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Marconi September 29, 2012 04:45

Airfoil grid for turbulent flows: high aspect ratios
 
Dear all,

Lately I developed a structured C-Grid around an airfoil which uses about 103,000 points in the whole computational domain. Specifically, it has got 440 points around the airfoil and 100 points in its wake. The farfield was set at 50 airfoil cords (the chord is equal to 1 m).

This grid was generated for a Re number equal to 1e6 and a y+ equal to 0.5 (the solver uses the sst turbulence model). Therefore, this grid has a minimum grid-wall distance equal to 1e-5 m.

This very small minimum grid-wall distance leads to very high aspect ratios around the airfoil (the max AR around the airfoil is about 1000), and even higher ARs in its wake (200,000).

If the Re number increases these ARs will increase proportionally. For a Re number of 10e6 the maximum AR around the airfoil can reach 10.000.

My question is: in your experience might these ARs affect my simulation results? Is there a way (using structured grids) to decrease these ARs without increasing the number of points?

Many thanks for your help.

Regards to all,

Marco

Martin Hegedus September 29, 2012 13:01

The grid you have sounds about standard. For a 2D grid some people like to go out a little further than 50 chords. Maybe 100 to 150. But, that doesn't make too much difference. Try it for a moderate angle of attack. As for the AR, it is what it is. You're biggest error will come from the turbulence modeling at higher angles of attack, i.e. stall.


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