Influence of the orifice shape on the local heat transfer distribution and axis switching by compressible jets impinging on flat surface

An experimental investigation is performed to study the effects of the orifice shape and Mach number (M) on the local heat transfer distribution by normally impinging compressible jets. Four different orifice cross-sections namely circular, elliptical, square and triangular are used and jets Mach number is maintained from 0.4 to 1in present study. The heat transfer is measured by thin foil IR technique for different nozzle to plate distances. To calculated Nusselt number, adiabatic wall temperature is used as a reference temperature. The stagnation point Nusselt number is significantly higher for circular orifice as compared to other three shapes while that for the elliptical orifice is minimum. Recovery factor distribution is independent of the Reynolds number and the Mach number. The square, triangular and elliptical orifice respectively undergoes a 45°, 180° and 90° axis switching.