volumeFracTest

Template Info

Target Parameters: CFD_volFracScale
Contact Models:
Particle Shapes: sphere multisphere

The setup consists of a cylindrical bin entirely filled with particles; see Figure 1. The total particle volume is measured on an Eulerian CFD grid. If real particles are porous, the volume representation might need to be corrected, since the volume fraction (defined as the ratio between the particle volume and the total volume of the bin) is an important factor in drag laws. This calibration template tries to match the volume fraction calculated by the CFD-DEM model with a reference volume fraction (e.g., from experimental measure) by varying the scaling factor CFD_volFracScale. The latter corresponds to the volScale factor of the CFD-DEM voidfraction models (see CFDEM®coupling documentation for more information), which is a factor scaling up (if volScale > 1) or down (if volScale < 1) the particle volume seen by the CFD field.

_images/bulkDensity_sketch.png — Figure 1: sketch of the simulation setup. An equilateral cylinder is filled with particles and the volume fraction is calculated on an Eulerian CFD grid. $d_{max}$ denotes the maximum particle radius (in case of polydisperse system), $CG$ is the coarsegraining factor and G_D_RATIO is the ratio between the diameter of the cylinder and the diameter of the largest coarsegrained particles.

Figure 1: sketch of the simulation setup. An equilateral cylinder is filled with particles and the volume fraction is calculated on an Eulerian CFD grid. $d_{max}$ denotes the maximum particle radius (in case of polydisperse system), $CG$ is the coarsegraining factor and G_D_RATIO is the ratio between the diameter of the cylinder and the diameter of the largest coarsegrained particles.

This template is designed to work together with bulkDensityTest and ErgunTest. The volume fraction scale factor, as well as the bulk density, should be calibrated before the ErgunTest.

Simulation Setup

Initialization

During the initialization, particles are poured into a cylindrical bin. The simulation automatically stops when the bin is full and the particles have settled. This is achieved by monitoring their kinetic energy. The finished packing is then written to a restart file. Then one CFDEMcoupling timestep is run and the volume fraction of the granular phase is measured.

Optimization

The optimization run only performs a single time step calulation to recalculate the volume fraction in the cylinder.

Quality Function

The quality function is the magnitude of the normalized difference of the target volume fraction and the current simulation volume fraction.

Measurement file

The relevant information for the calibration is the parameter CFD_particle_volume_fraction. However, due to current restrictions of the framework, Aspherix® Calibration needs a measurement file to be present. The content of this file is irrelevant and will not affect calibration.

Template parameters

General settings

Parameter	Default
scaleweight	1
pairGranModel	hertz
pairTangential	history
pairCohesion	off
pairRollingFriction	epsd
pairSurface	default
NPROC	4
dumpT	0.01 s
dump	0
G_D_RATIO	10

Note

G_D_RATIO is the ratio of cylinder diameter and largest coarsegrained particle diameter

Specific settings

Variable	Default	Meaning
CFD_particle_volume_fraction	undefined	The measured volume fracition of the material [-]
cfdemSolverBinary	cfdemSolverPimple	CFD-DEM solver