4. Dictionaries

4.1. couplingProperties dictionary

General:

In the couplingProperties dictionary the setup of the coupling routines of the CFD-DEM simulation are defined.

Location: $caseDir/CFD/constant

Structure:

The dictionary is divided into two parts, “sub-models & settings” and “sub-model properties”.

In “sub-models & settings” the following routines must be specified:

  • modelType

  • couplingInterval

  • voidFractionModel

  • locateModel

  • meshMotionModel

  • regionModel

  • IOModel

  • dataExchangeModel

  • averagingModel

  • forceModels

  • momCoupleModels

  • turbulenceModelType

In “sub-model properties” sub-dictionaries might be defined to specify model specific parameters.

Settings:

Reasonable example settings for the couplingProperties dictionary are given in the tutorial cases.

modelType

modelType refers to the formulation of the equations to be solved. Choose “A”, “B” or “Bfull”, according to Zhou et al. (2010). Model “A” requires the use of the force models gradPForce and viscForce, whereas “B” requires the force model “Archimedes”. “Bfull” refers to model type I.

couplingInterval

The coupling interval determines the time passing between two CFD-DEM data exchanges.

A useful procedure would be:

  1. Set the DEM time step in the LIGGGHTS input file according to the needs of the pure DEM problem.

  2. Set the couplingInterval, which refers to the DEM time steps. Depending on the problem you will need to have a close (small couplingInterval) or loose coupling.

  3. Choose the CFD time step in the controlDict. It must be equal to or smaller than the coupling time, otherwise you will get the error: “Error - TS bigger than coupling interval!”.

Example:

Choosing DEMts=0.00001s and couplingInterval=10 means that an exchange of data (=coupling) will happen every 0.0001s.

4.2. liggghtsCommands dictionary

General:

In the liggghtsCommands dictionary LIGGGHTS commands which are to be executed during a coupled CFD-DEM simulation are specified.

Location: $caseDir/CFD/constant

Structure:

The dictionary is divided into two parts, first a list of liggghtsCommandModels is defined, then the settings for each model must be specified.

Settings:

Reasonable example settings for the liggghtsCommands dictionary are given in the tutorial cases.

(Zhou, 2010) “Discrete particle simulation of particle-fluid flow: model formulations and their applicability”, Zhou, Z. Y., Kuang, S. B., Chu, K. W. and Yu, A. B., J. Fluid Mech., 661, pp. 482-510 (2010)