1. Introduction to Off Design Simulations
GasTurb 13 – Tutorial 3
Introduction to Off Design Simulations
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2. Off-Design Simulations
Let us begin with a jet engine. Select the most simple engine architecture, a Turbojet.
Select as Scope
Performance and then click
Off Design
A click on Standard Maps begins the off-design calculation.
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3. We Need Some Data…
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4. Off-Design Input Data Page
After reading the file, the cycle design point is calculated. This happens in the background.
The standard compressor and turbine maps are scaled in such a way that they fit to the cycle design point.
Now we calculate the cycle design point as an
off-design point
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5. Off-Design Point Summary
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The contents of this summary page is identical to that of the cycle design point

6. Operating Point Details
This is the Standard High Pressure Compressor Map file
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On this page those details of the operating point are presented that are not needed for a cycle design calculation.
This is the Standard High Pressure Turbine Map file

7. Compressor Map Copyright © GasTurb GmbH
The circle marks the cycle design point,
the yellow square marks the off-design operating point.
In this special case – because we have calculated the cycle design point in off-design mode – the yellow square is inside the circle.
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8. Turbine Map Copyright © GasTurb GmbH
The circle marks the cycle design point,
the yellow square marks the off-design operating point.
There are six different versions of a turbine map.
The y-axis can be Pressure Ratio or Corrected Work.
Here Turbine Pressure Ratio is shown over the product of Corrected Flow and Corrected Speed.
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9. Here Turbine Pressure Ratio is shown over Corrected Speed.
Turbine Map
Here Turbine Pressure Ratio is shown over Corrected Speed.
The corrected flow is shown as contour lines in % of the maximum corrected flow in the map
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10. Turbine Map Copyright © GasTurb GmbH
Here Turbine Pressure Ratio is shown with the same axes as a compressor map: Turbine Pressure Ratio over Corrected Mass Flow.
The disadvantage of this format is that all the speed lines nearly collapse.
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11. Thermodynamic Stations
Here you get all the details at the thermodynamic stations.
The engine geometry - all the flow areas at all stations - is among the results of the cycle design point calculation.
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12. Off-Design Input Data Copyright © GasTurb GmbH
Here you can choose whether
Relative Spool Speed ZXN or
Burner Exit Temperature ZT4 is given.
Enter 2 to make Burner Exit Temperature an input and use 1200 for it
Let us run a case with 1200 K
Burner Exit Temperature.
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13. The solution is found by iteration
Off-Design Result
The solution is found by iteration
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14. Compressor operating point for T4=1200K
Compressor Map
Cycle design point
Compressor operating point for T4=1200K
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15. Now let us calculate the complete sea level static operating line.
Off-Design Iteration
These are the estimated values of the iteration variables. If the iteration fails to converge, you can try with better estimates for the variables.
These are the variables of the iteration. Betavalues are auxiliary coordinates in component maps.
Iteration targets are flow continuity between components and power balances
Now let us calculate the complete sea level static operating line.
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16. Off-Design Input Operating Line
Reset to 1 and enter for the HPC Spool Speed ZXN also 1
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17. Operating Line Input Copyright © GasTurb GmbH
Increase the Number of Points to 20, then run the case by clicking the Operating Line button
The operating line commences with the single point which was calculated before the operating line window was opened. A series of points with decreasing gas generator spool speed will be calculated. The default step size of relative spool speed is
Answer No
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18. Compressor Operating Line
We will employ a handling bleed to cure that problem.
Here the compressor surges
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19. Off-Design Input Operating Line
Re-run the operating line
Enter numbers
in all 3 boxes
Click Controls to show the controls button group. Then click the Bleed button
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20. Repeat the Operating Line Calc
Answer this time
Yes
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21. Switch Automatic Bleed “On”
Enter 1 for the second operating line, then click Run
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22. Compressor Operating Lines With and Without Bleed
Let us have other views on the data
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With bleed the surge problem does not exist.

23. The Default Plot Copyright © GasTurb GmbH
With bleed the surge problem does not exist. However, with bleed the fuel consumption is higher…
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24. New Picture
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25. New Picture
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26. T4 = f(Corrected Spool Speed)
With bleed the surge problem does not exist; however, the burner exit temperature is significantly higher
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This slide ends the
Introduction to Off-Design Simulations Tutorial