turbulence models perform well for specific cases. This report is an attempt to establish a numerical approach to model the flow physics of the plume with all its aforementioned complexities and to understand its behavior, as well as to come up with the answer to the question, that which turbulence model is best suited for such cases. The study will act as a foundation and can be extended to pursue more complex studies like jet impingement on control surfaces of an aircraft, plume ingestion by aircraft air-intakes, etc. to name a few

ABSTRACT. A grid or lattice fins are unconventional control surfaces and they are being used in missiles and launch vehicles. They have many paneled flow channels called webs similar to honeycomb structures used in wind tunnel settling chamber, that are used over slender body configurations. The web thickness is reduced as small as possible to reduce the form drag and weight of the control surface. In the present study, at first, the effect of grid resolution and CFD models on the aerodynamic characteristics of a square concave grid fin is studied for an upstream velocity of 20 m/s. It is followed by a detailed study on the effect of upstream velocities and angle of attacks on aerodynamic coefficients. Here, the velocity and angle attacks are varied from 10 to 30 m/s and 0° to 15°. The grid fin has a non-dimensional chord length of C with five webs. The flow past the grid fin is examined with three different computational models; 4 equations k-ω SST, seven equations Reynolds Stress Model, and Large Eddy Simulation using commercial software ANSYS Fluent. The effect of grid resolution on the wake flow characteristics is examined by simulating the flow field with four different girds namely 7.92, 10.58, 15.91, and 38 million respectively. It was found that the grid resolution of 15.91 million with 5 number of cells in the thickness region showed the wake characteristics similar to fine grid resolution of 38 million. The variation in the flow field behind the wake is significant though the aerodynamics characteristics show negligible variation.

ABSTRACT. Control Surfaces are an integral part of any aircraft, especially a fighter aircraft, where the system is highly unstable and the necessary controls are provided by various control surfaces like aileron, elevon, rudder, flaps, slats etc. These surfaces are controlled by a system of computers depending on the stick input provided by the pilot. The integrity of these surfaces is of utmost importance when it comes to safety of the aircraft and the pilot. When missiles are fired in certain extreme maneuvers, control surfaces can be deflected to large angles and this can cause the missile plumes to impact on these surfaces. The present paper deals with the heat transfer analysis of missile plume on the deflected control surface (elevon) after its launch from an Indian fighter aircraft. The figure 1 shows the deflected control surface and missile at carriage location. The objective here is to study the missile plume temperature that would propagate inside the control surface (elevon) which is made of composite material and to assess the damage caused to the composite.

ABSTRACT. The missile plume ejected from a missile pose a risk to various components of aircraft that might get exposed to higher temperatures. Before clearing a firing envelope, it is therefore important to assess plume impingement characteristics for all the flight critical cases on aircraft structure especially the air intakes where there is high chance of hot gas ingestion. Hence integration of such stores on the aircraft requires standard established approach starting from missile plume simulation to the impact of the plume on the aircraft. Towards this A CFD study was carried out using Ansys Fluent to establish a numerical approach to model the flow physics of the missile plume for identification of its state variables. The plume interaction analysis was carried out using the data generated by missile vendor from CFD for both rigid plume approach and flexible plume approach. The gas ingestion characteristics across the air intake and thermal interference effects of the missile plume on various surfaces of aircraft were studied.

ABSTRACT. The nose bluntness is one of the key design parameters as it determines the aerodynamic characteristics of the body. Studies have shown that it also affects the stability of the body and plays an important role in determining the transition location. In this work, cones with varying nose radius are compared for the aerodynamics and the stability characteristics. A sharp cone is analyzed as the base geometry to understand the effect of nose bluntness. The domain is discretized using fine structured grids with high density near the surface to better capture the boundary layer features. First, laminar simulations of the flow over the cones were carried out using SU2. The boundary layer profiles were then extracted and validated with the profiles from literature. Subsequently, these profiles were fed into a python code to obtain the input file for the LST solver. The Eigen value spectrum obtained from the LST solver is analyzed for various frequencies and presence of unstable mode is captured if present. The procedure is repeated for various locations to obtain the Neutral Stability Diagrams for different cones with varying nose bluntness. The laminar flow-field is also analyzed to understand the change in flow features with increase in bluntness. It was observed that the instability region moves downstream with increase in nose radius. Hence increase in nose radius has a stabilizing effect on the flow.

ABSTRACT. Parachutes play a vital role as bluff bodies, serving as aerodynamic decelerators to stabilize and decelerate vehicles in free fall and ground vehicle applications. The intricate process of parachute inflation involves a complex interplay between fluid dynamics and structural dynamics. A model for the hemispherical folded parachute with detailed structures is established earlier [1]. In this study, we employ transient simulations of fluid-structure interaction (FSI) using LS-DYNA software to investigate the inflation dynamics of partially folded parachutes under infinite mass conditions. Initially, a flat disk parachute undergoes folding through free fall motion influenced by gravity, resulting in an intermediate folded model suitable for FSI analysis. This folded condition is taken as initial state for the FSI simulation. The study encompasses seven distinct flow conditions, comprising three cases each of constant velocity, constant density, constant dynamic pressure and constant initial mass flow rate. By analyzing the effects of these parameters on parachute dynamics, including drag coefficient, inflation time, surface area, maximum stress, and more, we aim to gain a comprehensive understanding of the parachute's behavior. Moreover, as the parachute is constructed from porous fabric material, this study incorporates the modeling of porosity.

ABSTRACT. With a rise in the production of high-performance resources, the need for efficient solvers that can exploit modern computing power also increases globally. The solution of the pressure Poisson equation for incompressible fluid mechanics problems does not satisfy the aforementioned need in terms of scalability. We present a computationally efficient solver for simulating incompressible two-phase flows using an independent transport equation for pressure, thereby avoiding the Poisson equation. The interface capturing technique used is the volume-of-fluid method under the operator-split framework, offering fully-explicit time integration. Several two-phase canonical test cases are simulated, and the results show that our solver can handle problems involving high-density ratio and surface tension effects.

