Wind tunnel tests for aerodynamic characteristics of multiple tandem circular cylinders

Multiple tandem circular cylinders are commonly used in the engineering field, and their complex aerodynamic characteristics bring a lot of difficulties in practical applications. In this study, a series of rigid model wind tunnel tests of a single circular cylinder and multiple (2,3,4) tandem circular cylinders are carried out at the Reynolds number Re= 3.4 x 104 and the spacing ratio L/D= 1.2-12.0 (ratio of center-to-center distance L between two adjacent cylinders to diameter D of a cylinder). The mean drag coefficient, fluctuating lift coefficient, pressure distribution, and Strouhal number of the single cylinder and multiple tandem cylinders are examined at the concerned L/D. Also, the effect of adding interfering cylinders on the aerodynamic characteristics is investigated by comparing the results of different numbers of the multiple tandem cylinders. The following results were obtained. Multiple tandem cylinders have the same critical spacing ratio, ranging from 3.5 to 4.0. Near the critical spacing ratio, the mean drag coefficients and fluctuating lift coefficients for the first two cylinders of the multiple tandem cylinders rise suddenly, while those for the rest of the cylinders drop abruptly. The Strouhal numbers for all the cylinders rise suddenly. Outside the critical spacing ratio, the aerodynamic characteristics of the multiple tandem cylinders are closely related to the number of cylinders, the position of cylinders as well as the spacing ratio. The increase in the number of backward interfering cylinders has a negligible effect on the aerodynamic forces of the first cylinder of multiple tandem cylinders. The increase in the number of forward interfering cylinders has a significant effect on the aerodynamic forces of the last cylinder.