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.

Hi,

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

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.

Hi,

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