# Prandtl number in compressible laminar boundary layer

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 September 15, 2014, 12:16 Prandtl number in compressible laminar boundary layer #1 Senior Member   Gonzalo Join Date: Mar 2011 Location: Argentina Posts: 120 Rep Power: 9 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 =*Cp/Pr, with = Thermal Conductivity Cp= Specific Heat = Dynamic Viscosity In order to do that I'm trying to use a variable 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, 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.

 September 19, 2014, 12:08 #2 Senior Member   Gonzalo Join Date: Mar 2011 Location: Argentina Posts: 120 Rep Power: 9 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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