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1Secondary Air System Component Modelling For Engine Performance
SimulationsA. Alexiou & K. Mathioudakis
Laboratory of Thermal TurbomachinesNational Technical University
of Athens
Secondary Air System Component Modelling For Engine Performance
Simulations
A. Alexiou &
K. Mathioudakis
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2Secondary Air System Component Modelling For Engine Performance
SimulationsA. Alexiou & K. Mathioudakis
Paper Objectives
Describe an object-oriented approach for modelling Secondary Air
Systems
Present the detailed modelling of some typical Secondary Air
System components
Validate the modelling against publicly available experimental
and/or computational results
Demonstrate the integration of such components in a whole engine
performance model
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3Secondary Air System Component Modelling For Engine Performance
SimulationsA. Alexiou & K. Mathioudakis
SECONDARY AIR SYSTEM MODELLINGCOMPONENT MODELS
o Generic Componento Orifice Componento Labyrinth Seal
Component
IMPLEMENTATION & VALIDATIONo Simulation Environment
Overviewo Test Cases
Pre-Swirl ChamberRotating CavitiesRotating HolesPre-swirl System
with Labyrinth Seals
o Whole Engine ModelSUMMARY & CONCLUSIONS
Contents
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4Secondary Air System Component Modelling For Engine Performance
SimulationsA. Alexiou & K. Mathioudakis
Secondary Air System Schematic
ORIFICESROTATING
DISC CAVITIESLABYRINTH
SEALS
PRE-SWIRL SYSTEM
DRIVE CONE CAVITY
RIM SEAL
ORIFICESROTATING
DISC CAVITIESLABYRINTH
SEALS
PRE-SWIRL SYSTEM
DRIVE CONE CAVITY
RIM SEAL
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5Secondary Air System Component Modelling For Engine Performance
SimulationsA. Alexiou & K. Mathioudakis
Secondary Air System Modelling: Current Approach
Dedicated Air System Model
Engine Performance Model
Values
for Bleeds & Returns for particular engine running
conditions
DisadvantagesThe Secondary Air System is a “black box” for
the
performance engineer.The Air System designer cannot assess
autonomously the
system performance as part of the whole engine model.Increased
scope for error during data exchange.
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6Secondary Air System Component Modelling For Engine Performance
SimulationsA. Alexiou & K. Mathioudakis
Secondary Air System Modelling: Proposed Approach
AdvantagesIndividual components or entire air systems can be
integrated
transparently in whole engine performance models.Different air
system design configurations can be constructed and
compared in a generic, flexible and intuitive manner.Component
changes visible during model exchanging.
Secondary Air System (SAS) components directly integrated in
engine model. Boundary conditions (IN/OUT m, Pt, Tt, Vφ)
communicated
through appropriate Ports.SAS component
(pre-swirl system)SAS Port
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7Secondary Air System Component Modelling For Engine Performance
SimulationsA. Alexiou & K. Mathioudakis
SECONDARY AIR SYSTEM MODELLINGCOMPONENT MODELS
o Generic Componento Orifice Componento Labyrinth Seal
Component
IMPLEMENTATION & VALIDATIONo Simulation Environment
Overviewo Test Cases
Pre-Swirl ChamberRotating CavitiesRotating HolesPre-swirl System
with Labyrinth Seals
o Whole Engine ModelSUMMARY & CONCLUSIONS
Contents
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8Secondary Air System Component Modelling For Engine Performance
SimulationsA. Alexiou & K. Mathioudakis
Component Models
Using the advantages of object-oriented modelling (such as
encapsulation, inheritance, abstraction aggregation and
polymorphism), it is possible to create secondary air system models
for a variety of engine configurations using three main components:
generic, orifice
and labyrinth seal.
For a specified component geometry, the inlet flow conditions
(m, Pt, Tt, Vφ) are linked to the outflow ones through the
conservation equations for mass flow, energy, axial and angular
momentum.
The component’s performance can be calculated for any valid
combination of input/output variables and component
characteristics.
