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GT-POWER as a tool for acoustic and dynamic optimization of exhaust systems
GT-SUIT User Conference 2009
Dr. –Ing. Youssef Mochkaai, Principal Engineer, Global Advanced Engineering
Frankfurt – 9 Nov 2009
2
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
Agenda
� Introduction
� Acoustic development of exhaust systems- Simulation tool
- Engine performance and acoustic
� Coupling 1D-3D
� Simulation without engine
� Optimization with DoE
� Conclusion
3
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
Introduction:
Target:� Pass-by level
� Tailpipe noise
� Subjective noise
dB(A)
1000 2000 3000 4000 5000 6000 1/min
100
200
300
400
500
600
700
800
900
1000
Hz
1
2
3
4
5
6
7
8
910
K14 APS A Mp14; Hinter AGA a=1,8m/1m
74EEC 70/157, R51.01China
76Article 30, TRIAS 20-1996Japan
74Not. 2000-65 (2000.6.15)Korea
80SAE J1470 or J986US
74
New targets in
2010
R 51-2, ISO 362
New measuring method will be introduced in 2010
Europe
Limit
Gasoline
[dB(A)]
ProcedureRegion
74EEC 70/157, R51.01China
76Article 30, TRIAS 20-1996Japan
74Not. 2000-65 (2000.6.15)Korea
80SAE J1470 or J986US
74
New targets in
2010
R 51-2, ISO 362
New measuring method will be introduced in 2010
Europe
Limit
Gasoline
[dB(A)]
ProcedureRegion
Target:� Muffler volume is fixed
� Diameter pipe is fixed
� Position is fixed
problem definition
How can this be solved ?How can this be solved ?
Target:� Backpressure
� Torque & Power100
113
125
138
150
163
175
188
200
213
225
238
250
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500
Engine speed [rpm]
To
rqu
e [
Nm
]
0
10
20
30
40
50
60
70
80
90
100
110
Po
we
r [k
W]
AcousticAcoustic
DesignDesign
ConflictConflict
Engine Engine
performanceperformance
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GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
Agenda
� Introduction
� Acoustic development an exhaust system- Simulation tool
- Engine performance and acoustic
� Coupling 1D-3D
� Simulation without engine
� Optimization with DoE
� Conclusion
5
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
Acoustic development: Exhaust system
� Hurdle:
- Find an optimum solution
- Damping of specific
frequencies
� Caveat:
- Physically testing of all
combinations is usually
impossible
L budget, time
� Solution:
Need to develop a search strategy and to use appropriate simulation tools
6
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
Acousticsand Gas Exchange
Simulation
Acoustic simulation tool: Why GT-Power?
Simulated sound
Source of acoustic and gas dynamicSource of acoustics and gas dynamics
Modeling of spatial geometrical structures
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GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
Boundary conditionsBoundary conditions
� GT-Power:
- Version V6.2
� Using engines:
- 4 & 6 cylinder, naturally-aspirated, turbo charged
- Full load
- Steady state & transient calculation
- Temperature Solver: „steadysteady”
� Microphone setting:
- Microphone distance (customer specification's)
- With ground effects
- Directivity of acoustic radiation: spherical
- Maximum microphone frequency: 1000 Hz
Validation
8
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000
rpm
To
rqu
e [
Nm
]
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000
rpm
To
rqu
e [
Nm
]
Engine performance and acousticEngine performance and acoustic
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000
rpm
To
rqu
e [
Nm
]
Position of Cross-overPosition of Cross-overPosition of Cross-over
Cross-over before central muffler
Cross-over after central muffler
∆∆∆∆= 10 Nm
Cross-over in central muffler
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000
rpm
To
rqu
e [
Nm
]
Position of Cross-overPosition of Cross-overPosition of Cross-over
1.5 Engine Order
20
30
40
50
60
70
80
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000
rpm
So
un
d p
ressu
re l
evel
dB
(A
)
1.5 Engine Order
20
30
40
50
60
70
80
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000
rpm
1.5 Engine Order
20
30
40
50
60
70
80
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000
rpm
A holistic view of engine / exhaust system is
necessary for optimization with respect to
acoustics (loudness, as well as sound) and
engine performance (gas exchange, torque
and overall power)
6-cylinder naturally aspirated
engine model
9
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
Agenda
� Introduction
� Acoustic development of exhaust systems- Simulation tool
- Engine performance and acoustic
� Coupling 1D-3D
� Simulation without engine
� Optimization with DoE
� Conclusion
10
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
GTGT--Power / Power / StarStar--CD and Fluent couplingCD and Fluent coupling
3D geometry of the
coupled cross-over
with detail of boundary
averaging zone
GT-Power model
Dual-flow exhaust system
CFD-Component
For the CFD the 1D model acts as a source of:
