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 lijie December 10, 2012 09:36

cavitation udf

hi everybody
i have tried to use DEFINE_CAVITATION_RATE for Merkle cavitation model.The udf is written as follows:

DEFINE_CAVITATION_RATE(Merkle_cav_rate,c,t,p,rhoV, rhoL,mafV,p_v,cigma,f_gas,m_dot)
{

real p_vapor=*p_v;
real dp,dp0,source;
real m_plus,m_minus;
dp= ABS_P(C_P(c,t),op_pres)-p_vapor;
dp0=ABS(dp);
source= dp0/(0.5*rhoL[c]*v_inf*v_inf);
if(dp<0.0)
{
m_minus=((c_dest/t_inf)*source*(rhoL[c]*rhoL[c]/rhoV[c]-mafV[c]*C_R(c,t)*rhoL[c]*rhoL[c]/(rhoV[c]*rhoV[c])))/(1-mafV[c]);
*m_dot=m_minus;
}
else
{
m_plus=(c_prod/t_inf)*source*C_R(c,t)*rhoL[c]/rhoV[c];
*m_dot=-m_plus;
}
}

the problem is：why i set vapor pressure as 3450,but the value of *p_v is always 3967.5??

thanks!!

 jamesg3373 December 10, 2012 09:41

Vapour pressure is temperature dependant.

See here:

http://www.engineeringtoolbox.com/cavitation-d_407.html

That's if I'm understanding your problem properly...

 lijie December 11, 2012 00:07

i didn't set any setting about temperature...
it is fine when i use singhal or zawart cavitation model in fluent.
the phase contours become weird if i use udf.
i think the problem is that the vapor pressure should be 3450,but become 3967.5.

 icem_cfd December 31, 2012 02:31

UDF for cavitation

Hi All,

I have an UDF for compressible flow.
My boundary condition are pressure inlet and pressure outlet.
am using cavitation model of Schner-Sauer of 2 phases gasoline liquid and gasoline vapour.
After compiling and run, the results of contours of density dont show much variation in density.
only near the outlet there is some variation in density, rest of the place the density is same.

is there any other UDF which defines viscosity, density for compressiblr flow ?

Kirti...

 icem_cfd January 3, 2013 01:10

Compressible flow UDF

Hi all,

I am using UDF for 2D Compressible flow simulation. The same UDF is used for simulation in solvers like CFX and also FLUENT. The results from CFX is giving proper variation in density, but in FLUENT the results are bit different, but close to CFX results i.e in CFX the result obtained for density change is from (7.78e2 - 8.86e2) kg/m3 and for same boundary condition simulation the FLUENT result for density is varying from (8.06e2 - 8.85e2) kg/m3.