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9Secondary Air System Component Modelling For Engine Performance
SimulationsA. Alexiou & K. Mathioudakis
Generic Component Model
Ω
rK
, AKrm
r
zin out
rN
, AN
rJ
, AJ
mix
STATOR
ROTOR
Q
Arbitrary geometry (discs, cones, cylinders)J Input flows and N
output flowsFully mixed flowWork and heat transfer from surrounding
K surfacesSAS examples: pre-swirl system chamber, compressor
inter-disc cavities,
drive-cone cavity
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10Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Generic Component Equations (I)
( )∑ ∑= =
φφ =⋅⋅−⋅⋅J
1j
K
1kkj,in,j,inj,inmix,mmix MVrmVrm
( )mix,kmix,kmixkkk,mk VrVrArC5.0M φφ −⋅Ω⋅−⋅Ω⋅ρ⋅⋅⋅⋅=
( )∑ ∑= =
⋅Ω+=⋅⋅−⋅⋅J
1j
K
1kkj,in,tj,pj,inmix,tmix,pmix MQTCmTCm
Angular Momentum Conservation Equation → Vφ,mix
Energy Conservation Equation → Tt,mix
Moment exerted by fluid on each surrounding surface, Mk (from
drag force equation):
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11Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Generic Component Equations (II)
Mixing total pressure, Pt,mix
( )refSSav TTAhQ −⋅⋅=
Axial momentum equation → Ps,mix
:
Convective heat transfer, Q:
( ) ( )( )⎥⎥⎥
⎦
⎤
⎢⎢⎢
⎣
⎡ζ+⎟
⎟⎠
⎞⎜⎜⎝
⎛ ⋅−⋅ζ−⋅=
−γγ
1
mix,s
Pmixmix,tmix,smix,t T
CmQT1PP
( )( )mix,tis,mix,t
mix
mix,zmix
J
1jj,inj,in,sj,in,zj,in
mix,s PPA
VmAPVmP −−
⋅−⋅+⋅=∑=
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12Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Orifice Component Model
α
Ω
L
rf
U
V
Vrel
φ
z1
2
d
Vφ
ir
α
Ω
L
rf
U
V
Vrel
φ
z1
2
d
Vφ
ir
Axial & radial holesRotating & stationary
is
hD m
mC =
Discharge Coefficient CD
corrected through correlations for:
Hole Reynolds numberInlet corner radiusHole lengthPressure
ratioIncidence angle
( ) i:DRe:D3'dL,2dr,21D CC1ffff1C f Δ+−⋅⋅⋅⋅−=
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13Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Orifice Component Equations
( )
21
22,1,12,2
1
1,t
2,s
1,t
1,t1
1,t
2,s1,this
VVrVr2
PP
1P
12
PP
Am
⎪⎪
⎭
⎪⎪
⎬
⎫
⎪⎪
⎩
⎪⎪
⎨
⎧
−⋅−⋅⋅Ω⋅+
⎥⎥⎥
⎦
⎤
⎢⎢⎢
⎣
⎡
⎟⎟⎠
⎞⎜⎜⎝
⎛−⋅
ρ⋅⎟⎟
⎠
⎞⎜⎜⎝
⎛−γγ⋅
⋅⎟⎟⎠
⎞⎜⎜⎝
⎛⋅ρ⋅=
φφφ
γ−γ
γ
α−⎟⎟⎠
⎞⎜⎜⎝
⎛α⋅
−= φ−
cosVVU
taniis
1,1 α−⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛
α⋅
+−= φ−
cosVV)VU(
taniis
21,z
21,1
Incidence Angle DefinitionAxial Holes Radial Holes
1-D, isentropic, compressible expansion of a perfect gas from
the upstream total pressure to the downstream static pressure and
considering the work transfer to the fluid:
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14Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Labyrinth Seal Component Model
Ω
1 2
cp
STATOR
ROTOR
FIN
Ω
1 2
cp
STATOR
ROTOR
FIN
)PR1ln(nPR1
TR
PCAm
t
2t
1,t
1,tD +
−⋅
⋅⋅Γ⋅⋅=
02.0pcpc
n1n1
1
+⋅
−−
=Γ
For flow through straight, staggered and stepped labyrinth
seals
CD
= 0.71 for 1.3 < c/t
< 2.3
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15Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
SECONDARY AIR SYSTEM MODELLINGCOMPONENT MODELS
