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-   -   3d Airfoil Modelling Problems (http://www.cfd-online.com/Forums/fluent/40155-3d-airfoil-modelling-problems.html)

Olly March 16, 2006 07:54

3d Airfoil Modelling Problems
 
Hi

I'm trying to model a 3d airfoil using fluent but am having problems getting the solution to converge. The times that it has converged there is a negative gauge pressure everywhere except for a small point at the front of the wing.

I've modelled the wing in a wing tunnel with the following boundary conditions: Inlet - Velocity inlet set to 40ms Outlet - Outflow All other walls set as Symmetry

I'm using the k-epsilon solver, i've tried changing the mesh a few times from coarse to fine but am having no luck an ideas?

Thanks

Oleksiy Dushyn March 16, 2006 09:50

Re: 3d Airfoil Modelling Problems
 
Hi,

- you should replace your symmetry doundary conditions by periodic ones;

- if you are simulating a static case do not make your mesh too fine otherwise you'll run to another problem with flow stability;

regards,

Alexey

Olly March 17, 2006 10:53

Re: 3d Airfoil Modelling Problems
 
Thanks for the reply,

I changed the outflow to an outlet pressure and this seems to solve the negative gauge pressure up and down stream of the airfoil.

I'm now having problems trying to get it to converge at all. the residual plots just go up and then it doesn't converge, what does this mean?

Thanks

Oleksiy Dushyn March 17, 2006 11:44

Re: 3d Airfoil Modelling Problems
 
As I've wtitten in my last posting if you want to get a good convergence you have to replace your symmetry BC by periodic ones.

Good luck

Olly March 17, 2006 12:12

Re: 3d Airfoil Modelling Problems
 
Thanks again, i have replaced the symmetry bc with periodic ones but with no success.

What would cause the residuals to go up?

Thanks

Oleksiy Dushyn March 17, 2006 13:55

Re: 3d Airfoil Modelling Problems
 
What initialization do you use?

Olly March 17, 2006 15:26

Re: 3d Airfoil Modelling Problems
 
I initalise it from the inlet, is that what you mean?

Riaan March 19, 2006 16:10

Re: 3d Airfoil Modelling Problems
 
1) use fmg-initialization

2) reduce your under-relaxation functions

3) does your mesh "CHECK" ok?



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