About SPH VE 6.7
FlowSolver 6.7 is a brand new flow solver method, added to Subscription Drop 7. This new flow solver is the most stable fluid solver, yet!
It is the recommended fluid solver, to be used from now on, for all kinds of fluid simulations. The 6.7 solver settles remarkably fast and distributes pressure within a fluid in a much better way than any fluid solver before, even when smaller kernel sizes are used. Low viscosity simulations will look much more life like and show a more 'splashy' behavior when compared to the older fluid solver variants.
It is important to understand that the acceleration limit for this type of solver should be set to 10 instead of 1000 which was necessary with the older solvers.
About SPH2 (6.3) Fluid Solver
The SPH2 algorithm is intended to become the new standard solver for particle based fluid simulations in thinkingParticles; SPH2 offers a much more forgiving nature with high pressure values appearing inside of the fluid; it also handles larger time steps much better than its predecessor SPH1.
SPH2 has algorithm specific options to offer a more refined control of pressure equalization over time. Fluids can be simply adjusted to act more lively or be more calm and equalize much better. Keep in mind; in general this is still a particle based SPH solver intended for faster flowing fluids creating lots of splashes. It is not really meant to create large scale ocean bodies of water.
In some sample files the FlowSolver's "ExternalSolver" output is connected into Bullet's "On" input. However, in certain cases this does not seem required.
To get Flow fluids behaving inside a Bullet Softbody or Rigidbody you can setup the softbody/rigidbody as an APF with an APField, APFInitiator (using Shape Distance), and an APFOutputTo (Out To: Boundary, and specify the fluid as the PGroup).