Unsteady correlation between pressure and temperature field on impinging plate for dual underexpanded jets

In this paper, dual underexpanded impinging jets are experimentally studied by measuring unsteady wall static pressure and temperature fields using high response semiconductor pressure sensors and infrared imaging camera(100 captures per sec) with dual converging sonic nozzles. The flow field is also visualized by means of high speed schlieren system (up to 70000 frame per second) to clarify the unsteady behavior of the jet structures such as barrel shock wave, and Mach disk. Experiments were performed with a blow down tunnel changing the parameters such as the nozzle to plate distance, the distance between the two nozzles, and wind tunnel pressure ratio. The nozzle to plate distance L and the distance between the two nozzles H are non-dimensionalized by the nozzle diameter D covering H/D=1.5, 2.0, and 3, L/D= 2, 3, and 4, and po/pb=1.0 − 5.0, where po and pb are stagnation pressure and back pressure respectively. Although the response of the infrared camera is quite different from that of the high speed camera, the unsteady correlation between the pressure and temperature fields is confirmed under some conditions. Also the high speed schlieren pictures and the wall static pressure fluctuations suggest that the generation of the Mach disk promote the unsteady behavior of the jets. After the confirmation of the correlation, a simple way to find the severe fluctuating region can be provided according to the two dimensional unsteady temperature images without a lot of unsteady pressure measurements.