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 L-1(*) = L-1/D = 3.5 - 5.25 and = L-2/D = 3.6 - 5.5, where L-1 is the center-to-center spacing between the upstream and middle cylinders, and L-2 is that between the middle and downstream cylinders. The variations in L-1(*) and in these ranges correspond to the phase lags phi(1) (between the upstream and middle cylinders) and phi(2) (between the middle and downstream cylinders) both changing from inphase to antiphase. The flow around the cylinders is more sensitive to L-1(*), than to, while both phi(1) and phi(2) have more influences on cylinder 1 than on the other two. An inphase condition (phi(1) = phi(2) = 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 (phi(1) = inphase/antiphase and phi(2) = antiphase/inphase) complements the opposite, a small fluctuating lift and fluctuating shear layer velocity.