Error using UDF to modify density

February 13, 2008, 17:11

Hello,

I am trying to specify an equation of state (instead of ideal gas law). I am using DEFINE_PROPERTY for this. As a first step I have written an UDF where I calculate the density of gas using ideal gas law and activate for density in the properties of air and also turned on the energy equation. The simulation diverges. Not sure why since the UDF as shown below is fairly straightforward. Works fine if I make rhoa=constant.

Can someone suggest any corrections.

Thanks in advance.

#include "udf.h" #define rg 287.03

DEFINE_PROPERTY(liquid, c, t) { real rhoa, p_operating, pres, temp;

p_operating = RP_Get_Real ("operating-pressure"); pres = C_P(c,t) + p_operating; temp=C_T(c,t);

rhoa=pres/(rg*temp);

return rhoa; }

n.sharifi · July 13, 2011, 08:35

Hello
I've encountered a problem like you.
when i simplify the problem and use an inviscid compressible flow with the same UDF define property macro, the other bugs are observed.
1) the cell center contour of T-static and T-total are the same !!!
2) the net mass flow rate is changed.
3) the maximum velocity is increased.

so i believe that we should introduce a static temperatue and static pressure calculation macros to the solver.but how can we do it and how does it hooked?
if you have an idea please note it. may be it useful for us.

February 13, 2008, 17:11	Error using UDF to modify density	#1
NRD Guest Posts: n/a	Hello, I am trying to specify an equation of state (instead of ideal gas law). I am using DEFINE_PROPERTY for this. As a first step I have written an UDF where I calculate the density of gas using ideal gas law and activate for density in the properties of air and also turned on the energy equation. The simulation diverges. Not sure why since the UDF as shown below is fairly straightforward. Works fine if I make rhoa=constant. Can someone suggest any corrections. Thanks in advance. #include "udf.h" #define rg 287.03 DEFINE_PROPERTY(liquid, c, t) { real rhoa, p_operating, pres, temp; p_operating = RP_Get_Real ("operating-pressure"); pres = C_P(c,t) + p_operating; temp=C_T(c,t); rhoa=pres/(rg*temp); return rhoa; }

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July 13, 2011, 08:35		#2
n.sharifi New Member Navid Sharifi Join Date: Oct 2010 Location: Iran, Tehran Posts: 10 Rep Power: 16	Hello I've encountered a problem like you. when i simplify the problem and use an inviscid compressible flow with the same UDF define property macro, the other bugs are observed. 1) the cell center contour of T-static and T-total are the same !!! 2) the net mass flow rate is changed. 3) the maximum velocity is increased. so i believe that we should introduce a static temperatue and static pressure calculation macros to the solver.but how can we do it and how does it hooked? if you have an idea please note it. may be it useful for us.