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Prandtl number in compressible laminar boundary layer

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Old   September 15, 2014, 12:16
Default Prandtl number in compressible laminar boundary layer
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Gonzalo
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Hi everybody:
I want to simulate the compressible flow over a flat plate in FLUENT setting the Prandtl number of the air as 1. So, using the equation \kappa=\mu*Cp/Pr, with
\kappa= Thermal Conductivity
Cp= Specific Heat
\mu= Dynamic Viscosity

In order to do that I'm trying to use a variable \kappa using a UDF:

Code:
#include "udf.h"
DEFINE_PROPERTY(thermal_conductivity,c,t)
{
real k_air;       
real tempt = C_T(c,t);
/*Using the Sutherland's law for viscosity*/
k_air= pow(1.716E-5*(273.11+110.56)/(tempt+110.56)*(tempt/273.11),1.5)*1006.43;
return k_air;
}
but the problem I'm facing is I can't get the solution converged. If I use, \kappa constant I can make my solution converge, but with the approach I'm trying to implement now, don't. Can someone help me? Is the approach I'm using correct? Thanks. Regards
Gonzalo
PS: If someone wants the solution settings I'm using, please ask me for that. But first, I want to know if I'm doing things well with my UDF.

Last edited by gfoam; October 2, 2014 at 09:03.
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Old   September 19, 2014, 12:08
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Gonzalo
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I found an error in the thermal conductivity formula, instead of:
Code:
k_air= pow(1.716E-5*(273.11+110.56)/(tempt+110.56)*(tempt/273.11),1.5)*1006.43;
must be:
Code:
k_air= 1.716E-5*(273.11+110.56)/(tempt+110.56)*pow((tempt/273.11),1.5)*1006.43;
I'm looking forward for better results, I'll tell you if I can get them. Regards
Gonzalo
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