Turbulent Mixing Noise from Underexpanded Non-circular Slot Jets

This paper experimentally investigates the far-field turbulent mixing noise from underexpanded triangular and square jets. The investigations are focused on the noise from vertices and edges of these non-circular jets, and in some cases the results are compared with those of circular jets. The jet pressure ratio is varied in the range of 2 to 6, and the acoustic measurements are carried out along the jet axial plane from 37° to 135° (measured from jet exit axis). The experimental results indicate that turbulent mixing noise levels vary linearly with emission angle, notably with two different gradient values along upstream and downstream. These results are ascribed to the two different turbulent scales, viz.; large scales and fine scales, in the jet flow. The turbulent mixing noise from screeching circular jets are found to be higher compared to triangular and square jets. However at higher pressure ratios, as the screech ceases, the turbulent mixing noise from all the jets (circular and other non-circular jets) becomes similar.