Experimental study on effects of wind direction angle on Strouhal number of two square cylinders arranged in line

In practical engineering applications, the direction of the incoming wind of the two square cylinders structures arranged in line is random. In order to fully and accurately grasp the variation law of the aerodynamic characteristics of the two square cylinders with the wind direction. Firstly, the time histories of aerodynamic coefficients for the two square cylinders at different spacing ratios (i.e., the ratios of the center-to-center distance between the two cylinders to the width of the cylinders (L/D), ranging from 1.2 to 8) under different wind directions (i.e., wind direction angle α varying from 0° to 90° at an interval of 5°) were obtained by pressure measurement wind tunnel tests of the rigid model. Then, the influence of wind direction angle on the Strouhal number of the two square cylinders arranged in line was studied by comparing and analyzing the amplitude spectrum of the time history of lift coefficient. The results show that the Strouhal number of the two square cylinders arranged in line can be divided into four categories according to the wind direction angle: α=0°(tandem arrangement), 0°<α≤35°, 35°<α<80°, and 80°≤α≤90°. At α=0°, the Strouhal numbers of the two cylinders vary little with the spacing ratio, and the values are generally smaller than those of the single cylinder. At 0°<α≤35° and 35°<α<80°, the Strouhal numbers of the two cylinders jump at critical spacing ratios of 2≤L/D≤3 and 1.8≤L/D≤2, respectively. A significant amplification effect is observed after the jump. At 80°≤α≤90°, the Strouhal numbers of the two cylinders are smaller than those of the single cylinder when 1.2≤L/D≤1.4, and close to them when 3≤L/D≤8. When 1.4<L/D<3, the changing rule of the Strouhal numbers is not obvious.