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.

The structure of a jet in cross flow at low velocity ratios

“…A recent description of this closed-loop, water tunnel facility is presented in Abraham. 17 The jet diameter is 10.3 mm and the free stream cross flow speed is 2.1 m/s, i.e., only slightly higher than the rest of the data in this paper. However, the cross-flow boundary layer thickness upstream of the jet in the NUWC facility is about 14 mm.…”

“…Before discussing trends we should briefly address the effect of finite transducer size on attenuating pressure levels, relying on the detailed analysis in Abraham and Keith. 14 Corcos 15 provides estimates of the ra- tio of the measured to ''true'' wall pressure autospectrum levels as a function of the variable d/2U c for a fully developed, equilibrium turbulent boundary layer flow ͑here d is the sensor diameter and U c is the wall pressure convection velocity͒. While the current investigation has a highly nonequilibrium flow, wall pressure array measurements 16 show a net convecting field similar to an equilibrium field with albeit nonspatially homogeneous autospectrum levels.…”

Hydrodynamic and hydroelastic analyses of a plate excited by the turbulent boundary layer

“…It is clear that most of the energy of WPF is concentrated around the convective peak and then any correlation data is mainly the representation of the convective character of the TBL. Unfortunately, only few experimental data concerning direct measurements of the wavenumber-frequency spectrum are available (Abraham, 1998;Choi and Moin, 1990;Panton and Robert, 1994;Farabee and Geib, 1991;Manoha, 1996) and, among them, a big spread of the spectra magnitude at low wavenumbers is present as reported for example by Hwang and Maidanik (1990).…”

Analysis of the scaling laws for the turbulence driven panel responses

“…In fact, most of the energy of WPF is concentrated around the convective peak and any correlation data are mainly the representation of the convective character of the TBL. Only direct measurements of the wavenumberfrequency spectra could give significant insight, but only few experimental data have been made by using this approach (Abraham, 1998), due to the complexity of the experimental set-up and of the data analysis.…”