On the Simulation of Supersonic Flame Holder Cavities with OpenFOAM

One of the next major advancements in the aerospace industry will be hypersonic flight. However, to achieve hypersonic flight, propulsion systems capable of reaching hypersonic speeds need to be developed. One of the more promising hypersonic propulsion systems is the scramjet engine, however, several problems still need to be explored before reliable scramjet engines can be produced, the biggest being keeping the engine ignited. This has led to the use of flame holder cavities to create a region of subsonic flow within the engine to allow combustion to occur. High experimental costs make the use of computational fluid dynamic (CFD) simulations attractive to explore these problems. Numerical simulation is effective but is plagued by high computational costs. The question remains, how can we utilize CFD simulation to quickly develop scramjets? To solve this, an OpenFOAM solver, known as rssFOAM was developed to simulate supersonic combustion using finite-rate chemistry. RssFOAM is used for the simulation of a supersonic flame holder cavity corresponding to a series of experiments from the Air Force Research Laboratory (AFRL). The effect of the type of turbulence model, size of the chemical mechanism, and geometry used for simulation are explored. These results collected are intended to help with the transition between high-fidelity research-level simulations and lower-fidelity design-level simulations. Results will be compared to experimental data and prior simulation results from the AFRL. The results show that RANS turbulence models are more than capable of these types of simulations and smaller less detailed chemical mechanisms can be used. The results also show that the importance of properly capturing the boundary layer does not allow for inlet geometries to be ignored

A Non-Reacting Passive Scalar Comparison of StarCCM and OpenFOAM in a Supersonic Cavity Flame Holder

The scramjet engine equipped with a modern-day airliner would allow for very quick travel across the United States. The major problem is that designing such an engine and testing it to make sure it is safe would cost millions if not billions of dollars. Computational fluid dynamics allows for complex designs to be tested but can still take many days, weeks, or even months to complete. With the use of computational fluid dynamics (CFD), the scramjet engine can be analyzed to determine a quicker way to test and develop a reliable configuration in addition to analyzing the effects of different fuels on performance and efficiency. The current problem, when using CFD to analyze the scramjet engine, is that it cannot solve the simulation in a timely manner, which is very important in industry. While there are solvers for CFD that have chemistry for combustion, they are extraordinarily complex and again take a large amount of time to converge on a solution. Even solvers that only include a small number of species, such as five to ten, require numerous days or even weeks to converge on a solution when using HPC. Using the passive scalar function within CFD programs, various fuels can be analyzed for mixing, combustion, and performance. The passive scalar mimics injecting dyed air into the geometry; the converged solution displays how the air (fuel) would distribute throughout the geometry as time passes on. In recent years, much research has been done on the scramjet engine, but much more research and testing are needed before the scramjet engine can become widely accepted for use. Currently, scramjet engines are only utilized for military applications including aircrafts and missiles. This thesis was conducted to research the effects of using passive scalar mixing to simplify the simulation process of combustion within a scramjet engine cavity. The simulations were performed using Reynolds Average Navier Stokes, Detached Eddy Simulations, and Large Eddy Simulation solvers in StarCCM. In addition, OpenFOAM utilized the sonicFOAM solver to perform simulations. The simulations were based on the Air Force Research Lab, AFRL, scramjet testing model. To assess the accuracy of the simulation results, it is crucial to validate the simulations against experimental data. Therefore, the simulation results were compared with David Peterson’s simulation results ([5],[6],[7]) and agreed

Some Insights into the Screech Tone of Under-Expanded Supersonic Jets Using Dynamic Mode Decomposition

