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Old   April 11, 2006, 12:26
Default convergence problem
  #1
tina
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hello everyone

I need some help with convergence issues, I am modelling flow around aircraft wings, viscous at mach 0.45, and I have y and z momentum not converging, would anyone be able to help on this matter. Do you think its a mesh problem, or boundary condition problem?
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Old   April 12, 2006, 18:33
Default Re: convergence problem
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James Date
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There's loads of things this could be! Checking the quality of your mesh is a good starting point. Making sure you have set the correct boundary conditions is also critical. After that there's a lot of tweaking with solver parameters which might also solve the problem. Many of these will be related to the method/models you are using, i.e. steady or transient, turbulence model.

I always start by creating a simple low density mesh and checking my boundary conditions are correct and that this model converges down the required residuals. Then I increase the mesh density and make sure the resolution is sufficient in the right areas, i.e. near wall/boundary layer and where high gradients are expected. The critical near wall first node spacing will depend on the turbulence model you are using.

I hope this helps.
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Old   April 13, 2006, 07:05
Default Re: convergence problem
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tina
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hey James

thank you for your help, I have actually tried that and it did converge with the coarse mesh , but the fine one is quite bad.Also, "The critical near wall first node spacing " , can you just explain a bit more about this.

thanx
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Old   April 13, 2006, 08:36
Default Re: convergence problem
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James Date
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Check out the best practice guidelines here for excellent info on near wall spacing and many other issues.

https://pronet.wsatkins.co.uk/marnet/

and also those of ERCOFTAC

http://www.ercoftac.org/SIGs/BPG.html

James
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