A Study on Flow Around Two Circular Cylinders in Staggered Arrangements (1st Report, Characteristics of Fluid Forces)

Abstract

The time-averaged and fluctuating fluid forces of two identical circular cylinders in staggered configurations were investigated experimentally at a Reynolds number of 5.5 × 104. Measurements were performed for stagger angles α=10°, 25°, 45°, 60° and 75°, and the spacing between two cylinders T/D=0.1-5.0, where α is the angle between the free-stream flow and the line connecting the centers of the cylinders, T is the gap width between the cylinders, and D is the diameter of the cylinders. The new findings for characteristics of the fluid forces of two cylinders are as follows. (i) Bistable nature of flow at a series of spacing ratio T/D is found for the setting angle α of two staged circular cylinders. Also, these are responsible for large difference in magnitudes of fluid forces acting on the two cylinders. (ii) In case of bistable flow at small spacing of two cylinders, a turbulent reattachment and detachment of gap flow between two cylinders cause flow patterns in which lift forces acting on those have greater difference. (iii) Another kind of bistable flow almost is similar to that at the critical spacing of two tandem cylinders for α=10° and 25°.