On forces and phase lags between vortex sheddings from three tandem cylinders

This paper presents dependence of forces and flow structures on phase lags between vortex sheddings from three tandem cylinders. The flow around the three cylinders of an identical diameter D is numerically simulated at a Reynolds number Re = 200 for spacing ratios L1*= L1/D = 3.5 - 5.25 and L2* = L2/D = 3.6 - 5.5, where L1 is the center-to-center spacing between the upstream and middle cylinders, and L2 is that between the middle and downstream cylinders. The variations in L1* and L2* in these ranges correspond to the phase lags ϕ1 (between the upstream and middle cylinders) and ϕ2 (between the middle and downstream cylinders) both changing from inphase to antiphase. The flow around the cylinders is more sensitive to L1* than to L2*, while both ϕ1 and ϕ2 have more influences on cylinder 1 than on the other two. An inphase condition (ϕ1 = ϕ2 = inphase) corresponds to a high fluctuating lift and fluctuating shear-layer velocity but a small drag, Strouhal number, and time-mean shear-layer velocity for the upstream cylinder. On the other hand, an out-of-phase condition (ϕ1 = inphase/antiphase and ϕ2 = antiphase/inphase) complements the opposite, a small fluctuating lift and fluctuating shear-layer velocity.