An experimental investigation of a turbulent shear flow with separation, reverse flow, and reattachment

Abstract

Experiments were performed in the highly turbulent and disturbed flow over a bluff plate with a long splitter plate in its plane of symmetry. The flow separates at the sharp bevelled edge of the bluff plate, forms a free shear layer on top of the reverse-flow region which is bounded on its other side by the splitter plate, and reattaches on the splitter plate over a narrow region curved in spanwise direction. Downstream of reattachment the shear flow adjusts slowly to the wall boundary conditions.Measurements of mean velocity, Reynolds-shear-stress and Reynolds-normal-stress distributions were carried out by hot-wire and pulsed-wire anemometry. The latter technique was used in those regions of the flow where reverse flow occurred or where the flow was highly turbulent. Spectra and integral lengthscales were measured to investigate the state and structure of the flow. The large-eddy structure in the inner region of the flow had lengthscales in the two cross-stream directions which were approximately equal, indicating a fast break-up of spanwise structures just downstream from separation.Mean and fluctuating quantities showed a self-similar behaviour in a short region upstream of reattachment and ‘profile similarity’ in the separated shear layer and along the splitter plate downstream from reattachment. Probability-density distributions of skin friction were measured and used to calculate mean and fluctuating values. No flapping of the reattaching shear layer could be observed. Pulsed-wire measurements revealed that the logarithmic law of the wall does not hold either in the reverse-flow region or in a region about half the length of the bubble downstream from reattachment.

Experimental and Numerical Study of Flow Structures Associated With Low Aspect Ratio Elliptical Cavities

“…Comparison of the results to those previously published in the literature, indicates that the same trend has been observed for velocity profiles downstream of a bluff plate (fence) with a splitter plate [101], rows of square plates [102], backward facing step [62], and two-dimensional obstacles [100] and [103]. It was concluded that the only solution to achieve a well-developed velocity profile of the desired thickness was a longer upstream length, which was not possible due to the limited length of the test section of the tunnel.…”

Effects of Freestream Turbulence on the Pressure Acting on a Low-Rise Building Roof in the Separated Flow Region

“…Akon and Kopp (2016) presented a systematic investigation of surface pressures occurring on surface mounted, three-dimensional bluff bodies, finding that the reduced mean pressure coefficient C * p defined in Ruderich and Fernholz (1986): produces a suitable match for a broad range geometric scales, building aspect ratios, and terrain conditions. Here C p refers to the mean pressure coefficient at the location of interest and C p,min refers to the lowest mean pressure coefficient observed in the tap line under the separation bubble.…”

Active and Passive Flow Control over the Flight Deck of Small Naval Vessels

“…Experimental and computational literature is readily available for two dimensional versions of this flow. 3,4,5,6,7,8,9 Figure 1.1 illustrates the general characteristics of this two dimensional flow. The dominant flow feature is the large recirculation region beneath the unsteady, separated shear layer.…”