Non Quasi-steady Effects of a Heaving Rectangular Cylinder at Low Reynolds Number*

This study is motivated by understanding the galloping instability of rectangualr cylinders in the Reynolds number range 1,000 < Re <10,000 (based on the cylinder thickness). The particular focus of the investigation is to examine the presence of non quasi-steady behavior over a range of reduced velocity, oscillation amplitude and Reynolds number. To this end, experiments are conducted in a water tunnel to characterize the unsteady force acting on, and the boundary layer around a rectangular cylinder undergoing forced harmonic oscillation. The results show that non quasi-steady effects are present even at reduced velocities as high as 30 and oscillation amplitudes as small as 20% of the cylinder thickness. An analysis is conducted to understand the role of the non quasi-steady component of the force in gallopoing instability of the cylinder, and how this role is affected by key parameters.