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Santiago Orrego. December 14, 2006 20:26

meshing a Naca 4412 airfoil - help
hello. Im analysing a Naca4412, and I need some recomendations of the way that I should mesh the rectangle that contains the airfoil (low Re). 1. What kind of face Spacing? (Angular, relative error, constant, volumen spacing ?) 2. If I should create a new Face Space, and refine the mesh around the airfoil or create a control point and refine the mesh ? 3. how can I change the type of the element? and know the dimension, so I can extrude the 2D shape? 4. How many layers in Inflation? what configuration in teh inflation?

Thanks in advanced Santiago.

Glenn Horrocks December 17, 2006 17:37

Re: meshing a Naca 4412 airfoil - help

These parameters depend on many things. Some things to consider are:
  1. <LI>What Re number? <LI>Is transition important? <LI>Is the foil stalling? <LI>Do you want transient results? <LI>Do you want accurate drag numbers or just the lift? <LI>Any any 3D effects eg wing tips?

These parameters affect both the choice of physics to model and the mesh.

Glenn Horrocks

Santiago Orrego. December 17, 2006 22:05

Re: meshing a Naca 4412 airfoil - help
1. Re=400.000

2. yes.

3. no.

4. no.

5. both.

6. not yet.

Do you have a tutorial or paper that specify what kind of mesh do I need? or some kind o guidance? Thanks a lot santiago.

Glenn Horrocks December 18, 2006 05:42

Re: meshing a Naca 4412 airfoil - help

In that case you really only have one option which is to use the transition model in CFX. That has the following implications:
  • <LI>You need the SST turbulence model with the transition model extensions. <LI>You need to have a mesh with a y+<=1, but not too small. <LI>Use either a hex mesh or inflation layers ensuring any transition to tets occurs well outside the boundary layer, including any transition induced separations. <LI>The maximum expansion ratio in the inflation layers is problem dependant, but the transitional turbulence model is a bit sensitive to expansion ratios above 1.05 (definitely) or 1.02 (sometimes). <LI>At this Re number the transition is likely to occur in the front half of the foil (unless this is a laminar flow airfoil) so make sure this region is well resolved. <LI>You will need a mesh fine enough to resolve the curvature at the front accurately <LI>It will be very sensitive to upstream turbulence conditions and possibly blockage factor as well <LI>It will also be sensitive to foil surface condition. You may need to artificially trip the turbulence at the correct spot.

Hope that helps. I think you will find some validation examples of the transitional turbulence model on the CFX-community website. If not your CFX support person should have some.

Glenn Horrocks

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