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Turbojet Multi-execution model


Before starting🔗

Set aside 30-40 minutes to finish all tutorial steps.

Go to settings and select imperial units.

What are we building?

This application is designed as a workshop, where we'll show how to build a simple turbojet model consisting of all essential parts. The resulting model will roughly resemble the famous GE J85 from 1950s.

You will learn how to:

  • How to control and run more than one a simulation at a time
  • Understand how the controls work for gas turbine.
  • Ability to to execute more than one experiment at a time.
  • Multi-execution, that is handling more than one simulation at a time.

Fuel control experiments🔗

  1. Create a new workspace for this tutorial, and call it BurnerControl.

  2. When the new workspace is loaded, open the left library pane to copy an experiment from the library into your workspace:

    a. Check that you can see the default package Workspace inside the new workspace.

    b. Navigate to JetPropulsion library, and duplicate the experiment below into your Workspace package such that you can edit it.

    - JetPropulsion.Experiments.GearedTurbofan.MultiPoint.Controlled
  3. Familiarize yourself with the fuel control used in this experiment.

    a. Right-click the control block farFromT4AndNc, and select “Show documentation”.

    b. In the right paramererization pane, cycle through values of parameters useConstraint and useConstraintOnly to yield each of the following modes, and observe how the icon of the control block changes accordingly.

    • Normal mode, in which we impose a given T4 unless the corrected speed exceeds its threshold,

    • Constraint only mode, in which we ignore the value of T4 and prescribe the corrected speed to the given threshold (to avoid arbitrary design fuel flow, this can only apply to off-design simulations)

    • No constraint mode, in which we ignore the corrected speed threshold and prescribe T4.

  4. Run a first experiment.

    a. Confirm that you simulate a design point at 35000 ft, Mach Number 0.78 and temperature offset of 10 K by reviewing the parameter in airData and atmosphere components.

    b. Simulate with the “A1: Simulate (single point)” custom function and store the design data under name toc (enter experiment mode and navigate to the experiment group in the right pane to check the design data name).

    c. Rename the simulation results to TOC.

    d. Enter experiment mode. In the ambient model sticky, uncheck onDesign to set up an off-design simulation.

    e. Reduce the altitude to 30,000 ft and simulate again with the “A1: Simulate (single point)” custom function. Rename the experiment to “Off-design at 30kft”

    f. Plot farFromT4AndNc.summary.T4 as a function of farFromT4AndNc.summary.fanSummary.NcqNcDes. The T4 is 1900 K as expected.

    g. Rename the results to “TOC 30kft”.

  5. Run a second experiment.

    a. In experiment mode, right click your experiment “Off-design at 30kft” and choose duplicate.

    b. Change the name of the duplicate to “Off-design at 40kft” and adapt the value of alt_par in the airData model accordingly.

    c. Simulate the experiment (again, per experiment definition, with custom function “A1 Simulate (single point)”.

    d. Rename the result to “TOC 40kft” and review the resulting T4 in your plot.

For the 30 kft case, T4 was 1900 K as demanded and the corrected shaft speed ratio slightly below 0.96. For this case, we now see that T4=1892K and the corrected shaft speed ratio is at its limit 1.0.

Accelerated exploration using multi-execution experiments🔗

We will now use an easier approach to run several simulations at once instead of keying values for one experiment at a time.

Create a multi-execution experiment changing altitude.

  1. In experiment mode, right-click the “Off-design at 40kft” experiment and choose duplicate.

  2. In the airData model, enter the altitude range from 30,000 ft = 9,144 m to 40,000 ft = 12,192 m with 11 values. Note how the range() and choices() operators. This link can be used for this but the current version of Modelon Impact may force you to enter the values in SI units (check the unit shown when you type into the sticky!). Choose the value in the appropriate unit for this purpose and name the experiment Off-design at 30-40kft.

  3. Run the experiment and rename the results to “TOC at 30-40kft”.

  4. Create additional plots by dragging the speed ratios for fan, IPC, HPC onto the canvas and by dragging T4 onto the canvas.


    The HPC is overspeeding at altitude above the design point altitude of 35,000 ft. The ratio of corrected speed to design point corrected speed is increasing beyond the threshold 1 then. It may be more appropriate for this particular model and the conditions we are analyzing to modify the controls to maintain the corrected speed ratio at 1 for the HPC instead of for the fan.

Changing the corrected speed ratio reference from fan to HPC.

  1. Switch back to experiment mode and open the parameterization dialog in the right pane (you may have to select the control block farFromT4AndNc and expand the “properties” section of the pane). Check whether you can change parameter compressorChoice.

  2. As you see, compressorChoice is greyed out in experiment mode. The reason is that it is a structural parameter and cannot be changed without recompiling. Note the orange point indicating this in the parameterization dialog. You have to switch to modeling mode and change the value to “High pressure compressor”. This will require model recompilation and it is not possible to associate this change with an experiment.

