DIRECT MEASUREMENTS OF TURBULENT BOUNDARY-LAYER WALL-PRESSURE WAVE-NUMBER-FREQUENCY SPECTRA

Direct measurements of streamwise wavenumber-frequency spectra of turb ulent wall pressure fluctuations were made in an acoustically quiet wa ter tunnel. A linear army of evenly spaced flush mounted pressure sens ors was used to measure the wall pressure field at 48 streamwise locat ions. This array provided over 24 dB of resolution resolution (sidelob e rejection) in the wavenumber domain, leading to an accurate estimate of the ''convective ridge'' and part of the subconvective and low wav enumber portions of the spectrum at discrete frequencies. Boundary lay er parameters, including the mean wall shear stress, boundary layer th ickness, displacement thickness, and momentum thickness, were derived from mean streamwise velocity measurements for 8100 < R-theta < 16, 70 0. Time and length scales derived from these parameters were used to n ondimensionalize the measured spectra. The effectiveness of different scalings for nondimensionalizing the low and convective wavenumber reg ions at discrete frequencies was evaluated.