The present study describes the numerical investigations concerning the injection and mixing/combustion phenomena of a secondary fuel gaseous jet through a transverse slot nozzle in a wall into a supersonic stream which is uniform outside of a turbulent boundary layer.
The numerical investigations are applied to the transverse injection of hydrogen form a sonic nozzle into a supersonic airstream. The equations were solved fully-implicitly using the LU-TVD implicit scheme, and algebraic eddy viscosity model of Baldwin-Lomax was used to model the turbulence. In the species transport and energy equations with radiation effect, diffusion coefficients based Fick's law and an assumption of unit Lewis number were applied.
The main purpose of the paper is to develop the three dimension reacting flow code for the fuel injection and to device the methods of combustion/mixing enhancement. The methods are consist of two categories; the configuration change of the injection nozzle and the design change of the combustor using the cavity.
First, for the injection nozzle the parameter is aspect ratio. Aspect ratio means ratio of lateral length to streamwise width of a slit nozzle. The results show that both inside inflow and slit side vortices should be considered from a viewpoint of the mixing. The mixing efficiency becomes the smallest at two points, where the aspect ratio is less and more than unity, respectively. The total pressure loss becomes the largest at aspect ratio of unity due to the high penetration. All results imply that a streamwise very long slit is desirable with respect to the mixing and the loss.
Secondary, the investigations concern the combustion enhancement when a cavity is used for the hydrogen fuel injection through a transverse slot nozzle into a supersonic hot air stream. The cavity is of interest because a recirculating cavity flow would provide a stable flame holding while enhancing the rate of mixing or combustion. Several inclined cavities with various aft wall angle, offset ratio and length are evaluated for reactive flow characteristics. The cavity effect is discussed from a viewpoint of total pressure loss and combustion efficiency. The combustor with cavity is found to enhance mixing and combustion while increasing the pressure loss, compared with the case without cavity. But it is noted that there exists an appropriate length of cavity regarding the combustion efficiency and total pressure loss.
