Calculation of turbulence kinetic energy and dissipation rate

Mondal131211 · February 11, 2020, 21:33

Hi Foamers,

Hope all of you are doing well. I am now working on pure natural convection along a heated plate which is a well known topic in CFD. Actually, the reason of my post is about initializing the turbulent kinetic energy (k) and dissipation rate (omega) for a pure natural convection. I know how to calculate k and omega for forced convection using the formula,
k=3/2*(I*U)^2 (I-Tur intensity, U-Reference Velocity).................(1)

omega=k^0.5/(Cmu*l) (Found in OpenFOAM documentation).............(2)
For a forced convection I can easily get the the value of k from Eqn (1) using velocity U. Once I get the value of k, I am also able to calculate omega.

But for a pure natural convection, how can we know the exact velocity? As I know so far velocity depends on density differences for a pure natural convection.

Lets assume the value of k is zero for natural convection as there is no exact velocity. Then how can I calculate omega except k from Eqn (2)?

I am really confused about this silly question. I hope there are lots of people out here to clear my confusion about this topics. If I am unable to understand you about my topics, plz feel free to ask me more info. I am happy to give more information.

Thank you very much in advance.

Cheers

Razon

geth03 · May 29, 2020, 04:17

did you run a few simulations just to see how sensitive your simulation is to initial values of k and omega??

when i run simulations, regardless of the initial value for those, the same value will be calculated after some time and after that i get the same results.

would you share your 0-directory files for those?

February 11, 2020, 21:33	Calculation of turbulence kinetic energy and dissipation rate	#1
Mondal131211 Member Mondal Join Date: Sep 2018 Location: Canberra ACT Posts: 68 Rep Power: 7	Hi Foamers, Hope all of you are doing well. I am now working on pure natural convection along a heated plate which is a well known topic in CFD. Actually, the reason of my post is about initializing the turbulent kinetic energy (k) and dissipation rate (omega) for a pure natural convection. I know how to calculate k and omega for forced convection using the formula, k=3/2(IU)^2 (I-Tur intensity, U-Reference Velocity).................(1) omega=k^0.5/(Cmu*l) (Found in OpenFOAM documentation).............(2) For a forced convection I can easily get the the value of k from Eqn (1) using velocity U. Once I get the value of k, I am also able to calculate omega. But for a pure natural convection, how can we know the exact velocity? As I know so far velocity depends on density differences for a pure natural convection. Lets assume the value of k is zero for natural convection as there is no exact velocity. Then how can I calculate omega except k from Eqn (2)? I am really confused about this silly question. I hope there are lots of people out here to clear my confusion about this topics. If I am unable to understand you about my topics, plz feel free to ask me more info. I am happy to give more information. Thank you very much in advance. Cheers Razon

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May 29, 2020, 04:17		#2
geth03 Senior Member Join Date: Dec 2019 Location: Cologne, Germany Posts: 355 Rep Power: 8	did you run a few simulations just to see how sensitive your simulation is to initial values of k and omega?? when i run simulations, regardless of the initial value for those, the same value will be calculated after some time and after that i get the same results. would you share your 0-directory files for those?