And my current meshing strategy is (I update this as I learn more 
) :
- Decide on the wind-tunnel wall sizes and location of the geometry in it, then define these in the Background Mesh Box coordinates. For me, that BMB (on my left/right symmetrical geometry), was about double the wingspan wide, centered in triple the height of the geometry (but much more for just a wing and more if at high aoa’s) and with a BMB length 4 times the length of the geometry with geometry positioned one geometry length back from the front of the BMB.
- Set Parameters for number of x,y,z cells on the Background Mesh Box (I started with about ~50 inch mesh squares, it is these cells that get divided by mesh refinements on the geometry. BUT, in the end, 15 inch squares were best for this 125 inch half span wing based on final BMB dimensions and final refinement levels chosen)
- A wing geometry should have 3 spanwise edges, 1 at the leading edge at the smallest radius of the airfoil and 2 at the trailing edge. The multi taper wing was split into spanwise planform taper surfaces with ‘rib’ surface edges at each change in taper. You can not have intersecting solids in your geometry, so far I boolean all my touching solids together into one solid in CAD but I expect later to use multiple touching solids but that do not intersect. So far I have only used solids, but I understand that single surface meshes and closed meshes can be used but likely with the same touching/intersecting rules.
- You might have to create a narrow surface break near the plane of symmetry to get Surface refinements to act on the symmetry edge of some surfaces (you may likely only have to do this if your geometry is already a 1/2 model of symmetrical item).
- I use a cartesian box to provide a refinement ‘outside’ the geometry that is refined at level 2 so that the air gets ready to hit the geometry in smaller cells. I am using about 1/2 the length of x,y and z dimensions of BMB and positioned sorta like the BMB is positioned around the geometry.
- I use a cartesian box to enclose the geometry pieces (ie Wing, Horizontal stabs, Fins, Fuselage) and create a Region Refinement for all of them at a Level 5 refinement level.
- I used a Surface Refinement on all the wing surfaces to try to get all the edges of the surfaces clearly defined in the mesh. I had to go to Level 10 fineness to minimize the effect of edge jaggies and to keep the trailing edge defined all the way to the wingtip. Unfortunately, I had to change the Level back to 8 when I started layering the mesh since the layering algorithm was choking on the small face sizes and deflating everywhere, so the level was a balance between edge sharpness and layering results.
- To keep total number of faces low, I set the edge distance of the Surface Refinement to 0.
- Set layering variables to match your needed yPlus, reference length and speed. Here is where I finally figured out how to do this.
- To determine if my layering has succeeded sufficiently, I no longer look at clips of my mesh (very tedious). I just use my method of getting a weighted % inflated value for the mesh from the last % inflated chart in the meshing log. This post should show how to create the weighted % inflated mesh parameter.
- To get my yPlus between 30 and 300 without too many layer deflation zones, I am using only 2 layers at an expansion ratio of 1.1 or 1.2. I use the old post processor to look at my yPlus range on the on a surface plot of yPlus onto the geometry (this is done on the results of a CONVERGED simulation). The old post processor lets you turn off the bounding box and internal mesh to do this and I can’t figure out how to do the same in the new post processor.
- Make sure Parameter ‘Use relative size for layers’ is off (false).
- Add Darrens Tweaks (see this post)
Someday when I have to do this again, I will be coming back here to remember what I did
Dale