Direct Measurements of Turbulent Boundary Layer Wall Pressure Wavenumber-Frequency Spectra

Abstract

Direct measurements of streamwise wavenumber-frequency spectra of turbulent wall pressure fluctuations were made in an acoustically quiet water tunnel. A linear array of evenly spaced flush mounted pressure sensors was used to measure the wall pressure field at 48 streamwise locations. This array provided over 24 dB of resolution (sidelobe rejection) in the wavenumber domain, leading to an accurate estimate of the “convective ridge” and part of the subconvective and low wavenumber portions of the spectrum at discrete frequencies. Boundary layer parameters, including the mean wall shear stress, boundary layer thickness, displacement thickness, and momentum thickness, were derived from mean streamwise velocity measurements for 8100 < Rθ < 16,700. Time and length scales derived from these parameters were used to nondimensionalize the measured spectra. The effectiveness of different scalings for nondimensionalizing the low and convective wavenumber regions at discrete frequencies was evaluated.