Jet screech is an intense pure tone which has attracted decades of research interest due to its possible detrimental effect on engineering structures. Its modes and closure mechanisms have been investigated analytically, experimentally, and numerically; however, there are still outstanding questions regarding the generation and propagation of instabilities in the near-field region. Recent studies have identified that these instabilities travel inside the jet potential during the screech process to form the complete feedback loop. Using dynamic mode decomposition on a three-dimensional pressure near field from large-eddy simulation results, the present study examines the viability of modal decomposition to provide further insights into the screech mode and its associated characteristics, and investigates the effect of temperature mixing in jet screech. The results show that modal decomposition identifies the helical structure of screech mode. Furthermore, a method is proposed to reveal the temporal evolution of dynamic screech mode. It was found that the bulk behavior of the pressure field at screech frequency propagates backward toward the nozzle exit.Ministry of Education (MOE)The authors gratefully acknowledge the support provided for this study by the Singapore Ministry of Education AcRF Tier-2 Grant (Grant No. MOE2014-T2-1-002)

Open FOAM simulations of the supersonic flow around cones at angles of attack

The supersonic flow around conical bodies is a very important issue in aerospace engineering, with many applications in internal and external supersonic aerodynamics. Non-viscous supersonic flow about yawing cones is essentially 3-dimensional, but it shows some characteristics regarding the conical flow around circular cones with zero angle of attack. In this latter case, the complete flow structure is axisymmetric and can be described by an ordinary differential equation known as the Taylor-Maccoll equation.Fil: Lorenzon, Denis. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Aeronáutica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; ArgentinaFil: Elaskar, Sergio Amado. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Aeronáutica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; Argentin

Aeroacoustics of Supersonic Jet Interacting with Solid Surfaces and its Suppression

The noise generated by supersonic jet is of primary interest in the high-speed flight. In several flight conditions jet exhaust of the propulsion system interacts with solid surfaces. For example, jet impingement on ground for a rocket lift-off, or interactions influenced by the integration of the engine with the airframe. Such complex applications require consideration of the role of acoustic-surface interactions on the noise generation of the jet and its radiation. Numerical analysis of supersonic jet noise involved in these scenarios is investigated by employing Hybrid Large Eddy Simulation – Unsteady Reynolds Averaged Simulation approach to model turbulence. First, the supersonic impinging jet noise reduction using aqueous injectors is investigated. The technique employed to suppress impingement noise, involves injecting liquid water from the ground surface. The Volume of Fluid model is adopted to simulate the two phase flow. The flow field and acoustic results agree well with the existing experimental data. The possible mechanisms of noise reduction by water injection are investigated. Second, supersonic jet noise reduction by employing the shielding effect of a flat plate parallel to the jet is investigated. The numerical simulations model the shielding effect of the flat plate on the acoustics of supersonic jet, and results agree with the corresponding experimental data. The physical mechanisms involved in the flow-surface interactions are investigated. With understanding these mechanisms, a slightly wavy plate is proposed including theoretical background to determine the parameters needed for the way wall to provide acoustic reduction efficiently. Results show that the proposed wavy shield can effectively reduce both the level and extent of the jet noise source as compared to that of a flat shield

Large-Eddy Simulation of Time Evolution and Instability of Highly Underexpanded Sonic Jets

High-pressure jet injection into quiescent air is a challenging fluid dynamics problem in the field of aerospace engineering. Although plenty of experimental, theoretical, and numerical studies have been conducted to explore this flow, there is a dearth of literature detailing the flow evolution and instability characteristics, which is vital to the mixing enhancement design and jet noise reduction. In this paper, a density-based solver for compressible supersonic flow, astroFoam, is developed based on the OpenFOAM library. Large-eddy simulations of highly underexpanded jets with nozzle pressure ratios from 5.60 to 11.21 at a Reynolds number around 10(5) are carried out with a highresolution grid. A grid-convergence study has been conducted to confirm the fidelity of the large-eddy simulation results. The large-eddy simulation results have also been validated against available literature data in terms of the time-averaged near-field properties of underexpanded jets. The turbulent transition processes are revealed based on the instantaneous flow features and are quantitatively resolved according to the jet penetration and maximum width. The vorticity analysis is conducted to understand the turbulent transition mechanism, and it is found that the vortex stretching term plays a leading role on the distortion of the vortex rings in the near field of the jets. The dominant instability modes of jets, visualized by helicity, are quantitatively revealed based on the spectrum and relative phase of pressure fluctuation. The single helical modes corresponding to a phase angle close to +/- 180 deg with the 1 + 1 helices are dominant for nozzle pressure ratios of 5.60 and 7.47, whereas the complex and multiple helices for the other two higher nozzle pressure ratios are due to the superposition of the single and double helical modes. In addition, the performance of the coarse mesh and different subgrid-scale models on capturing the dominant instability characteristics in large-eddy simulation of underexpanded jets is investigated

