Particle Output Data

The M-Star Particles/Bubbles Output panel provides a complete description of particle behavior in your simulation. These output properties include individual particle motion/properties, ensemble statistics, spatial fields constructed from the local particle population, as well as particle exit statistics. These outputs are designed for users to understand how particles move and interact, how well they are dispersed, how they exchange mass with the fluid, how long they stay in the system, and where they exit.

Ensemble Statistics and Reduced Data

Particle output data is printed to a Particle Statistics file that summarize ensemble averaged particle properties over time. These statistics include quantities such as total particle count, mean particle diameter, and total interfacial area. They also include ensemble-total quantities such as the volumetric mass transfer coefficient (\(kLa\)) and total heat transfer rate. This data is written to ASCII text files at the Statistics Output Write Interval.

Particle-Resolved Data

M-Star tracks every particle individually through space and time. Each particle retains its identity and properties over time, including diameter, shape, composition, and any user-defined particle properties. Particles can report on the fluid properties surrounding each particle, including local fluid velocity and strain rate. These local fluid properties are useful for probing local fluid properties and predicting local transport coefficients. The particle-resolved datasets are printed to a binary .vtp file for visualization and analysis within M-Star Post. Each particle family is written to its own file using the dynamic particle family name. The printing is synchronized with the Plane/Probe Write Interval as well as the Volume Write Interval. This makes the output frame-consistent for visualization and animation in both 2D and 3D renderings.

Particle-Derived Fields

In addition to tracking individual particles, M-Star maps the particle population onto the computational lattice to create Eulerian fields. These are spatial fields defined at every lattice voxel, just like the fluid outputs. Typical particle-derived fields include local particle volume fraction, local volumetric mass transfer quantities, and local specific surface areas. This field data is printed directly to the slice and volume .vti files for visualization and analysis alongside other field data within M-Star Post. The field printing is synchronized with the Plane/Probe Write Interval as well as the Volume Write Interval.

Exit Statistics and Residence Time Data

M-Star automatically tracks particles that leave the domain and records exit statistics for residence time analysis. A unique particle exit file is written for each particle family with a filename coupled to the dynamic particle family name. For each particle that exits the system, this file presents an accumulated list of the exiting the Particle ID, time added, exit time and location, and key particle properties. This data is useful for computing particle residence time distributions (RTDs), exit age distributions outlet composition, and pathway behavior.

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Nearest-Neighbor Distance

M-Star computes nearest-neighbor distance to quantify how well particles are dispersed. This output is enabled using the Compute Nearest Neighbor Distribution option. Each particle is assigned a scalar value equal to the distance to its closest neighboring particle. This is stored directly in the .vtp particle output files and can be visualized as a color on each particle.

In addition to this visual output data, each particle set with Blend Time enabled produces (i) a tab-separated ASCII .txt file that contains ensemble-reduced statistics and (ii) a set of tab-separated ASCII .txt files that describe the time evolution of the expected and realized nearest-neighbor probability density functions. A preview of the data printed as part of this calculation is listed in the Statistics Output Data preview panel.

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Particle Screens

In addition to tracking particles throughout the full domain, M-Star allows you to define particle screens on Output Planes. A particle screen records the moment when a particle crosses a specified plane and captures its state at that instant. This provides a mechanism for measuring local particle fluxes and spatial landing-point distributions along selected planes within the system. Particle screen output data is written in three complementary forms, corresponding to the three levels of information produced by the screen.

The first output stream consists of particle-resolved screen datasets, which provide a direct record of the individual particles that intersect the screen. These datasets are written as binary .vtp files for visualization and analysis in M-Star Post. A unique file is created for each screen, with the name SliceScreenParticles_{Axis}_{Intercept}.pvd, where Axis and Intercept correspond to the Axis Direction and Intercept Value.

The second output stream appears directly on the associated Output Plane .vtk file. In addition to the particle-resolved screen data, M-Star maps the screen-crossing events onto the output plane to form an areal landing-point number-density field. This field is defined on the Output Plane mesh and is written as an additional variable in the corresponding screen Output Plane dataset, enabling visualization of the spatial distribution of particle impacts.

The third output stream is a reduced statistical report written to ASCII .txt files. This output is computed from the Output Plane (slice) number-density field, not from the individual particle landing events. The reduction operates directly on the discretized field defined over the screen surface and reports raw and derived statistics such as total particle count, mean landing-point density, standard deviation of landing-point density, and the coefficient of variation of the landing-point density.