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Onera M6 3D validation

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Old   September 12, 2014, 10:41
Default Onera M6 3D validation
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Hello dear forumers
Greetings!

AFter completing the 2D validation of NACA0012 I now move to validate 3D Onera M6. I take following guidelines for my study:

http://www.grc.nasa.gov/WWW/wind/val.../m6wing01.html

I download the stp file for wing and create the tunnel around it. PLease bare in mind I am now just meshign the wing with perfect hex and hence I keep the tunnel size small until I am happy about the mesh and blocking methods. Once I am ok with the blocking, i replace the geometry with bigger dimain (30 chord length to all 3 sides) and then associate edge to curve. This is I do because so I dont have to zoom in and zoom out while deciding on the blcoking. The final mesh will also has Y+ values close to 1 so to resolve the boundary layer and gradual increase from wall to domain boundaries. I will do some transonic simulation too so I will make sure the mesh is fine to capture the bow shock and trailing edge shock.

PLease have a look my mesh so far:













Any advise on whether I need to change the blocking method? I see dome shape inlet in many case studies but it is hard to block so I choose simple rectangle tunnel.

THank you for all the suggesion, this form is very helping
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Old   September 12, 2014, 12:20
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You'll get a better response from the ICEM forum - ask there.

What skewness and orthogonality are you getting from mesh? What are the expansion ratios? And is this compatible with CFX? For high speed compressible numerics I think the factors I mentioned are important.
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Old   September 12, 2014, 14:35
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Hi Ricochet, thank you for the kind coment

I have experience and skill of ICEM CFD and CFX for basic working but external compressible flow very difficult to simulate correct. I post here because I get advise about CFX only here.Every CFD package is different needs for the meshes and hence it make sense to ask experts in CFX about the distribution of mesh. BUt you are right, i post there too so i get more advise

Sorry I did not posted the quality metrix because I yet not finished the meshing. But I make sure that for final mesh the elements is cuboidel and skewness, orthogonal quality and determinant of all element is between 0.7 to 1. I use bigeometric agorithm for mesh noding but can't force expansion ratio because ICEM switch from parabolic law to hyperbolic law if nodes and ratio I specify not match to parabolic law. So ratio change than what I specify. But I generally make sure ICEM keep ratio between 1.1 to 1.3.But i thoght CFX create polyhydral control volumes on nodes and then calculate fluxes on polyhydron faces, so really quality of mesh matter??

I make sure in CFX that I captur shear layers and gradient good, specially the shock waves and transition at leading age and separation at trailing age. CFX have high resolution scheme with bounding so i am hopign that it switch discretisatiotion scheme to first order near shock so no oscilation due to second order. I am reading literature on this and will update the post with learning
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Old   September 12, 2014, 17:32
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I would consider a C grid for this. It is likely to be much better quality.

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But i thoght CFX create polyhydral control volumes on nodes and then calculate fluxes on polyhydron faces, so really quality of mesh matter??
The importance of mesh quality depends on what you are modelling. If you are modelling low Re flow then quality does not matter so much. If you are modelling compressible flow or multiphase flow it is very important. If you are modelling surface tension it is critical.

The best thing to do it try a few meshes on your geometry and find out for your specific case how sensitive it is.
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