• dynamically changing boundary conditions
• average values for pressure and gas
temperature
For the 1D model, the CFD component is a
black-box that is expected to provide an
appropriate response to fluid dynamical input
values (velocity, temperature, density, etc…)
6-cylinder,
naturally aspirated engine
model
11
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
Results 1D/3D CouplingResults 1D/3D Coupling
Acoustic:
� Both simulations reproduce
the measured tailpipe noise
level in the 3rd order without
any appreciable difference
� 1D simulation provides a
good representation at lower
flow velocities (at low engine
speeds, lower engine orders
dominate)
� At middle/upper engine
speeds, the 1D/3D
simulation improves
correlation with
measurement (3D effects
become increasingly
important at higher mass
flows)
Cold End
0
25
50
75
100
125
150
175
200
225
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Engine speed [1/min]
Ba
ck
pre
ss
ure
[m
ba
r]
Measurement
1D-Simulation
1D/3D-Simulation
220
230
240
250
260
270
280
290
300
310
320
330
340
350
360
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Engine speed [1/min]
To
rqu
e [
Nm
]
Measurement
1D-Simulation
1D/3D-Simulation
∆∆∆∆ = 10 Nm
� The 1D/3D simulation results of backpressure and torque shows
good correlation with the measurements
3.0 Order
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Engine speed [1/min ]
So
un
d p
ressu
re level d
B(A
)
Measurement
1D-Simulation
1D/3D-Simulation
1.5 Order
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Engine speed [1/min ]
12
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
Results 1D/3D Coupling:Results 1D/3D Coupling: Influence of the mesh size on Influence of the mesh size on Tailpipe noise Tailpipe noise
1.5 Engine Order
35
40
45
50
55
60
65
70
75
80
85
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Engine speed [1/min ]
So
un
d p
ressu
re l
evel
dB
(A)
Measurement
1D-Simulation
1D/3D-Simulation: mesh with 60000 cells
1D/3D-Simulation: mesh with 18000 cells
1D/3D-Simulation: coarse mesh
� Coarse mesh affects the computed noise levels of the sub-harmonic engine orders
adversely
CPU-time per engine speed
15 min
mesh with 60000 cells 33 hr
mesh with 18000 cells 10 hrcoarse mesh 4 hr
1D/3D
Simulation method
1D
13
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
1D-Simulation
1D/3D-Simulation
Pre
ssu
re d
rop
[m
bar]
Engine speed [1/min]
Results 1D/3D Coupling:Results 1D/3D Coupling: pressure drop across the crossoverpressure drop across the crossover
The higher mass flow The higher mass flow
causes flow separationcauses flow separation
More pronounced More pronounced
communication communication
between the two between the two
strandsstrands
� Crossover modelling details have a strong influence on the calculated pressure drop (high local velocity and pressure gradients)
14
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
Agenda
� Introduction
� Acoustic development of exhaust systems- Simulation tool
- Engine performance and acoustic
� Coupling 1D-3D
� Simulation without engine
� Optimization with DoE
� Conclusion
15
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
Simulation without engine model: procedure Simulation without engine model: procedure
GTGT--Power engine modelPower engine model
SourcesSources
Exhaust system modelExhaust system model
Transient pressure, temperature and mass flowTransient pressure, temperature and mass flow
16
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
50
55
60
65
70
75
80
85
90
95
100
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Engine speed [1/min]
So
un
d p
ress
ure
lev
el
dB
(A)
Simulation without engine model: resultsSimulation without engine model: results
Simulation with engine modelSimulation with sources
� Simulation with sources requires 75 % less CPU time than the simulation with the
associated engine model
� Exhaust system without layout modifications
0
20
40
60
80
100
120
140
160
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500
Engine speed [rpm]
Bac
kp
ress
ure
[m
ba
r]
Cold End
Before central muffler
Before rear muffler
17
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
146
94
38
146
94
38
146
95
38
0
25
50
75
100
125
150
175
200
225
250
Cold End Before central
muffler
Before rear
muffler
Measurement position
Backp
res
su
re [
mb
ar]
6500 rpm, (732 kg/h; 882°C)
Total
50
55
60
65
70
75
80
85
90
95
100
105
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
So
un
d p
ressu
re level d
B(A
)
1
Simulation with enginemodel: perforated baffleSimulation with enginemodel: closed bafflerSimulation with sources:closed baffler
3.0 Order
50
55
60
65
70
75
80
85
90
95
100
105
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
6.0 Order
50
55
60
65
70
75
80
85
90
95
100
105
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
1.5 Order
50
55
60
65
70
75
80
85
90
95
100
105
