Spray characteristics of a liquid fuel jet in a tandem backward-facing step cavity in supersonic flow

The influences of the backward-facing step and injection schemes on the spray characteristics of a liquid jet in a tandem backward-facing step cavity were investigated experimentally using high-speed photography and Schlieren techniques under a Mach 2.0 supersonic crossflow for the first time. The instantaneous structures of the spray and wave structures of the air-flow field were accurately captured by the high temporal resolution experimental technology. It is found that exist complex wave structures in the tandem backward-facing step cavity. A dimensionless spray factor was defined to describe the concentration of spray inside the cavity qualitatively. As a result, it is revealed that for the short backward-facing step cavity, the injection scheme near the upstream inlet has a higher penetration depth but a lower spray distribution, while the injection scheme near the cavity has a more spray distribution. For the long backward-facing step cavity, the injection scheme near the upstream inlet also has a higher penetration depth and the injection scheme near the sharp corner of the backward-facing step has a more sufficient spray distribution. The long backward-facing step cavity-based combustor with the upstream wall transverse injection is an optimized injection scheme to both improve penetration and spray distribution inside the cavity. Finally, a penetration depth formula is proposed to explain the spray distribution behaviors in a tandem backward-facing step cavity.