Heat Transfer to Arrays of Impinging Jets in a Crossflow

Abstract

Convective heat transfer measurements are reported for staggered arrays of round turbulent air jets impinging upon a heated flat surface. Spent air was constrained by skirts to exit at one end of the test section, thus establishing a crossflow. Geometric variables included the jet hole diameter d, the streamwise spacing X and spanwise spacing Y between jet holes, and the standoff distance Z between the orifice plate and the target plate. Three patterns of holes, all having d = 3.5 mm, were tested. Their (X, Y) were (4d, 4d), (4d, 8d), and (8d, 4d). Values of the standoff were Z = d, 2d, and 3d; and tests were run for 4, 6, and 8 rows of holes. The airflow was varied to achieve a range of mean jet Reynolds number from 2500 to 25,000. Microfoil heat flux sensors were used to determine streamwise variations in (spanwise-averaged) heat transfer. Excellent resolution was obtained by employing a sensor whose streamwise dimension is considerably less than one hole diameter d. Heat transfer profiles were periodic, with a peak corresponding to each spanwise row of holes. Such peaks were displaced in the steamwise direction by the crossflow, and those nearest the exhaust end of the channel exhibited the largest deflections. Array-averaged heat transfer coefficients were obtained by numerically averaging the local measurements; values agree well with the results of other experiments on similar impingement-with-crossflow systems.