Enhancement of jet shear layer mixing and surface heat transfer by means of acoustic disturbances

Abstract

The objective of this thesis is to investigate how the surface heat transfer of an impinging jet flow can be increased by acoustic actuation of which changes the turbulence characteristics of the flow. This work is built upon experimental studies which includes flow visualization experiments and surface heat transfer measurements. A loudspeaker system which is controlled by means of a function generator is used for the purpose of actuating impinging jet flow. Acoustic waves in different waveforms, frequencies and amplitudes which are generated by the loudspeaker reaches the jet nozzle, resulting in the formation of an oscillating component on the mean nozzle velocity since the actuation itself is in the form of a periodic fluctuation. It is this oscillating component that actuates the shear layer of the jet flow. Reynolds number is kept at 10.000 for all experimental cases. Influence of nozzle geometry is investigated by using sudden and smooth contracting (with a curvature of 5 degree polynomial) nozzles. Dimensionless nozzle-to-plate spacing is adjusted between 2, 4 and 6. Strouhal number, which is the non-dimensional form of actuation frequency is changed between0 < St < 1. The amplifier, which is used for generating sine and square waves, is set for 1.5 and 2 Volts amplitudes.