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Dynamic Simulation of Gas Turbine Engines
Aircraft- and power generation gas turbines have to meet increasingly high
efficiency and performance requirements. In addition, in the course of adverse
dynamic operations such as start-up, shutdown and load changes the engines
are subject to:
 Extreme aerodynamic, thermal and mechanical stresses. Design point
calculations do not account for additional stresses originating from
dynamic operation
 A non-linear dynamic computational tool provides detailed essential
information regarding dynamic behavior of gas turbine engines under offdesign or any extreme adverse operation condition.
 TPFL has developed a powerful computational tool, GETRAN
 Further enhancement of GETRAN is a Ph.D. topic
TPFL: The Turbomachinery Performance and Flow Research Laboratory
Texas A&M University
M. T. Schobeiri
Gas Turbine Engines, Generic Components, Modeling
Twin-Spool Aircraft
Gas Turbine Engine
High Efficiency Power Generation
Gas Turbine Engine with Sequential
Combustion
TPFL: The Turbomachinery Performance and Flow Research Laboratory
Texas A&M University
M. T. Schobeiri
Components Common to All Gas Turbine Engines
Gas turbine components of different geometric configurations fulfill the
same function and are described by the same set of conservation equations.
Conventional Combustion Chamber
Generator
Inlet nozzle
Multi-stage compressor
Multi-stage compressor
Inlet nozzle
EV-Combustiors
Multi-stage turbine
Exit diffuser
This common characteristic is utilized for code development and architecture
of GETRAN, which is
 A GEneric modularly structured computer program for Simulating the
TRANsient behavior aircraft and power generation gas turbine engines
TPFL: The Turbomachinery Performance and Flow Research Laboratory
Texas A&M University
M. T. Schobeiri
Gas Turbine Components, Generic Modules
Example of Components and module representation in GETRAN:
 Uncooled and cooled turbine stage, compressor, combustion chamber
For more details refer to Text: M.T. Schobeiri Turbomachinery Flow Physics
And Dynamic Performance, Springer-Verlag First Edition (Second Edition in
Press)
Turbine stage
representation
Velocity diagram
Turbine module
representation
Casing with stator cooling channels
Compressor stage
representation
1 = Fuel inlet
m = Fuel mass flow
2 = Swirl generator
m
3 = Combustion zone
m
4 = Primary liner
1 = Inlet diffuser
3 = Primary zone
5 = Liner
2 = Swirl generator 4 = Secondary zone 6 = Exit
Velocity diagram
F
M
P
= Mixing mass flow
= Primary air mass flow
m
5 = Secondary flow zone
6 = Secondary liner
= Secondary air mass flow
m
= Total secondary air mass flow
7 = Mixing zone
Q
S
8 = Exit
Combustor module representation
Turbine module
representation
F
Q
= Heat flow generated by fuel combustion
= Heat flow generated by flame radiation
RF
Combustor component
TPFL: The Turbomachinery Performance and Flow Research Laboratory
Texas A&M University
M. T. Schobeiri
Non-linear Dynamic Engine Simulation Steps
 Step 1: Expedite the engine hardware components:
 No. of spools
 No. of shafts, May be different from the no. of spools
 No. of compressors stages on each spool
 No. of turbine stages on each spool
 No. of combustors
 No. of diffusers, nozzles, recuperators, controllers etc.
 Step 2: Generate the schematics of the engine that includes all modules with
addressing.
 Step 3: Provide a detailed input file that accounts for the geometry of the
entire engine and some components characteristics at design point.
 Step 3: Based on the geometry given, above GETRAN calculates the
behavior at the design and any adverse off-design operation prescribed by
the user.
 An example shows, how the simulation works.
