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k-epsilon wall conditions again. Where is friction?

Posted 28 apr 2010, 15:25 GMT-4 1 Reply

John
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Hi, I've had some success at k-epsilon modelling in pipes including thermal flow, and it's time to get back into it. My next hurdle is friction due to pipe roughness. I was hoping for a relatively simple modification of the wall equations to be able to accomodate roughness, but I can't find that modification in the literature, nor can I find any examples previously done in Comsol. And yet I'm sure it must have been... Any pointers?

Thanks, John
p.s. I've ordered a 2001 ASME paper by Durbin that has a hopeful looking title, wont get that paper until next week though...
p.p.s And tomorrow I get a sneak preview of 4.0 - maybe COMSOL has already solved it for me?? :-)
1 Reply Last Post 29 apr 2010, 12:38 GMT-4
John
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Posted: 1 decade ago 29 apr 2010, 12:38 GMT-4
Also, in text books they always refer to boundary shear stress, tau_s.

Along the surface of pipe, I see K_z_chns2 = (eta_chns+etaT_chns)*(2*nr_chns*u2r+nz_chns*(u2z+v2r))

what are nr_chns and nz_chns.... is K_z_chns2 the same tau_s ?

I had been aniticipating something like: (eta_chns+etaT_chns)*u2r

Thanks, J.
Also, in text books they always refer to boundary shear stress, tau_s. Along the surface of pipe, I see K_z_chns2 = (eta_chns+etaT_chns)*(2*nr_chns*u2r+nz_chns*(u2z+v2r)) what are nr_chns and nz_chns.... is K_z_chns2 the same tau_s ? I had been aniticipating something like: (eta_chns+etaT_chns)*u2r Thanks, J.

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