Flow Characteristics of a Rectangular Cylinder with a Cross-Section of Various Width/Height Ratios Submerged in Oscillatory Flow

The forces acting on and the flow patterns around a rectangular cylinder with a cross-section of width/height ratio of 0.2-3.0 submerged in oscillatory flow were studied by using a U-tube water tank. Measurements of both in-line and transverse forces on a rectangular cylinder were made in a wide range of Keulegan-Carpenter number (KC) from 1 to 160. The force signals were analyzed spectrally to obtain major frequencies. Flow visualization was also employed to confirm the relationship between flow patterns and force coefficients. In this paper we discussed the influence of the width/height ratio of the rectangular cylinder on the flow patterns and the fluid dynamic characteristics of the cylinder in oscillatory flow. It was found that the drag force coefficient C_D of the cylinder with d/h=0.6 ratios becomes the biggest beyond KC〓120, compared to that with other d/h in oscillatory flow. The good correlation between C_D and wake width has been successfully obtained. The variations of C_D values in low KC number region were classified into three groups, flat-plate-type, square-cylinder-type and circular-cylinder-type by the d/h ratio. In the cases of d/h=0.4 and 0.6, a phenomenon was found that the flat-plate-type can be shifted to square-cylinder-type by changing KC number. Based on the analysis of the major frequency components of the fluctuating transverse forces, it revealed that the value of Strouhal number reduced by the maximum velocity is similar with the result in the case of a uniform flow.