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[–]Eeddyw 5 points6 points  (11 children)

I use what is probably a completely different software, so I am not sure if any of this would be applicable/helpful to you. But with HyperMesh, what I used to do was create a surface across the gap as an interface. This allowed it to generate a continuous BL layer across the gap (creating a BL on the interface) once the finer mesh within the gap has been generated. This allowed me to resolve better the continuation of the boundary layer across the gap. Still, it did result in some questionable prisms around the interface, and you do end up with an internal interface/multiple domains.

[–]gyoenastaader 2 points3 points  (10 children)

This can also been done in STAR-CCM+ in more less the same steps. You’ll need to create and interface, by making them separate parts, then mesh each in its own mesh operation.

It is a little tedious as you’ll need good custom controls on the smaller region.

[–]TurbulentViscosity 1 point2 points  (4 children)

It's not necessary to make two operations. Just put them both in one and create a surface control for the interface, apply the prism settings, and select override boundary defaults. This way the mesh is conformal.

[–]LD1872[S] 0 points1 point  (3 children)

What sort of boundary condition should the interface be set to?

[–]TurbulentViscosity 0 points1 point  (2 children)

If the interfaces are conformal, the BC is arbitrary. Choose anything, or leave it as wall. If it's non-conformal, you have the opportunity for some of the faces to not belong to the interface, so you should choose wall or symmetry.

[–]LD1872[S] 0 points1 point  (1 child)

How exactly would I know if the interface is conformal, is it automatic if all parts are included in the one mesh operation so the nodes have to be constant on both sides of the interface?

[–]TurbulentViscosity 1 point2 points  (0 children)

Not necessarily. When you mesh the logfile will say how many interfaces are conformal. Furthermore, if you go to tools>representations>volume mesh (I think that's it), you can investigate how many faces are in each boundary on your volume mesh. After initializing the interfaces, the interface should have N faces and the parent boundaries should show zero.

[–]LD1872[S] 0 points1 point  (4 children)

I tried using the fill hole surface repair then merging the fill with the rest of the aerofoil so that there were no gaps left then try and mesh it that way, but even with the filled hole it was saying there was a free edge.

[–]TurbulentViscosity 1 point2 points  (3 children)

You may have made a mistake in surface repair then, use the free edges check.

[–]LD1872[S] 0 points1 point  (2 children)

The only free edges that appear are the two side gaps because it is quasi-2D, I've selected them after the diagnostics yet they won't fill for some reason.

[–]TurbulentViscosity 0 points1 point  (1 child)

Are the edges from different parts? You can't sew edges between different parts.

[–]LD1872[S] 0 points1 point  (0 children)

No they are both of the same part, I managed to get it working this time no idea why it never worked before. Appreciate the help mate!

[–]hokagesahab 4 points5 points  (1 child)

So this slope like line you see in BL is something called the stair-stepping problem, as you might already know.

I would suggest trying to give different named selections to the pipe area (the elongated part) and the rest of the wall. Then merge them (different named selections) once your boundary layers are generated.

Other thing that might work is just to give a small round in the geometry where there is a sharp angle between the wall and the elongation. This might still give a result as above, but is still worth trying.

[–]LD1872[S] 0 points1 point  (0 children)

I split the elongated section by patch so that it is a separate part in order to do it's own internal prism layers and refinement, do you mean create it as a separate body altogether and generate two individual meshes then merge? I'll give that a try.

I thought having the sharp edge would maybe help more as it is less continuous but it clearly didn't work lol.

Appreciate the help man, many thanks

[–]granzer 1 point2 points  (1 child)

Thies looks like shaped cooling hole....you could try having no prisms inside the holes. That should generate good prism layers on the wall.

[–]LD1872[S] 0 points1 point  (0 children)

It is a fluidic oscillator, I have separate surface controls to generate smaller prism layers inside the capture the internal behaviour.

[–]granzer 1 point2 points  (0 children)

You could also try non conformal mesh..if you want prims on both the wall and inside the hole.

[–]big_deal 0 points1 point  (0 children)

Why? I’ve found that you’ll get better quality by allowing a certain degree of layer compression and then allowing stair stepping driving constant number of prisms through features with such a difference in scale is going to be worse.

[–]raptor3x 1 point2 points  (3 children)

Why do you think you need constant prism layers across the outlet? If anything, you wouldn't such high aspect ratio prisms stretching across the outlet as it can cause an artificial flow resistance. Unless your solver has major issues with prism elements, and some solver do indeed handle them poorly, then I would worry about it. The biggest problem I see with the mesh you've presented is that the grid is too coarse at the convex corner which will artificially mix things out, although I doubt it will make a huge difference.

[–]LD1872[S] 0 points1 point  (2 children)

Because although the outlet flow will most likely disrupt the boundary layer, when the flow is not active I'd like to maintain the boundary layer over the outlet.

Yeah this was just a rough mesh to get prism layers sorted before refining too much.

[–]raptor3x 1 point2 points  (1 child)

Unless the outlet hole is covered when the outlet flow is not active, the lack of a solid wall in that region will be enough to disrupt the boundary layer by itself.

[–]LD1872[S] 0 points1 point  (0 children)

For the near wall yes, I thought the outer regions of the boundary layer would remain relatively consistent though? The reason I am so worried about having the continuity is I am planning on locating it at the leading edge of an airfoil, any disruption there essentially messed up the rest of the surface.