ABSTRACT. Aircraft are threatened by infrared (IR) tracking missiles, which have specific wavelengths of IR signals originating from the high-temperature plume generated during flight. The aircraft exhaust gas emits mid-wave IR signals in the range of 3-5 μm wavelength. There is a need to reduce IR signals from the aircraft plume. Although flares can be used as decoys, their effectiveness is limited by the rapid advancements in IR tracking missile technology. In this study, we injected water and carbon particles to reduce the IR signal from the plume. Using the three-dimensional compressible Reynolds Averaged Navier-Stokes equations, we simulated the exhaust gas flow under cruising and ground conditions. The discrete phase model was used to describe the effects of injected particles on the flow. The total flow rate of particles represents 20% of the overall plume flow rate. In cruise conditions, the plume showed stable flow, while in ground conditions, the plume showed a different scenario with the Kelvin-Helmholtz Instability caused by the velocity difference between the plume and the air and the presence of non-negligible particles. This instability substantially influenced the characteristics of flows and particles, distinguishing them from those observed in cruising conditions.

ABSTRACT. A comprehensive solution technique has been developed to simulate the multiphase flow problems with heat and mass transfer. The numerical technique uses a finite difference in-house solver. The interface between the liquid and the gaseous phase has been captured using a coupled-level-set and volume-of-fluid (CLSVOF) method. The interface is advected with the interface velocity which is separately calculated by solving a Poisson equation for evaporation. The mass flux from the liquid to vapor region is calculated based on the temperature gradient at the liquid-vapor interface. The mass transfer rate obtained from the solver is validated against the d^2 law for a static droplet. The algorithm is then deployed to study the collision of two drops undergoing evaporation. The interaction of two identical drops undergoing head on collision in the coalescence regime is examined by activating the evaporation process. The evaporation is prominent at the interfacial space between the drops owing to the high temperature gradient. The effect of the mass transfer on the surface and kinetic energy of the drops are analyzed by considering the different levels of superheat between the drop and the ambient temperature.

ABSTRACT. In the present study, a pore-scale simulation approach is used to analyze the heat and mass transfer processes in the heat pipe. Due to its topographic structure almost similar to the sintered wick structure used in the heat pipes, Triply-Periodic-Minimal-Surface (TPMS) based Fisher-Koch lattice is used for geometrical modelling of the porous wick structure for the first time. A relatively smaller heat load of 1000 W/m2 is applied at the evaporator and condenser sections. Therefore, the effect of contact angle variation at solid-liquid-vapour interface is studied using the parameters like, temperature distribution, interface shape, and heat pipe limits (capillary, boiling, and entrainment), for heat transfer performance

ABSTRACT. Despite the recognized potential of Bubbly Drag Reduction (BDR) in reducing frictional drag along the immersed surface of marine vessels, its application has been limited due to unstable performance under various conditions. Recently, novel studies have discovered that void waves, which cluster bubbles periodically in the streamwise direction, can enhance BDR. Therefore, understanding the behavior of void waves in the two-phase boundary layer along walls is essential. However, such studies using numerical simulation have not been widely conducted due to certain limitations. To overcome these challenges, this study established a numerical model by introducing several approaches, such as changing channel shape and artificially generated void waves. The calculations were performed using the interIsoFoam solver of OpenFOAM, employing the cutting-edge iso-Advector technique for the Volume of Fluid (VOF) model. The simulation was set up based on an experimental channel with a length of 300 mm, and both flat and expanded channel conditions were utilized for comparison. The expanded channel introduces a 1° downward inclination angle at the bottom wall to induce variation in the boundary layer thickness along the streamwise direction. Bubble injection and void wave frequencies were set at 500 Hz and 50 Hz, respectively. Our results indicate that in the expanded channel conditions, the bubble clusters demonstrate an accelerated spreading speed and a decreasing moving velocity downstream, compared to those in a flat channel.

ABSTRACT. The droplet size distribution plays a crucial role in governing the behavior of dispersed droplets in multiphase flows involving spray atomizations. The extent of droplet sizes produced during the breakup and atomization process significantly affects the evaporation and subsequent combustion of fuel droplets in a combustion system. Therefore, it is imperative to grasp the statistical parameters pertaining to droplet analysis in such flows. This study numerically models the breakup and atomization process of a Liquid-Jet-in-Crossflow (LJICF) using a compressible formulation of the VOF-LPT coupled solver, which is developed in OpenFOAM. The model's validation has already been carried out for a liquid jet in a crossflow case regarding the liquid jet trajectory and mean droplet sizes, as in Bhatia et al. (2023). In this study, we present a comprehensive analysis of droplet statistics obtained from the atomization of a liquid jet in a crossflow case at two different momentum flux ratios. Further, the discussion

ABSTRACT. For Computational Fluid Structure Acoustic Interaction (CFSAI), in a 2D-Cartesian and axisymmetric coordinates, the present article is on proposition of a low-Mach approximated Perturbed Euler Equation (PEE) for hydrodynamic splitting-based model of sound generation due to unsteady fluid-flow. A single-line modification in an in-house code changes the solver from 2D to axisymmetric, and the obtained solutions for two test-cases demonstrate excellent agreement with published literature. The novel low-Mach approximated PEE helps to reduce computational cost and unnecessary spurious frequencies in acoustic solution. A coupled in-house FSAI solver, which is easy to change framework, obtain accurate acoustic solution for low-Mach cases, and easy-to-implement is presented here.

ABSTRACT. This research enables the use of high-order finite-difference schemes in conjunction with line-based methods for the investigation of the acoustic fields predicted by the compressible Navier-Stokes equations on stretched, curved, and unstructured meshes. To illustrate these procedures, upto 6th order explicit or compact spatial discretization coupled with upto 10th order implicit low-pass filters are implemented along Hamiltonian paths. Even in the presence of significant grid discontinuities, the inclusion of the low-pass high-order filter retains the advantages of the high-order technique. Application of this algorithm and benchmarking comparisons with available exact solution for the scattering and diffraction for various geometries are presented.

