Saving Output Data

Data Sampling

Overview

These simulation parameters control the type of data saved by the simulation, as well as the output frequency. Users should balance data generation with disk space availability and analysis requirements.

Triple Plane

The solver records output data along a set of triple planes pointing in the x-, y-, and z-directions. The position of these planes along these three directions is defined by the triple plane location (or origin). By default, the triple plane origin is the centroid of the tank. Users can elect to position this origin anywhere inside the fluid domain.

Planes are printed at the Slice Output interval.

Additional planes can be rendered by defining an additional output plane See - Output Plane section below.

Output Options

Enable or disable output variables along each plane.

Point

Location of triple plane intersection point

Probe

Static probes are points inside a fluid domain that record the time-evolution of local fluid properties (e.g. velocity, pressure, vorticity, energy dissipation rate, etc.). For static probes, users specify a probe location and a probe sampling time interval. The data is printed to a probeData file. The position of static probes remains constant over the duration of a simulation.

Location

Probe Location, [Template units]

Sample Interval Time

Sample interval, [Seconds]

Moving Probe

Moving probes are dynamic points inside a fluid domain that record the time-evolution of local fluid properties (e.g. velocity, pressure, vorticity, energy dissipation rate, etc.). For moving probes, users specify an injection location and injection time. Moving probe data is printed at the same frequency as the slice output, and recorded in a movingProbeData file. Moving probes can be assigned a diameter and density, or can be treated as massless tracer particles should either value be zero.

Starting Location

Probe Location [Template Units]

Start Time

Start time [seconds]

Diameter

Diameter of moving probe [Template Units]

Density

Density of moving probe [kg/m 3 ]

Output Plane

Output planes are x-,y-, or z-planes used to display the time-evolution of fluid properties across the domain. After defining the direction of the plane, users enter or select a plane position along this direction. For example, if the user chooses to define an x-plane, they will be prompted to select a Mount Point along the x-axis that positions the x-plane. Only points inside the domain can be selected as Mount Points. Users also have the option of declaring planes to be a Particle Screen. A Particle Screen, when used in tandem with particles, automatically computes a heat map describing the frequency at which particles cross the plane.

Options

Enable or disable output variables

Output options include the instantaneous and time-averaged value of:

  • Velocity [m/s]

  • Mean Velocity [m/s]

  • Resolved Strain [1/s]

  • Resolved Kinetic Energy [m^2 / s^2]

  • Vorticity [1/s]

  • Pressure [Pa]

  • Eddy Dissipation Rate [W/kg]

  • Temperature [K] (when thermal field is active)

  • Scalar field concentration (for each scalar field)

  • Viscosity (when modeling non-Newtonian fluids)

Is Particle Screen

Set to true to enable particle screen output for plane.

When active, the solver records the position, velocity, age, originID, diameter, and particleID of all particles crossing the plane. This list is presented as a VTK file, which stores land points and associated particle properties for visualization and data extraction.

Particle Screen Start Time

This is the time in seconds defining when the screen begins to tracking particle crossings. The default is zero.

Particle Screen Stop Time

This is the time in seconds defining when the screen stops tracking particle crossing. The default is -1 which implies the end of the simulation.

Value

Plane intercept value along defined Axis Direction [Template Units]

Axis Dir

Plane normal direction

Visible

Enable/disable the visibility of this component

Output Volume

Volume output refers to full 3D data output of the fluid, particles, scalar fields, interface, and moving surfaces. Volume data can be rendered as a movie or converted into a spreadsheet or histogram to analyze flow fields/transport.

Since volume data files may be large, users have the option to specify a volume output start time. The default value is zero, implying that volume file output begins at the start of the simulation. With this parameter, users can delay the start of the volume output and save disk space.

Start Time

Output Start Time [Seconds]

Time at which to begin printing 3D volume output.

Stop Time

Output Stop Time [Seconds]

Time at which to stop printing 3D volume output.

Since volume data files may be large, users have the option to specify a volume output stop time that is different from the end of the simulation.

Output Interval

Output interval [Seconds]

In general, volume data should be output every 1,000-10,000 timesteps to properly balance the computational cost associated with printing the data with the need for sufficient temporal resolution during post-processing.

When producing real-time animations volume data, the animation frame rate should match the Volume Output Interval value set here.

Output Options

Output Variables [Selection]

To help control the size of the volume files, users can select which state variables and fluid properties to include in the output volume.

