Spectral Features of the Pressure Distribution Around a Cylinder Oscillating in Still Water

Abstract

In this paper, the pressure field on a circular cylinder oscillating close to a plane bed in still water is investigated to assess the effects of proximity of the cylinder to the bed. The range of Keulegan-Carpenter (KC) numbers of the oscillatory cylinder in the present study is between 15 and 40. The flow is in the subcritical regime since the Reynolds number of oscillating cylinder was between 9 500 and 26 000. Two different gaps between the cylinder and the plane expressed as ratios of the diameter of the cylinder are 0.1 and 1.0. The cylinder and the plane bed are both smooth. The frequency spectra of pressure measured at 36 positions around the cylinder have been obtained for the different KC numbers and the gap ratios. A wavelet analysis is used for the simultaneous time-frequency representation of the pressure fluctuations in order to identify the flow induced transitory characteristics. Such a representation shows clearly the abrupt changes in the pressure distribution that are attributed to vortex shedding. The results show that changes in the pressure variations are not at the same phase with the velocity fluctuations indicating the inability of pressures to respond to velocity variations simultaneously.