Effect of orientation on the wake of a square cylinder at low Reynolds numbers

Experimental investigation of flow past a square cylinder at Reynolds numbers of 97 and 187 is reported. Cylinder orientations of 0 to 60° with respect to the mean flow have been considered. Two-component hotwire anemometry has been adopted for velocity measurements. The wake of the cylinder has been visualized using a pulsed laser sheet to understand the flow structure. Measurements have been carried out in the near wake, mid-wake and far wake of the cylinder. The effects of orientation and Reynolds number on Strouhal number, drag coefficient, time-average and rms velocity distributions, decay of velocity fluctuations and power spectra are of interest. There is a dominant peak of vortex shedding in the near wake velocity spectra over the range of Reynolds numbers studied. The Strouhal number and drag coefficient are correlated to the cylinder angle. A change in the cylinder orientation leads to an early appearance of quasi-periodicity and hence three-dimensionality, owing to the asymmetric nature of the wake. The shape of the mean velocity profiles, fluctuations and the rate of decay show a strong dependence on the cylinder orientation in the near wake, though the dependence weakens in the far wake. Among the angles studied, the wake of a cylinder whose orientation is 22.5° with respect to the incoming flow is surprisingly vigorous, and shows strong three-dimensionality. The data of the present work is useful for assessing flow interaction with cylindrical structures of square cross-section.