Experimental Facility Development Toward Sound-Excitation Effects on Forced Convection Heat Transfer

Abstract

In light of the background in periodic boundary-layer forcing as employed for flow control applications, the present work discusses the role of standing acoustic waves toward convective heat transfer modification in a turbulent straight channel flow. To this end, a dedicated low-speed wind-tunnel facility is designed, analyzed, and built, and it is specifically geared toward comprehensive investigation of sound-excited heat transfer for different aerodynamic and acoustic boundary conditions. To identify frequency ranges conducive toward exciting acoustic resonances, both in the transverse and longitudinal directions, a detailed numerical analysis of the acoustic resonance behavior is carried out. Resulting mode patterns and arising pressure nodes and antinodes are discussed in detail. On selected transverse and complex coupled modes, experimental surface temperature measurements are carried out by steady wideband liquid crystal thermometry. Findings indicate that, depending on the matched eigenfrequency and standing wave pattern, a slight elevation or reduction of heat transfer (locally and globally) is possible, whereas no change is observed for the pure traveling wave forcing. Although the acoustically induced changes are small in magnitude, the dependence on the excitation frequency is clearly quantifiable beyond the measurement error.