Recent analytical advances in understanding the performance continuum (the thermodynamic spectrum) for air-breathing engines based on fundamental second-law considerations have clarified scramjet and ramjet operation, performance, and characteristics. Second-law based analysis is extended specifically in this work to clarify and describe the performance characteristics for dual-mode scramjet operation in the mid-speed range of flight Mach 4 to 7. This is done by a fundamental investigation of the complex but predictable interplay between heat release and irreversibilities in such an engine; results demonstrate the flow and performance character of the dual mode regime and of dual mode transition behavior. Both analytical and computational (multi-dimensional CFD) studies of sample dual-mode flow-fields are performed in order to demonstrate the second-law capability and performance and operability issues. The impact of the dual-mode regime is found to be characterized by decreasing overall irreversibility with increasing heat release, within the operability limits of the system.

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Thermodynamic Analysis of Dual-Mode Scramjet Engine Operation and Performance

A numerical investigation of an experimental dual-mode scramjet configuration is performed. Both experimental and numerical results indicate significant upstream interaction for this case. Several computational cases are examined: these include the use of jet-to-jet symmetry and entire half-duct modeling. Grid convergence, turbulence modeling, and wall temperature effects are studied in terms of wall pressure predictions and flow-field characteristics. Wall pressure comparisons between CFD and experiment show fair agreement for the jet-to-jet case. However, further computations of the entire half-duct show the development of a large sidewall separation zone extending much further upstream than the separation zone at the duct centerline. This sidewall separation is the dominant feature in the CFD-generated flowfield but is not evident in the experimental data, resulting in a unfavorable comparison between CFD and experimental data. Current work aimed at resolving this issue and at further understanding asymmetric flow-structures in dual-mode flow-fields is discussed.

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Three-Dimensional Effects in Modeling of Dual-Mode Scramjets

Asymmetric Flow-Structures in Dual Mode Scramjet Combustor With Significant Upstream Interaction

A Numerical Investigation on Shear Coaxial LOX/GH2 Jet Flame at Supercritical Pressure

Three-dimensional numerical study of a scramjet combustor

Numerical estimation of turbulence temperature fluctuation effect on hydrogen-oxygen reaction process

This paper presents an accurate and reliable numerical method for simulating compressible free shear layers in a scramjet engine. A special attention is focused upon the proper modeling effort of the turbulence and temperature fluctuation effect in the Reynolds-averaged simulations. As the specific turbulence model, a two-equation k — e model is adopted instead of the widely-used algebraic model. To take the temperature fluctuation effect into account, a two-equation type transport model is solved and the modified Arrhenius type reaction rate equation is used. Numerical simulation results for four types of flows typically found in a scramjet engine are shown, and detailed discussion is given about the prediction capability of our numerical code and the critical problems concerning free shear layers in a scramjet engine such as the effect of flow compressibility on the free shear layer growth rate, key factors to affect the flame holding and the effect of turbulence temperature fluctuation on the combustion process.

Parallel numerical simulation of compressible free shear layers in a scramjet engine

A diffusion flame by subsonic hydrogen jet injection into still air is numerically simulated with a fine grid system whose grid spacing is several times as large as the Kolmogorov scale. The computational scheme is based on a finite volume method and no turbulence model is used. The results show fairly good agreement with experiments in terms of the flame lift-off height. The fractal dimensions of interfaces are analyzed and it is shown that the fractal dimension of the hydrogen jet is around 2.4 in non-reacting regions, which coincides with the experimental measurements and that the fractal dimension decreases in reacting regions.

Satoru Ogawa

Papers

Numerical estimation of turbulence temperature fluctuation effect on hydrogen-oxygen reaction process

Parallel numerical simulation of compressible free shear layers in a scramjet engine

Numerical Analysis of Fractal Feature of Hydrogen-Air Jet Flame