Abstract: A flow around three equispaced square cylinders arranged in equilateral left-triangular and right-triangular is numerically investigated at a Reynolds number of 100 using a finite-volume method. The spacing ratio g is set at 1.5, 2.0, 3.0, 3.5, 4.0 and 5.0 and the flow is supposed to be laminar. The numerical results show that, in the case of left-triangular arrangement, the spacing ratio has a significant effect on the flow pattern. A periodic bi-stable gap bias flow is observed at g=1.5. The bias flow effect becomes weaker gradually with the increase of spacing ratio in the range from 2.0 to 3.0, and an asymmetric flow pattern appears in the wake flow of cylinder B and C. The bias flow almost disappears and an in-phase synchronized vortex shedding can be observed at g=3.5. But it is interesting that an anti-phase synchronized vortex shedding in the wake of cylinder B and C is observed when g is greater than or equal to 4.0, and flow pattern exhibits a symmetric feature with respect to the free stream direction. In the case of right-triangular arrangement, the spacing ratio has little influence on the flow characteristics and the bias flow phenomenon isn’t observed for all spacing ratios considered. The features of drag and lift of each cylinder are significantly different from that of flow post a single square cylinder. For example, the mean drag coefficient of each cylinder is greater than that of flow around a single cylinder at g4.0 in the case of right-triangular arrangement. Meanwhile some differences of the flow patterns and the dynamics of cylinders between the flow around the three square cylinders and three circular cylinders are pointed out.

Key words: drag, flow around three square cylinders, lift, numerical simulation, spacing ratio