ABSTRACT. The study presents a comprehensive computational analysis of a multi-element combustor operating on gaseous methane-oxygen propellants, with a focus on the accurate calculation of acoustic pressure dynamics. The combustor features a multi-element configuration, with seven shear coaxial injector elements. Numerical simulations based on the complex Eddy dissipation concept (EDC) model are conducted to gain insights into the overall combustion process. Comprehensive combustion and acoustic simulations are performed to extract the sound-speed field for accurate calculation of acoustic modes in the combustor. To evaluate the influence of sound speed on acoustic pressure, a comparative study is conducted by considering both constant and variable sound speed conditions in the combustor. The analysis of the acoustic pressure modes reveals significant differences between the combustor with spatially varying sound speed fields used from CFD simulation and the conventional assumption of constant sound speed throughout the combustor. The results emphasize the importance of considering variable sound speed for the accurate estimation of acoustic pressure dynamics, especially tangential and radial modes in the combustor.

ABSTRACT. The current study is performed to understand the flow behavior as well as to calculate the noise levels inside the cavity. The nature of cavity flow is highly unsteady & due to interactions between the vortices and pressure waves, high acoustic noise is generated inside the cavity which is not favorable for the equipment installed inside the cavity. Therefore, studies are being conducted with the aim to understand the flow physics and at the same time reducing the noise-levels generated within the cavity. There is a benchmark case of M219 cavity which was tested in Wind Tunnel and the SPL values were obtained using the pressure taps installed at different locations inside the cavity. This study is conducted on M219 cavity for transonic flow using CFD and the data has been compared with the data available from the experiments. The study has been conducted for 2D cavity model as well as 3D model. The main objective is to study the turbulence inside the cavity while also determining the acoustic noise levels. The flow conditions are set in the transonic regime (M=0.85) & the Reynold’s number is calculated using the length of the cavity which comes to 67,83,000. In the present study, it is observed that the SPL values for 2D case are over-predicted when compared with the 3D case. Also, the observation was made that the aft section of the cavity was inherently having the highest noise levels.

ABSTRACT. Flow-induced acoustics in an idealized weapon bay cavity is investigated at supersonic speed of Mach 1.4 using unsteady CFD simulations involving hybrid RANS/LES models. Results are presented for a rectangular cavity of length-to-depth ratio of 6.4 and length-to-width ratio 2 using DES and IDDES approaches. The numerical findings are complemented with experimental measurements and predictive capability of popular numerical approaches assessed. The IDDES predictions of pressure power spectra are found to be in a better match with test data than the DES results. These studies indicate tonal noise level in the cavity of about 165 dB which occurs at second dominant mode. The overall sound pressure level is observed to be of the order of 175 dB, which occurs at the rear wall of the cavity. This study was precursor to the development of a flow control strategy to attenuate the sound pressure levels in the cavity.

ABSTRACT. Unsteady pressure fields around aerodynamic objects are of keen interest to the aerospace community owing to the stringent requirements in structural design and certification. The work provides an assessment of the ability of the present day DES based CFD solvers to accurately predict the unsteady pressure fields. With this objective, flow past a cylinder at Mach number 0.1285 and Reynolds number of 166000 is simulated using DES based on Spalart-Allmaras turbulence model. Sensors are placed circumferentially around the cylinder for recording the unsteady pressure field. The mean and rms values of Cp from simulations are compared with the experimental data from NASA benchmark test cases. DES captures the characteristics of Cprms in the wake but the suction peak in mean Cp curve is not fully captured. The frequency spectra match well with experiments. The amplitude of pressure fluctuations from DES are lower compared to the experimental data. Time-averaged flow-field quantities such as mean streamwise velocity, spanwise vorticity and 2D turbulent kinetic energy are compared with the experimental data and a good match is obtained. The length of recirculation region in the wake is overpredicted in the time-averaged flow field from DES. The results obtained are encouraging.

ABSTRACT. Large-eddy simulation (LES) of flow past a low mass ratio circular cylinder (m* = 10) that is free to vibrate in transverse and in-line directions is performed at supercritical flow regime (Re = 3*10^5). In this regime, the boundary layer transitions to a turbulent state via the formation of a laminar separation bubble (LSB). The regime is associated with weakened vortex shedding, which results in subdued vortex-induced vibrations (VIV). We study the effect of reduced speed, 2≤U*≤11, on the amplitude and frequency response and identify the U* range for synchronization/lock-in. The desynchronized state is associated with low amplitude oscillations due to weak vortex shedding occurring via C(2S) mode. In contrast, the vortex shedding becomes stronger in the synchronized/lock-in regime, and the mode changes to 2Po , leading to an increase in the oscillations amplitude.

ABSTRACT. Flow phenomenon past a rapidly rotating elliptic cylinder was studied numerically using ANSYS FLUENT 2021 R2. The parameters blockage ratio (β), and non-dimensional rotational velocity (α) were varied for a fixed Reynold number (Re) of 200. Vorticity contours and streamlines are analyzed and explained in detail to give insights into the flow characteristics past the elliptic cylinder. The vortices dissipate quickly as the rotational rate and blockage increases. Moreover, hovering vortices was observed for α=2. The stability of the flow was explained using the critical points in the streamline plot. The study was concluded by analyzing moment coefficient values for possible cases of autorotation.

ABSTRACT. Flow-induced vibration (FIV) of filaments attached to four side-by-side circular cylinders is studied in laminar flow regime. The effect of flexibility on the flow behavior and vibration response is investigated. The flow past vibrating filaments is compared with that for flow past rigid filaments. Periodic oscillation of the filaments with regular vortex shedding is observed at low U*, whereas there is an observed aperiodic vibration with irregular spatial flow structure at high U*. Proper Orthogonal Decomposition is carried out to identify the dominant structural mode in the response. The mode shapes are compared with the Euler-Bernoulli modes.

ABSTRACT. This study investigates the impact of bulk viscosity on the flow over two side-by-side cylinders. While Stoke's hypothesis, which assumes zero bulk viscosity, is widely used in fluid dynamics, it becomes invalid for diatomic or polyatomic gases where rotational and vibrational energy cannot be neglected. The research becomes particularly relevant for Mars missions due to the predominance of carbon dioxide gas in the Martian atmosphere, which has a significant bulk-to-shear viscosity ratio. The computational model employs a modified dbnsTurbFoam solver (density-based Navier-Stokes) in FOAM-Extend 4.0 and incorporates the bulk viscosity term in the governing equations. The simulations are conducted for diatomic and polyatomic gases, considering different gap-to-diameter ratios and Reynolds numbers. The results provide insights into flow physics and highlight the importance of considering bulk viscosity in predicting compressible flows. The study also validates the computational model by comparing it with experimental data on flow over a single rotating cylinder.