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Engine speed [1/min]
4.5 Order
50
55
60
65
70
75
80
85
90
95
100
105
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Engine speed [1/min]
9.0 Order
50
55
60
65
70
75
80
85
90
95
100
105
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Engine speed [1/min]
So
un
d p
ressu
re level d
B(A
)
1
Simulation without engine model: comparison of variantsSimulation without engine model: comparison of variants
� Modification of rear muffler design
HH-Resonator90Hz
� Small changes in rear muffler have no significant influence on tailpipe noise and
backpressure
18
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
� For a large design change of the exhaust system it is
recommended to use the engine model
146
94
38
116
65
38
119
68
38
0
25
50
75
100
125
150
175
200
225
250
Cold End Before central
muffler
Before rear
muffler
Measurement position
Backp
ressu
re [
mb
ar]
6500 rpm, (732 kg/h; 882°C)
Simulation without engine model: comparison of variantsSimulation without engine model: comparison of variants
� Without central muffler
Total
50
55
60
65
70
75
80
85
90
95
100
105
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
So
un
d p
ressu
re level [d
B(A
)]
Simulation with engine model:with central muffler
Simulation with engine model:without central muffler
Simulation with sources:without central muffler
3.0 Order
50
55
60
65
70
75
80
85
90
95
100
105
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
6.0 Order
50
55
60
65
70
75
80
85
90
95
100
105
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
1.5 Order
50
55
60
65
70
75
80
85
90
95
100
105
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Engine speed [1/min]
4.5 Order
50
55
60
65
70
75
80
85
90
95
100
105
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Engine speed [1/min]
9.0 Order
50
55
60
65
70
75
80
85
90
95
100
105
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Engine speed [1/min]
So
un
d p
ressu
re level [d
B(A
)]
19
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
Agenda
� Introduction
� Acoustic development of exhaust systems- Simulation tool
- Engine performance and acoustic
� Coupling 1D-3D
� Simulation without engine
� Optimization with DoE
� Conclusion
20
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
AcousticAcoustic optimizationoptimization with DoE in GTwith DoE in GT--Power: Working PrincipalPower: Working Principal
Optimized simulation time Creation of the acoustic source
Verification with original engine model
Modeling of the exhaust system� Parameterization of the model� Definition of independent variables
Strategies
applied
Analysis
Selection of simulation
methodology (type of DoE)
SPL (A)SPL (A)
Optimized DesignOptimized Design
21
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
Acoustic optimization with DoE in GTAcoustic optimization with DoE in GT--PowerPower
Base Base DesignDesign
2.0 Order
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120
1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500
Engine speed [rpm]
SP
L d
B(l
in)
Target
Measurement: Base Design
Simulation: Base Design
4.0 Order
60
65
70
75
80
85
90
95
100
105
110
115
120
1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500
Engine speed [rpm]
Optimized Optimized DesignDesign
2.0 Order
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120
1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500
Engine speed [rpm]
SP
L d
B(l
in)
Target
Measurement: Base Design
Simulation: Base Design
Measurement: Optimised Design
Simulation: Optimised Design
4.0 Order
60
65
70
75
80
85
90
95
100
105
110
115
120
1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500
Engine speed [rpm]
DoEDoE
� Results: Sound pressure level
22
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
� Results: influence of baffle perforation and position
AcousticAcoustic optimizationoptimization with DoE in GTwith DoE in GT--PowerPower
Number of holes in baffleS
ou
nd
pre
ssu
re level [d
B]
Additional important information on the damping of the specific frequencies
23
GT-Suite-Conference – 09.11.2009 – Frankfurt / M.
Dr. Y. Mochkaai
ConclusionConclusion
� The ability of GT-Power to conduct a complete system analysis
(intake/engine/exhaust) with comparatively low computational effort is a
great advantage.
� Coupling of 1D and 3D simulations shows that an improvement in the
results can be achieved. In particular, when large mass flows prevail
and the geometries give rise to significant 3-dimensional flow effects,
there is the need to go into 3D.
� For small design changes of the exhaust system, acoustical analysis
can be done using sources instead of an engine model.
� Integration of DoE in the simulation procedure is a significant step
towards more efficient product development providing optimized
solutions.
Thank you for your attention
Dr. –Ing. Youssef Mochkaai, Principal Engineer, Global Advanced Engineering