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grids around airfoils at high aoa

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Old   October 9, 2002, 07:42
Default grids around airfoils at high aoa
  #1
uygun
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I am trying to build grids around different airfoils to obtain viscous flow solutions at high angle of attacks (between -25 to +25 deg). Could anyone help me and give some info about grid point distribution at downstream of airfoils for high angle of attack flow simulations? If possible could you send me some jpeg files of grid files built before for the high aoa flow analysis. Thanks a lot...
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Old   October 9, 2002, 08:14
Default Re: grids around airfoils at high aoa
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John Andrews
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Unfortunately I haven't seen a systematic study of what you want. I imagine you'll have to do a lot of experimentation yourself, using lots of different grids (you want lots of grid points where you get separation, right?). If you're using structured grids, I have found MeshPilot (free software) very useful for generating airfoil grids quickly - see http://www.shore-cfd.com . Good luck.
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Old   October 9, 2002, 09:45
Default Re: grids around airfoils at high aoa
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uygun
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For grid generation, I use GRIDGEN. The problem is that Do I have to rearrange grid distribution at downstream dependinding on the aoa (especially high aoa, above 15 deg ) to resolve wake region?
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Old   October 9, 2002, 09:58
Default Re: grids around airfoils at high aoa
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John Andrews
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That depends on what your original grid distribution is. I suggest that you successively refine your grid until the solution "stops changing" - then you'll know that your grid is fine enough.

As a very rough guide, you should always try to have a relatively refined area of your grid where flow gradients are high.

Of course, deciding when your solution has "stopped changing" is a whole new problem!

There are probably plenty CFD people out there who'd advocate using adaptive grid refinement to help out with this type of situation.

I hope that's at least slightly helpful!
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Old   October 9, 2002, 10:14
Default Re: grids around airfoils at high aoa
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uygun
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Instead using adaptive grid, I am trying to build some new formulas that can be applied at downstream at high aoa flows so that they form a good guide for the starting grid and reduced the no of grids generated and cost less time ofcourse. I have no problem with upstream and over the airfoil but I have to try downstream. Thanks alot
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Old   October 9, 2002, 10:57
Default Re: grids around airfoils at high aoa
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Mark
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This may be a bit of a simplified way of getting a result but you could leave the airfoil in a level position and change the airflow direction, i.e change the x and y magnitudes, to represent the aoa???

Mark.
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Old   October 9, 2002, 11:07
Default Re: grids around airfoils at high aoa
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uygun
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Thanks Mark, but that's not what I am asking. I am asking for the grid node distribution at downstream for high aoa like 25 deg or 35 deg.
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Old   October 10, 2002, 07:12
Default Re: grids around airfoils at high aoa
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Dave
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Is your simulation a steady state simulation ? As this would effect your mesh distribution down stream. What you are effectively doing is turning a stream lined body into a bluff body. With a stream lined body the grid resolution is really high, so for these high AoA's I would guess you're really going to have to pack the grid in there, even for a steady simulation ?? Dave
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Old   October 10, 2002, 10:01
Default Re: grids around airfoils at high aoa
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uygun
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"so for these high AoA's I would guess you're really going to have to pack the grid in there, even for a steady simulation ?? Dave" Thanks Dave, I study steady state. Do I have to increase resolution in the wake region for both near and far downstream region? I mean how should be the grid resolution at 3,4,5,6 chords away from the airfoil in wake region?
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Old   October 11, 2002, 08:30
Default Re: grids around airfoils at high aoa
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uygun
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Thanks a lot.
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