Global Variable Data Sources¶

Selections¶

Fluid¶

When the Data Source is set to Fluid, the global variable is constructed from reductions of fluid-field quantities across the lattice. This allows you to track single-valued statistics—such as maxima, averages, or deviations—of any fluid property or UDF-defined field over a specified region of the domain. Fluid-based global variables are commonly used to monitor quantities like the maximum velocity magnitude, mean turbulent energy dissipation rate (EDR), or average species concentration in a zone of interest.

This source is particularly useful when you want to condense voxel-level fluid properties into a single runtime signal that captures domain-wide or region-specific behavior. For example, you might track maxima, averages, or deviations of velocity, pressure, or species concentrations to monitor performance, scale-up, or process safety.

Maximum velocity magnitude is useful for monitoring whether flow intensity exceeds design limits or for normalizing particle slip velocities. Mean turbulent energy dissipation rate (EDR) within the impeller zone provides a single measure of energy input into the fluid, often correlated with mixing efficiency or scale-up. Sum of species concentration in a reaction zone tracks the total reactant or product mass present in a subvolume. Minimum dissolved oxygen concentration ensures that oxygen does not fall below critical thresholds for biological processes. Relative standard deviation (RelStdDev %) of temperature quantifies how uniform or non-uniform thermal conditions are across the fluid domain.

Reduction

The global variable performs a reduction over fluid-field or quantities (e.g., velocity, pressure, strain rate, dissipation, species concentration). The reduction collapses the sampled values into a single scalar result.

Minimum: The lowest fluid value in the domain.
Maximum: The highest fluid value in the domain.
Sum: The total sum of values across the selected region.
Mean: The average fluid value across the region.
StdDev: The standard deviation of the sampled fluid values.
RelStdDev: % | The relative standard deviation, normalized by the mean and expressed as a percentage.

If no Child Geometry is specified, the reduction operates over the entire fluid domain. If a Child Geometry is defined, the reduction is restricted to that subvolume, allowing you to monitor localized statistics (e.g., mean shear rate in the impeller swept zone, maximum velocity in a draft tube, etc.).

Interval Option

The Interval Option defines how often the global variable is updated when reducing fluid data.

Every Time Step: The reduction is recomputed at every solver time step. This provides high-resolution temporal data but increases computational cost.
Custom Interval: s | The reduction is only recomputed at user-specified intervals. This reduces overhead when coarse temporal sampling is sufficient.

Global Variable UDF (Fluid)

depends on UDF expression | This UDF defines the custom field variable to be calculated as part of the global variable reduction. One output must be defined within the UDF: a floating-point variable named value. The values calculated by this UDF are fed into the reduction operation. This can be either a voxel-based or a particle-based local UDF, depending on the data source.

Download Sample File: Global Variable Fluid

Particles¶

The Particle source is particularly useful when you want to extract statistical summaries of particle populations, either across the full domain or within a specified region. It allows particle-level properties (diameter, velocity, temperature, etc.) to be reduced to a single scalar, making them easy to reuse in UDFs, optimization schemes, or process monitoring.

Examples include mean particle diameter, which tracks size evolution in agglomeration or breakup; sum of particle volumes, which measures local volume fraction of the dispersed phase; maximum particle velocity, which identifies erosion/wear risks; standard deviation of particle concentration, which indicates clustering or poor mixing; relative standard deviation of particle temperature, which measures thermal uniformity; and sum of particle collisions per voxel, which quantifies stress in dense suspensions.

Data Source Particle Name

A Data Source Particle Name must be selected to define which particle set is included in the reduction. This allows targeting of specific particle populations (e.g., inertial particles, tracers, droplets) while excluding others.

Reduction

Minimum: The lowest fluid value in the domain.
Maximum: The highest fluid value in the domain.
Sum: The total sum of values across the selected region.
Mean: The average fluid value across the region.
StdDev: The standard deviation of the sampled fluid values.
RelStdDev: % | The relative standard deviation, normalized by the mean and expressed as a percentage.

Interval Option

The Interval Option defines how often the global variable is updated when reducing fluid data.

