Surface aerosound from a model wing/flap in an anechoic room

Abstract

The aerodynamic sound generated by a small scale wing model interacting with a 4‐in. jet has been investigated experimentally in NASA‐AMES anechoic chamber. The investigation consists of two parts. The first part is concentrated on the jet shear layer/wing interaction noise. The second part is the study of noise associated with separated flow. Cross‐correlation techniques are used to discriminate against unwanted noise. The results of experiment 1 show that the sound generated by shear layer/wing interaction is 10 dB higher than the free jet noise. A round guide attached to the jet exit reduced the farfield sound by 8 dB. The rms pressure in the nearfield is found to be inversely proportional to the third power of the distance from generating eddies. The typical Strouhal number of sound generated, based on the shear layer thickness and the mean flow speed, is 0.17. The results of the sound experiment show that on the separation side of the wing the generating eddies are located near the trailing edge, as expected. The noise generating eddies propagate downstream with the convection velocity and are not triggered until they reached the trailing edge. The convection speed is found to be 0.85 times the jet mean flow speed, as judged by signal time delays.