Effect of Variable Phase Transverse Acoustic Fields on Coaxial Jet Forced Spread Angles

Abstract

Abstract : An experimental study on the effects of a variable phase transverse acoustic field on the inner jet spreading angle of a N2 shear coaxial jet at near critical pressures is presented. The jet spreading angle is an important parameter which characterizes the mixing between two flows. The transverse acoustic field is generated by two piezo-sirens which have a variable phase between them so the position of the jet with respect to the pressure and velocity field can be adjusted. The main parameter investigated is the spreading angle of the dark inner jet core. The angle measurements are made from approximately 1000 backlit images. The shear coaxial injector used here is similar to those used in cryogenic liquid rockets. The acoustic field is driven at a frequency of 3.0 +/- 0.1 kHz. It was observed that acoustic forcing has the strongest effect on the inner jet spreading angles at moderate values of the outer to inner jet momentum flux ratio, providing further evidence of the existence of a regime where the inner jet is most vulnerable to acoustic excitation effects.