ABSTRACT. Undamped wake-induced vibration of a flexibly mounted square cylinder in the wake of a stationary square cylinder in tandem arrangement and vice-versa is explored numerically in this paper. The flexibly mounted cylinder is free to oscillate in the transverse direction while the other cylinder is held stationary. The gap between the two cylinders is fixed S/D = 5.5. simulation carried out for mass ratio, m* = 10 at Reynolds number 100 over a reduced speed, U* range of 1-15. Flow characteristics, fluid forces, and wake vortex modes are analyzed. Unsteady vortex-structure interactions between the body and the upstream wake are the source of wake-induced vibrations of the downstream cylinder. The outcomes are contrasted with an isolated flexible square cylinder with the same structural properties.

ABSTRACT. The study investigates the flow of a particle-laden gas over a circular cylinder in a four-way coupled Eulerian-Lagrangian framework. The coupling between the phases considered is a two-way exchange of momentum between the particle and fluid phases and particle-particle collisions. The laminar fluid phase is solved using a finite volume solver while the Lagrangian particle phase is solved using the discrete element method (DEM). The fluid exchanges momentum with the inertial particles by application of lift and drag forces while the particles interact with each other by collision and friction forces. The Reynolds number based on obstacle diameter is 200, which is typically in the vortex shedding regime. The flow Mach number is 0.1 and the particle Stokes number is 2.05. The addition of particles increases the drag on the cylinder in two ways: direct collision with the cylinder and changing the fluid properties around the cylinder, like an increase in stagnation pressure. The addition of particles causes a delay in boundary layer separation and reduces the dissipation of vorticity downstream in the cylinder wake. It also reduces the vortex shedding frequency and the effect is more prominent with increasing particle volume fraction. The particles are seen to be concentrated around the vortices while the vortex centers are mostly free of particles, especially in the near wake of the cylinder.

ABSTRACT. In this study, a skeletal mechanism is developed for ethylene to describe the formation of unsaturated chain hydrocarbons and polycyclic aromatic hydrocarbons (PAH) in premixed flames. The detailed mechanism, consisting of 664 species and 3582 reactions, is successfully reduced to a skeletal mechanism with 123 species and 729 reactions without affecting primary factors like ignition delay time (IDT) and laminar burning velocity. The newly derived skeletal model demonstrated improved predictive accuracy compared to experimental data. Path flux analysis (PFA) using the CHEM-RC code is employed to achieve this reduction. Validation of fourteen species C2 to C16 carbon numbers in a 1-D premixed tubular reactor using Chemkin confirmed the capability of the reduced mechanism, as the species profiles matched well with measured data.

ABSTRACT. The inlet airflow into gas turbine combustor is divided into multiple streams such as mass flow through swirler, primary air jet and dilution air jet. In the present analysis, effect of primary air stream on the combustion performance of combustor is investigated. Six different CFD simulations are carried out to represent different conditions of mass flow rate of primary air streams. The results of computational analysis are compared with results of experimental data. Better matching between the computational analysis and experimental results are observed.

The geometry of combustor is divided into multiple elements using meshing software. In addition to continuity and momentum equations, K-e turbulence model is used. Reacting flow CFD simulations are carried out using mixture fraction approach in fluent software. In the reacting flow CFD simulations 20 number of species are considered.

The mid-plane velocity, temperature and species contour is generated for six different operating conditions. With increase in primary air stream mass flow rate, the higher temperature zone is shifted to the central recirculation zone. With increase in primary air stream mass flow rate, significant drop in exit temperature of combustor is observed.

ABSTRACT. This study explores the efficient numerical simulation of fuel particle-laden flow in an aviation engine combustor using Euler-Lagrangian coupling. Incorporating Lagrangian liquid particles directly into the simulation requires assumptions about particle size and position after atomization, often leading to overlooked uncertainties in the calculations. We investigate the influence of assuming different distributions of particle positions after atomization near the fuel injector on the particle size distribution within the combustor. By conducting Euler-Lagrangian simulations in a single sector of the combustor, we find that the initial atomization near the nozzle has minimal impact on particle distribution inside the combustion chamber. Consequently, for our simulation, the effect of atomization near the nozzle is disregarded. Our findings suggest that the deviation between simulation and experimental results can be attributed to the effects of secondary breakup resulting from slit-air and evaporation. This research enhances our understanding of fuel spray behavior in aviation engine combustor.

ABSTRACT. We evaluate the Porosity/Distributed Resistance (PDR) approach-based CFD tool PDRFoam for hydrogen safety applications. The PDR approach is a hybrid computational approach where the small-scale effects are modelled semi-analytically, and the large-scale effects are explicitly calculated using CFD. Explosion variables for different cases from the HySEA project are obtained (using PDRFoam) and analysed. The predictions from PDRFoam agree with the experiments; the solver is reliable and economical compared to the body-fitted CFD solvers.

ABSTRACT. The flow field associated with Annular Truncated Plug Nozzle (ATPN) is studied using computational tools and the results are compared with experimental data. The pressure ratios considered for analysis allow the transition of the base wake from open to closed wake regime. The present work is an attempt in using DES based tool to obtain a better prediction of supersonic base flows in ATPN wherein the flow expands in both streamwise and azimuthal directions unlike linear plug nozzles. The results obtained are encouraging.

ABSTRACT. The paper discusses the CFD study of an ejector nozzle fitted around a convergent-divergent nozzle. The studies are carried out for different ejector diameters and lengths as well as different nozzle and ejector pressure ratios. The studies are performed for various freestream Mach numbers and the performance of the ejector nozzle is evaluated.

