Low wavenumber turbulent boundary layer wall pressure and shear stress measurements from vibration data on a cylinder in pipe flow.

摘要

The response of a structure to turbulent boundary layer (TBL) excitation has been an area of research for roughly fifty years. However, uncertainties persist surrounding the low wavenumber levels of TBL surface pressure and shear stress spectra. In this experimental investigation, a cylindrical shell with a smooth internal surface is subjected to TBL excitation from water in fully developed pipe flow at 6.1 m/s. The cylinder's vibration response is used to inversely determine low wavenumber TBL surface pressure and shear stress levels. A three-dimensional experimental modal analysis is also conducted on the water-filled cylindrical shell to determine structural parameters used to extract these levels.;The cylinder's radial vibration response for certain lightly damped modes is used to determine TBL surface pressure at lower streamwise wavenumbers than previously reported (k1/k c 0.01). The nearly constant low wavenumber pressure level determined from these measurements is roughly 40 dB below the convective peak level. This level falls midway between the Smol'yakov (2006) and Chase (1987) TBL models and is roughly 25 dB lower than the Corcos (1964) model. The current data is a few decibels below the lower bound of related measurements in air by Farabee and Geib (1975) and Martin and Leehey (1977). Simple wavenumber white forms for the TBL surface pressure spectrum at low wavenumber are discussed.;Low wavenumber fluctuating shear stress levels in both the cross-flow and streamwise directions are determined using directionally uncoupled low-order cylinder modes in the circumferential and axial directions. This data addresses a critical gap in available literature regarding experimental low wavenumber shear stress data. The low wavenumber shear stress levels in both the cross-flow and streamwise directions are determined to be roughly 10 dB higher than those of normal pressure. As is the case for various models of TBL pressure, these measurements suggest that a nearly constant value for normalized shear stress at low wavenumber is valid over a broad range of frequencies. The same wavenumber white model forms suggested for low wavenumber TBL surface pressure are also appropriate for shear stress.