Every Time Step: The reduction is recomputed at every solver time step. This provides high-resolution temporal data but increases computational cost.
Custom Interval: s | The reduction is only recomputed at user-specified intervals. This reduces overhead when coarse temporal sampling is sufficient.

Global Variable UDF (Particles)

Download Sample File: Global Variable Particles

Probe¶

When the Data Source is set to Probe, the global variable is linked directly to a specific probe defined in the model. Unlike reductions over fluids or particles, probe data are inherently single-valued and localized to the probe’s position. This means there is no need for a reduction type or child geometry—the probe definition itself specifies both the location and the property being measured.

Data Source Probe Name

Identify which probe supplies the data. Multiple global variables can reference different probes, allowing you to extract and reuse probe data at runtime for calculations, controls, or feedback.

Interval Option

The Interval Option defines how often the global variable is updated when reducing fluid data.

Every Time Step: The reduction is recomputed at every solver time step. This provides high-resolution temporal data but increases computational cost.
Custom Interval: s | The reduction is only recomputed at user-specified intervals. This reduces overhead when coarse temporal sampling is sufficient.

Global Variable UDF (Probe)

depends on UDF expression | This UDF defines the custom field variable to be calculated as part of the probe output. This expression can produce raw data or manipulate it to generate custom signals. One output must be defined within the UDF: a floating-point variable named value. The values calculated by this UDF are fed into the reduction operation. This will be a particle-based local UDF.

Download Sample File: Global Variable Probe

Interfaces¶

When the Data Source is set to Interfaces, the global variable is constructed from reductions performed along a fluid–fluid or fluid–air interface. This enables you to track single-valued statistics of interfacial quantities, such as surface area, fluxes, or custom UDF-defined properties, over the entire interface or within a specified child geometry.

Because interface data are inherently tied to the liquid–gas (or liquid–liquid) boundary, this source is especially useful for problems where mass transfer, surface tension effects, or phase interactions are important. For example, you might calculate the total interfacial area available for gas–liquid transfer, evaluate a custom UDF describing flux across the interface, or track how the maximum curvature of the interface evolves over time.

This source is particularly useful when you want to extract single-valued statistics of interfacial phenomena, such as phase boundaries between liquid and gas or between immiscible fluids. By reducing properties along the interface, you can track quantities that directly govern mass transfer, surface tension effects, and multiphase transport. Reductions can be applied over the entire interface or restricted to a region by assigning a Child Geometry.

Examples include the total interfacial area, which is the sum of interface surface area, useful for gas–liquid mass transfer correlations; the maximum interfacial flux, which identifies peak transport hot spots across the boundary; the sum of interfacial oxygen transfer, which integrates custom UDF-defined flux across the surface; and the relative standard deviation of concentration at the interface, which quantifies heterogeneity in transport driving forces.

Reduction

Minimum: The lowest fluid value in the domain.
Maximum: The highest fluid value in the domain.
Sum: The total sum of values across the selected region.
Mean: The average fluid value across the region.
StdDev: The standard deviation of the sampled fluid values.
RelStdDev: % | The relative standard deviation, normalized by the mean and expressed as a percentage.

Interval Option

The Interval Option defines how often the global variable is updated when reducing fluid data.

Every Time Step: The reduction is recomputed at every solver time step. This provides high-resolution temporal data but increases computational cost.
Custom Interval: s | The reduction is only recomputed at user-specified intervals. This reduces overhead when coarse temporal sampling is sufficient.

Global Variable UDF (Interfaces)

Download Sample File: Global Variable Interfaces

Time¶

When the Data Source is set to Time, the global variable is defined directly as a function of simulation time. Unlike fluid, particle, or interface sources, no reductions are performed and no child geometry can be specified. Instead, the global variable simply evolves according to time-based rules.

This source is particularly useful when you want to create a time-dependent signal that can be referenced elsewhere in the simulation. For example, driving a boundary condition with a sinusoidal or ramping function; defining a reference clock for feedback controllers; or introducing a simple, analytic input signal into optimization studies.

Global Variable Time UDF

depends on UDF expression | This UDF defines the custom field variable to be calculated as a function of time and other global variables. One output must be defined within the UDF: a floating-point variable named value. The values calculated by this UDF are fed into the reduction operation. This is a System UDF.

