In multiphase cavitation analyses solution is not converging and continity is not sat

sanjiiv · June 1, 2016, 01:41

Hello people,
I am working on multiphase analyses in fluent,i still now not able to find the continuity equation satisfied , i.e. mass flow rate difference not coming to zero in my analyses it comes values around for ex: + or - of 12345 atleast, i dont know why and the solution is not converging at all after some 10000 iterations in transient analyses at the time step of 10 per iterations and time step size of 0.001714.
I meshed this domain in GAMBIT of around 28000 structure quad mesh elements by blocking.And i used fluent for solving this problem, in multiphase i used two phases one is for water and other is for water vapour....in this analyses i try to solve for cavitation developed over the body in order to reduce the drag on the body, at last i can see the cavitation (vapour phase formed elliptical around the body in contour)but the continuity equation that is the difference of mass fluxes is not coming to zero,there is always a difference of around 5 digit value as i mentioned above.
and the incoming and outgoing mass flow rate value is around value of exp 9 terms ..i think its too high ..

for a cfd simulation without satisfying the continuity equation the analyses is wrong ..and in this analyses solution convergence is also not occuring after 10000 iteration in transient case..i dont know why whats the problem in my analyses ,always mass is adding up in between inlet and outlet can any one plz help me with this analyses..and i try to solve this analyses in steady state pressure or temperature coupled or divergence occure..plz some body help me...

Thank u,

CFD-fellow · June 1, 2016, 02:27

Hi
Have u done your simulation without cavitation? first converge it without cavitation to see if the problem is with your cavitation or no with something else such as mesh scale, mesh resolution or any other wrong setup.

sanjiiv · June 2, 2016, 22:18

Hello,

I have tried this problem with atleat hundred of time ,as like you said altering the mesh upto 4 to 6 times andthe I analysed nothing is working .
But,The problem is coming with mass flux not balancing (=0) between inlet and outlet , pressure report values are extremely high.
It comes in Mpa,sometimes Gpa.I dont know why?..

If you sir or anyone liked to see my Problem details and definition ..
I will sent you the complete details of it please post your mail ID here,

Thanks for your concern,
regards,
sanjiiv

June 1, 2016, 01:41	In multiphase cavitation analyses solution is not converging and continity is not sat	#1
sanjiiv New Member sanjeev kumar.m Join Date: May 2016 Posts: 13 Rep Power: 9	Hello people, I am working on multiphase analyses in fluent,i still now not able to find the continuity equation satisfied , i.e. mass flow rate difference not coming to zero in my analyses it comes values around for ex: + or - of 12345 atleast, i dont know why and the solution is not converging at all after some 10000 iterations in transient analyses at the time step of 10 per iterations and time step size of 0.001714. I meshed this domain in GAMBIT of around 28000 structure quad mesh elements by blocking.And i used fluent for solving this problem, in multiphase i used two phases one is for water and other is for water vapour....in this analyses i try to solve for cavitation developed over the body in order to reduce the drag on the body, at last i can see the cavitation (vapour phase formed elliptical around the body in contour)but the continuity equation that is the difference of mass fluxes is not coming to zero,there is always a difference of around 5 digit value as i mentioned above. and the incoming and outgoing mass flow rate value is around value of exp 9 terms ..i think its too high .. for a cfd simulation without satisfying the continuity equation the analyses is wrong ..and in this analyses solution convergence is also not occuring after 10000 iteration in transient case..i dont know why whats the problem in my analyses ,always mass is adding up in between inlet and outlet can any one plz help me with this analyses..and i try to solve this analyses in steady state pressure or temperature coupled or divergence occure..plz some body help me... Thank u,

June 1, 2016, 02:27		#2
CFD-fellow Senior Member Behrooz Jamshidi Join Date: Apr 2013 Posts: 110 Rep Power: 13	Hi Have u done your simulation without cavitation? first converge it without cavitation to see if the problem is with your cavitation or no with something else such as mesh scale, mesh resolution or any other wrong setup. sanjiiv likes this.

June 2, 2016, 22:18	Thank you very much for your concerned reply..	#3
sanjiiv New Member sanjeev kumar.m Join Date: May 2016 Posts: 13 Rep Power: 9	Hello, I have tried this problem with atleat hundred of time ,as like you said altering the mesh upto 4 to 6 times andthe I analysed nothing is working . But,The problem is coming with mass flux not balancing (=0) between inlet and outlet , pressure report values are extremely high. It comes in Mpa,sometimes Gpa.I dont know why?.. If you sir or anyone liked to see my Problem details and definition .. I will sent you the complete details of it please post your mail ID here, Thanks for your concern, regards, sanjiiv