Customize the Prandtl number in the k-epsilon mode

ClydeL · May 9, 2021, 00:05

Hello experts,

I want to customize the Prandtl number in the k-epsilon model for liquid metal simulations. I have the correlation equations for the Prandtl number, but I have no idea which Prandtl number should I define.

There are TKE Prandtl number, TDR Prandtl number, Energy Prandtl number and Wall Prandtl number in the Viscous Model dialogue box. I have read some threads in the forum, and I know that TKE refers to the effective Prandtl number in the equation of k, TDR refers to the effective Prandtl number in the equation of epsilon, and the Energy Prandtl number and Wall Prandtl number work in a similar way.

So, should I define all four Prandtl number with the same correlation equations? Or I just need to define some of them?

LuckyTran · May 10, 2021, 17:08

You said that you want to edit the turbulent Prandtl number in the k-epsilon equation... but there is a Prandtl number for k and a Prandtl number for epsilon. So you need to figure out what you actually want to do...

If you want to edit only the k-epsilon equation (which is actually two equations) you should not touch any of the other turbulent Prandtl numbers. I don't know what your correlation is but you may be looking to edit 1 or 2 turbulent Prandtl numbers but not all of them. If you have only one correlation then you probably only need to edit 1 of the numbers. But now you need to figure out if it's the TKE or TDR Prandtl number.

So what is this correlation? Dig it up in the literature. If there is some theoretical background accompany it then it is usually quite easy to figure out.

Tian Hongkang · November 20, 2021, 08:59

Hello, my friend! Now I have the same problem as you. I need to simulate the flow and heat transfer of liquid metal. Do you know where to define turbulent Prt in OpenFOAM?

Tian Hongkang · November 20, 2021, 09:01

Quote:

Originally Posted by ClydeL

Hello experts,

I want to customize the Prandtl number in the k-epsilon model for liquid metal simulations. I have the correlation equations for the Prandtl number, but I have no idea which Prandtl number should I define.

There are TKE Prandtl number, TDR Prandtl number, Energy Prandtl number and Wall Prandtl number in the Viscous Model dialogue box. I have read some threads in the forum, and I know that TKE refers to the effective Prandtl number in the equation of k, TDR refers to the effective Prandtl number in the equation of epsilon, and the Energy Prandtl number and Wall Prandtl number work in a similar way.

So, should I define all four Prandtl number with the same correlation equations? Or I just need to define some of them?

Hello, my friend! Now I have the same problem as you. I need to simulate the flow and heat transfer of liquid metal. Do you know where to define turbulent Prt in OpenFOAM?

LuckyTran · November 20, 2021, 15:22

If you want to change the turbulent Prandtl number in the wall function, that is specified as the boundary condition property.

If you want to change the global turbulent Prandtl number in the turbulence model itself, that is specified in the turbulenceProperties dictionary and usually by declaring Prt. If in doubt, run your sim using printCoeffs to see what are the model coefficients for your particular turbulence model.

Tian Hongkang · November 20, 2021, 23:11

Quote:

Originally Posted by LuckyTran

If you want to change the turbulent Prandtl number in the wall function, that is specified as the boundary condition property.

If you want to change the global turbulent Prandtl number in the turbulence model itself, that is specified in the turbulenceProperties dictionary and usually by declaring Prt. If in doubt, run your sim using printCoeffs to see what are the model coefficients for your particular turbulence model.

Thank you for your advice.
I want to change the globle turbulent Prandtl number in the turbulence model. But I still don't know where to go to modify. I've set printCoeffs to on, but there is no information about turbulent Prandtl number at the terminal. Do you know in which dictionary file this parameter can be changed. Thank you again!

May 9, 2021, 00:05	Customize the Prandtl number in the k-epsilon mode	#1
ClydeL New Member Nianqi Li Join Date: May 2019 Posts: 1 Rep Power: 0	Hello experts, I want to customize the Prandtl number in the k-epsilon model for liquid metal simulations. I have the correlation equations for the Prandtl number, but I have no idea which Prandtl number should I define. There are TKE Prandtl number, TDR Prandtl number, Energy Prandtl number and Wall Prandtl number in the Viscous Model dialogue box. I have read some threads in the forum, and I know that TKE refers to the effective Prandtl number in the equation of k, TDR refers to the effective Prandtl number in the equation of epsilon, and the Energy Prandtl number and Wall Prandtl number work in a similar way. So, should I define all four Prandtl number with the same correlation equations? Or I just need to define some of them? Tian Hongkang likes this.

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May 10, 2021, 17:08		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,763 Rep Power: 66	You said that you want to edit the turbulent Prandtl number in the k-epsilon equation... but there is a Prandtl number for k and a Prandtl number for epsilon. So you need to figure out what you actually want to do... If you want to edit only the k-epsilon equation (which is actually two equations) you should not touch any of the other turbulent Prandtl numbers. I don't know what your correlation is but you may be looking to edit 1 or 2 turbulent Prandtl numbers but not all of them. If you have only one correlation then you probably only need to edit 1 of the numbers. But now you need to figure out if it's the TKE or TDR Prandtl number. So what is this correlation? Dig it up in the literature. If there is some theoretical background accompany it then it is usually quite easy to figure out.

November 20, 2021, 08:59		#3
Tian Hongkang New Member Outside North America Join Date: Nov 2021 Posts: 14 Rep Power: 5	Hello, my friend! Now I have the same problem as you. I need to simulate the flow and heat transfer of liquid metal. Do you know where to define turbulent Prt in OpenFOAM?

November 20, 2021, 15:22		#5
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,763 Rep Power: 66	If you want to change the turbulent Prandtl number in the wall function, that is specified as the boundary condition property. If you want to change the global turbulent Prandtl number in the turbulence model itself, that is specified in the turbulenceProperties dictionary and usually by declaring Prt. If in doubt, run your sim using printCoeffs to see what are the model coefficients for your particular turbulence model.