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k-epsilon in rough pipes

Posted Jul 21, 2009, 2:03 p.m. EDT 0 Replies

John
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Hi, I am modelling high velocity gas entering via a porous media into a tube. I'm using the leaking-wall formulation in COMSOL k-epsilon. Hotter gas enters near the bottom of the tube and cooler gas enters half-way up. Reynolds about 1.e5 - 1.e6.

Somewhat to my surprise, the resulting turbulent kinetic energy is quite low along the pipe. As a corollary, at the top of the pipe I have more of a radial gradient in temperature than I would have expected: the hotter gas stays in the middle of the tube and takes a distance (many diameters) to reach equilibrium with the cooler gas.

My dwplus_chns is about 400 so I think I've meshed the inside of the tube well enough.

I wonder if it is the smoothness of the pipe which is keeping turbulence down....? Is there a simple way to add a rough-wall friction factor to the k-epsilon wall boundary condition?

Regards, John
0 Replies Last Post Jul 21, 2009, 2:03 p.m. EDT
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