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-   -   bouyancy term in epsilon equation (http://www.cfd-online.com/Forums/main/948-bouyancy-term-epsilon-equation.html)

Michael June 25, 1999 09:53

bouyancy term in epsilon equation
 
Hi all,

i have a question about the standard k-eps model.

In the CFD code I use there's the possibility to add an extra term in the epsilon equation taking in account bouyant effects.

This term has the form.

.... = .....+C1 eps/k (P+C3 max(G,0))+ ....

with G=-mu_eff/rho/sigma g Div(T)

Through the constant C3 I can switch this extra term on.

Simulating the natural convection at a cube in a room with colder counterflow from the ceiling I get a total different flow field depending on including the extra term.

With that term on there is a large plume which reaches even the ceiling while without that term the plume gets reversed by the counterflow directly above the cube and transported through the floor outside.

Could anyone give some explanation about that term ?

Thanks,

Michael

Sasha Becker June 25, 1999 10:20

Re: bouyancy term in epsilon equation
 
Hai MIchael,

the additional term in CFX-4 copes for the turbulence production by unstable layers of hot fluid below cold fluid. Here the hot fluid will rise up and the cold fluid will rise down, they influence together and produce additional turbulence. By that the flow pattern will change completely. The term should be included especially for natural convection.

I hope it helps.

Sasha


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