Unsteadiness of flow separation in an asymmetric supersonic nozzle

Using flow visualization and dynamic pressure measurement technology, the shock structure and dynamic pressure on the wall in an asymmetric supersonic nozzle with flow separation were experimentally measured. The time and frequency domain features of the wall pressure were analyzed to obtain the characteristics of the unsteady flow in different modes of flow separation inside the nozzle. The results show that when the Nozzle Pressure Ratio (NPR) increased from 1.8 to 12.70, the flow field structure inside the nozzle shifted from the downward to upward pattern. On the upper wall of the nozzle, there were three different modes of flow separation: Restricted Shock Separation (RSS), end effect, and Free Shock Separation (FSS). On the lower wall, the main mode of flow separation was FSS. In the RSS mode, the separation data began to deviate from the Schmucker's criterion. In both the RSS and end effect modes, the wall in the intermittence region was under low-frequency pressure and the shock motion exhibited obvious low-frequency characteristics. In the end effect mode, the frequency value was slightly higher as the reattachment point comes in very close proximity to the nozzle lip, the separated shear layer impinges on the nozzle exit, and instability of the separated shear layer has obvious influence on motion of the separation shock. © 2022, Beihang University Aerospace Knowledge Press. All right reserved.