Strouhal numbers of rectangular cylinders at incidence: A review and new data

Abstract

Experimentally determined Strouhal numbers for a family of rectangular cylinders with side ratios (B/D) ranging from 0·04 to 1·0 and with angles of attack from 0° to 90° are presented. Tests were conducted both in a water channel with Reynolds numbers between 7·2 × 102 and 3·1 × 104 and in a wind tunnel with Reynolds numbers between 8·8 × 103 and 8·1 × 104, based on the projected cross stream dimension and the mean velocity. In addition, the mean drag as well as the mean and fluctuating lift were measured as functions of the angle of attack in the wind tunnel tests for B/D =0·25, 0·5 and 1. The Strouhal number of all except the thinnest plate showed qualitatively similar behavior with changing angle of attack. The general tendency is for a rapid rise in the Strouhal number to occur at relatively small angles of attack. This rapid rise is associated with reattachment of the separated shear layer. The angle of attack where reattachment and, hence, the rapid rise in Strouhal number occurs is dependent on the B/D ratio. After the sudden rise, the Strouhal number levels off with a further increase in angle of attack. As the angle of attack approaches 90°, there is a sudden decline in the value of the Strouhal number, again associated with shear layer-comer interaction (i.e. detachment). For the thinnest plate, the Strouhal number was found to be essentially independent of the angle of attack over a wide range of angles. Measured force coefficients show a strong dependence on the angle of attack, suggesting that for 0·5 ≤ B/D ≤ 2·0 there is an optimum incidence that makes most efficient use of the load-bearing capacity of the structure. The present data agree well with available results from previously published papers which are reviewed.