Download Sample File: Global Variable Time

Interval Option

The Interval Option defines how often the global variable is updated when reducing fluid data.

Every Time Step: The reduction is recomputed at every solver time step. This provides high-resolution temporal data but increases computational cost.
Custom Interval: s | The reduction is only recomputed at user-specified intervals. This reduces overhead when coarse temporal sampling is sufficient.

Stats Value¶

When the Data Source is set to Stats Value, the global variable is linked directly to a quantity that is already reported in the solver’s statistics framework. Instead of being computed fresh through reductions or UDFs, the global variable simply mirrors values that would normally be written out to the statistics file, making them available at runtime. The statistic of interest is taken from the Stat Lister Form, which is accessed via the form.

By selecting from the Stats Selection menu, you can choose from a wide variety of monitored statistics, including:

Fluid-based metrics: Velocity, strain rate, turbulence quantities, species concentrations
Interface properties: Interfacial area, fluxes, or curvature
Particle set statistics: Diameters, velocities, blend times, or residence times
Thermodynamics and scalar fields: Energy, enthalpy, or custom scalar variables
Boundary data: Inlet/outlet mass fluxes, pressures, or flow rates
Body interactions: Forces, torques, or collision data from static or moving bodies

Stats Selection

Clicking the Stats Selection button opens a browser window listing all available statistics organized by category (e.g., fluid, particle sets, interfaces, bodies, inlets/outlets, thermodynamics). From this menu, you can select the specific output signal you want the global variable to track. Once chosen, the selected statistic is reported back in the Stats Selection field.

Because Stats Value variables mirror values already produced by the solver, no Child Geometry, Reduction, or UDF is required. These variables are inherently single-valued and update in sync with the solver’s statistics engine.

Download Sample File: Stats Value

Static Body¶

When the Data Source is set to Static Body, the global variable performs reductions over variables defined along a selected static surface (e.g., vessel walls, inlets, baffles, pipes). This lets you condense particle–wall or fluid–wall interactions into a single value that can be used anywhere in the solver.

This setup is particularly useful when you want to monitor surface-level physics during runtime, such as maximum wall shear stress (cleaning validation); mean pressure on a baffle (mechanical loading); total particle impact energy on a wall (erosion prediction); or net heat flux across a vessel wall.

Data Source Static Body Name

This specifies which static body (e.g., inlet pipe, vessel wall, baffle) is the subject of the reduction. Each named surface in the model can be referenced individually, allowing you to isolate statistics for specific regions of the geometry.

Reduction

Minimum: The lowest fluid value in the domain.
Maximum: The highest fluid value in the domain.
Sum: The total sum of values across the selected region.
Mean: The average fluid value across the region.
StdDev: The standard deviation of the sampled fluid values.
RelStdDev: % | The relative standard deviation, normalized by the mean and expressed as a percentage.

Interval Option

The Interval Option defines how often the global variable is updated when reducing fluid data.

Every Time Step: The reduction is recomputed at every solver time step. This provides high-resolution temporal data but increases computational cost.
Custom Interval: s | The reduction is only recomputed at user-specified intervals. This reduces overhead when coarse temporal sampling is sufficient.

Global Variable UDF (Static Body)

depends on UDF expression | This UDF defines the custom variable to be computed along the static body surface. One output must be defined within the UDF: a floating-point variable named value. This is a local UDF, calculated on a voxel-by-voxel basis using the local fluid properties. The UDF is only applied along the cells touching the solid surface.

Download Sample File: Global Variable Static Body

Moving Body¶

When the Data Source is set to Moving Body, the global variable performs reductions over variables defined along a moving surface mesh, such as an impeller, agitator, or rotating baffle. This allows you to condense particle–surface or fluid–surface interactions on moving boundaries into a single scalar value usable throughout the solver.

This source is particularly useful when you want to monitor performance metrics of moving equipment at runtime, such as maximum or mean blade shear stress (cleaning validation or erosion risk); total torque or power draw on an impeller; summed particle impact forces across a moving agitator; or relative velocity differences between fluid and impeller surfaces for mixing diagnostics.