ABSTRACT. Computational Fluid Dynamics (CFD) simulations for each angle of attack are expensive when it comes to transonic airflow. To overcome this issue, model reduction techniques have been developed over the years. This paper introduces a modified approach called Proper Orthogonal Decomposition-Radial Basis Functions (POD-RBF) for model reduction in transonic airflow over an RAE 2822 wing. The proposed POD-RBF method effectively captures essential flow dynamics while significantly reducing computational complexity. The study contributes to the understanding of model reduction techniques for transonic airflow simulations, facilitating the development of efficient computational tools for aerodynamic analysis, airfoil design optimization, and accelerating research in transonic flows. The trained model showed a deviation of less than 5% from the target value.

ABSTRACT. The future tactical aircraft will pursue improvement in weight, aerodynamic drag, and overall efficiency. In pursuit of this, one of designs for fighter aircraft includes the elimination of the conventional vertical tail. This configuration without a vertical tail is referred to as a Bio Inspired Rotating Empennage (BIRE) operating similarly to a bird’s tail. To analyze the aerodynamic forces and moments, the conventional baseline aircraft, the F16, and a modified F16 shape that has had vertical tail removed, are compared in terms of aerodynamic analysis. Stability and controllability of the modified F16 are compared to the baseline F16.

ABSTRACT. In this work, a Roe-type Riemann solver for incompressible two-phase fluid flows with volume of fluid (VOF) formulation is developed for flux calculation. Two test problems, 2D Rayleigh-Taylor instability and 3D non-axisymmetric merging bubbles, are solved to access the efficacy of the Riemann solver for incompressible two-phase flows.

ABSTRACT. This study establishes a numerical model for solid-gas two-phase flow in lunar regolith particle layers. This study uses a new, two-way coupled dusty-gas flow model in a direct simulation Monte Carlo (DSMC)-discrete element method (DEM) framework. Using this model, gas–gas collisions probabilistically, while grain–grain interactions are modelled deterministically. Most crucially, a multiphase fluid-solid two-way coupling method models multiphase fluid-particle interaction macroscopically by incorporating momentum and energy exchange between the phases. The coupled framework determines how particle diameter affects gas and grain phases and dust erosion. The two-way coupled gas–grain interaction model is examined for its sensitivity to particle diameter. This work combines the first principles of physics with numerical calculations to improve plume-surface interaction predictions for future missions that will enter, descend, and land on planetary and satellite bodies.

ABSTRACT. Three-dimensional simulations of droplet impact on an inclined surface are performed using a contact-line friction model to verify the validity of the model. The comparison with corresponding experiments and numerical simulations shows that the present simulations can reproduce the experimental observation reasonably well, like the existing simulations, which use the experimentally measured relationship between the contact-line velocity and contact angle. This suggests that the contact line friction model can be used to achieve more generic simulations that do not require prior experimentation.

ABSTRACT. We have extended the traditional point-force method to model suspended small particles, incorporating a force partitioning approach for slightly larger particles. Our approach effectively handles particle sizes between the limits of the point-force and immersed-boundary methods. By distributing the momentum exchange term based on particle area and volume fraction within each grid cell, we achieve accurate results for the flow field, comparable to the highly resolved immersed boundary method. Furthermore, our method efficiently models the segregation of mixed-sized particles in liquid flows when combined with the immersed-boundary method.

ABSTRACT. We present the effect of fixed value vs fixed gradient boundary conditions (BCs) on the electric potential to simulate current-driven MHD in the open-source CFD code OpenFOAM. We find that not only boundary condition type but its place of application is also important. Our analysis and findings are related to the typical case of diverging current (from the concentrated current collector, CC), such as in a liquid metal electrode. In these cases, the current density and the magnetic field are not divergence-free. To quantify the errors associated with them, we use the sum of the local normalized errors in current density and magnetic field. We conclude that the fixed gradient BC of the electric potential applied at the CC (BC3 in our case) is the most appropriate BC to simulate these cases based on the least continuity error in the current density.

ABSTRACT. The flow in a duct with time-varying magnetic field is simulated to identify the flow characteristics and pressure gradient developed. Maxwell's equations are combined to form the induction equation which is solved along with the Navier-Stokes. The governing equations for incompressible flow are solved using Eulerian velocity correction method for pressure using finite element method. The working fluid is liquid sodium commonly encountered in nuclear industry. The code is validated for steady case before discussing unsteady cases. The production of magnetic helicity and flow helicity are also examined for various strengths of magnetic fields.

ABSTRACT. The aerodynamic characteristics of vortex dominated close-coupled canard wing body (CCWB) configuration at transonic speeds are highly sensitive to the mesh resolution. Therefore, an efficient and accurate mesh adaptation approach is essential for the numerical simulation of such configurations. In this paper, a new mesh adaptation approach based on the anisotropic 3D mesh adaptation module of ANSYS is proposed. The accuracy and efficiency of the proposed approach are validated by comparing the numerical results with experimental data. The results show that the proposed approach can capture the aerodynamic characteristics of vortex dominated CCWB configuration at high angle of attack in transonic speeds accurately and efficiently.

ABSTRACT. Metric-field based anisotropic mesh adaptation provides a suitable framework for mesh adaptation since metric fields can embed both the size and the anisotropy (stretching ratio and orientiation) of the mesh elements and optimal metric fields can be obtained analytically. Since flow around aerospace vehicles is dominated by anisotropic features such as boundary layers and shocks, using anisotropic elements can make the adaptation even more efficient. While the previous investigations focused on adapting triangular grids using metric fields, we extend the framework of metric-field based mesh adaptation to quad meshes. An optimum continuous metric field is first obtained using the minimization of interpolation error in Lq-norm from the initial triangular mesh. This continuous metric field is given as input to the metric-conforming mesh generator (e.g. BAMG, which is used in the present study) to get the discrete optimum triangular mesh for the next adaptation cycle. The triangular mesh is then recombined using a matching approach such as Blossom-Quad to generate the quad-dominant mesh.

