Radiated noise from turbulent boundary layers in dilute polymer solutions

Abstract

Measurements of radiated noise and wall-pressure fluctuations in a turbulent boundary layer in water are described. A comparison is made between results obtained in pure water and in dilute solutions of drag-reducing polymers. A new experimental geometry was developed to obtain these measurements. The experiment consisted of a spiral-shaped plate which was rotated about its central axis in a stationary fluid, generating a turbulent boundary layer upon its inner surface. This boundary layer is shown to resemble that upon a flat plate in a uniform free stream. Wall-pressure fluctuations under the boundary layer were measured with piezoelectric transducers mounted flush in the wall of the spiral plate. Noise radiated from the boundary layer was measured with a stationary transducer located outside of the boundary layer. All measurements were made as a comparison between water and dilute polymer solutions. It is shown that polymer additives cause significant reductions in both the radiated noise and wall pressure spectra. These reductions are greatest at high frequencies, corresponding to Strouhal numbers greater than one.