Fluid Output Data

In M-Star CFD, the fluid is represented as a set of continuous Eulerian fields defined throughout the computational domain. At every location, the solver maintains local state variables including velocity and pressure; density and viscosity; scalar or species concentration; temperature and related thermal quantities; and strain- or shear-rate–related measures, along with other user-derived voxel variables.

Because these fields exist everywhere in space and evolve in time, M-Star provides multiple mechanisms to extract and visualize them during a simulation. These mechanisms are configured through the Output Panel and associated sampling and output rate settings.

Two primary categories of data are produced: reduced statistical fluid outputs for plotting aggregated fluid quantities over time, and surface and volume spatial visualization outputs for examining how fluid properties vary throughout the domain.

Reduced Statistical Fluid Output

These are compact, pre-processed, reduced quantities that are written to text-based statistics files. These include averages, integrals, extrema, forces, and other global or region-based metrics associated with the fluid, suitable for plotting and reporting. The Statistics page provides a complete list of the raw and reduced statistical data available for output.

Surface and Volume Outputs

These are geometry-aware datasets that preserve spatial structure. They are written in binary VTK formats suitable for post-processing in M-Star Post and similar tools.

M-Star supports sampling at two levels:

  • 2D Slice Output: These planes and surfaces constitute a planar cut (or slice) through the domain that returns a spatial field map over an area. This is the most common visualization for examining internal flow structure. These outputs can be produced at specific locations by Output Planes or Output Surfaces to a model.

  • 3D Volume Output: This volume output constitutes full 3D field data for the domain or a specified region. Because of data size, volume output is typically written less frequently or under specified conditions. The extents of this output are automatically defined by the Main Lattice.

Fluid Interface Output

For multiphase or immiscible systems, M-Star can export Fluid Interface data as an additional spatial dataset. The interface is defined as an isosurface of the phase-fraction (VOF) field, representing the boundary between fluid phases (e.g., gas–liquid or immiscible liquid–liquid interfaces).

These outputs are written as VTK surface datasets and are commonly used to visualize interface deformation, breakup, and free-surface evolution. They can also be used to visualize filling and draining processes, as well as changes in free-surface level due to gas holdup from sparged gas.

Sampling Probes and Sampling Lines

In addition to reduced statistical data (which is computed over the full fluid domain), localized reductions and field interrogation can be performed using sampling probes, sampling lines, control volumes, or global variables with local fluid reductions.