Development and Application of Rotation and Curvature Correction to Wray-Agarwal Turbulence Model

Computational Fluid Dynamics (CFD) is increasingly playing a significant role in the analysis and design of aircrafts, turbomachines, automobiles, and in many other industrial applications. In majority of the applications, the fluid flow is generally turbulent. The accurate prediction of turbulent flows to date remains a challenging problem in CFD. In almost all industrial applications, Reynolds-Averaged Navier-Stokes (RANS) equations in conjunction with a turbulence model are employed for simulation and prediction of turbulent flows. Currently the one-equation (namely the Spalart-Allmaras (SA) and Wray-Agarwal (WA) and two-equation (namely the k-ε and Shear Stress Transport k-ω) turbulence models remain the most widely used models in industry. However, improvements and new developments are needed to improve the accuracy of the turbulence models for wall bounded flows with separation in the presence of adverse pressure gradients, and for flows with rotation and curvature (RC) such as those encountered in turbomachinery, centrifugal pumps and the rotating machinery in other industrial devices. The goal of this research is to enable the eddy-viscosity type turbulence models to accurately account for the rotation and curvature effects. To date, there have been two approaches for inclusion of RC effects in turbulence models, which can be categorized as the “Modified Coefficients Approach” which parameterizes the model coefficients such that the growth rate of turbulent kinetic energy is either suppressed or enhanced depending upon the effect of system rotation and streamline curvature on the pressure gradient in the flow and the “Bifurcation Approach” which parameterizes the eddy-viscosity coefficient such that the equilibrium solution bifurcates from the main branch to decaying solution branches. In this research, the uncertainty quantification (UQ) is applied to examine the sensitivity of RC correction coefficients and the coefficients are modified based on the UQ analysis to improve the model’s behavior. Both these approaches are applied to the widely used turbulence models (SA, SST k-ω and WA) and they show some improvement in predictions of turbulent flow in all benchmark test cases considered, namely the flow in a 2D curved duct, flow in a 2D U-turn duct, fully developed turbulent flow in a 2D rotating channel, fully developed turbulent flow in a 2D rotating backward-facing step, flow in a rotating cavity, flow in a stationary and rotating serpentine channel, flow in a rotor-stator cavity and in a hydrocyclone as well as two wall-unbounded turbulent flow cases. All the simulations are conducted using the commercial software ANSYS Fluent and the open source CFD software OpenFOAM. The success of this research should enhance the ability of the RANS modeling for more accurate prediction of complex turbulent flows with rotation and curvature effects. In addition to the RANS modeling of RC effects, a new DES model incorporating the WA2017m-RC turbulence model (referred to as the WA2017m-RC-DES model) is developed and validated against experimental and DNS data. Further improvements are obtained with the DES model in some test cases

Validation of rhoCentralFoam for Engineering Applications of Under-Expanded Impinging Free Jets

A numerical validation study of under-expanded impinging jet is conducted using OpenFOAM, an open-source computational fluid dynamics (CFD) library. RhoCentralFoam, a density based, compressible flow solver with a two-equation shear stress transport (SST) turbulence model is used on an axisymmetric model to reduce the computation cost. Major features of the flow were compared to an experimental study by Henderson et al., with a nozzle pressure ratio (NPR) of 4.0 and nozzle to plate spacing between 1.65-4.16. Of the features measured, the Mach diamond spacing, super-sonic core, and shear layer are all accurately predicted, while the recirculation bubble in the impingement region and acoustic phenomenon are suppressed. The model is then applied pneumatic nebulizer medical device, which generates a low-pressure vortex by confining the impingement region. Several geometric features are varied to determine their influence on the rotating vortex, of which the nozzle to plate spacing was most influential