Convective heat transfer characteristics from combined mechanical and supply pulsed radial reattaching jets

Abstract

The heat transfer characteristics of combined mechanically and supply pulsated radial reattaching jets, CPRJR, were documented as a function of nozzle exit angle (0° and 20°), non-dimensional gap height (0.05 and 0.13), non-dimensional flow guide height (0.8 and 1.16), mechanical pulsation rate (5 and 10 Hz), mechanical to supply pulsation rate (1:1, 1:2, 1:3, and 1:4), phase angle (0° and 180°), and Reynolds number (1683 and 2366). Air was forced through a supply pulsation mechanism and then through a pulsated nozzle diverter apparatus. The air impinged on a heated plate where instantaneous heat flux and surface temperature measurements were collected and analyzed on instantaneous, ensemble-averaged, and area-averaged bases. CPRJR heat transfer can be characterized as a frequency interference of mechanical and supply pulsation effects. Significant improvement, up to 72%, over the corresponding mechanical pulsation case was found to occur for a supply-to-mechanical ratio of 3:1 with a phase angle of 0°. In general, the increased heat transfer rates were associated with the an increase in surface-directed momentum caused by increased cycle “on” mass flow rate and corresponding entrainment.