The scaling of the wall pressure fluctuations in polymer-modified turbulent boundary layer flow

Wall pressure fluctuations and integrated skin friction were measured benea th a turbulent boundary layer that was modified by adding drag-reducing pol ymer to the pure water flow. The measurements were performed on an axisymme tric model, equipped with an isolated cylindrical drag balance section, and placed in the test section of the 0.3048-m-diam water tunnel at ARL Penn S tate. Data were acquired at a free-stream velocity of 10.7 m/s with pure wa ter and with polymer added to the water at concentrations of 1, 5, 10, and 20 weight parts per million. Nondimensionalization of the wall pressure flu ctuation frequency spectra with traditional outer, inner, and mixed flow va riables failed to adequately collapse the data. The mean square wall pressu re fluctuations were found to scale linearly with the wall shear stress. Po lymer addition had little effect on the characteristic time scale of the fl ow. These properties were used to develop a novel form of the nondimensiona l wall pressure fluctuation spectrum that provided the best collapse of the measured data. (C) 2000 Acoustical Society of America. [S0001-4966(00)0510 7-9].