Measurement of turbulent boundary layer unsteady wall pressures beneath elastomer layers of various thicknesses on a plate

The attenuation of turbulence induced wall pressure fluctuations through elastomer layers was studied experimentally and analytically. Wall pressure statistics were measured downstream from a backward facing step, with no elastomer present and beneath 2, 3, and 4 mm thick elastomers in a water tunnel facility. The step height, h, was 0.635 cm, and the wall pressures were measured at non-dimensional distances of x/h = 10, 24, 36 and 54 downstream from the step. The attenuation of the wall pressure spectra beneath the elastomer layers that was measured experimentally was then compared to analytical model predictions. An analytical elastomer transfer function, which models the transfer of turbulent boundary layer wall pressures on the surface of an elastomer to the normal stresses through the elastomer, was applied to the turbulent boundary layer wall pressure spectra measured in the absence of an elastomer layer and compared to spectra measured beneath the 2, 3, and 4 mm thick elastomers. The attenuation of the turbulent boundary layer wall pressure spectra through the elastomer layer using the analytical elastomer transfer function was in excellent agreement with the attenuation measured experimentally through all thicknesses of elastomer and at all free stream velocities at which the experiments were performed.