Modeling Scramjet Flows with Variable Turbulent Prandtl and Schmidt Numbers

Xiao, Xudong; Hassan, Hassan; Baurle, Robert A.

doi:10.2514/6.2006-128

Cited by 14 publications

(4 citation statements)

References 11 publications

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“…Similar results have been reported by Keistler et al,69 who report that the PDF approach in Girimaji 70 has a highly dissipative effect on the concentration variance, resulting in poor agreements with the measurements. To avoid the high computational cost of the PDF approach, Xiao et al 71 model the high-order terms using evolution equations for the variance of mass fraction and enthalpy and by applying the procedure to two hydrogen/air chemical kinetic mechanisms for a scramjet combustor.…”

Section: Combustion Modeling Effortsmentioning

confidence: 99%

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A Critical Review of Scramjet Combustion Simulation (Invited)

Ladeinde

2009

47th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition

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A review of scramjet combustion simulation is provided in this paper. The topics covered include the fundamental problem of supersonic mixing layers, high-speed combustion modeling efforts, and actual calculations of realistic scramjet combustors. The review shows that the RANS approach dominates the turbulence modeling of the system, with only a handful of LES work. Also, virtually all the numerical works are based on low-order schemes, and the combustion models that have been used for realistic simulations solve the species evolution equations with assumed PDF closures, although there seems to be a growing use of the flamelet methods. Spray modeling for scramjet combustion has not received enough attention.2 for high-speed combustion applications, emphasizing on the salient features and shortcomings of the averaged equation set. Some of the models in Ref [1] have been implemented in VULCAN, a widely-used, multi-grid, fluxdifference-split, finite-volume code, developed by the Air Force and NASA for high-speed (ramjet, scramjet) reacting flow simulation. The precise models and solution procedure in this code are documented in White and Morrison. 2 Tishkoff et al. 3 presents the state of supersonic combustion research, including modeling and simulation, as an outcome of a joint AFRL/NASA meeting in May of 1996, in which the state-of-the-art in hydrocarbon and/or hydrogen-fueled scramjet research was examined, with suggestions for the future direction and needs of basic research in support of scramjet technology.Other relevant reviews, albeit applicable mostly to low-speed combustion, include Givi, 4 who provides a review of the state-of-the-art in subgrid scale modeling as required for large-eddy simulation (LES) of turbulent combustion. Closure complexities caused by chemical reactions are the focus, while Givi 5 presents a review devoted primarily to subgrid scale (SGS) closure based on the filtered density function (FDF), which is a method that is analogous to the probability density function (PDF) modeling. A more recent review of the FDF method is provided in Ref [6]. Heinz 7 highlights the fundamental differences between the Reynolds-averaged Navier-Stokes (RANS) and LES combustion models for premixed and non-premixed turbulent combustion.Finally, Grinstein 8 addresses modeling issues relevant to CFD of turbulent non-premixed jet flames, including subgrid and supergrid modeling. Transitional jet diffusion flames of the hydrogen/air and propane/air types are reviewed, while the jets studied involve laminar initial conditions, preferential diffusion effects, weak axial forcing, negligible streamwise vorticity, and negligible azimuthal non-uniformities, as well as the impact of aspect ratiodependent vortex topological and dynamical features on the development of the jet diffusion flame. Models for turbulence, chemical reactions, volume expansion, and heat release are discussed, as are models for the dominant features of the couplings between the various phenomena.Unlike the foregoing reviews, which either did n...

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Section: Combustion Modeling Effortsmentioning

confidence: 99%

“…It is also evident that the combustion models are fairly standardevolution equations for the species mass fractions with assumed PDF closure. Figure 4 shows a sample species concentration from the scramjet simulation of Xiao et al, 71…”

Section: Sample Scramjet Combustion Calculationsmentioning

confidence: 99%

A Critical Review of Scramjet Combustion Simulation (Invited)

Ladeinde

2009

47th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition

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“…While the smaller values of y + may in some cases mitigate the inaccuracies in wall heat flux caused by the turbulence model, changing the values of Sc t and Pr t , or using another turbulence model may also be necessary to improve agreement between the simulation and experiment. Alternatively, the implementation of dynamically calculated turbulent Schmidt and Prandtl numbers, such as the model developed by Xiao et al (2007), may be more appropriate.…”

Section: Comparison Between the Simulation And Experimentsmentioning

confidence: 99%

Mixing and combustion enhancement in a Mach 12 shape-transitioning scramjet engine

Barth¹

118

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are to investigate and characterize the flow physics behind the Mach 12 REST engine's current performance, and then attempt to improve its combustion performance by tailoring the engine's fuel injection to its internal flow field without otherwise modifying the engine geometry. To meet these aims, the engine was studied both numerically and experimentally.The first-ever combusting simulations of a REST scramjet operating at Mach 12 conditions were performed for the Mach 12 REST engine using the CFD research code US3D. The simulations covered a range of conditions, including: unfuelled engine flow, inlet-fuelled flow, and various combined inlet/combustor fuelling configurations. The simulations were found to match well with the experiments they were designed to reproduce and be compared against. A comparison of simulations with experimental inflow conditions and their equivalent flight conditions on an otherwise identical engine showed that experiments in the T4 Stalker tube reproduce engine pressure and heat flux distributions well. The tunnel condition tends to capture less incoming flow than the engine at flight conditions, which leads to the ground-tested engine over-predicting the engine equivalence ratio.The Mach 12 REST inlet was found to produce a thick "bubble-shaped" boundary layer along its bodyside compression surface, due to the compression effects of the inlet sidewalls acting on a thick turbulent boundary layer ingested from the vehicle forebody. This thick boundary layer forces the majority of inlet-captured air into a high-density, high Mach number flow region along the engine cowlside wall . The inlet also produces a symmetric pair of high-temperature swept separations that enter the engine isolator along the sidewalls of the engine. When fuel is injected from the bodyside surface of the inlet, it remains trapped inside the thick, turbulent boundary layer, where it becomes well-mixed and begins to burn just upstream of the inlet throat.i As much as 50% of this fuel is burned by the time it enters the engine isolator, while its injection and burning increases the inlet's drag by less than 5%. This burning bodyside flow region thermally compresses the remaining air flow within the engine isolator, and provides a source of heat and combustion radicals for the ignition of fuel injected further downstream. Overall combustion efficiency of inlet-injected fuel at the engine exhaust plane was found to be nearly 80% at high equivalence ratios.Flow within the Mach 12 REST combustor is strongly shock-dominated. This is caused by both the cowl closure shock train transmitted from the inlet, and a strong recompression shock generated at the start of the combustor. This recompression shock is generated by the flow passing over a backward step at the entrance to the combustor, and is reinforced on the cowlside of the engine by compression caused by the engine flow path turning to realign with the nominal direction of flight. Fuel injected from the face of the combustor step was combined with inlet injection in...

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“…This is probably due to the variability of Pradtl and Schmidt turbulent numbers. The importance of taking this factor into account is shown, for example, in [6] and [7]. In this paper constant values: Pr Sc 0.9…”

Section: Verification Of the Mathematical Modelmentioning

confidence: 99%