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.
The occurrence of reverse ow in a channel when an obstruction is placed at the entry is already known. In this article an attempt is made to bring out the mechanism that governs this phenomenon. Flow visualisation and pressure measurements are employed for this purpose. The obstruction at the front end of the channel is essential for triggering the reverse ow. For reverse, stagnant and slow forward ow, sharp changes in pressure occur at the two ends of the channel. The resulting ow ÿeld gives rise to a delicate balance of pressure along the channel that controls the ow direction and magnitude. It is argued that there is a limitation on the maximum reverse ow achievable.
Reverse flow inside a parallel plate channel can be achieved by placing an obstruction at the entry. The present work is carried out to study the influence of (i) splitter plates behind the flat plate obstruction at the front end and (ii) splitter plates placed at the rear end of the channel in tandem with the obstruction at the front. The results show that the splitter plate at the front end has a slight unfavourable effect due to a little reduction in the reverse flow. However, when the splitter plate is placed at the rear end, it interferes with the alternate formation and shedding of vortices near the rear end. This interference depends upon the length of the splitter plate and also on its position relative to the exit of the test channel. The resulting flow field causes an increase in the magnitude of the reverse flow which remains constant over a wide range of splitter plate positions.
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