# Target-mass-flow-rate:CONVERGENCE PROBLEMS

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 March 3, 2010, 07:01 Target-mass-flow-rate:CONVERGENCE PROBLEMS #1 New Member   Join Date: Jul 2009 Posts: 25 Rep Power: 9 Hi, I'm modelling the flux over an airplane and I'm modelling the mass-flow outlet in the air intalke of the motor using the bc: -pressure outlet+target mass flow rate The flux is compressible (M=0.8) I've great convergence problems: the solution is not converging AT SECOND ORDER and in addiction to this the simulation goes on very slowly. Can you help me? How can I solve this problems? thanks!

 March 3, 2010, 16:26 #2 New Member   Join Date: Feb 2010 Location: Germany Posts: 12 Rep Power: 9 Hi, I'm making a cavitation analysis in a valve so there's high speed and i also have problems of convergence. What i would suggest you is - start being totally sure about your viscosity model - calculate an initial solution with first order convergence - decrease tolerance so that you will get a more accurate solution - start changing to second order but step by step (first pressure and continue with the others) till you see which one gives you problems Maybe you can modify something by knowing where you have problems to converge. Also use a coarse mesh to start so that the problem is not the mesh. I hope i can help you

 March 3, 2010, 16:50 #3 New Member   Join Date: Jul 2009 Posts: 25 Rep Power: 9 Hi mems, thank you for your reply! One fast question, first of all: you use for your simulation a positive or a negative gauge pressure for the pressure outlet (with target mass flow rate?)? If the reference pressure in the aerodynamic field is 0 Pa, and if I use a positive gauge pressure air will "try" to get into the field, right? And so if I want air to go out from the domain I must set a negative gauge pressure, it's right? thanks! sara

 March 3, 2010, 17:02 #4 New Member   Join Date: Feb 2010 Location: Germany Posts: 12 Rep Power: 9 Gauge pressure is always difficult to know the behaviour. i'm using 0 Pa for both Mass Flow Inlet and Pressure Outlet, cause my domain is the valve, I have no aerodynamic field. I'm still checking my boundary conditions so i cannot help you with this. Sorry, mems

 March 3, 2010, 17:04 #5 New Member   Join Date: Jul 2009 Posts: 25 Rep Power: 9 Thanks for your reply! You are kind! I try to open a new tread and ask for this question... Bye and thanks sara

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