# Problem with the convergence for CFX solve

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 August 23, 2013, 22:54 Problem with the convergence for CFX solve #1 New Member   Join Date: Aug 2012 Posts: 17 Rep Power: 4 Hi. I'm architect learning a bit about aerodynamic and Ansys. I want to simulate the wind along a street with a small barrier (wall) in the middle using CFX. So, following some tutorials and posts found here, I built a domain, the mesh, set up the boundary condition (wall no slip for ground, front plane and black plane, inlet, outlet, and opening for the sky) and ran a simulation with a good result. Here I have some screenshots of the mesh and results: http://imgur.com/a/2lEQn http://imgur.com/a/ZChY3 The problem is that I wanted to change the inlet wind (originally a normal velocity of 6m/s) for a parabolic wind velocity profile from the inlet face in the domain using these expressions: Dt= 2[m] Ue= 6[m s^-1] Vel= Ue*(y/Dt)^0.36 http://imgur.com/a/kMxzf But now the CFX solve doesn't have convergence. http://imgur.com/a/vJ1or Someone understand what should I change or improve?

 August 24, 2013, 14:50 #2 Senior Member   Bruno Join Date: Mar 2009 Location: Brazil Posts: 236 Rep Power: 12 You simulation is converging, it's just doing so in a slower rate. Let it run for a few hundred iterations (not just the 100 CFX uses as default). You might also want to play with the timestep you're using. Set a physical timescale to a fraction of lenght_scale/velocity_scale, which for your case I suppose would be 0.1/3 to 1/3 s.

 August 25, 2013, 03:33 #3 New Member   Join Date: Aug 2012 Posts: 17 Rep Power: 4 Thanks for your response, brunoc. I'll try your suggestions and will publish here the results.

 August 25, 2013, 19:59 #4 New Member   Join Date: Aug 2012 Posts: 17 Rep Power: 4 Hi, I followed the suggestions but the solver doesn't reach a convergence, yet. http://imgur.com/a/zlVKX Originally, with a inlet wind of 6m/s (flat velocity profile) 50 iterations were enough to get a convergence. I only changed the speed wind parameter for a expression to get a parabolic wind velocity profile, but now I don't have convergence at all. Any other suggestions?

 August 25, 2013, 20:34 #5 Senior Member   Bruno Join Date: Mar 2009 Location: Brazil Posts: 236 Rep Power: 12 Have you also tried changing the timestep?

 August 25, 2013, 23:49 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 10,803 Rep Power: 85 This FAQ gives a range of suggestions: http://www.cfd-online.com/Wiki/Ansys...gence_criteria

 August 26, 2013, 02:32 #7 New Member   Join Date: Aug 2012 Posts: 17 Rep Power: 4 brunoc, ghorrocks, thanks for you help. I fixed it the problem. It was my fault, because just now I'm learning Ansys. I had put the expression Vel in a wrong field in the Inlet's details. Now, I have a good convergence, again. Thanks

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