Hi, is it possible to get one fluid to affect the motion of another, but not vice versa? A naive L affect R doesnt seem to work, as this starter hipfile illustrates. While the rbd object affects both (great) im wondering how I might go about getting a “bottom layer” fluid to propagate through a “top layer” fluid. Somehow take the surface field of one fluid and use it to update the collision field of the other? Any masters able to provide some guidance? thanks!

I haven't looked at your file, so I'm not sure if this is exactly what you're after, but you can actually use “density” point attributes to make one set of points lighter than another. They'd be solved with one flip solver.

right, so that was my first inclination. thats great if you are able to get enough stability going between the two. In this case I have a fast moving emitted layer that i want rushing across the top of a fliptank without disturbing it too much. I use a ground plane to ensure there is separation between the dynamics of the top layer, but that kills my fliptank. Can i have a ground plane only apply to the emitted fluid and not the tank? Are there ways to combine two flip solvers/objects? write out the bottom fluid and use its vel field to disturb the top top fluid?