Using Mission Data with Transient Analysis in Altair Flow Simulator


A transient analysis in Flow Simulator (FS) often requires boundary conditions that change with time. A mission component is used to store a table of time dependent data. A controller is used to transfer data from the mission component to the model boundary conditions.
Creating a Mission Component
A mission component is a convenient method for storing all time-dependent data in the model. There are 2 ways to get to the mission component window.
A column labeled “Time” is always required in a mission. The first and last times in the mission must encompass the start and stop time of the transient analysis. (i.e. The transient stop time can’t be 600 seconds for this mission with the last time of 500 seconds.) The FS solver will use linear interpolation to extract mission data from the table, so use sufficient time inputs to accurately describe the mission.
The mission data table can be filled manually in the FS GUI, but this only works well for short missions with only a few parameters. For larger tables, the numerical data can be copied and pasted from other programs such as Excel. An even faster approach is to fill the mission table by reading from an existing mission file. The mission file does need a specific format. One way to see the format is to create a sample mission in the FS GUI and click the “Write a new Mission File” button. The resulting text file is the general format needed for the mission read.
Excel is a useful tool for creating a new mission. Using a “.” Instead of a “,” to represent a decimal point can avoid problems with this process.
The “PRINT_TIME_STEP” column is a special parameter used for custom print time control. This column will not appear in the mission window, but it will appear in the Transient Run Control Parameters window.
Once the mission is created, the mission data can be used in a controller to apply boundary conditions to model items such as flow chambers, flow elements, thermal nodes, and thermal resistors.
Using a Mission Transfer Controller
A controller using the “Mission Transfer” relation is an easy way to apply mission data directly to model items. This type of controller can apply multiple items from one controller, and there can be multiple mission transfer controllers in the model.
Using a Python Controller
A controller using a python script takes more time to setup than the “Mission Transfer” relation but it allows the mission data to be manipulated. For instance, a chamber pressure may be a known fraction of pressure in a mission parameter. The python script can easily make the calculation and apply the pressure to a chamber. The number of parameters required in the mission can be reduced if some of the boundary conditions can be calculated by the python controller.
Using a 1D Table Controller
A controller using a 1D table contains all the time dependent data, so it does not use data from the mission except for the TIME. This is not the recommended approach, but it is included for completeness. One benefit of the 1D table is that there can be more time dependent data with this approach. The mission component is limited to about 50 parameters in FS version 2025 (will be increased to 200 parameters in 2025.1). A model can have multiple 1D table controllers with different time dependent data so the number of time dependent parameters can be very large.
Rotor Speed and Reference Flow Rate
A model that requires a rotation speed (ex: gas turbine or electric motor) can use the mission to specify the rotation speed vs. time. The “Reference Conditions” window in Analysis Setup contains these settings. The Reference Flow Rate is only used for post-processing so is optional. The Shaft Rotor Speeds are required since they are used during run time for cavities, element rotation, vortex rotation and other calculations.