# how to get gas viscosity in the fluent

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 April 29, 2014, 06:30 how to get gas viscosity in the fluent #1 New Member   Happy_weekend Join Date: Jan 2014 Posts: 21 Rep Power: 6 Problem description: I am writing a DPM udf for coal combustion. In the UDF, we need to use the gas phase viscosity to compute the Stokes number in the related formula. Question1: Is there any argument that we can directly use to get the gas viscosity? For example, if we want to use particle velocity, we can use argument P_VEL(P). Question2; If not, how to get the gas viscosity? Could anyone help me with this? Many thanks advance.

 April 30, 2014, 09:12 #2 Senior Member   François Grégoire Join Date: Jan 2010 Location: Laval University, Canada Posts: 389 Rep Power: 11 Edit: Look for Material Property Macros in the UDF Manual. https://www.sharcnet.ca/Software/Flu...df_tab_cell_12 Last edited by macfly; April 30, 2014 at 11:22.

April 30, 2014, 10:06
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 Originally Posted by macfly Hi, How did you define the mixture viscosity in Fluent? Mass weighted mixing law? Ideal gas mixing law? I think there is no direct mean to retrieve the mixture viscosity in Fluent, another great example of a very basic functionality not available in Fluent . In your udf, you can retrieve individual species viscosity with prop_mu (see udf manual) and then calculate the mixture viscosity according to the way you defined it.
1, mixture viscosity :Mass weighted mixing law.
2, I think you mean that I can only compute the gas viscosity by using the individual mass concentration, individual viscosity and the viscosity mixing law in the UDF.

3, could I use the effective viscosity or turbulence viscosity in the turbulence model to represent the gas viscosity to compute the Stokes number? because we can directly get the effective or turbulence viscosity by the argument C_MU_EFF(c,t) and C_MU_T(c,t).

Stokes number=ρp*Vp*Dp^2/9*Dc*μg
ρp, particle density, Vp particle velocity, Dp particle diameter, Dc obstacle diameter, μg gas viscosity.

 April 30, 2014, 11:18 #4 Senior Member   François Grégoire Join Date: Jan 2010 Location: Laval University, Canada Posts: 389 Rep Power: 11 I was wrong, you found the Material Property Macros, what you need is in these macros. I'm not familiar with DPM, I can't tell which viscosity you should use in the Stokes number.

May 1, 2014, 07:02
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Quote:
 Originally Posted by macfly I was wrong, you found the Material Property Macros, what you need is in these macros. I'm not familiar with DPM, I can't tell which viscosity you should use in the Stokes number.