Measurement of Low-Wavenumber Components of Turbulent Boundary Layer Wall Pressure Fluctuations

Abstract

A taut 2 in. by 20 in. rectangular membrane was mounted flush in one wall of a subsonic wind tunnel with its long dimension in the direction of mean flow. Measurements were taken of the displacement response at the membrane midpoint to turbulent boundary layer excitation. The determination of response spectral density at resonances up to that of the (19, 1) mode for several tunnel speeds, together with measurement of membrane loss factors at these resonances, permitted calculation of low-wave-number components of wall pressure wavenumber-frequency spectral density well separated from the convective ridge. Results are compared with convective ridge levels measured previously in the same facility. Acoustic contamination was determined from the cross spectrum of settling chamber pressure and test section wall pressure. The membrane response to acoustic excitation alone was found to be appreciably below the total response. [Work supported by the Naval Ship Systems Command.]