In this investigation the complex unsteady flow through and around a channel in the presence of an obstruction at the entry is studied by solving directly the unsteady Navier-Stokes equations. Depending on the location of the obstruction, the flow through the channel either reverses its direction, stagnates or continues in the same direction as that of the flow outside but with reduced magnitude. The Reynolds number of 4000 is considered, as experimental results are available for comparison. The computed results are in close agreement with experiments. The computations help with better understanding of the phenomenon of reverse flow and fluid pumping. © 2005 Published by The Japan Society of Fluid Mechanics and Elsevier B.V. All rights reserved.

E. G. Tulapurkara

Algorithms

Approximation theory

Boundary conditions

Flow patterns

flow visualization

Laminar flow

Navier Stokes equations

Reynolds number

Unsteady flow

MARKER AND CELL (MAC) METHOD WITH THIRD ORDER UPWINDING

REVERSE FLOW

UNSTEADY LAMINAR FLOW

Channel flow

FLUID DYNAMICS

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IIT Madras

Fluid Dynamics Research

The occurrence of reverse flow 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 flow. For reverse, stagnant and slow forward flow, sharp changes in presence occur at the two ends of the channel. The resulting flow field gives rise to a delicate balance of pressure along the channel that controls the flow direction and magnitude. It is argued that there is a limitation on the maximum reverse flow achievable.The occurrence of reverse flow 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 visualization and pressure measurements are employed for this purpose. The obstruction at the front end of the channel is essential for triggering the reverse flow. For reverse, stagnant and slow forward flow, sharp changes in pressure occur at the two ends of the channel. The resulting flow field gives rise to a delicate balance of pressure along the channel that controls the flow direction and magnitude. It is argued that there is a limitation on the maximum reverse flow achievable.

On the mechanism of reverse flow in a channel with an obstruction at the entry

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.

Influence of splitter plate on the reverse flow in a channel

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. © 1994 American Institute of Physics.

Fulltext

Physics of Fluids

Reverse flow in channel-effect of front and rear obstructions

In the present study the flow through and around a parallel walled channel with various obstruction geometries placed at the channel entry is investigated. The flow inside the channel is found to be either stagnant, reverse, or in the forward direction depending upon the position of the obstruction. Experiments were carried out with various obstruction geometries like square, triangular, circular and semi-circular to study the effect of the shape of the geometry on the reverse flow phenomenon. Of the four, the triangular geometry gave the maximum reverse flow. The square and the semi-circular gave almost the same as the flat plate. The maximum forward flow also depends upon the shape of the obstruction geometry. To study the effect of the afterbody length the rectangular shape was chosen and models of different afterbody lengths were investigated. It is seen that the shorter afterbody lengths give a higher reverse flow. The maximum forward flow velocity however is higher for larger afterbody lengths. © 1993 Springer-Verlag.

Experiments in Fluids

Reverse flow in channel-influence of obstruction geometry

Flow phenomena in a channel with different shaped obstructions at the entrance

Reverse flow in channel with obstruction at entry

Journal	Fluid Dynamics Research
ISSN	01695983
Open Access	No