Output options include the instantaneous and time-averaged value of:

  • Velocity [m/s]

  • Mean Velocity [m/s]

  • Resolved Strain [1/s]

  • Resolved Kinetic Energy [m^2 / s^2]

  • Vorticity [1/s]

  • Pressure [Pa]

  • Eddy Dissipation Rate [W/kg]

  • Temperature [K] (when thermal field is active)

  • Scalar field concentration (for each scalar field)

  • Viscosity (when modeling non-Newtonian fluids)

See Output Files for a complete list of the output files produced by the solver.

Output Box Option

Output Box Option [Selection]

To help manage the size of the volume files, users can select which portion of the system domain to include in the volume output. By default, the entire domain is specified.

To manage file size with an appeal to symmetry, users may elect to export only one half or one quarter the full domain for volumetric representation.

Alternatively, to focus on a region of interest inside the domain (e.g. the trailing vortex), users may choose to output only a sub volume surrounding the impeller.

File Size

Estimated size of each file written [GB]

Reference information reported to the users. The size of individual volume output files is controlled by (i) the size of the lattice and (ii) the number of reported variables.

The total number of volume files written (which informs the total expected disk usage), is governed by the volume output frequency and the duration of the volume output. The duration of the volume output is the difference between the volume output stop and the volume output start.

Number Written

Number of files written [Count]

Total number of output files that will be produced by the simulation. Related to the duration of the volume output and the volume output frequency.

Total Disk Usage [GB]

Total estimated disk usage

Reference information computed by multiplying the number of volume files to be written by the estimated size of each volume file.

Box Lower Corner

Bounding box lower corner [Template units]

The lower corner of the bounding box used to define the user-defined output box.

Box Upper Corner

Bounding box upper corner [Template units]0

The upper corner of the bounding box used to define the user-defined output box.

Visible [Selection]

Enable/disable the visibility of this component in the GUI window.

Run-time Calculations

Auto Blend Calculation

Users can automatically calculate the tank blend time using the Calculate Tank Blendtime command. After selecting this option from the Menu, users will be prompted to enter a particle injection point, number of particles, and injection time. These values represent the location, quantity, and time at which tracer particles are added to the system. Next, users will be prompted to specify a number of sub volumes in the x-, y- and z-directions. These sub-volumes are used to calculate the coefficient of variation of particles across the tank. The extents of these bins, the amount of fluid inside each bin, and the equilibrated particle count are reported in the solver log file prior to the first iteration.

At a time interval equal to the Slice Output time interval, the solver reports the instantaneous Blending COV and the normalized particle concentration in each bin.

The precision of the COV calculation is related to the number of bins and the number of particles. In general, users should inject at least 5000 particles per sub-volume.

For free surface simulations, the particle injection point should be below the fluid height.

Number Bins X

Number of bins in X direction

Number Bins Y

Number of bins in Y direction

Number Bins Z

Number of bins in Z direction

Start Time

Auto blend calculation start time [s]

Number Of Particles

Number of particles

Particle Injection Point

Start point of particles [Template Units]

Particle Density

Density of the particles used in the autoblendtime calculation

Particle Diameter

Diameter of the particles used in the autoblendtime calculation [Template Units]

Visible

Enable/disable the visibility of this component

Mean Age

For open systems, users can automatically calculate the transient mean age distribution using the Calculate Mean Age command. After selecting this option from the Menu, users will be prompted to select an age source from among the inlets, a calculation start time, and an age diffusion coefficient. The age diffusion coefficient is related to the molecular self-diffusion coefficient. The spatial variation in the mean age is printed to volume and slice output files. The mean age at each outlet is printed to output.

The transient mean age represents two physical values. First, it represents the average age of molecules at a given point inside the tank, relative to the time these molecules entered the system via the selected inlet. Second, the represents the mean residence time of molecules at a given point inside the tank. For systems with a single outlet, the mean age at the outlet is equal to the volume averaged mean-age. The volume averaged mean age is also equal to the mean residence time of the system.

Start Time

Start Time, [seconds]

Time at which to begin the mean age calculation

Diffusion Coefficient

Age diffusion coefficient, [m^2/s]

Diffusion coefficient of the age variable. Typically equal to the molecular diffusion coefficient.

Selected Inlet

Selected inlet for mean age calculation

Local Residence Time Distribution

This is an advanced component used to compute a local residencne time distribution (RTD) within a given sub-set of the tank

Start Time

RTD Start Time [s]

Box Lower Corner

Bounding box lower corner

Box Upper Corner

Bounding box lower corner