Theory for the Fluid–Particle Interaction Interface
The Fluid–Particle Interaction Interface combines the Particle Tracing for Fluid Flow and Laminar Flow interfaces to model the motion of particles in a fluid in which the acceleration or deceleration of particles creates a significant volume force that affects the motion of the fluid. The Fluid–Particle Interaction node computes a volume force that is equal in magnitude and opposite in direction to the total drag force that the fluid exerts on particles.
If particles are released into the fluid at a constant mass flow rate, it is possible to significantly reduce the simulation time and computational cost by combining a time-domain calculation of the particle trajectories with a Stationary solver for the calculation of the pressure and fluid velocity. The two calculations can then be performed using an iterative procedure that alternates between them until a self-consistent solution is attained.
An iterative solver loop that consists of a time-dependent solver for computing particle trajectories and a stationary solver for computing all other dependent variables can be set up automatically using the Bidirectionally Coupled Particle Tracing study step, described in the COMSOL Multiphysics Reference Manual.