A test was conducted to measure and map the unsteady pressure fluctuations over the surface of a smooth, cantilevered, circular cylinder in the supercritical Reynolds number range from 2.5 x 105 to 7.5 x 105. Lift fluctuations were measured, hot-wire wake surveys were made, and the effects of boundary-layer tripping were investigated. Power spectral densities were computed from recordings of the fluctuations, and cross-correlation coefficients were determined.
Pressure fluctuations were found to be small in magnitude but with relatively high axial correlation except at the points of flow separation. Definite evidence of periodicity was found in the pressure fluctuations excluding those in the region of flow separation. Fluctuating lift was found to be random in nature in the supercritical regime. Power spectra of wake velocity fluctuations after transition showed largely turbulent patterns with perhaps some dominance at Strouhal number near 0.4 seen on occasion. Localized boundary-layer tripping caused earlier flow separation, significant increases in pressure and lift fluctuations, a greater degree of axial correlation, and a shift in the power spectra to indicate periodic effects.
