Mixing of swirling jets in a supersonic duct flow

Hydrogen fuel injected into a scramjet combustor must mix rapidly if complete combustion is to occur within a reasonable streamwise distance. An experiment has been conducted to determine whether the addition of swirl will improve the mixing of a supersonic jet of fuel simulant (helium or air) injected at 30 deg to the wall into a confined Mach 2 airflow. The swirling jets were created by injecting the fuel simulant tangentially into a cylindrical chamber and accelerating it through a convergent-divergent nozzle. The flow was visualized by imaging Rayleigh scattering from a laser light sheet, and the plume penetration and cross-sectional area were obtained. The plumes from the swirling and nonswirling jets had comparable penetration and area, but the swirling jets contained substantially less mass flow, suggesting better mixing efficiency. Interaction of streamwise vorticity within the plumes of the swirling jets with their images in the duct wall caused the plumes to be inclined laterally to the freestream.