What's the most efficient method to avoid the final hair generated going through the mesh when simulated with wind.

Should we push it all out with ‘hair collide with vdbSOP’?

In these kinds of cases I drop down a collide with vdb node at the end of the groom stack. (sorry if the term is wrong, I don't have Houdini in front of me). Set the last two values to 1 (push and lift..?) It must remain at the end of the stack or it does not work correctly.

I find the built-in wind with the groom not that useful. You may want to zero it out then add in a wind via the simulation step, or if your character is walking you may not even need it as velocity will kick in?

Do you do that on the groom or the hair generate? Looking to make production quality up close hair, so nothing can go through the head. Happy to run overnight sims to achieve it too.

In my test, I placed the collide with VDB SOP at the bottom of the groom. So before deforming or simming. I also used custom VDBs rather than the default convert system that exists in each of the steps. (i.e. groom, deform, sim). If you dive inside you'll see that each node keeps it's own copy of the VDB (just a vdbFromPOlygons) when you use that feature. By using a custom VDB (similar to deform geometry collision output) you can save some memory because you are pointing to a single VDB rather than a unique one for each step.

you can also use the a collision object, i would create a big blob that have the shape of the head (avoid having open areas like eyelids or mouth)

i would play with the subframes and increase the solver resolution. and i would use a regular wind node

check fabio for houdini, comes with a lot of tools
http://polybevel.wixsite.com/fabio-hair-system [polybevel.wixsite.com]