Reverse flow in channel-effect of front and rear obstructions

Abstract

The occurrence of reverse flow in a channel when a bluff body is kept at the entry is already known. In the earlier investigations, attention was focused on the generation of the reverse flow with bluff bodies, such as flat plate and other geometries, having the same width as the channel. The separation of the shear layers from the obstruction at the front end and the interaction of the shear layers at the rear end are mainly responsible for the reverse flow. To gain further insight into the phenomenon, the effects of the width of the obstruction at the front and that of placing another at the rear end in tandem with the front one are examined in this study. It is observed that the reverse flow occurs even when the width of the flat plate (b) is less than the channel width (w); the lower limit being b/w=0.6. At this b/w the reverse flow velocity is small, but it increases progressively with b/w until a maximum of about 30% of the forward velocity is attained for b/w≥2.0. However, reverse flow as high as 0.6 times the free-stream velocity is obtained when another plate is kept close to the rear end in addition to the front plate. Further increase in the reverse flow to 0.83 times the free-stream velocity has been achieved by replacing the flat plate model at the rear with a semicircular scoop.

Reverse flow in a square duct with an obstruction at the entry

“…This was done so that the struts supporting the duct and the obstruction do not interfere with the view, as the camera for the particle image velocimetry (PIV) studies and visualization are located below the tank (Figs. [3][4]. The duct is located midway in the channel, below the water level, with its center line 100 mm from the water surface.…”

“…A maximum reverse flow of (U i /U ∞ ) = 0.28 was obtained for the obstruction with a triangular shape. The effects of obstructions both at the entry and at the rear end of the test channel were investigated by Tulapurkara et al [4]. Studies were carried out by placing flat plates and semicircular scoops at the rear end (normal to the channel axis) in addition to the obstruction at the front end.…”

A numerical study on the mechanism of reverse flow in a channel without obstruction at the entry

“…In subsequent studies, various facets of the phenomenon like the influence of the geometry of the obstruction (Gowda et al, 1993), the effect of obstructions placed both at the entry and the rear of the test channel (Tulapurkara et al, 1994), and the influence of splitter plates (Gowda et al, 1997) were investigated. In subsequent studies, various facets of the phenomenon like the influence of the geometry of the obstruction (Gowda et al, 1993), the effect of obstructions placed both at the entry and the rear of the test channel (Tulapurkara et al, 1994), and the influence of splitter plates (Gowda et al, 1997) were investigated.…”

Influence of splitter plate on the reverse flow in a channel

“…2. It is essentially the same as that used in the earlier studies (GT, Gowda et al, 1993;Tulapurkara et al, 1994). It consists of a tank of 2.5m x 1.5m, with a depth of 150 mm, at one end of which are located two sets of aluminium discs (vanes) with suitable spacing in between them.…”

“…Among these geometries it was found that the reverse flow is maximum in the case of a triangle. Tulapurkara et al (1994) obtained a significantly higher value of the reverse flow velocity by placing plate and semi-circular scoop at the rear end of the test channel in tandem with the obstruction at the front. The increase in the reverse flow was achieved mainly due to the guidance of the external flow into the test channel by the plate and the scoop.…”