o Generic Componento Orifice Componento Labyrinth Seal
Component
IMPLEMENTATION & VALIDATIONo Simulation Environment
Overviewo Test Cases
Pre-Swirl ChamberRotating CavitiesRotating HolesPre-swirl System
with Labyrinth Seals
o Whole Engine ModelSUMMARY & CONCLUSIONS
Contents
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16Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Simulation Environment Overview
libraries
palette
Output Window
Engine Diagram(schematic view)
Experiment EL file(Simulation View)
Experiment Results(Simulation View)
Component EL file(Code View)
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17Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Test Cases: Pre-Swirl Chamber
( )2RH
2RH,rel,tPN,tP
rTTC2
⋅Ω
−⋅⋅=Θ
Adiabatic Effectiveness
PN
in,in r
V⋅Ω
=β φ
Inlet Swirl ratio
2RH
S
2
RH
PNin rm
M21rr2
⋅Ω⋅⋅
−−⎟⎟⎠
⎞⎜⎜⎝
⎛⋅β⋅=Θ
Theoretical value of Θ
( )P
RH,mix,RH2
RHmix,tRH,rel,t C2
Vr2rTT
⋅
⋅⋅Ω⋅−⋅Ω+= φ
Pre-swirlNozzles
ReceiverHoles
Pre-swirlChamber
Relative Total Temperature
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18Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Test Cases: Pre-Swirl Chamber
-1
-0.5
0
0.5
1
1.5
2
2.5
3
0.0 0.5 1.0 1.5 2.0 2.5 3.0
βin
Θ Present WorkTheoreticalComputed
Pre-swirlNozzles
ReceiverHoles
Pre-swirlChamber
Pre-swirlNozzles
ReceiverHoles
Pre-swirlChamber
Lewis et al, ASME GT-2006-90132
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19Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Test Cases: Pre-Swirl Chamber
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0.0 0.5 1.0 1.5 2.0 2.5 3.0βin
β mix
Present WorkComputed
Pre-swirlNozzles
ReceiverHoles
Pre-swirlChamber
Pre-swirlNozzles
ReceiverHoles
Pre-swirlChamber
Lewis et al, ASME GT-2006-90132
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20Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Test Cases: Pre-Swirl Chamber
Geis
et al, J. Eng. Gas Turbine and Power, 126 (4), pp. 809-815
0.97
0.98
0.99
1
1.01
1.02
1.03
0 0.5 1 1.5 21/βmix
T t,re
l,RH /
T t,P
N
Measured (PR=1.10) Present Work (PR=1.10)Measured (PR=1.35)
Present Work (PR=1.35)
Tt,rel,RHTt,PN
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21Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Test Cases: Pre-Swirl Chamber
Geis
et al, J. Eng. Gas Turbine and Power, 126 (4), pp. 809-815
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0 0.5 1 1.5 21/βmix
MR [N
m]
Measured (PR=1.10) Present Work (PR=1.10)Measured (PR=1.35)
Present Work (PR=1.35)
ROTOR
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22Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Test Cases: Pre-Swirl Chamber
Geis
et al, J. Eng. Gas Turbine and Power, 126 (4), pp. 809-815
50
100
150
200
250
0 50 100 150 200Ωrm [m/s]
V φ,m
ix [
m/s
]
Present WorkMeasuredIsentropic
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23Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Test Cases: Rotating Cavities
Alexiou et al, Int. J. Experimental Heat Transfer, 13, pp.
