Fluid resistance on a disk oscillating sinusoidally in a liquid at rest.

An experimental investigation was performed to study the fluid resistance acting on an oscillating disk over a wide range of Reynolds numbers. Data were reduced by the method of Fourier analysis to obtain average values of the added-mass and drag coefficients over one cycle of oscillation, i.e., kav andCDav respectively. The relationships between these coefficients and the modified Reynolds number, d2ω/v, were found to change between two regions of d2ω/v, where the flow pattern induced by the disk also changed. In the Reynolds number region where inner circulations are induced exclusively, kav and CDav decreased with an increasing d2ω/v and kav was independent of the amplitude of oscillation. In the Reynolds number region where inner and outer circulations coexist, kav was dependent only on the amplitude ratio, a/d; CDav was almost independent of d2ω>/v and correlated well with a/d, provided d2ω/v200. The maximum force on the disk during a cycle of oscillation was also examined. Empirical equations for the added-mass, drag and maximum resistance coefficients were presented for each region. The average power number, NPav, was defined and correlations for NPav were theoretically derived from those obtained for CDav.