EXPERIMENTAL STUDY ON FLOW CHARACTERISTICS OF A RECTANGULAR CYLINDER WITH A CROSS-SECTION OF VARIOUS WIDTH/HEIGHT RATIOS SUBMERGED IN OSCILLATORY FLOW

摘要

The forces acting upon 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 Utube water tank. Measurements were made of both in-line and transverse forces of rectangular cylinders in a wide range of Keulegan-Carpenter number (KC) from 1 to 160. The force signals were spectrally analyzed to determine the dominant frequencies, and the flow visualization technique was also employed to understand the correspondence between the flow patterns and the force coefficients. In this paper we discussed how the width/height ratio of the cylinder to influence the flow patterns and the aerodynamic characteristics of a rectangular cylinder. We found that a drag coefficient CD of the d/h=0.6 cylinder becomes the biggest beyond KC≈120, compared with other cases of the d/h cylinder in oscillatory flow. The good correlations between KC number and the flow patterns, and CD and wake width were shown. From the predominant frequency components of the fluctuating transverse forces, it was found that the values of Strouhal numbers reduced by a maximum velocity are similar to the results in the case of a uniform flow for d/h≤1.0.