GasTurb 12 – Tutorial 3
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INTRODUCTION TO
OFF DESIGN SIMULATIONS
Off-Design Simulations
Let us begin with a jet engine.
Select the most simple engine
architecture, a Turbojet.
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Select as Scope
Performance and then click
Off Design
A click on Standard Maps begins
the off-design calculation.
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We Need Some Data…
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 theyNow
fit to
cyclethe cycle
wethe
calculate
design
point
as an
design point.
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off-design point
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Off-Design Point Summary
The contents of this summary
page is identical to that of the
cycle design point
Operating Point Details
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This is the Standard High
Pressure Compressor Map file
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
Compressor Map
The circle marks the cycle
design point,
the yellow square marks the
off-design operating point.
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In this special case – because
we have calculated the cycle
design point in off-design
mode – the yellow square is
inside the circle.
Turbine Map
The circle marks the cycle
design point,
the yellow square marks the
off-design operating point.
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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.
Turbine Map
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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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Turbine Map
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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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.
Off-Design Input Data
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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.
Off-Design Result
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The solution is
found by
iteration
Compressor Map
Cycle design point
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Compressor
operating point for
T4=1200K
Off-Design Iteration
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Iteration targets are flow
These are the estimated
values ofbetween
continuity
These are the variables
theofiteration variables.components
If the iteration
and power
the iteration. Betavalues fails
are to converge, you can try with
balances
auxiliary coordinates in
better estimates for the variables.
component maps.
Now let us calculate the
complete sea level static
operating line.
Off-Design Input
Operating Line
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Reset to 1 and enter for the HPC
Spool Speed ZXN also 1
Operating Line Input
Increase the Number of Points to 20,
The
line commences
with the
then run
theoperating
case by clicking
the
single
point
which
was
calculated
Operating Line button
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 0.025.
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Answer
No
Compressor Operating Line
We will employ a
handling bleed to cure
that problem.
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Here the
compressor
surges
Off-Design Input
Operating Line
Re-run the
operating line
Click Controls to show the
controls button group. Then
click the Bleed button
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Enter numbers
in all 3 boxes
Repeat the Operating Line Calc
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Answer this time
Yes
Switch Automatic Bleed “On”
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Enter 1 for the second
operating line, then
click Run
Compressor Operating Lines
With and Without Bleed
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Let us have other views
on the data
With bleed the
surge problem
does not exist.
The Default Plot
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With bleed the surge
problem does not exist.
However, with bleed the fuel
consumption is higher…
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New Picture
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New Picture
T4 = f(Corrected Spool Speed)
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With bleed the surge problem does not
exist; however, the burner exit
temperature is significantly higher
This slide ends the
Introduction to Off-Design Simulations
Tutorial