Low-Reynolds k-eps models

p_agoodboy · February 17, 2011, 22:46

Hi everybody,

Anybody knows if it is possible to use low-Reynolds k-eps models in Fluent?
To clarify, in low_Re models the coefficients C_mu, C_eps1 and C_eps2 are modified based on flow characteristics or the distance from wall (different approaches in different models), and two source terms are also added to k and eps transport equations.
To summarize, I wanna know if it is possible to employ user defined coefficients rather than constant ones in Fluent and add new terms to the turbulence transport equations.

alastormoody11 · February 18, 2011, 01:48

Hi,

you can change the constants used for the k-e model using a journal file if you want after each time step or iterations if you want. To get the basic framework you can record a journal file where manually change the constats. Using this as a reference you can add your own functions to the code to change it between time steps.

I do not think that you can add source terms to the existing equations though.

If it is a low- Re flow you could also use the k-w model.

p_agoodboy · February 18, 2011, 21:48

Thank you for your help.
Could you please give me more explanation about journal files? or tell me where can I obtain more info.
In fact, I should decide whether Fluent is capable enough for my problem or I better proceed to an in-house code. It is actually a determining step for my PhD thesis.
How much using a journal file can increase computational cost? (I mean solution time)
I should model a rather complicated mixed convection turbulence flow and I need to examine different turbulence models so it is important for me to have enough freedom in using software.

p_agoodboy · February 18, 2011, 22:05

I should add that the coefficients are functions of position too, so it is not enough to change them in each time step but in each cell.

February 17, 2011, 22:46	Low-Reynolds k-eps models	#1
p_agoodboy New Member Join Date: Nov 2010 Posts: 8 Rep Power: 16	Hi everybody, Anybody knows if it is possible to use low-Reynolds k-eps models in Fluent? To clarify, in low_Re models the coefficients C_mu, C_eps1 and C_eps2 are modified based on flow characteristics or the distance from wall (different approaches in different models), and two source terms are also added to k and eps transport equations. To summarize, I wanna know if it is possible to employ user defined coefficients rather than constant ones in Fluent and add new terms to the turbulence transport equations.

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February 18, 2011, 01:48		#2
alastormoody11 Senior Member Join Date: Jun 2009 Posts: 100 Rep Power: 17	Hi, you can change the constants used for the k-e model using a journal file if you want after each time step or iterations if you want. To get the basic framework you can record a journal file where manually change the constats. Using this as a reference you can add your own functions to the code to change it between time steps. I do not think that you can add source terms to the existing equations though. If it is a low- Re flow you could also use the k-w model.

February 18, 2011, 21:48		#3
p_agoodboy New Member Join Date: Nov 2010 Posts: 8 Rep Power: 16	Thank you for your help. Could you please give me more explanation about journal files? or tell me where can I obtain more info. In fact, I should decide whether Fluent is capable enough for my problem or I better proceed to an in-house code. It is actually a determining step for my PhD thesis. How much using a journal file can increase computational cost? (I mean solution time) I should model a rather complicated mixed convection turbulence flow and I need to examine different turbulence models so it is important for me to have enough freedom in using software.

February 18, 2011, 22:05		#4
p_agoodboy New Member Join Date: Nov 2010 Posts: 8 Rep Power: 16	I should add that the coefficients are functions of position too, so it is not enough to change them in each time step but in each cell.