Hydrodynamic In-Line Force Coefficients of Oscillating Bluff Cylinders (Circular and Square) at Low Reynolds Numbers

摘要

An attempt to measure indirectly the hydrodynamic drag (c_D) and inertia (c_M) coefficients on oscillating bluff cylinders (circular and square) in quiescent fluid at low Reynolds numbers (low Stokes number) is presented. The Keulegan-Carpenter number was below 15. The experimental approach is based on performing free-decay tests of a spring-mounted cylinder submerged in a water tank. The identification of the instantaneous modal parameters (damping and frequency), via Hilbert transform, of the decaying oscillations allows the determination of (c_D) and (c_M) by direct comparison with the damping and natural frequency of the system in still air (tank without water). Advantages and shortcomings of this novel experimental approach are presented along the paper.