A Study on Flow Field and Behavior of Underexpanded Impinging Jet on a Cone

In order to investigate the flow field and behavior of underexpanded impinging jet on a cone, the flow field is visualized by schlieren and shadowgraph method, and the pressure distributions on the cone are measured. A cone used for the experiment has a cone angle of 120 deg. The pressure ratio across the nozzle NPR, the ratio of stagnation to ambient pressure, is varied from 2.0 to 4.0 at the nozzle-cone distance non-dimensionalized by the nozzle diameter from 1.0 to 3.5. The shape of the pressure distribution on the wall has different types at different nozzle-cone distances. The visualized flow patterns show that the expansion regions and compression regions are present in the wall jet which can also be seen from the wavy distribution of the pressure. The plate shock, which forms in front of the cone, varies its geometry between flat type and bow type dependent upon nozzle-cone distance. The flat type shock wave is obtained when it is in the expansion region of the jet and the bow type shock when in the compression region. This is qualitatively valid regardless of NPR. When the nozzle-cone distance is short, the jet is very stable without any flow oscillation, while the oscillation occurs more violently as the nozzle-cone distance becomes larger. It is probably due to the more unstable nature of the jet boundary at distance further from the nozzle.