ABSTRACT. Overset mesh methodology allows generation of independent component–wise grids, simplifying the mesh generation process. The tremendous flexibility overset mesh methodology offers makes it an ideal choice for unsteady dynamic simulations involving moving bodies. A robust and efficient overset mesh method can be effectively employed for establishing an automated CFD process. In particular, unstructured data based overset algorithms are most suited for industrial CFD solvers like HiFUN . The present work pertains to implementing an unstructured data based overset mesh methodology in the flow solver HiFUN. The overset HiFUN solver is validated for representative unsteady test cases. The capability of the overset HiFUN solver for a moving body dynamic problem involving store separation is presented

ABSTRACT. In the present study, a large eddy simulation (LES) of deflagration of a premixed methane-air mixture at a stoichiometric proportion is performed. The geometry considered is a semi-confined combustion chamber with three obstacles mounted inside. Simulations were carried out using the XiFoam solver. Two LES sub-grid scale (SGS) combustion models proposed by Charlette et al. (Combust. Flame, 2002) and Colin et al. (Phys. Fluids, 2000) are implemented in the XiFoam. The results obtained are compared against the experimental data. Both the SGS combustion models are able to predict the increase in flame speed as a result of flame obstacle interaction. Further, they show satisfactory results in capturing the acceleration and deceleration behavior of the flame speed. However, the flame speed prediction by the model of Colin et al. was slightly overestimated. Though the peak overpressure predicted by both models is in good agreement with the experimental data, the model of Colin et al. predicts an early occurrence of the peak overpressure.

ABSTRACT. Atomization and combustion of liquid oxygen (LOX) and gaseous hydrogen (GH2) is a workhorse method for large liquid rocket engines. Atomization of LOX jet under subcritical pressures is a similar process to a common liquid like water. However, presence of GH2 at 300 K, compared to the 77 K temperature of LOX jet triggers vaporization of LOX on the surface and a sheath of gaseous oxygen (O2) is formed around the cryogenic liquid core. We investigate the dynamics of such a vaporizing subcritical LOX jet with the help of an interface capturing approach based on the level‒set and volume‒of‒fluid methods. Dual‒criteria adaptive mesh driven second‒order accurate spatial discretization schemes were used along with first‒order, time‒accurate marching for solving a set of interface, momentum, mass, and energy transport equations, together with rigorous accounting of temperature‒dependent thermophysical properties. We thus account for surface tension variations due to temperature gradients in the flow field. Our study is based on a unique operating point of a circular cavity combustor shown in Figure 1 and investigated extensively by Heidmann and coworkers [1] for its ability to generate stable as well as multiple regimes of unstable LOX‒GH2 combustion. This operating point is shown in Figure 2a and results in stable LOX‒GH2 combustion depicted in Figure 2b. An intact cryogenic liquid core and bulk breakup of LOX jet are the two features of atomization under combustion conditions. We do not include combustion in the present investigations and focus only on the vaporizing LOX jet, with all other conditions being same as the operating point of Figure 2a. Assuming that the jet breakup mechanism is not affected by the temperature of background flow, we used the known conditions for stable operating point (□) and located the probable LOX jet breakup regime in the “atomization” mode of Ritz’ diagram (Figure 2c). Clearly, the morphological features of burning LOX jet core (Figure 2b) indicate a relatively undisturbed core length contrary to the expected structure of atomization of a fully turbulent LOX jet. Evidently, cold LOX jet might not break up at all unless heated externally. The computations were performed using single LOX round jet embedded in the flow of GH2 jet because the jet‒to‒jet interactions would be minimal for the selected operating point. A computational domain covering 15o‒sector of the circular cavity (see Figure 1b) was built as shown in Figure 3. Efficient handling of a dynamic interface between the GH2 and LOX phases required a dual‒criteria solution‒adaptive mesh that resolved the interface and jet core on a relatively coarse base mesh resulting in less than 106 computational cells with a fixed temporal resolution of 1 μs. We first tracked the LOX‒GH2 interface in the hope that a bulk breakup would be observed. However, the jet did not exhibit any expected tendency to break up. A snapshot at t = 1 ms in Figure 4a shows that the jet surface is perturbed at its tip and it exhibits a less developed Klystron effect due to the piling up of liquid on to the mass contained in the jet tip that is flowing against the resistance of the background flow. Jet fluid immediately upstream of the tip is under the influence of a perturbed surface with barely detectable helical surface instability. Two successive interface trackings were then performed by forcing the jet flow rate to oscillate sinusoidally and the evolved state of perturbed jet obtained using the second of these computations (A = 20 %, ω = 104 rad/s) is shown in Figure 4b at t = 1 ms. This state is characterized by multiple relatively well‒developed Klystron structures spaced equally apart. The LOX jet eventually broke up under the influence of a helical surface instability first triggered near the jet tip, as shown in Figure 5. LOX jet vaporized at 134.4 K (PC = 2.16 MPa, TLOX,in = 77 K, corresponding to □ of Figure 2a) and Figure 4 shows the maps of O2 vapor, now part of the background flow and potentially also combustible. Vapors lingered in the near‒field close to the jet injector face and in the wake of every Klystron structure. Each of these locations is characterized by at least one ring vortex structure and more varied vortex structures lie close to the jet surface. Klystron structures are continuously evolving features of the perturbed vaporizing LOX jet and the morphological features of their circular tips evolve differently as the properties of the jet surface and mixture composition evolve with time. A larger surface area is created with every fold in these tips (Figure 5) and these are also the regions where surface tension, σLOX → 0 due to heating and vaporization. Our computations reveal that a highly perturbed LOX jet generates extra surface area due to the transformation of accumulated mass into Klystron structures. Atomization then occurs at the trailing edges of the circular wing‒like extensions of the Klystron while bulk breakup commences when the helical instability triggered at the base of Klystron propagates upstream on the jet column. Future work in this area would address the influence of vanishing surface tension found in the extremities of the Klystron structures and also on the jet surface where instabilities are eventually triggered.

ABSTRACT. Ethylene-fueled scramjet combustor is numerically explored. Three-dimensional Favre Averaged Navier Stokes equations and the Reynolds stress transport equation model are solved. A single-step global reaction with infinitely fast chemistry is considered to model turbulence–chemistry interaction. Experimental condition of a backward-facing step-based combustor where gaseous ethylene is injected from the floor of the combustor into Mach 2.5 vitiated air is taken as the test case for validation. Both non-reacting and reacting flows are simulated. Insight into the combustion process inside the combustor is obtained by analyzing various flow parameters. For a higher equivalence ratio, there is significant upstream interaction. Computed wall pressure matches very well with the experimental results for non-reacting and reacting flows.

