Numerical study on mixing and injection systems in supersonic combustor

Abstract

A numerical study on mixing of hydrogen injected into a supersonic air stream has been performed by solving Two-Dimensional Navier-Stokes equations. An explicit Harten-Yee Non-MUSeL Modified-flux-type TVD scheme has been used to solve the system or equations, and a zero-equation algebraic turbulence model to calculate the eddy viscosity coefficient. In this research the mixing characteristics have been investigated for several main flow and side flow inlet parameters. It has been found that recirculation plays an important role to enhance mixing by increasing the gradient of mass concentration. The performance of combustor has been investigated by varying (i) the distance of injector position from left boundary, (iii) the injector angle and (iii) the mach number of the main air stream. For varying injector distance the results show that the configuration for small distance of injector position has high mixing efficiency but the upstream recirculation cannot evolve properly which is an important factor for flame holding capability. On the other hand, the configuration for very long distance has lower mixing efficiency due to lower gradient of hydrogen mass concentration on the top of injector caused by.the expansion of side jet in both upstream and downstream of injector. For moderate distance of injector position large and elongated upstream recirculation can evolve which might be activated as a good flame holder. For varying injecting angle (taking as anticlockwise) investigation shows that small (8=30°) and large (8=120° and 150°) injecting angles have no significant upstream recirculation. Upstream recirculation is dominant for injecting angle 60° and 90°. Perpendicular injection i.e. injecting angle (8=90°) increases both the mixing efficiency and flame holding capability. Small injecting angle (8=30°) and very large injecting angle (8=150°) have good flame holding capability but not mixing efficiency. The Mach number of the air stream is changed as (3, 3.25, 3.5, 3.75 and 4). It is found that strong interaction is occurred between the main and injecting flows for higher Mach number (M=4). Higher Mach number increases both the mixing efficiency and flame holding capability. So air stream in supersonic flow having Mach number 4 might act as a good flame holder and become efficient in mixing.