Experimental study on aerodynamic characteristics of two tandem square cylinders

Aerodynamic characteristics of two tandem square cylinders are investigated in horizontal and diagonal arrangement respectively, with the variation of the spacing ratio (i.e. the center-to-center space P versus the width B of the square cylinder) P/B = 1.75-5 at Re = 8 × 104 in the present study. The study focuses on the aerodynamic characteristics of diagonal tandem cylinders and the comparison with those of horizontal tandem cylinders. The results show that the aerodynamic characteristics of two diagonal square cylinders are distinctly different from those in the horizontal arrangement. At the small spacing, the mean and fluctuating aerodynamic coefficients, the maximum of mean negative pressures and the fluctuating pressures for diagonal tandem cylinders are noticeably larger than those of horizontal tandem cylinders due to a pair of recirculation flows. It is interesting that there are multiple peaks in the power spectra of diagonal tandem cylinders. The Strouhal numbers corresponding to the predominate peak of diagonal tandem cylinders are clearly smaller than those of horizontal tandem cylinders at the same spacing ratio. Additionally, the inter- and intra-cylinder correlations of aerodynamic forces for two types of arrangements change diversely with the variation of the spacing ratio. Moreover, the flow modes should be different from those of two horizontal tandem cylinders, which could be concluded to three regions in the investigated spacing ratio.