dt_prel
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R
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9999999.9
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Temporal interval at which particles are to be released from a particle source (in s).
By default particles are released only at the beginning of a simulation (t_init=0). The time of the first release (t_init) can be changed with package parameter particle_advection_start. The time of the last release can be set with the package parameter end_time_prel. If dt_prel has been set, additional releases will be at t = t_init+dt_prel, t_init+2*dt_prel, t_init+3*dt_prel, etc.. Actual release times may slightly deviate from thesel values (see e.g. dt_dopr).
The domain of the particle source as well as the distance of released particles within this source are determined via package parameters pst, psl, psr, pss, psn, psb, pdx, pdy and pdz. By default, one particle is released at all points defined by these parameters. The package parameter particles_per_point can be used to start more than one particle per point.
Up to 10 different groups of particles can be released at the same time (see number_of_particle_groups) where each group may have a different source. All particles belonging to one group have the same density ratio and the same radius. All other particle features (e.g. location of the source) are identical for all groups of particles.
Subgrid scale velocities can (optionally) be included for calculating the particle advection, using the method of Weil et al. (2004, JAS, 61, 2877-2887). This method is switched on by the package parameter use_sgs_for_particles. This also forces the Euler/upstream method to be used for time advancement of the TKE (see initialization parameter use_upstream_for_tke). The minimum timestep during the sub-timesteps is controlled by package parameter dt_min_part.
By default, particles are weightless and transported passively with the resolved scale flow. Particles can be given a mass and thus an inertia by assigning the package parameter density_ratio a non-zero value (it defines the ratio of the density of the fluid and the density of the particles). In these cases their radius must also be defined, which affects their flow resistance.
Boundary conditions for the particle transport can be defined with package parameters bc_par_t, bc_par_lr, bc_par_ns and bc_par_b.
Timeseries of particle quantities in netCDF format can be output to local file DATA_1D_PTS_NETCDF? by using package parameter dt_dopts.
For analysis, additional output of particle information in equidistant temporal intervals can be carried out using dt_write_particle_data (file PARTICLE_DATA?).
Statistical informations (e.g. the total number of particles used, the number of particles exchanged between the PEs, etc.) are output to the local file PARTICLE_INFOS?, if switched on by the parameter write_particle_statistics.
If a job chain is to be carried out, particle informations for the restart run (e.g. current location of all particles at the end of the run) is output to the local file PARTICLE_RESTART_DATA_OUT?, which must be saved at the end of the run and given as an input file to the restart run under local file name PARTICLE_RESTART_DATA_IN? using respective file connection statements in the mrun configuration file.
The output of particles for visualization with the graphic software dvrp is steered by the package parameter dt_dvrp. For visualization purposes particles can be given a diameter using the parameters dvrp_psize and particle_dvrpsize (this diameter only affects the visualization). All particles have the same size. Alternatively, particles can be given an individual size and a color by modifying the user-interface (subroutine user_init_particles). Particles can pull a tail behind themselves to improve their visualization. This is steered via the parameter use_particle_tails.
So far, the particle transport realized in PALM does only work duly in case of a constant vertical grid spacing!
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bc_par_lr
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C*15
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cyclic
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Lateral boundary condition (x-direction) for particle transport.
By default, cyclic boundary conditions are used along x. Alternatively, reflection (bc_par_lr = 'reflect' ) or absorption (bc_par_lr = 'absorb' ) can be set.
This lateral boundary conditions should correspond to the lateral boundary condition used for the flow (see bc_lr).
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bc_par_ns
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C*15
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cyclic
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Lateral boundary condition (y-direction) for particle transport.
By default, cyclic boundary conditions are used along y. Alternatively, reflection (bc_par_ns = 'reflect' ) or absorption (bc_par_ns = 'absorb' ) can be set.
This lateral boundary conditions should correspond to the lateral boundary condition used for the flow (see bc_ns).
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density_ratio
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R(10)
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cyclic
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Ratio of the density of the fluid and the density of the particles.
With the default value the particles are weightless and transported passively with the resolved scale flow. In case of density_ratio /= 0.0 particles have a mass and hence inertia so that their velocity deviates more or less from the velocity of the surrounding flow. Particle velocity is calculated analytically and depends on (besides the density ratio and the current velocity difference between particles and surrounding fluid) the particle radius which is determined via radius as well as on the molecular viscosity (assumed as 1.461E-5 m*2/s).
If density_ratio = 1.0, the particle density corresponds to the density of the surrounding fluid and the particles do not feel any buoyancy. Otherwise, particles will be accelerated upwards (density_ratio > 1.0) or downwards (density_ratio < 1.0).
With several groups of particles (see number_of_particle_groups), each group can be assigned a different value. If the number of values given for density_ratio is less than the number of groups defined by number_of_particle_groups), then the last assigned value is used for all remaining groups. This means that by default the particle density ratio for all groups will be 0.0.
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dt_dopts
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R
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cyclic
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Ratio of the density of the fluid and the density of the particles.
With the default value the particles are weightless and transported passively with the resolved scale flow. In case of density_ratio /= 0.0 particles have a mass and hence inertia so that their velocity deviates more or less from the velocity of the surrounding flow. Particle velocity is calculated analytically and depends on (besides the density ratio and the current velocity difference between particles and surrounding fluid) the particle radius which is determined via radius as well as on the molecular viscosity (assumed as 1.461E-5 m*2/s).
If density_ratio = 1.0, the particle density corresponds to the density of the surrounding fluid and the particles do not feel any buoyancy. Otherwise, particles will be accelerated upwards (density_ratio > 1.0) or downwards (density_ratio < 1.0).
With several groups of particles (see number_of_particle_groups), each group can be assigned a different value. If the number of values given for density_ratio is less than the number of groups defined by number_of_particle_groups), then the last assigned value is used for all remaining groups. This means that by default the particle density ratio for all groups will be 0.0.
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