INFLUENCE OF THE SHAPE OF THE ORIFICE ON THE LOCAL HEAT TRANSFER DISTRIBUTION OF A FLAT PLATE IMPINGED BY UNDER-EXPANDED SONIC JETS

摘要

Experiments are carried out for the circular, square, and equilateral triangular orifices of the same contraction ratio in order to explore the heat transfer characteristics for nozzle pressure ratios of 2.36, 3.04, 3.72, 4.4, and 5.08 at z/d = 2, 4, 6, and 8. The presence of vena contracta and shock cells and its locations are estimated from the impact pressure distribution along the axial direction. The pressure drop during the initial expansion is minimal for the equilateral triangular orifice. However, this pressure drop is comparable for the square and circular orifices. The heat transfer characteristics of the circular orifice are nearly axisymmetric, but that for non-circular jets are asymmetric, and the three dimensional effects are clearly observed. This is inferred through the spatial gradients of the Nusselt number and adiabatic wall temperature distributions. The linear correlations for the average Nusselt number are proposed for the circular, square, and equilateral triangular orifices.