The document describes the PISO loop algorithm for coupling discrete element method (DEM) and computational fluid dynamics (CFD) simulations. It involves initializing values, solving the momentum and pressure-correction equations in a predictor-corrector manner to update fluid fields, calculating void fraction and transferring forces between the DEM and CFD solvers at each time step, and iterating the coupled DEM-CFD calculation until the end time is reached.

1. PISO Loop
Set Initial Values
t
=
0
Solve Momentum Equation
(Predictor Step)
Compute Fluid Void Fraction, Set f=0
Solve Pressure-Correction Equation
(Corrector Step) + f
Correct Pressure and Flux Fields + f
f=f+ρf (1 − εf )
Up−u
dt
Transfer Total f For DEM Calculation
t < T end ? End
Set Particle Loads
Solve Newton-Euler Equations
t = t + dt ?
Transfer New Particles Position,
Linear, and Angular Velocities
DEM Loop (LIGGGHTS)
CFD Loop (OpenFOAM)
t
=
t
+
dt
Yes No
Inner
Loop
No
t
=
t
+
dt
n
Yes
Volume Penalization IBM