Periodic Streamwise Variations of Heat Transfer Coefficients for Inline and Staggered Arrays of Circular Jets with Crossflow of Spent Air

Abstract

Heat transfer characteristics were measured for inline and staggered arrays of circular jets impinging on a surface parallel to the jet orifice plate. The impinging flow was constrained to exit in a single direction along the channel formed by the jet plate and the heat transfer surface. In this configuration the air discharged from upstream transverse rows of jet holes imposes a crossflow of increasing magnitude on the succeeding downstream jet rows. Streamwise heat transfer coefficient profiles were determined for a streamwise resolution of one-third the streamwise hole spacing, utilizing a specially constructed test surface. These profiles are characterized by significant periodic variations. The downstream amplitudes are diminished by the increasing crossflow magnitude, but can persist for at least ten rows of holes. Results were obtained for streamwise hole spacings of 5, 10, and 15 hole diameters; transverse hole spacings of 4, 6, and 8 diameters; and channel heights of 1, 2, and 3 diameters. The number of transverse hole rows was fixed at ten for all configurations. The characteristics of the periodic variations are presented and discussed as a function of the geometric parameters, including the effect of hole pattern.