Upload
lekien
View
232
Download
10
Embed Size (px)
Citation preview
Pulsating Flow Impact on Turbocharger Turbines
Ricardo Martinez-Botas
Srithar Rajoo
Turbocharger Research Group
Pulsating Exhaust Flow
Internal Combustion Engine: Reciprocating, positive
displacement
Turbocharger Turbine: Rotodynamic, steady flow device
•Turbine design and matching is largely based on steady flow performance.
Turbine Design Methodology
Design Condition – m, P, T, W, N
Euler Turbomachinery Equations + free Vortex + Continuity + Sweifel Criterion +
losses
Velocity Triangles
Geometries
Final Geometry
Unsteady Spectra
• Turbocharger is exposed to a wide range of unsteady events 1. Engine Load Transients(~1 Hz) 2. Exhaust pulse (10~100Hz) 3. Blade wake passing 4. Turbulent fluctuations
• Exhaust pulsations sit in an interesting area
•How does unsteady flow influence performance?
•Which components of the turbine can be treated as quasi-steady and which cannot
Velocity Triangle – Pulsating Flow
Steady Flow Design Condition
incidence
W
U
Cm
0
0.1
0.2
0 6 0 12 0 18 0 2 4 0 3 00 3 6 0ωt (Degrees)
min
st ( k
g/s )
f = 40 Hz
f = 60 Hz
b
1
1
3
3
2
2
EXP
-100
-80
-60
-40
-20
0
20
40
0 60 120 180 240 300 360
Inci
denc
e An
gle Phase Angle
20Hz 80Hz
Optimum Incidence
Most Energy
-100
-80
-60
-40
-20
0
20
40
0 60 120 180 240 300 360
Inci
denc
e An
gle Phase Angle
20Hz 80Hz
Optimum Incidence
Most Energy
Velocity Triangle – Pulsating Flow CFD
30kRPM
48kRPM
Turbine Unsteady Performance
0.00
1.002.00
3.004.00
5.00
6.007.00
8.009.00
10.00
1 1.4 1.8 2.2 2.6 3Pressure Ratio (P01/P5)
Mas
s Fl
ow P
ar. (
kg/s
T 0
1/P01
)
Lean VaneStraight VaneSteady Straight
x 1e-540Hz, 80% Speed, 40deg
0.00
1.002.00
3.004.00
5.00
6.007.00
8.009.00
10.00
1 1.4 1.8 2.2 2.6 3Pressure Ratio (P01/P5)
Mas
s Fl
ow P
ar. (
kg/s
T 0
1/P01
)
Lean VaneStraight VaneSteady Straight
x 1e-560Hz, 80% Speed, 40deg
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
1 1.4 1.8 2.2 2.6 3Pressure Ratio (P01/P5)
Mas
s Fl
ow P
ar. (
kg/s
T 0
1/P01
)
Lean VaneStraight Vane
Steady Straight
x 1e-540Hz, 80% Speed, 70deg
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
1 1.4 1.8 2.2 2.6 3Pressure Ratio (P01/P5)
Mas
s Fl
ow P
ar. (
kg/s
T 0
1/P01
)
Lean VaneStraight Vane
Steady Straight
x 1e-560Hz, 80% Speed, 70deg
Mass flow parameter vs. Pressure ratio
Turbine Unsteady Performance
-1.00-0.80-0.60-0.40-0.200.000.200.400.600.801.001.201.40
0.2 0.4 0.6 0.8 1 1.2 1.4Velocity Ratio (U/Cis)
Effic
ienc
y (h
t-s)
Lean VaneStraight VaneSteady Straight
40Hz, 80% Speed, 40deg
-1.00-0.80-0.60-0.40-0.200.000.200.400.600.801.001.201.40
0.2 0.4 0.6 0.8 1 1.2 1.4Velocity Ratio (U/Cis)
Effic
ienc
y (h
t-s)
Lean VaneStraight VaneSteady Straight
60Hz, 80% Speed, 40deg
-1.00-0.80-0.60-0.40-0.200.000.200.400.600.801.001.201.40
0.2 0.4 0.6 0.8 1 1.2 1.4Velocity Ratio (U/Cis)
Effic
ienc
y (h
t-s)
Lean VaneStraight VaneSteady Straight
