Experimental Study on Hydrodynamic Damping of an Oscillating Cylinder Under Small Keulegan-Carpenter Numbers

This paper presents an experimental study on the hydrodynamic drag and inertia coefficients, which were decomposed from the total measured force through Morison equation, of an oscillating cylinder in quiescent water under small Keulegan-Carpenter number (K) conditions. The objective of this study is to address a discrepancy demonstrated by Ren et al. (J. Fluid Mech., vol. 913, 2021, A36) where drag coefficients determined in experiments under small K conditions deviated significantly from those of the analytical solution and direct numerical simulations (DNS). Two experimental inaccuracies responsible for this deviation are identified. The first one is associated with the additional inertia force induced by the oscillating load cell, leading to an overestimation of the inertia coefficient. The second is related to the non-synchronized measurements of signals by multiple sensors. A tiny phase difference between the force (recorded by the load cells) and motion (recorded by the accelerometer) signals is demonstrated to cause significant change in the drag coefficient. Finally, a post-processing strategy is proposed in this study to reduce these inaccuracies. After implementing this strategy, the calculated force coefficients agree well with those obtained from the analytical solutions and DNS.