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-   -   buoyancy source term in k-e model (http://www.cfd-online.com/Forums/phoenics/52272-buoyancy-source-term-k-e-model.html)

Catherine Meissner June 20, 2008 11:25

buoyancy source term in k-e model
 
Hello, I try to activate the buoyancy source term in k-e model. But I am not sure how to do it correctly. I would be glad if someone could help!

I solve the temperature equation (TEM1) and use constant density so that the model should use the boussinesq approximation. Then I have to set 5 parameters according to the PHOENICS description BUOYA=0.0;BUOYB=0.0;BUOYC=-9.81;BUOYD = -BETA ;BUOYE = TEM1,ref The formular of the buoyancy term is given as Gb = ENUT * BETA * gi * {TEM1,i}/PRT(TEM1) everything is clear except the last parameter. Why should I give a constant temperature here? In my opinion BUOYE determines TEM1,i and this temperature is not constant!!! Can anybody tell my what BUOYE is? Thanks in advance,

Catherine


Jalil Ouazzani June 24, 2008 04:25

Re: buoyancy source term in k-e model
 
When using the boussinesq, you have first the classical source term in the momentum equation which is simply BuoYC*buoyd*(Tem1,i - buoye) (the buoye is a fixed reference temperature around which Taylor expansion of density has been made). Then you have the possibility of activating the effect of buoyancy in the k-e equations which use the term Gb (in this term there is no use of Buoye).

Catherine Meissner June 24, 2008 04:34

Re: buoyancy source term in k-e model
 
Hi Jalil, that makes thing understandable. This means if I define buoye then i get automatically a source term in the momentum equation? In my case the reference temperature (buoye) should vary with height. But I am not able to set this :(


Jalil Ouazzani June 26, 2008 06:32

Re: buoyancy source term in k-e model
 
Hello Catherine, I don't see the need to vary even in height the Tref but in case this is necessary, you can use your own source using either ground coding or inform (and in this case you will be able to vary all parmeters in your source term). It is quite easy to implement it. Jalil

Catherine Meissner June 26, 2008 07:33

Re: buoyancy source term in k-e model
 
Hi Jalil, it would be good to have tref varying with height if you consider the atmosphere. Tref is then the (potential) temperature in each atmospheric level. If you lift a parcel then you get different buoyancy effects in different heights. But in this case also BUOYD should be variable which is not the case. One way arround is indeed the inform for tref and to replace the whole buoyancy term in the momentum equation by this. But for BUOYD I am not able to give a Inform replacement. Catherine



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