Flow instability in obstructed channel flow

A body of finite size is moving freely inside, and interacting with, a channel flow. The description of this unsteady interaction for a comparatively dense thin body moving slowly relative to flow at medium-to-high Reynolds number shows that an inviscid core problem with vorticity determines much, but not all, of the dominant response. It is found that the lift induced on a body of length comparable to the channel width leads to differences in flow direction upstream and downstream on the body scale which are smoothed out axially over a longer viscous length scale; the latter directly affects the change in flow directions. The change is such that in any symmetric incident flow the ratio of slopes is found to be cos ⁡ ( π / 7 ) , i.e. approximately 0.900969, independently of Reynolds number, wall shear stresses and velocity profile. The two axial scales determine the evolution of the body and the flow, always yielding instability. This unusual evolution and linear or nonlinear instability mechanism arise outside the conventional range of flow instability and are influenced substantially by the lateral positioning, length and axial velocity of the body.

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Numerical Investigation of Instability and Transition in an Obstructed Channel Flow

AIAA Journal ◽

10.2514/2.1111 ◽

2000 ◽

Vol 38 (7) ◽

pp. 1173-1178 ◽

Cited By ~ 10

Author(s):

Kyung-Soo Yang

Keyword(s):

Numerical Investigation ◽

Channel Flow ◽

Obstructed Channel Flow

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Channel Flow Instability in Presence of Weak Distributed Surface Suction

AIAA Journal ◽

10.2514/2.968 ◽

2000 ◽

Vol 38 (2) ◽

pp. 372-374 ◽

Cited By ~ 2

Author(s):

J. J. Szumbarski ◽

J. M. Floryan

Keyword(s):

Channel Flow ◽

Flow Instability ◽

Surface Suction

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Free-surface flows with near-critical flow conditions

Canadian Journal of Civil Engineering ◽

10.1139/l96-936 ◽

1996 ◽

Vol 23 (6) ◽

pp. 1272-1284 ◽

Cited By ~ 24

Author(s):

H. Chanson

Keyword(s):

Free Surface ◽

Channel Flow ◽

Open Channel ◽

Flow Instability ◽

Open Channel Flow ◽

Surface Characteristics ◽

Free Surface Flows ◽

Critical Flow ◽

Flow Conditions ◽

Weir Flow

Open channel flow situations with near-critical flow conditions are often characterized by the development of free-surface instabilities (i.e., undulations). The paper develops a review of several near-critical flow situations. Experimental results are compared with ideal-fluid flow calculations. The analysis is completed by a series of new experiments. The results indicate that, for Froude numbers slightly above unity, the free-surface characteristics are very similar. However, with increasing Froude numbers, distinctive flow patterns develop. Key words: open channel flow, critical flow conditions, free-surface undulations, flow instability, undular surge, undular broad-crested weir flow, culvert flow.

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Elastic Turbulence of Aqueous Polymer Solution in Multi-Stream Micro-Channel Flow

Micromachines ◽

10.3390/mi10020110 ◽

2019 ◽

Vol 10 (2) ◽

pp. 110 ◽

Cited By ~ 1

Author(s):

Jiayan Tai ◽

Yee Cheong Lam

Keyword(s):

Flow Field ◽

Channel Flow ◽

Flow Instability ◽

Flow Behavior ◽

Power Spectra ◽

Micro Channel ◽

Polymer Molecules ◽

Aqueous Solvent ◽

Micro Channels ◽

Flow Field Characteristics

Viscous liquid flow in micro-channels is typically laminar because of the low Reynolds number constraint. However, by introducing elasticity into the fluids, the flow behavior could change drastically to become turbulent; this elasticity can be realized by dissolving small quantities of polymer molecules into an aqueous solvent. Our recent investigation has directly visualized the extension and relaxation of these polymer molecules in an aqueous solution. This elastic-driven phenomenon is known as ‘elastic turbulence’. Hitherto, existing studies on elastic flow instability are mostly limited to single-stream flows, and a comprehensive statistical analysis of a multi-stream elastic turbulent micro-channel flow is needed to provide additional physical understanding. Here, we investigate the flow field characteristics of elastic turbulence in a 3-stream contraction-expansion micro-channel flow. By applying statistical analyses and flow visualization tools, we show that the flow field bares many similarities to that of inertia-driven turbulence. More interestingly, we observed regions with two different types of power-law dependence in the velocity power spectra at high frequencies. This is a typical characteristic of two-dimensional turbulence and has hitherto not been reported for elastic turbulent micro-channel flows.

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