ABSTRACT. With the goal of conducting computationally inexpensive investigations, a transient reacting flow simulation tool based on Reynolds averaged Navier Stokes (RANS) through the k-ε model is described for stationary flame applications. In particular, the OpenFOAM open-source platform is employed with the Eddy Dissipation Concept (EDC) model to simulate the interaction between turbulence and chemistry. The experimental data from the turbulent, non-premixed Sandia D jet flame, is chosen for a thorough comparison of velocities, temperature, and species. The predictions demonstrate the suitability of the model for modeling turbulent non-premixed flames satisfactorily.

ABSTRACT. Large pressure loss happens during flow turns due to the secondary flows arising out of centrifugal forces or its gradients. C. R. Gerlach and E. C. Shroeder propose a novel shaping technique for minimizing pressure loss at duct elbows by weakening centrifugal force gradients. Gerlach shaping modifies the duct cross-section so that velocity is increased at the outer wall and decreased at the inner wall. In this paper, Gerlach shaping based design of bends is analysed and newer designs are proposed. Analysis of flow field inside the original and shaped geometries of two test cases namely a square elbow and RAE M 2129 S-duct show that the improvement in pressure loss characteristics is significant. The superiority of the proposed designs is hence established.

ABSTRACT. Numerical investigation of flow in a twin-intake has been carried out at different back-pressure ratios. The Reynolds number is 100000, and the free-stream Mach number is 1.5. A stabilized finite element scheme is applied to solve the three-dimensional unsteady compressible Navier-Stokes equations. Various flow regimes and shock structures formed are illustrated. These shock structures vary with increasing back pressure, starting with multiple shock reflections at the inlet for a supersonic outflow and forming a bow shock at higher back-pressures, after which unstart of the intake is observed. The effect of sideslip on the intake for a supersonic outflow is shown. The effect of back-pressure on mass flow rate, the total pressure recovery, and the distortion index is studied.

ABSTRACT. This paper presents a numerical study on the performance of a submerged S-Shaped intake kept in the vicinity of a set of cruciform wing surfaces for high subsonic flows. It is observed that placement of the wings around the intake mouth considerably affects the quality of flow through the intake. Presence of the wings mainly affects flow distortions whereas its effect on pressure recovery remains mild. Analyses of the results brings out that flow quality, compared to a wingless intake, may improve or degrade the depending on the wings placement w.r.to intake mouth. It is also observed that, effect on intake flow quality due to small side slip angle in presence of wings are not as high as in their absence. This study helped in reducing the adverse effect of the presence of wings on intake performance.

ABSTRACT. Mechanical vortex generators (VGs) are small elements projected from the wall to enhance local turbulence and hence reduce the flow separation. It is broadly classified into vane type and wheeler type VGs. Further, depending on the nature of vortex generation, the vane type VG is further classified into co-flow vortex generator and counter flow VG. The present study focuses on the effect of vane type VGs on serpentine duct of subsonic air-intake system. Numerical simulations are performed for the serpentine duct with and without VGs. The flow field describes the nature of VGs on the level of Turbulence Kinetic Energy (TKE).The shape of counter rotating VG is such that the production TKE is higher and locally confined. Hence, it has generated larger disturbance to the core flow than the co-rotating vortex generator. The locally generated turbulence helped in delay of flow separation, and at the same time the turbulence levels are high due to the presence of vortices along the flow, all the way to Aerodynamic Inlet Plane (AIP). Both counter rotating and co-rotating VGs helped on reducing flow distortion by compromising the total pressure recovery. As comparing co-rotating and counter rotating VGs, the co-rotating VG has shown better flow uniformity and total pressure recovery against counter rotating VGs due to close placement of individual vanes to generate the required vortices.

ABSTRACT. The risk of airborne disease transmission, exemplified by pandemics like the SARS-CoV-2 pandemic, is influenced by a several of complex, interrelated factors. In this work we analyze airborne disease transmission integrating three critical aspects influencing it: droplet dispersion dynamics, risk of infection, and environmental factor. Using implicit large eddy simulations coupled with discrete droplet modeling, we carryout droplet dispersion simulations to analyze the droplet dispersion dynamics during human speech. To assess the risk of infection posed by the respiratory droplets, we integrate a dose-response model that we developed into the simulation framework. The model was employed to analyze the risk of infection to virtual susceptible subjects as well as actual subjects with detailed respiratory tract and inhalation modeling. This framework is employed to analyze impact on disease transmission by inter-personal factors such as facial direction, environmental factors such as humidity and temperature as well as the factosy like wind.

ABSTRACT. Immersed boundary method (IBM) is widely used for simulating complex geometries in structured grids. However, this entails a disadvantage when simulating internal flows. The presence of grids outside the flow domain is unnecessary and leads to the wastage of memory and computational resource. The multi-block-multi-mesh framework captures the geometry using multiple blocks fitted close to the body, reducing excess grids. This also has the advantage of using different grid spacing in the blocks. The solver is parallelized using OpenMP to efficiently use a single node system.

ABSTRACT. The blood is a non-Newtonian fluid with a shearthinning nature. In case of blood flow through mechanical heart valves, most of the studies consider Newtonian model for viscosity as it involves large diameter arteries. In the current work a detailed comparative study is carried out and differences in leaflet kinematics, vortex structures, wall stresses and viscous stresses are reported. The leaflet closing velocity reduces while using non-Newtonian model. Also, the asymmetric behavior of leaflets decrease in case of non-Newtonian model. Furthermore, significant decrease in vortex structures is observed in case of non-Newtonian model as compared to Newtonian model.

ABSTRACT. Results of numerical modelling is an important supporting document for pre-market approval at US FDA. There are challenges floated by FDA for numerical modelling such as nozzle, centrifugal blood pump. A detailed numerical study of the flow inside the blood pumps shall help understand the causes of hemolysis and thrombosis of the blood while passing through the pump. It is seen that velocity profile modelled using CFD technique is highly dependent on the turbulence model chosen. The current work presents a comparative study of different turbulence models in capturing velocity profile at different radial locations in the pump. In the study, it is observed that k-ε model can capture velocity profile more accurately as compared to other turbulence models at the narrow blood passage region between rotor and housing, and at diffuser regions of the blood pump.

