# Introduction to Off Design Simulations

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Introduction to Off Design Simulations
GasTurb 12 – Tutorial 3 Introduction to Off Design Simulations Copyright © Joachim Kurzke

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. Copyright © Joachim Kurzke

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 Copyright © Joachim Kurzke

Off-Design Point Summary
Copyright © Joachim Kurzke The contents of this summary page is identical to that of the cycle design point

Operating Point Details
This is the Standard High Pressure Compressor Map file Copyright © Joachim Kurzke 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

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. Copyright © Joachim Kurzke

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. Copyright © Joachim Kurzke

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 Copyright © Joachim Kurzke

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. Copyright © Joachim Kurzke

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. Copyright © Joachim Kurzke

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. Copyright © Joachim Kurzke

The solution is found by iteration
Off-Design Result The solution is found by iteration Copyright © Joachim Kurzke

Compressor operating point for T4=1200K
Compressor Map Cycle design point Compressor operating point for T4=1200K Copyright © Joachim Kurzke

Now let us calculate the complete sea level static operating line.
Off-Design Iteration Iteration targets are flow continuity between components and power balances 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. Now let us calculate the complete sea level static operating line. Copyright © Joachim Kurzke

Reset to 1 and enter for the HPC Spool Speed ZXN also 1 Copyright © Joachim Kurzke

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 Copyright © Joachim Kurzke

Compressor Operating Line
We will employ a handling bleed to cure that problem. Here the compressor surges Copyright © Joachim Kurzke

Re-run the operating line Click Controls to show the controls button group. Then click the Bleed button Enter numbers in all 3 boxes Copyright © Joachim Kurzke

Repeat the Operating Line Calc

Switch Automatic Bleed “On”
Enter 1 for the second operating line, then click Run Copyright © Joachim Kurzke

Compressor Operating Lines With and Without Bleed
Let us have other views on the data Copyright © Joachim Kurzke With bleed the surge problem does not exist.

With bleed the surge problem does not exist. However, with bleed the fuel consumption is higher… Copyright © Joachim Kurzke