I have these Vellum fluid particles:



They just explode upon simulation for one single frame:



I don't get what's happening here. Where does the force come from?

Haven't done much vellum fluids so can't help you much, other than telling you Surface Tension seems to be the culprit (in vellumsolver1: Advanced/Fluids/Surface Tension).

It turns out to be mass/density. I'm not sure why mass per particle causes this explosion, but setting density works perfectly fine.