C-grid or O-grid for airfoil?
Hi,
I've coded a NS solver based on cartesian grids and I'm now extending it to structured grids. My main objective is to simulate airfoils, possibly extending to 3D. Hence, is there a clear choice to use c or o-grid for airfoils? Please explain why. Also I've download a grid generator for airfoil known as UGRID which can generates 2d structured o-grid for airfoils. Is there similar type of program which can generate c-grid for airfoil as well? Thanks alot! |
Re: C-grid or O-grid for airfoil?
Dear Quarkz,
As far as airfoil simulations as concerned, I find no distictive reason why an O-grid should be preferred over a C-grid or viceversa for all kinds of problems. However, a C-grid CAN be preferred as the grid will be aligned to the wake or slipstream at the trailing edge of the airfoil. Particularly, in context of adaptation, wherin you have a viscous flow past airfoil, a boundary layer and the wake are common features. The BL and the wake are to be adapted in the streamwise direction ( to resolve it better). The use of a C-grid will help you achieve this easily, whereas it is not the case for an O-grid. However on a relatively fine grid, results on both O- and C- grids are found satisfactory. If you are intersted in handling more complicated geometries you can try UNSTRUCTURED grids as well. I am not sure of any program for C-grid generation available, but if you are able to use an O-grid generator with a cartesian meshing and match them, a C-grid can be generated, though some effort is needed in that direction. Hope this helps Regards, Ganesh |
Re: C-grid or O-grid for airfoil?
For viscous flow a C-grid is preferred because it allows you to resolve the wake. To really resolve the wake, you would actually need a different C-grid for each angle of attack. Often enough this is not done, which somewhat weakens this argument for using a C-grid. More important than resolving the complete far wake is the nice resolution of the region right behind the trailing edge.
O-grids are good enough for inviscid flow, where they have the advantage of reduced cell count as compared to C-grids. The resolution in normal direction is high only where you really need it: right on the airfoil surface. The region behind the trailing edge is not well resolved, which makes the use of O-grids questionable in case of viscous flow. You may still get good results even for viscous flow, depending on the particular case. |
Re: C-grid or O-grid for airfoil?
Hi,
thank everyone! I'm writing an NS solver hence it seems that I will need to use C-grid. However, I only 've got a free 2D O-grid generator, Ugrid which is simple to use and user-friendly. Does anyone know of a c-grid generator (free/commercial) for airfoil. I prefer one where i just enter the x/y coord and a reasonable mesh can be generated. Thanks again |
Re: C-grid or O-grid for airfoil?
Hi,
just to add that my main interest is in finding lift and drag of airfoil. in that case, is c-grid still more suitable than o-grid? thanks again |
Re: C-grid or O-grid for airfoil?
There is C-grid Generator for free.
The name of the program is "MeshPilot" And you can download this program through the following website. http://www.shore-cfd.com/html/shore_...eshpilot.shtml and maybe this program support naca series airfoil. And I have questions. Now I trying to make 2-D airfoil grid for N-S(Spalart-Allamas). Airfoil is RAE 2822. But it is difficult to make this grid. Do you know how to determine 1. Boundary layer thickness 2. Grid spacing 3. Etc. ^^ I'm poor at CFD. Is there reference or technical guide book for grid making? Thanks, in advance~ |
Re: C-grid or O-grid for airfoil?
You can see again the "Fletcher book" T2, there is a source programm (in Fortran) for mech generation (C-grid) around naca airfoil utilising the algebraica methods (multi-surfaces elements)
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