Reverse flow in a channel with an obstruction at the entry

Abstract

In this study the flow through and around a parallel-walled channel with an obstruction (flat plate) placed at the channel inlet is investigated. Depending on the position of the obstruction, the flow inside the channel is in a direction opposite to that outside, stagnant or in the same direction as outside but with reduced magnitude. Flow visualization in water is used to examine the fluid motion, although some wind tunnel measurements have been made and are also reported. The parameters that have been varied are the gap between the obstruction and the entry to the channel, the length of the channel and the Reynolds number. The maximum value of the reverse flow velocity is found to be about 20% of that of the flow outside. The maximum forward velocity inside the channel (when it occurs) is only about 65% of the outside velocity even for very large gaps between the obstruction and the channel entrance. A tentative explanation is offered for the observed features.

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

“…Flow visualization studies by Kabir et al [7,8] cover a range of Reynolds numbers up to 9,000. They confirmed the results found by Gowda and Tulapurkara [2] that the reverse flow is at its maximum value for the ratio of g/w = 1.5. Bhuiyan et al [1] observed that the reverse flow also occurs in non-Newtonian fluid flows.…”

“…The shear layer interaction seen in Fig. 6 is different from that for the channel [2]. The absence of vortical or recirculating separated regions within the duct near the rear and the front ends in Fig.…”

“…Reverse flow in the case under study is expected to be triggered due to the low pressure behind the obstruction as in the channel case [2]. The primary reason for the differences observed between the two cases (i.e., the square duct and the channel) is the difference in geometry: the present case is threedimensional and the channel case is two-dimensional.…”

“…The magnitude of the velocity was expressed as a ratio of velocity, U i , in the central part of the test channel to the free stream velocity, U ∞ . In this figure, the results for a circular duct [9] and a channel [2] are shown for comparison. In the square duct, the variation is different from the two-dimensional channel case.…”

“…It should be pointed out that the flow field will be more complex in arterial flows due to the elastic nature of the arteries. Gowda and Tulapurkara [2] appear to have been the first researchers to observe the reverse flow phenomenon inside a channel. They studied the influence of gap (g), the length of the test channel (L), and the Reynolds number (Re) based on the channel width (w) and the free stream velocity U ∞ .…”