# cavitation udf

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 December 10, 2012, 09:36 cavitation udf #1 New Member   TAIWAN, R.O.C. Join Date: Dec 2012 Posts: 2 Rep Power: 0 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!!

 December 10, 2012, 09:41 #2 New Member     James Goodwin Join Date: Nov 2012 Location: Liverpool UK Posts: 13 Rep Power: 7 Vapour pressure is temperature dependant. See here: http://www.engineeringtoolbox.com/cavitation-d_407.html That's if I'm understanding your problem properly... Last edited by jamesg3373; December 10, 2012 at 11:32.

 December 11, 2012, 00:07 #3 New Member   TAIWAN, R.O.C. Join Date: Dec 2012 Posts: 2 Rep Power: 0 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.

 December 31, 2012, 02:31 UDF for cavitation #4 New Member   keerthiraj shetty Join Date: Dec 2012 Posts: 2 Rep Power: 0 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...

 January 3, 2013, 01:10 Compressible flow UDF #5 New Member   keerthiraj shetty Join Date: Dec 2012 Posts: 2 Rep Power: 0 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. Kindly give your needfull sugestions kirti

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