Experimental study of wakes behind submerged solid plate and porous plate

Wake flows of a submerged solid plate and a porous plate have been studied experimentally at sufficiently large ambient Reynolds numbers. Behind porous plates of relatively small porosity, ß - 19% to 30%. an unsteady bubble (UB) wake was formed. As porosity increased to a critical value, ß = 51%. flow meandering stopped occurring, a stable recirculating bubble (SB) was formed. The wakes ofa7.5 cm high submerged solid plate were investigated withdifferent water depth H and water layer above the plate, H 1 . For a thin layer of overflow, H 1 / H= 0.12, vortex shedding wasobservedinthe wake. The vigour of the shedding reduced becaminga less vigorous unsteady bubble (UB)as H 1 / H was increased to 0.21. When the overflow depth islarger than the height of the submerged plate, for instance H 1 ∣H = 0.56, a stable bubble (SB) occurred. A strong three-dimensional effect was observed in the near wake and it appears to be a quasi-two dimensional flow at a downstream distance of 1.5 to 2.0 times of diameter. It is also shown that flow stability theory can be applied to the flow pattern formation for both cases.