Data Source Moving Body Name

Specifies which moving body is referenced (e.g., an impeller or agitator blade). Each defined moving mesh in the model can be selected independently, enabling you to isolate statistics for a particular component.

Reduction

Minimum: The lowest fluid value in the domain.
Maximum: The highest fluid value in the domain.
Sum: The total sum of values across the selected region.
Mean: The average fluid value across the region.
StdDev: The standard deviation of the sampled fluid values.
RelStdDev: % | The relative standard deviation, normalized by the mean and expressed as a percentage.

Interval Option

The Interval Option defines how often the global variable is updated when reducing fluid data.

Every Time Step: The reduction is recomputed at every solver time step. This provides high-resolution temporal data but increases computational cost.
Custom Interval: s | The reduction is only recomputed at user-specified intervals. This reduces overhead when coarse temporal sampling is sufficient.

Global Variable UDF (Moving Body)

depends on UDF expression | This UDF defines the custom variable to be computed along the moving body surface. One output must be defined within the UDF: a floating-point variable named value. This is a local UDF, calculated on a voxel-by-voxel basis using the local fluid properties. The UDF is only applied along the cells touching the moving surface.

Download Sample File: Global Variable Moving Body

Property Link¶

When the Data Source is set to Property Link, the global variable is tied directly to a property already defined in the model tree. This allows you to expose geometry parameters, object properties, or simulation constants as global variables that can be referenced anywhere in the solver.

Clicking the Property Link field opens the Property Selection browser, where you can navigate through the simulation model tree to pick the property of interest. Examples include:

Impeller diameter, speed, or position
Vessel or pipe dimensions
Free-Surface elevation
Predefined thermodynamic or scalar properties
User-specified parameters stored in the setup

This source is particularly useful when you want to reuse a parameter defined during model setup (e.g., impeller speed) in runtime calculations (e.g., Reynolds number, power draw correlations); couple geometric or operating parameters into optimization or parametric studies without re-entering values; or link control laws or runtime expressions to design parameters defined elsewhere in the model tree.

Property Link: Once a property is selected, the property is displayed in the Property Link field, and the corresponding value is reported in the Property Value field. Unlike other data sources, Property Link does not perform reductions or sampling—it simply mirrors a preexisting property, keeping the global variable synchronized with the value used in the model.
Property Value: The value for the property selected in the Property Link field. It can be accessed in UDFs, controllers, or optimization routines just like any other global variable.

CSV File¶

When the Data Source is set to CSV File, the global variable is driven by values read from an external comma-separated text file. This makes it possible to bring experimental measurements, precomputed signals, or controller outputs generated by other software directly into the solver at runtime.

This source is particularly useful when you want to drive the solver with external or pre-defined data streams that evolve with time. Examples include:

Importing experimental feed-rate schedules from a bioreactor to replay lab conditions.
Driving an impeller speed profile from a CSV file that specifies time-varying agitation rates.
Applying historical plant data (e.g., DO or pH measurements) as runtime signals for validation.
Coupling to an external optimizer or controller that writes control setpoints into a CSV file during simulation.
Replaying oscillatory boundary conditions (e.g., inlet velocity ramps or periodic gas flow rates) without writing a custom UDF.
Feeding in precomputed data from another software package to guide runtime physics.

CSV File Source

The CSV File Source section defines how the external data is read. By configuring these fields, the global variable will continuously update with the most recent value from the CSV, synchronized to simulation time.

CSV File Name: dimensionless | The name of the CSV file containing the input data. This file should be located within the simulation working directory.
CSV File Delimiter: dimensionless | This defines how columns in the file are separated. Supported options are Comma, Tab, or Space.
CSV Time Column: dimensionless | The column index (1-based) specifying simulation time. The solver uses this column to align external data with its own time base.
CSV Value Column: dimensionless | The column index containing the values to be read in as the global variable.
CSV Timeout: s | Maximum allowable time to wait for new data to appear in the file (useful in live-coupling scenarios).
CSV File Poll Interval: s | Interval at which the solver checks the file for new data.

Download Sample File: CSV File Source