40Hz, 80% Speed, 70deg
-1.00-0.80-0.60-0.40-0.200.000.200.400.600.801.001.201.40
0.2 0.4 0.6 0.8 1 1.2 1.4Velocity Ratio (U/Cis)
Effic
ienc
y (h
t-s)
Lean VaneStraight VaneSteady Straight
60Hz, 80% Speed, 70deg
Efficiency vs. Velocity ratio
Turbine Unsteady Performance
UNSTEADY PULSE FLOW MEANS TURBINE OPERATES OVER A
WIDE RANGE
OVERALL BEHAVIOUR IS PREDICTED FROM SIGNIFICANT DATA EXTRAPOLATION
PULSE FLOW RELIES ON TURBINE EXTRAPOLATION
11
1D Simulation Treatment
Time
Pres
sure
Exhaust Manifold (Wave Action) Unsteady pulse at the Turbine node
Steady-state performance
Regulated two-stage Turbo GT-POWER
Standard Procedure
GAS DYNAMICS INSIGNIFICANT
(ZERO PATH LENGTH)
1D WAVE ACTION MODEL OF ENGINE & EXHAUST
STEADY-STATE GAS TEST STAND PERFORMANCE
ASSUMPTIONS
TURBINE IS A NODE
(ZERO VOLUME)
STEADY STATE PERFORMANCE
RESPONSE
QUASI-STEADY ASSUMPTION
MODEL TURBINE
UNSTEADY PULSE FOLLOWING
EXTRAPOLATED MAP
Map Extension in Simulation
• 1-D simulation take limited gas stand data and extrapolate • Unsteady pulse Wave Action in the manifold means that the model
relies on a significant amount of the off design extrapolation
Limited data
Extrapolation
Time
Pres
sure
Unsteady range
NEED FOR EXPERIMENTALLY MEASURED EXTENDED TURBINE PERFORMANCE MAPS
Steady & Pulsating Flow Test Rig Imperial College London
• Pulse generator has two rotating ‘chopper plates that produce pulses into a single or twin entry turbine
OUTER LIMB INNER LIMB
Rotating chopper plate produces pulsating flow
Eddy Current Dyno 60kW / 60kRPM
MAP WIDTH: Conventional turbine maps are narrow in range • Efficiency → Velocity ratio, ≈0.6 ÷ 0.8 • Mass flow parameter → Pressure ratio, ≈1.9 ÷ 2.3 (at 100% speed)
0
1
2
3
4
5
6
7
1 1.5 2 2.5 3
MAS
S FL
OW
PAR
AMET
ER
PRESSURE RATIO
50% Speed 60% Speed 70% Speed
80% Speed 90% Speed 100% Speed
50% SPEED
100% SPEED
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.2 0.4 0.6 0.8 1 1.2
EFFI
CIE
NC
Y
VELOCITY RATIO 50% Speed 60% Speed 70% Speed
80% Speed 90% Speed 100% Speed
50% SPEED
100% SPEED
Velocity Ratio 50%, 100% speed
0.6 ÷ 0.8
Pressure ratio 50% speed
Pressure ratio 100% speed
1.2 ÷ 1.4 1.9 ÷ 2.3 0
1
2
3
4
5
6
7
1 1.5 2 2.5 3
MAS
S FL
OW
PAR
AMET
ER
PRESSURE RATIO
50% Speed 60% Speed 70% Speed
80% Speed 90% Speed 100% Speed
50% SPEED
100% SPEED
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.2 0.4 0.6 0.8 1 1.2
EFFI
CIE
NC
Y
VELOCITY RATIO 50% Speed 60% Speed 70% Speed
80% Speed 90% Speed 100% Speed
50% SPEED
100% SPEED
Maps obtained are 3-4 times wider than conventional (100% speed)
Maps obtained are 3-4 times wider than conventional (100% speed)
Maps Extension
QUASI-STEADY ASSUMPTION WHAT DOES IT MEAN ?
Quasi-steady assumption
PR(t) T(t)
TIME
PRES
SUR
E R
ATI
O
t
PR(t)
UNSTEADY PULSE
N(t) Nconst
PRconst Tconst
UNSTEADY CASE AT TIME = t STEADY CASE
Mas
s Fl
ow
Pressure Ratio
ṁquasi
PR(t)
STEADY-STATE MAP
ṁ(t) = ṁquasi ?
