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

Abstract

Fluctuating wall shear stress under turbulent boundary layer (TBL) excitation is studied 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 vibration response of the cylinder is used to inversely determine low-wavenumber TBL shear stress levels. Both the cross-flow and streamwise directions are examined using directionally uncoupled low-order cylinder modes in the circumferential and axial directions. These data address 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. A simple wavenumber white model form established for low-wavenumber TBL surface pressure is also shown to be appropriate for shear stress.