Observation of unsteady motion induced by counterflow jet on blunt body in hypersonic flow

초록

This study focuses on the drag reduction phenomenon caused by counterflow. Experimental studies were performed using a hypersonic shock tunnel to observe the effect of drag reduction caused by unstable counterflow. In the long penetration mode, a considerably asymmetric shock wave structure was observed. Horizontal and vertical oscillations occurred, resulting in asymmetric changes in the recirculation region when the injection pressure was low. Based on the experimental results, it was confirmed that the surface pressure decreased near recirculation regions, contributing to the drag reduction. In contrast, the occurrence of reattachment shock could result in a large increase in surface pressure. These results suggest that the drag reduction effect depends on not only the penetration length but also the flow structure. At a specific injection pressure, the Long Penetration Mode (LPM) and Short Penetration Mode (SPM) alternated; however, when the injection pressure was sufficiently high, only the SPM occurred, and a transition to a completely stable flow occurred. A maximum drag reduction of approximately 53% was observed in this hypersonic flow experiment.

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