Scalar Fluctuation Modeling for High-Speed Aeropropulsive Flows

Brinckman, Kevin; Calhoon, William H.; Dash, S. M.

doi:10.2514/1.21075

Cited by 61 publications

(34 citation statements)

References 22 publications

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“…In general the values will vary throughout the flowfield. Some work has been done in the area of variable turbulent Prandtl and Schmidt number modeling [114][115][116][117]. Most of these models relate the thermal (or mass) diffusivity to the scalar variance of temperature (or species mass fractions), then solve modeled transport equations for that variance and its dissipation rate.…”

Section: Thermal and Mass Effectsmentioning

confidence: 99%

Modeling of turbulent free shear flows

2015

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a b s t r a c tThe modeling of turbulent free shear flows is crucial to the simulation of many aerospace applications, yet often receives less attention than the modeling of wall boundary layers. Thus, while turbulence model development in general has proceeded very slowly in the past twenty years, progress for free shear flows has been even more so. This paper highlights some of the fundamental issues in modeling free shear flows for propulsion applications, presents a review of past modeling efforts, and identifies areas where further research is needed. Among the topics discussed are differences between planar and axisymmetric flows, development versus self-similar regions, the effect of compressibility and the evolution of compressibility corrections, the effect of temperature on jets, and the significance of turbulent Prandtl and Schmidt numbers for reacting shear flows. Large-eddy simulation greatly reduces the amount of empiricism in the physical modeling, but is sensitive to a number of numerical issues. This paper includes an overview of the importance of numerical scheme, mesh resolution, boundary treatment, sub-grid modeling, and filtering in conducting a successful simulation.Published by Elsevier Ltd.

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Section: Thermal and Mass Effectsmentioning

confidence: 99%

Modeling of turbulent free shear flows

2015

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“…For compressible flows simulations, the energy field also plays an important role in the flow evolution, and it is customary to extend dynamic models to the computation of the turbulent Prandtl number [36,37]. Following the similarity approach of the LDKM, the expression for the temperature-velocity correlation can be expressed exactly at the test-filter level, and the over-specified system is again solved using a least squares method:…”

Section: F Génin and S Menonmentioning

confidence: 99%

Dynamics of sonic jet injection into supersonic crossflow

Génin

Menon

2010

Journal of Turbulence

110

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The interaction between a sonic air jet and a supersonic air crossflow is simulated using large-eddy simulation (LES). A hybrid numerical methodology is used here to capture shock waves locally with minimal dissipation of the turbulent structures. The dynamic subgrid closure model employed for the LES permits a fully localized evaluation of the closure coefficients, such that there are no ad hoc adjustable parameters. Simulation of the experimental study of Santiago and Dutton (J. Propul. Power, vol. 13, 1997, pp. 264-273), where detailed measurements of the mean velocity and turbulent fluctuations have been acquired, is reported. The LES results show fairly good agreement with the experimental data for the mean and statistical fluctuations of the velocity field. The numerical study is then extended to two other jets in crossflow conditions to study the impact of the free-stream Mach number and of the jet to free-stream momentum ratio on the structure of the jet and on the dynamics of the interaction.The vortical structures of the time-averaged fields are identified and related to their equivalent in subsonic jet in crossflow. Horseshoe, counter-rotating, and steady wake vortices and also hanging vortices and windward vortex pairs are highlighted from the statistical results of all three cases. An analysis of the dynamics of the unsteady interaction is presented next. Similar to the low-speed jet in crossflow, vortex generation through Kelvin-Helmholtz instabilities is observed on the windward side of the jet. Furthermore, an unsteady deformation of the windward barrel shock is identified and found to induce the ejection of pockets of unshocked jet fluid, and highly vortical shear vortices are formed. Hanging vortices, generated by the skewed mixing layer on the sides of the jet, are found to remain quasi-steady in the course of the interaction. Large-scale and unsteady vortices along the sides of the jet column are highlighted for the lower jet to free-stream momentum ratios, whereas these instabilities appear weaker for higher momentum ratio. In this case, however, the presence of windward vortices is clearly identified. These structures form at the boundaries of the recirculation zone ahead of the shock and are convected along the upper boundary of the jet. Finally, wake vortices are observed but appear to play a minor role in the mixing process.

