Experimental Investigation of Flow Over a Transversely Oscillating Square Cylinder at Intermediate Reynolds Number

Abstract

This paper presents an experimental study of flow over a square cylinder oscillating in transverse direction. The Reynolds number selected for present study is 485. Limited study has also been made for two other Reynolds numbers, namely, 295 and 775. The objective of the present study is to modify the nearwake flow structure using actuation of the cylinder for possible reduction in drag force. Transverse oscillations to the cylinder are provided using electromagnetic actuators. The flow field is investigated using twodimensional (2D)particle image velocimetry (PIV) system, hotwire anemometer (HWA), as well as flow visualization techniques. The effect of oscillation frequency and the amplitude on parameters like Strouhal number, drag coefficient, recirculation length, power spectrum, and Reynolds stress are studied. It is observed that the recirculation length is reduced significantly with increase in forcing frequency, and consequently drag coefficient is also reduced. For a constant forcing frequency, the vortex strength is reduced with the increase in the amplitude. Further, variation of instantaneous spanwise vorticity shows that separated shear length decreases with increase in forcing frequency. As a result, vortices are moved closer to the cylinder. These phenomena affect the forces acting on the cylinder. Lockon is also observed at a frequency close to the vortex shedding frequency of the stationary cylinder.