Quasi-Steady Assumption: Efficiency
• Is the unsteady efficiency simply an integration of steady-states at each instance in the pulse ?
TIME
PRES
SUR
E R
ATI
O
t
PR(t)
EFFI
CIE
NC
Y
.
PRESSURE RATIO
UNSTEADY PULSE STEADY-STATE MAP
η(t)q-s
PR(t)
= ?
∑∑=
in
outavgUS tW
tW)()(
,
η
( )∑
∑−
− ⋅=
QSin
QSQSinavgQS tW
ttW)(
)()(,
ηη
Filling and Emptying vs. Quasi Steady
• To illustrate this effect: The same pressure ratio across the turbine (1.6) produces two different unsteady mass parameters.
• Steady behaviour in between both (in this case).
turbine ‘filled’ steady
turbine ‘empty’
VOLUME DISPLAYS ‘FILLING AND EMPTYING’ BEHAVIOUR
VOLUTE LENGTH DISPLAYS WAVE ACTION
UNSTEADY MASS FLOW OF TURBINE STAGE
BEHAVIOUR IS NOT QUASI-STEADY
Turbine Modelling Options
1-D turbine Model vs. Experiment
Experimental testing schematic diagram 1-D turbine model schematic diagram
• Volute modelled as series of “pipes” with finite length & volume. • Quasi-steady pressure loss boundary to represent the flow restriction due to the
rotor.
Instantaneous mass flow rate:
1-D turbine Model vs. Experiment
Modelling unsteady effects in 1D
Swallowing capacity:
1-D turbine Model vs. Experiment
Modelling unsteady effects in 1D
Integration with Mean Line Model
1-D turbine Model vs. Experiment
Modelling unsteady effects in 1D
Unsteady power:
1-D turbine Model vs. Experiment
Integration with Mean Line Model
Modelling unsteady effects in 1D
Unsteady efficiency:
1-D turbine Model vs. Experiment
Integration with Mean Line Model
INSTANTANEOUS EFFICIENCY DIFFICULT TO DEFINE ACCURATELY AVERAGED OVER A CYCLE, MEASURED UNSTEADY EFFICIENCY DEPARTS FROM THE QUASI-STEADY PREDICTION
UNSTEADY PULSE FLOW PERFORMANCE CANNOT BE
ASSUMED TO BE QUASI-STEADY
ATTEMPTS TO IMPROVE TURBINE PERFORMANCE UNDER PULSATING FLOW
ONE IDEA
ACTIVE / PASSIVE CONTROL TURBINE
Operation
tsp PPTcmW η
γγ
−=
−1
01
201 1
20 – 60 Hz pulse Frequency
Concepts
Experiment
Internal Spring Stiffness = 12.3 N/mm
Picture of the Laboratory Arrangement
x∆
-10
0
10
20
30
40
50
60
Turb
ine
Act
ual P
ower
(kW
)
One Pulse Cycle (~0.05s)
Case 1-20Case 2-20Case 3-20
A
B
-10
0
10
20
30
40
50
60Tu
rbin
e A
ctua
l Pow
er (k
W)
One Pulse Cycle (~0.05s)
Case 1-20Case 2-20Case 3-20
20 Hz Flow, N turbine ~ 30000 , Natural Oscillation
Results
20Hz Pulsation and ~30000rpm
Settings Cycle Average Power (kW)
Average Power (kW) A
Average Power (kW) B
Case 1 8.91 23.55 1.89
Case 2 8.62 21.83 2.24
Case 3 8.43 18.36 3.64
70deg 8.34 18.47 3.62
65deg 8.39 19.91 2.98
60deg 8.27 21.34 2.05
50deg 8.19 21.98 1.54
40deg 8.22 22.41 1.45
Case 1 8.91 23.55 1.89
Cycle Average Power in Case 1-20 is 6.2% higher than 65deg vane setting.
ACT SIMULATION
ACT bsfc 210.1g/kWh at amplitude 0.2 and phase shift ~70° 2.1g/kWh improvement over the standard VGT =2% bsfc improvement
bsfc