299-328
0
0.01
0.02
0.03
0.04
0.05
0 2 4 6 8 10 12 14Bo
ΔT/
T
Present WorkMeasured
SHAFT
DISCSSHROUD
CA
VITY
SHAFT
DISCSSHROUD
CA
VITY
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24Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Test Cases: Rotating Holes –
Axial
Dittmann
et al, J. Eng. Gas Turbine and Power, 127, pp. 383-388
0.4
0.5
0.6
0.7
0.8
0.9
1
0 5 10 15 20 25 30 35 40 45Incidence Angle, i (deg)
CD
Present WorkMeasured
Pre-swirlNozzles
ReceiverHoles
Pre-swirlChamber
Pre-swirlNozzles
ReceiverHoles
Pre-swirlChamber
L/d=5.66r/d=0.2α=0°NRH
=24
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25Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Test Cases: Rotating Holes –
Axial
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8βmix
CD
Present WorkCFDMeasured
Pre-swirlNozzles
ReceiverHoles
Pre-swirlChamber
Pre-swirlNozzles
ReceiverHoles
Pre-swirlChamber
Lewis et al, ASME GT-2006-90132
L/d=1.25r/d=0α=0°NRH
=60
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26Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6βmix
CD
Pre-swirlNozzles
ReceiverHoles
Pre-swirlChamber
Pre-swirlNozzles
ReceiverHoles
Pre-swirlChamber
Test Cases: Rotating Holes –
Axial
Chew et al, ASME GT-2003-38084
L/d=0.86r/d=0α=0°NRH
=72
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27Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
0.0
0.1
0.2
0.3
0.4
0.5
0.6
20 25 30 35 40 45Incidence Angle, i (deg)
CD
Measured: ΔΩ=0Present Work ΔΩ=0Measured: ΔΩ>0Present Work
ΔΩ>0
ROTOR
SHAFT
ROTOR
SHAFT
Test Cases: Rotating Holes –
Radial
Alexiou et al, Int. J. Heat and Fluid Flow, 21, pp. 701-709
L/d=0.45r/d=0.067α=0°NRH
=12
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28Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Test Cases: Pre-swirl System with Labyrinth Seals
-0.5
0
0.5
1
1.5
0 0.5 1 1.5
βmix
ΘPresent WorkMeasured
Pre-swirlNozzles
ReceiverHoles
Pre-swirlChamber
Inner Labyrinth
Seal
Outer Labyrinth
Seal
Pre-swirlNozzles
ReceiverHoles
Pre-swirlChamber
Inner Labyrinth
Seal
Outer Labyrinth
Seal
Chew et al, ASME GT-2003-38084
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29Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Whole Engine Model (I)
Pre-Swirl System
H.P.C. Air System
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30Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Whole Engine Model (II)
0.964
0.968
0.972
0.976
0.98
0.984
0.988
0.8 0.85 0.9 0.95 1 1.05 1.1βmix
T t,re
l,RH/T
t,PN
0.6
0.62
0.64
0.66
0.68
0.7
CD
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31Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
SECONDARY AIR SYSTEM MODELLINGCOMPONENT MODELS
o Generic Componento Orifice Componento Labyrinth Seal
Component
IMPLEMENTATION & VALIDATIONo Simulation Environment
Overviewo Test Cases
Pre-Swirl ChamberRotating CavitiesRotating HolesPre-swirl System
with Labyrinth Seals
o Whole Engine ModelSUMMARY & CONCLUSIONS
Contents
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32Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Summary & Conclusions
An approach for modelling secondary air systems within an
object-oriented environment for gas turbine engine performance
simulations was presented.
The modelling of selected components was presented in detail.
The components were used to simulate various air system
configurations and the predicted results are consistent with
available experimental data and computational results.
An example of adding parts of an air system to a whole engine
performance model was given to demonstrate the benefits of this
approach.
The flexibility of the simulation environment and the generality
of the component modelling approach allow easily different air
system configurations to be constructed and evaluated, both on
their own and as part of a complete engine performance model.
Since the approach presented allows components to be represented
in varied levels of detail, it is possible to create more realistic
models early in the engine design process.
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33Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
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34Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Friction Coefficients
( ) 2.05
o
i8.0m Rer
r1sin07288.0C −ϕ
− ⋅⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛−⋅θ⋅=
fm CrL2C ⋅⋅π⋅=
( )[ ] 2f10f 6.0CRelog07.4C −ϕ −⋅⋅=
For free disks or cones with non-zero inner radius and half
angle θ:
For a smooth cylinder of length L:
where
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35Secondary Air System Component Modelling For Engine
Performance SimulationsA. Alexiou & K. Mathioudakis
Heat transfer Coefficient Correlations
Natural Convection from a Vertical Plate:
Natural Convection from Upper Surface of heated Plate:
Forced Convection from a Flat Plate:
Lk
Pr492.01
Ra67.068.0h 94
169
25.0
av ⋅
⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎠⎞
⎜⎝⎛+
⋅+=
LkRa1.0h 31av ⋅⋅=
for Ra < 109 for Gr > 109
LkRa54.0h 25.0av ⋅⋅= L
kRa15.0h 31av ⋅⋅=
for 104
≤
Ra < 107 107
≤
Ra < 1011
LkRePr036.0h 8.0z
31av ⋅⋅⋅=
LkRePr662.0h 5.0z
31av ⋅⋅⋅=
for Rez
< 5×105 for Rez
≥
5×105
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