– PIC (Particle in Cell) and FLIP (Fluid Implicit Particle) are two different methods blender uses to calculate the motions of the particles (more precisely the velocities).
– PIC is less accurate, but stable. More PIC produces more viscous fluids as a consequence of numerical dissipation (due to a double interpolation).
– FLIP better maintains individual particle velocities, is very accurate but can become chaotic and instable. More FLIP produces less viscous fluids and more noise on the surface.
– PIC/FLIP is a hybrid method which mixes (linear combination) PIC and FLIP.
– Blender default value for Flip Ratio is 0.97 which gives good stability and accuracy.
– Flip Ratio=1.0 :a completely FLIP simulation (lot of splashes, more unstable)
– Flip Ratio=0.0 :a completely PIC simulation (less splashes, more stable)
– As always, remember: Blender is not “real simulations” oriented, we will never obtain a “real” simulation as everything is based on approximate physics that lead to approximate solutions, so choose the parameters that give you the simulation you like more!
– In this example see how 8 different values of Flip Ratio affect a simulation. Note how Flip Ratio=0 does not produce splashes while Flip Ratio=1 too many: