Flowfield characteristics on a vent slot mixer in supersonic flow

A research was conducted on a new mixing device referred as a "vent slot mixer", using experimental and computational methods. The experiment was conducted in a laboratory-scale supersonic wind-tunnel of Mach number 2. Inflow air was under atmospheric air condition, and hydrogen gas was used as fuel. In addition, the computational simulation approach was performed to support the experimental result. The vent slot mixer can directly entrain the main airflow into the recirculation region, inducing complex flow structures in the recirculation region. This also leads to gradual development of the shear layer to reduce the total pressure loss mainly induced by a recompression shock. Contrary to typical shear layers of step mixer, for the vent slot mixer, two-dimensional large-scale structures and weak shocks were clearly identified around the shear layer through experimental and computational methods. When the fuel was injected from one circular injector in the recirculation region, the high fuel concentration of the vent slot mixer was evenly distributed along the spanwise direction, but with the step mixer the fuel was highly concentrated along the region downstream of the injector. Therefore, the vent slot mixer is effective to uniformly spread the fuel toward the spanwise direction in the recirculation region. As the fuel injection rate increased, the shear layer downstream of the vent slot mixer grew uniformly along the spanwise direction; consequently, shock structures such as a recompression shock and weak shocks on the shear layer were significantly mitigated at J = 3.2.