Turbulent airflow noise production and propagation patterns of a subsonic jet impinging on a flat plate

Abstract

Turbulent airflow noise production is examined utilizing a four-inch diameter jet impinging on a flat plate. The analysis utilizes cross-correlation techniques to investigate the far field sound pressure relationship to turbulent sources produced near the plate surface. The variables examined include the effects of jet speed, the angle of the plate with respect to the jet axis, the location of the turbulent source from the plate center, the location of the far-field microphone, and the plate-jet distance. The cross-correlation techniques allow discrimination of the far-field sound pressure related to the turbulent noise source located near the surface of the plate. By rotating the far-field microphones, directivity patterns are obtained for a source located a particular distance from the plate center. The resulting cloverleaf shaped directivity patterns indicate a quadrupole source, verifying Powells developments on Lighthills theory on jet noise. The variations of the parameters of the experiment allow a comparison of the directivity patterns for each condition. [Work was performed through the UCLA School of Engineering with the experimental data collected at the NASA-Ames research facility.]