Heat transfer distribution and shadowgraph study for impinging underexpanded jets

In the present study, the influence of impinging underexpanded jets on local heat transfer is studied for nozzle pressure ratio (NPR) ranging from 2.4 to 5.1. To measure the local temperature distribution, a thin metal foil technique with Infrared camera is used. The adiabatic wall temperature is taken as the reference temperature for calculating local Nusselt number and recovery factor. The flow structure distributions captured with the shadowgraph technique are compared with the local Nusselt number and recovery factor distributions. Shadowgraph images show that the shock structure in the flow region plays an important role in governing the local heat transfer distribution over the plate. To propose a generalized correlation for local heat transfer for underexpanded jets, three contoured nozzles of exit diameter of 3.6 mm, 5.67 mm and 8.37 mm are studied. Proposed correlations for the local heat transfer show good agreement with the experimental results for larger nozzle to plate distances.