ABSTRACT. A numerical study of flow past a non-spinning flying disc is carried out at two different angles of attack (=0, 10 degrees), and two different Reynolds numbers, Re (=10000, 100000). Leading edge flow separation is observed for certain cases along with flow reattachment leading to a recirculation bubble whose size varies with Re and angle of attack. A secondary vortex is also observed in certain cases. The effect of Re and angle of attack on the formation of these flow features is discussed.

ABSTRACT. Large eddy simulation of flow past a dimpled circular cylinder of aspect ratio AR=1 and dimple depth(k) to the cylinder diameter(D) ratio k/D=0.01 is carried out for Re = 2e4 to Re =1.2e5. Compared to a smooth cylinder of the same AR, the drag crisis is observed at lower Re on the dimpled cylinder. We explore the mechanism of drag crisis when the boundary layer transitions from laminar to turbulent state.

ABSTRACT. An asymmetrical boundary layer separation happens along the advancing and retreating ball surfaces when a flow passes over a spinning ball. This results in the ball deflection with positive lift force, known as the Magnus effect. In contrast, at some Reynolds numbers (Re) or non-dimensional spin factors (α), the ball deflects in the opposite direction of the Magnus force, known as the inverse Magnus effect. The inverse Magnus effect is typically accompanied by the formation of a laminar separation bubble (LSB) on the advancing side of the spinning ball. In the present study, high-fidelity computations are performed for a flow over a smooth spinning ball using a transient incompressible solver of OpenFOAM. The Reynolds number for the present study is 1 × 105, and the spin factor range is from 0 to 1. The unsteady turbulent flow over a stationary smooth ball at the same Reynolds number has been carried out using RANS (Reynolds averaged Navier-Stokes), DES (detached eddy simulation). Particular attention has been given to surface pressure distributions, vortex structures behind the ball, and mean quantities such as non-dimensional drag and lift forces. The non-dimensional surface pressure distribution on the sphere has been computed using RANS and DES and compared with the experimental results. For the subcritical flows, the Strouhal number (St) for large-scale shedding due to the Kelvin–Helmholtz instability at Re=1 × 105 is ∼ 189 ( Achenbach [1]). The computed Strouhal number is ∼ 0.18 in the DES simulation is closer to the benchmark value

ABSTRACT. Numerical study of the flow past a spinning cricket ball is carried out at a fixed spin ratio (α = 0.1). α is defined as the ratio of maximum tangential speed on the surface of the cricket ball to the free stream speed. The Reynolds number, Re is based on the free stream speed and the diameter of the ball. The effect of Re has been studied on the drag, lift, and side forces acting on the spinning cricket ball. The ranges of Re at which the Magnus and the Inverse Magnus effects occur have been identified. They are characterized by positive and negative lift forces, respectively. Magnus effect on a spinning cricket ball causes it to remain in air for a longer duration than a non-spinning cricket ball. Conversely, the inverse Magnus effect exerts a negative lift on the ball causing it to ‘dip’ earlier. The presence of laminar separation bubble for the spinning cricket ball is revealed similar to that of non-spinning ball. The trailing wing tip like vortices have also been observed.

ABSTRACT. Developing accurate and reliable codes to simulate the anti-icing and de-icing processes is crucial to analyze the performance of ice protection systems either in the preliminary design stage or in the certification process. A unified computational framework consisting of air, droplet, runback water, and heat conduction solvers was developed to simulate the anti-icing process pertinent to aircraft icing. The conjugate heat transfer method was utilized to couple different solvers by exchanging thermal boundary conditions at the interface. Two solvers were developed to study the effects of updating the convective heat transfer coefficient on the anti-icing performance of the ice protection system. Analyzing the results shows that updating air flow-filed results in better agreement with experimental data compared to the decoupled solver, especially in the leading edge's aft region. Moreover, the computationally efficient loosely coupled solver shows good agreement with results obtained by the expensive tightly coupled solver.

ABSTRACT. Computational Fluid Dynamics is an important tool and has gone to be an irreplaceable part of any research in the aerospace domain. The main objective of this research work is to develop a CFD tool to solve axisymmetric compressible Navier-Stokes equations with turbulence modelling. The solver is modulated so as to allow it to be used for planar flows as well as different flow conditions (laminar or turbulent) and is also designed to handle different types of grids (structured, unstructured and hybrid). Finally, the numerical solutions of planar and axisymmetric bodies are presented and compared with the standard data.

ABSTRACT. High-energy lasers find diverse applications in the industrial and defense sectors. This paper introduces a solver developed to study the phenomenon of laser fluid interaction in a confined domain. The fluid medium is modeled with the incompressible Navier-Stokes equations employing the Boussinesq approximation and the laser beam propagation is modeled using the paraxial equation. Navier-Stokes equations are solved explicitly using stream function-vorticity formulation. The paraxial equation is solved using the split-step method. The solver is validated. Closed-domain effects are observed.

ABSTRACT. Computational Fluid Dynamics (CFD) to be simply put in layman's terms, defines the interaction of fluids with any obstacle. These interactions can be studied through experimentation and simulations. Although experimentation has been the traditional approach to study fluid flow and interactions, the way CFD is explored has undergone a massive shift with the advancements of simulation programs. For water and coastal modeling, water modeling tools have been developed and released into the market that can run multiple and repetitive simulations all whilst allowing for the possibility of changing the initial parameters. The development of such tools incurs a cost and comes with a cost to the user. With the advent of open-source tools which is a result of increased access to the internet and connectivity between scholars around the globe, numerical modeling tools are available as open-source programs rather than as a product. The benefits of working with an open-source tool come from the plausibility of any researcher from any part of the world being able to understand the core of the program and make any additions to the program itself as needed. This increases the capacity of the tool to be upgraded continuously. This paper aims to show the vast potential that the tool REEF3D holds through a case study of a CFD simulation all while highlighting how open-source tools can create a major impact on the field of CFD