Experiments and Simulations on the Accelerating/Decelerating Flow on a Square Cylinder

We investigate the high-Reynolds accelerating and decelerating flows around a square cross-sectional cylinder through experiments and simulations. This flow has been well characterized for steady inflow conditions, but no conclusive studies are available when the inflow velocity varies. Wind-tunnel experiments are performed together with high-fidelity Large-Eddy Simulations (LES) to investigate the effect of Gaussian-type inflow accelerations and decelerations. The Reynolds number ranges between \( Re =1.720\times 10^4\) and \(6.536\times 10^4\) . The numerical results are compared with experiments, and an excellent agreement is found. During the investigated accelerations and decelerations, constant-frequency time cells are found in the wake vortex shedding. The values of the frequency between two subsequent time cells increase during the accelerations, and approaching the acceleration peak, the duration of the time cells shortens. The vortex-shedding Strouhal number decreases within the time cells since the velocity increases. The opposite occurs for the decelerating flow.