TPFL: The Turbomachinery Performance and Flow Research Laboratory
Texas A&M University
M. T. Schobeiri
Non-linear Dynamic Engine Simulation Steps
Example: Simplified engine decomposition showing major components
LP-compressor stage Combustion chamber LP-turbine stage
m
4
F
mS
2
m
mS1 mSi
mP
5
mM
mA mF
A
Inlet
3
Exit
7
m1
m2
m3
6
JT-2SZO
HP-compressor stage
HP-turbine stage
Cooled HP-turbine stage
m = Fuel mass flow
m = Air mass flow
m = Primary air mass flow
m = Secondary air mass flow
F
P
A
S
TPFL: The Turbomachinery Performance and Flow Research Laboratory
Texas A&M University
M. T. Schobeiri
Non-linear Dynamic Engine Simulation Steps
Example: Simplified engine decomposition showing major components
Simulation of a twin-spool Core engine
Similation Schematic of a Twin-Spool Core Engine, Module Addressing
FT
F Vi
Ni
NS
Si
Ti j
=
=
=
=
Fuel valve
Nozzle
Speed sensor
Shaft
th
j turbine stage of i thspool
= Signal flow
= Air flow
= Gas flow
= Fuel flow
BV
FV1
BV1
8
Multivariable Control System
BV = Bypass valve
C = j compressor stage of i spool
CC = Combustion Chamber
D = Diffuser
FT = Fuel tank
9
10
11
13
12
CC1
14
15
16
T21
T22
T23
18
19
20
17
S2
C21
1
C22
3
2
C23
C24
5
4
C25
6
7
21
S
JT-2S2S1
C
C12
C13
C14
C15
T
T12
Note: GETRAN requires the Design point data to simulate any type
of adverse off-design Operation conditions
TPFL: The Turbomachinery Performance and Flow Research Laboratory
Texas A&M University
M. T. Schobeiri
T13
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Modeling Technology: Example Combustion Chamber
Each component is modeled by a set of partial differential equations
Physical components of a combustion Chamber
Modular representation
mF
mF
1
mS t
4
mSt
mP
mP
mS
mS
j
1
2
3
6
7
8
mM
QRF
j
Q
m P Fj
mSt
mF
mA mF
m St
1
5
mIn
P In
ToIn
mM
mA
3
2
4
5
6
Simulation Schematic of a Jet Engine Combustion Chamber
1 = Inlet diffuser 2= Swirl generator 3= Primary zone (red)
4 = Secondary zone (blue) 5 = Liner 6 = Exit
m Sj
1: Fuel inlet
2: Swirl generator
3: Combustion zone 4: Segments
5: Secondary air zone
6: Casing
7: Mixing zone
m = Fuel mass flow
m = Total secondary air mass flow
F
m = Mixing mass flow
M
m = Primary air mass flow
P
St
Q = Heat generated by fuel combustion
Fj
Q = Heat generated by flame radiation
j
RF
For the above combustion model, we have system of 7 PDEs:
3 PDE on the air (cold side blue),
3 PDE on hot (gad side red),
1 PDE the metal side
A complete gas turbine engine has several system of PDEs.
The type of adverse operation condition determine the boundary conditions
TPFL: The Turbomachinery Performance and Flow Research Laboratory
Texas A&M University
M. T. Schobeiri
m Out
POUT
ToOUT
One Example of an Adverse Operation
For forcing a gas turbine with split shaft into rotating stall and surge
40
1.10
1.05
20
1.00
/D
Power (MW)
Power shaft
Given power turbine schedule
30
Power shaft
10
0.95
0
Gas generator shaft
0.90
Gas generator shaft
-10
0.85
Gas generator power response
-20
0.80
0
2.5
5
7.5
10
12.5
15
0
2.5
5
Time (s)
10
12.5
15
160
Compressor Mass Flows (kg/s)
160
Compressor Mass Flows (kg/s)
7.5
Time (s)
120
LP-Compressor
80
40
0
-40
120
IP-Compressor
80
40
0
-40
0
5
10
Time (s)
15
0
5
10
15
Time (s)
Note: the high frequency surge with intermittently positive and negative mass flow
GETRAN, row-by-row compressor and turbine component calculation.
s (kg/s)
TPFL: The Turbomachinery Performance and Flow Research Laboratory
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Texas A&M University
M. T. Schobeiri
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