Large Eddy Simulation of Flow and Heat Transfer in a 90 deg Ribbed Duct With Rotation: Effect of Coriolis and Centrifugal Buoyancy Forces

[+] Author and Article Information
Samer Abdel-Wahab, Danesh K. Tafti

Mechanical Engineering Department, Virginia Tech, Blacksburg, Virginia 24061 USA

J. Turbomach 126(4), 627-636 (Dec 29, 2004) (10 pages) doi:10.1115/1.1791648 History: Received October 01, 2003; Revised March 01, 2004; Online December 29, 2004
Copyright © 2004 by ASME
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Streamwise periodic computational domain. Flow is in the x direction and rotation vector is along the +ve z axis.
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Mean streamlines on the leading side of the center plane z=0.5 for two rotation numbers and increasing Richardson number. The large separation region behind the rib grows on the leading side, while remaining constant on the trailing side (not shown).
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Contours of mean velocity at x=0.5 at the midrotation number with increasing Richardson number. Illustrated is the strong impingement of flow onto the smooth sidewall which is enhanced by centrifugal buoyancy forces. The left and right sides of the figures show averaged vertical and lateral velocities, respectively. A positive lateral velocity implies impingement on the side wall.
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Turbulent kinetic energy at the center of the duct and midway between ribs (x=0,z=0.5). (a) Effect of Coriolis forces at different rotation numbers; distribution is symmetric about y=0.5 for Ro=0. (b) Effect of centrifugal buoyancy at Ro=0.18. (c) Effect of buoyancy at Ro=0.68. Generally, tke is increased near the trailing side (bottom) and decreases near the leading side (top). The effect of centrifugal buoyancy on tke is similar to that of Coriolis forces.
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Turbulent shear stress at the center of the duct (x=0,z=0.5) for two different rotation numbers and for varying Richardson numbers. There is a large increase in turbulent shear stress on the trailing side (bottom) due to centrifugal buoyancy forces.
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Contours of surface averaged Nusselt numbers for Ro=0.39 and Ri=29.7. Sidewall impingement on the trailing side of the smooth wall dominates heat transfer augmentation in that section. The reattachment region on the trailing side shows heat transfer augmentation of 6, which is a local maximum.
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Comparison of average Nusselt number augmentation ratios at the leading and trailing sides with experiments. Liou et al. 16: Re=10 000, e/Dh=0.136 and P/e=10; Parsons et al. 13: Re=5000, e/Dh=0.125.P/e=10; Wagner et al. 15 Re=25 000, e/Dh=0.1,P/e=10, buoyancy information in table above.




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