Hi friends I am working on temperature disturbution on fins in heat exchangers ,my boundary conditions for coolent flow -inlet(velocity-inlet),outlet(OUTFLOW) Air flow-inlet(velocity-inlet),outlet(Pressure-outlet)

my prob is my solution does not converge ,for first 70 iteration it reachesa residue of 3.4X 10E-3 from there onwards its keep on flutuating between 4.23X 10E2 2.55x10E-2 ,evn afetr 400 iteration ,wat cud be the prob

Help me to solve this prob

Hi; Your convergence problem can be refered to many things. A general option to help solution convergence, is decreasing under relaxation factors. Of course, you should not set them below (0.1). For unsteady calculations, this problem can be refered to a high time step. You should decrease its value. If you model a compressible problem, it is strongly recommended to do not use velocity for inlet boundary. You should use pressure inlet or far field or mass flow rate B.C. If you use a turbulence model, take care about Y+ on your wall B.C. Take care about your choosen computational domain. For an external flow, you should locate your external boundaries far enough from bodies or generally high gradient regions. Oh, a main mistake can be about the location of outflow B.C. You must locate this B.C. far enough in a region with zero velocity gradient.

hope this help you

ROOZBEH

I'd suggest not to mix, if possible outflow and pressure outlet boundary conditions. Usually a pressure outlet allows to obtain a more stable and better converging solution.

Hi

ap