No abstract

3D numerical simulation of flow fields in a combustion chamber of a scramjet engine using an SST turbulence model with an explicit compressibility correction was performed and the results were compared to the experimental results. The characteristics of the turbulent combustion flow fields were analyzed via the numerical results and presented. In order to identify the mechanisms of turbulent combustion in supersonic flows, the evolutions of governing dimensionless parameters in the flow fields were investigated based on the theory of combustion and the available numerical results. It was found that the supersonic combustion takes place in the region of fully developed turbulence and that the strongest effects of turbulence and combustion processes appear in the vicinity of the injector. The unsteady effects and the local flame extinction phenomenon induced by turbulent flows were found to be negligibly small, and the steady flamelet approximation will hold for practical applications. scramjet, turbulent combustion, flamelet approximation, numerical simulation Citation:Gao Z X, Lee C H. A numerical study of turbulent combustion characteristics in a combustion chamber of a scramjet engine.

No abstract

A numerical method using AUSMDV scheme and k-ω SST turbulence model with an explicit compressibility correction was developed, and a 3-D numerical simulation of a supersonic flow field with a vertical sonic jet of hydrogen was performed. Good agreement between numerical results and experimental data validated the reliability of the numerical method. Whereafter, two parameters, mass-weighted average total pressure and mixing efficiency, were defined to evaluate the mixing performance of different injection schemes. Based on the numerical method and evaluation criterion, the mixing characteristics of different injection schemes were studied in detail. It was found that for the mixing field of supersonic transverse jet, the near-field mixing is controlled by convection transport while the far-field mixing is controlled by mass diffusion; the circular-hole injection causes a loss of total pressure comparable to the slot injection, but can induce a much higher mixing efficiency because of its 3-D flow characteristic; the variation of injection angle under circular-hole injection mainly affects the near-field mixing degree, and among the five injection angles studied in the present paper, angle 120° is the optimal one; with the increase of the ratio between injector space and diameter, the induced mixing efficiency increases while the caused loss of total pressure can grow greatly; the two-stage injection method designed through reducing the injector area to keep the same hydrogen mass flowrate can induce a much higher mixing efficiency while only a bit larger loss of total pressure when compared to the single-stage injection, and hence the two-stage injection is superior to the single-stage injection. The research results can direct the design of the fuel injection method in the combustor of scramjet engine. supersonic mixing, mixing efficiency, injection scheme, numerical simulation Citation:Gao Z X, Lee C H. Numerical research on mixing characteristics of different injection schemes for supersonic transverse jet.

The compressible-boundary-layer stability can be considerably influenced by base flow distortion. The distortion may originate from perturbations of flow parameters, such as the Mach number. In this paper, sensitivities of the boundary layer stability to certain flow parameters are derived analytically by utilizing the homotopy analysis (with codes shared), in conjunction with a direct-adjoint stability theory. The sensitivities can be categorized according to the routes the distortion evolves. Route I is that parameters distort the base flow (Sensitivity A), which, in turn, affect the eigenvalue of the linear stability equation (Sensitivity B). Route II gives rise to the effects of flow parameters onto eigenvalues caused by direct perturbation of the linear operators (Sensitivity C). Results indicate that Sensitivity A is characterized by the only peak found on the sensitivity profile that corresponds to the maximum gradient of base flow; for Sensitivity B, production terms, e.g., the mean-shear terms, are found to be significant, while for Sensitivity C, which is rarely discussed in existing literature, the pressure gradient terms in the momentum equations are dominant in affecting the stability via route II. Furthermore, route II can be more significant than route I. Having examined the variation of the mean shear gradient, d(ρ¯du¯/dy)/dy, near the critical layer yc, it is proven that the sensitivity of the eigenvalue to the velocity or temperature distortion is negative at yc under certain assumptions, particularly for the temperature-relevant sensitivity that has hardly been discussed before.