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Initialisation

1) The dsmcInitialiseDict dictionary

The dsmcInitialiseDict dictionary is located in the system/ folder. The initial number density of all species present in the gas mixture (see A.1 Species thermophysical properties), modal temperatures and velocity are given in the following subdictionary

configurations
(
    configuration
    {
        type    dsmcMeshFill;

        numberDensities
        {
             Ar            1.4e20;
        };

        translationalTemperature     273.0;
        rotationalTemperature        0.0; 
        vibrationalTemperature       0.0;
        electronicTemperature        0.0;

        velocity        (100 0 0);
    }
);

where the type dsmcMeshFill indicates that the entire grid is going to be populated with particles. To start with a grid free of DSMC parcels, leave the configurations() list empty.


2) DSMC parcel vs. real particles

The number of real particles represented by a single DSMC parcel is set in the constant/dsmcProperties dictionary

nEquivalentParticles            2e7;

There should be a minimum of 20 DSMC parcels per cell whenever possible and nEquivalentParticles should be set accordingly.


3) Creating the 0/ folder

In the working directory, type in:

dsmcInitialise+

This command line will create the 0/ folder. Simulators data is stored into the 0/lagrangian/dsmc/ subfolder and two volume fields, cellLevel and dsmcSigmaTcRMax, are printed. The main DSMC executable will always look for these information in the time folder corresponding to the starting time.

 

3.1 Simulators data

In the 0/lagrangian/dsmc/ folder, the files listed in the Table below are created. Each of them contains a dataset of size number of DSMC parcels.

File Meaning
positions positions in Cartesian space
U velocity vector
typeId species index, cf. species list given in the dsmcProperties dictionary
newParcel -1 if seeded at t = 0 or index of the patch the simulator entered the domain
origProcId index of the processor dealing with the simulator
origId local particle index in processor origProcId
classification not used, to be revised
   
ERot rotational energy
vibLevel vibrational energy level for each vibrational energy mode
ELevel electronic energy level

 

3.2 Initial volume fields

  • dsmcSigmaTcRMax is a first estimate of the maximum value taken by the product of the collision cross-section by the relative speed. For a gas mixture, it is usually obtained by considering the properties (diameter, omega, alpha) of the most abundant species. As the simulation proceeds, this field is updated as soon as a new local maximum is found. It requires no user intervention.

  • cellLevel represents the level of refinement of each cell. At t = 0, it is equal to 0 which means that all cells are root cells (they cannot be further coarsened). This field will only be used when the AMR flag is passed as an argument to the main DSMC executable.