  3. After the change to “High pressure compressor”, return to experiment mode and select the “Off-design at 30-40kft” experiment again. As expected, the modifications do not list the change of the compressorChoice to “High pressure compressor” but the experiment is also valid for these choices. Press the button to simulate again with custom function “A1: Simulate (single point)”.

  4. You can tell from the text next to the simulate button, that the model is first compiled this time and then again simulated. When you get the results, you see that the corrected speed ratios are more meaningful this time. None of the ratios exceeds the threshold 1.0.

  5. Save these views, for instance by moving the mouse pointer above the eye (below the simulate button) and choose “Save as…”. Enter a name such as “Speed ratios” and deactivate these plots to create space on the model canvas.

Thrust hooks🔗

In this section, we will create some basic samples of plots relating specific fuel consumption and net thrust. Substantial detail and engineering work can go into this while the following provides a few directions on how to run the require experiments conveniently.

  1. In the results you generated previously (called “TOC at 30-40kft with NcqNcDes 1”), search for specific fuel consumption (e.g., type “sfc” into the filter box in the “calculated values” section and make sure to unselect components on the canvas or select only the cycleProperites component on the lower left).

  2. Drag and drop cycleProperties.SFC to the model canvas to create a new plot.

  3. Search for net thrust Fn and drag cycleProperties.Fn onto the x-axis (also called abscissa) of the plot. Review the result. Is this a thrust hook already? You likely figured that it is not. We freeze T4 at 1900 K and vary the altitude. We instead want to vary both the altitude and the T4 values (later, we also want to change the Mach Number based on altitude but we simplify this aspect for now).

  4. Return to experiment mode and duplicate your experiment “Off-design at 30-40kft” to a new experiment, which you call “Thrust hook at 20-40kft and 1000-1900K”.

  5. Edit the range operator for alt_par to span values from 30,000 ft = 9,144 m to 40,000 ft = 12,192 m in 3 steps, i.e., with 5,000 ft difference. If we take too small steps here the lines will later be too close to each other.

  6. Select the control block farFromT4AndNc on the model canvas and click the small eye to show the sticky for the key parameters of this model, too. Enter values for TtCombOutPrscrPar, i.e., T4, ranging from 1600 K to 1900 K in 25 K steps, i.e., range(1000, 1900, 21).

  7. Simulate the experiment and review the results.

  8. Click at a few markers to understand the results (you can for instance see the selected values in the slider at the bottom of the canvas). The top line therefore corresponds to the lowest altitude of 30,000 ft, the middle line to 35,000 ft and the bottom line to 40,000 ft. Note how the right-most marker has a stronger color. This means that several transparent markers are drawn on top of each other because for a small range of T4 values no difference in results appeared. This is because of the limiting through the shaft speed. Create additional plots to confirm this!

  9. For instance, select the control block farFromT4AndNc and type “ncq” into the filter. Drag farFromT4AndNc.summary.hpcSummary.NcqNcDes to the model canvas.

  10. Change the filter to “ttc” while maintaining the selection of control block farFromT4AndNc on the canvas. Drag farFromT4AndNc.TtCombOutPrscr onto the x-axis of the new plot. Note that this is the prescribed value and not the true or sensed value (the latter would not be meaningful here as this will be limited by the maximum corrected speed logic in the control block). See how the speed ratio is flat for the lower altitude as prescribed T4 reaches 1900K.

  11. Lastly, create a line at zero altitude and Mach Number 0.25. This corresponds to so-called rolling take-off conditions. From the cases close to the design point we simulated so far, it is often required to converge intermediate altitude/Mach Number/T4 combinations for non-trivial models to ensure reliable convergence.


    This is required when going to the rolling take-off conditions for this model, too.

Typically, we use a custom function “A2: Simulate (single point, with stepping)” for convenience. We could use this once to converge a single RTO condition and use the functionality to initialize from previous results in the graphical interface.

However, in this case we simply use the A2 custom function in all points as follows (and therefore apply the stepping more often than required to eliminate one intermediate step).

  1. Duplicate the experiment “Thrust hook at 30-40kft and 1600-1900K” and call the new experiment “Thrust hook at 0ft and 1600-1900K”.

  2. In experiment mode, set altitude to 0 ft = 0 m and the Mach Number to 0.25 in the airData model.

  3. In the analysis section of the experiment group, switch to the A2 custom function. In the “initialize from” field, select the previous result named TOC. The other custom function inputs dMn, dalt, ddTs define the maximum step size in SI units [-], [m], [K] between the intermediate values starting at the selected previous result (e.g., for altitude 35,000 ft = 10,668 m) and the prescribed result (according to our experiment setup, e.g., for altitude 0 ft = 0 m).

  4. Simulate the model and review the thrust hook at rolling take-off conditions.

You have now controlled your gas turbine engine accross a range of different operating conditions which which posed many different requirements in terms of shaft speed, thrust and so on. All of this has been possible with off-the-shelf components and Modelon Impact experiment mode. This concludes the tutorial.