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“…First, accurate predictions of the time-averaged reactive scalar profiles (obtained experimentally through gas-sampling) can be achieved using 2D RANS models. [17][18][19][20][21] In some cases, this is through a trial and error procedure, as the predicted location of the flame is sensitive to the assumed state of the incoming boundary layer, the choice of hydrogen-air oxidation mechanism, and the type of turbulence closure involved. It is an open question whether a more 'high fidelity' method, such as LES or LES/RANS, can provide equivalent or better predictions.…”

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confidence: 99%

“…[17][18][19][20][21] In the experiment, vitiated air is passed through a Mach 2.5 nozzle into a stepped-wall combustor, where it mixes with sonic hydrogen injected through a vertical slot. (Figure 1) The experiments provide data for inert gas mixing (in which nitrogen gas is used to replace oxygen in the air stream) and mixing followed by combustion (with oxygen present in the air stream).…”

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confidence: 99%

LES/RANS Simulation of a Supersonic Reacting Wall Jet

Edwards

Boles

Baurle

2010

48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition

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This work presents results from large-eddy / Reynolds-averaged Navier-Stokes (LES/RANS) simulations of the well-known Burrows-Kurkov supersonic reacting wall-jet experiment. Generally good agreement with experimental mole fraction, stagnation temperature, and Pitot pressure profiles is obtained for non-reactive mixing of the hydrogen jet with a non-vitiated air stream. A lifted flame, stabilized between 10 and 22 cm downstream of the hydrogen jet, is formed for hydrogen injected into a vitiated air stream. Flame stabilization occurs closer to the hydrogen injection location when a threedimensional combustor geometry (with boundary layer development resolved on all walls) is considered. Volumetric expansion of the reactive shear layer is accompanied by the formation of large eddies which interact strongly with the reaction zone. Time averaged predictions of the reaction zone structure show an under-prediction of the peak water concentration and stagnation temperature, relative to experimental data and to results from a Reynolds-averaged Navier-Stokes calculation. If the experimental data can be considered as being accurate, this result indicates that the present LES/RANS method does not correctly capture the cascade of turbulence scales that should be resolvable on the present mesh. Instead, energy is concentrated in the very largest scales, which provide an overmixing effect that excessively cools and strains the flame. Predictions improve with the use of a low-dissipation version of the baseline piecewise parabolic advection scheme, which captures the formation of smaller-scale structures superimposed on larger structures of the order of the shear-layer width.ombustion processes occurring in high-speed propulsion devices can be strongly impacted by finite-rate chemistry and turbulence / chemistry interactions, as well as large-scale unsteady behavior caused by intermittent ignition events, shock / boundary layer interactions, and vortex dynamics. The state of the practice in high-speed engine component simulations [1] solves the Reynolds-Averaged Navier-Stokes (RANS) equations, expanded to include separate equations for species transport. Closure is usually accomplished through two-equation turbulence models in conjunction with Boussinesq and gradient-diffusion assumptions. Chemical reaction source terms are usually formulated using the law of mass action, and the effects of turbulence fluctuations on reaction rates are either completely ignored or modeled via eddy break up and/or assumed PDF methods. This standard model been used successfully in the design of scramjet-powered vehicles such as NASA's Hyper-X, the University of Queensland's HyShot program, and the U.S. Air Force's Scramjet Engine Demonstrator, but the ability of the model to handle highly transient physics of the types mentioned above is questionable at best. C Recent work [2][3][4][5] has focused on the development of a class of hybrid large-eddy simulation / Reynoldsaveraged Navier Stokes (LES/RANS) strategies specially designed for strongly-i...

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Scalar Fluctuation Modeling for High-Speed Aeropropulsive Flows

Cited by 61 publications

References 22 publications

Modeling of turbulent free shear flows

Modeling of turbulent free shear flows

Dynamics of sonic jet injection into supersonic crossflow

LES/RANS Simulation of a Supersonic Reacting Wall Jet

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