Motion inertia and parented grids

[japetus]

I'm doing some sims with a rocket-like object, having long plumes of smoke and fire. It's going well, except I seemed to have run into a bit of a question concering how Motion Inertia and Adaptive Grid work together to effect the motion of the smoke/fluid. Maybe I'm just doing it wrong, but the motion seems to be very differrent traveling through a grid vs. a grid parented to a moving object. The first works as I would expect, the second looks like the smoke is exploding upwards. Motion inertia is turned on I'm on Phoenix 4.41 and Max 2022, I should probably upgrade, but wanted to see if I was doing anything wrong first.

[Svetlin.Nikolov]

Indeed, it is very different since when the grid is moving with inertial forces enabled, it's basically like a static grid that has wind in it. This blurs and smooths out the moving fluid.

This effect could often even be used in case the grid is moving too fast and needs a lot of steps per frame to catch up to moving objects.

[japetus]

Hmm so would it be possible to get a result more along the lines of the sim on the left with a parented grid? I was able to get the effect I needed by using very large max adaptive grid and having it shrink at a certain temperature, which worked well enough for what I needed. I feel like this should be called out in the help docs since it's implied that parenting the grid to an emitter to save grid size would not have such an effect.

[Svetlin.Nikolov]

Ah, I better check the docs and correct it, but indeed if you use adaptive grid that shrinks it would not have these wind formations in it - you solved it the right way!