UNIFORM-FLOW PAST ONE (OR 2 IN TANDEM) FINITE-LENGTH CIRCULAR CYLINDER(S)

The problem of uniform flow past one (or two in tandem formation) fini te length circular cylinder(s) is investigated experimentally in the p resent paper. For the case of flow past a single finite length cylinde r, it is found that the flow that separates from the free end interact s strongly with those that separate from the sides and results in a th ree-dimensional now. This separated Bow from the free end delays the i nteraction between the separated Bows from the sides, resulting in a l ess negative wake pressure and a lower drag when compared with flow pa st an infinitely long cylinder. Spanwise effects were found to be stro nger over the longest (h/d = 8) cylinder investigated, with the spanwi se drag coefficient increasing towards the free end. Vortex shedding w ith some regularity can be detected only at y/h = 0.95 and y/h less th an or equal to 0.5 (with weak spectral peak) of the h/d = 8 cylinder, with corresponding Strouhal numbers equal to 0.08 and 0.191, respectiv ely. For flow past two tandem finite length circular cylinders, althou gh the transition from reattached flow to co-shedding flow is still ob served, due to the highly three-dimensional nature of the flow, the ch ange no longer takes place over the entire span simultaneously. When t he dimensionless spacing between the cylinders increases from one (cyl inders touching), the co-shedding flow structure was first detected ne ar the free end and its extent later expands towards the mounted end w ith further increase in cylinders spacing, at the expense of the reatt ached flow region. At very small spacing between the cylinders, a thir d flow structure which is characterised by having lower surface pressu re over the windward part of the downstream cylinder was also observed . Spanwise variation of the drag that acts on both cylinders was obser ved. The magnitude of the drag coefficient was found to be strongly de pendent on the flow structure involved and normally varies as a direct consequence of the variation in the wake pressure. The overall trend is that of higher local drag towards the free end.