Numerical Investigation of Bare and Ducted Horizontal Axis

5th International Conference on Ocean Energy ICOE 2014, November 4-6, Halifax, NS Canada
Numerical Investigation of Bare and Ducted Horizontal
Axis Marine Current Turbines
Presented by: Mahrez Ait Mohammed
PhD student
Dept. of Ship Structure Mechanics Center,
ENSTA Bretagne, France.
Pr. Mostapha Tarfaoui & Dr. Jean Marc Laurens
ENSTA Bretagne, France.
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Context
•
Various global studies have shown that marine currents have a
large potential as a predictable sustainable resource for
commercial scale generation of electrical power.
•
There are many areas of the world in which extreme tidal
currents are observed.
•
The Celtic sea being the most dense in terms of renewable energy
potential. (Tidal energy and offshore wind)
→ In the region of the Cherbourg peninsula in France :
•
The most attractive tidal site in France is the sea
passage known as Le Raz Blanchard in French and the
Race of Alderney in English.
•
The water depth allows for the marine turbine systems
to exceed 20 meters diameter without causing any
perturbation to maritime traffic and the current velocity
peaks above 3m/s.
•
In order to present some realistic numerical results, the
present study is using these data as input.
2
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
•
•
The water depth allows for the marine turbine systems
to exceed 20 meters diameter without causing any
perturbation to maritime traffic and the current velocity
peaks above 3m/s.
In order to present some realistic numerical results, the
present study is using these data as input.
Rotor
Hub
The most attractive tidal site in France is the sea
passage known as Le Raz Blanchard in French and the
FLOW
Race of Alderney in English.
20 m
•
Yaw system
Column
10 m
→ In the region of the Cherbourg peninsula in France :
10-15 m
Context
2
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Presentation Overview
 Objective
 Hydrodynamic design
•
Blade Element Momentum Theory
•
Boundary Element Method (Panel Method)
•
Reynolds Averaged Navier-Stokes Solution
•
Performance
experiments
•
Bare turbine design (without duct)
comparison
between
theory
and
data
 Ducted turbine design
•
Effect of the addition of duct
•
Shape design of ducted turbine
 Conclusion and future perspectives
3
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Objective
Bare turbine design
Ducted turbine design
Is a duct a good idea?
Before discussing the pros and the cons, let us examine the hydrodynamic
performance of both systems.
4
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Presentation Overview
 Objective
 Hydrodynamic design
•
Blade Element Momentum Theory
•
Boundary Element Method (Panel Method)
•
Reynolds Averaged Navier-Stokes Solution
•
Performance
experiments
•
Bare turbine design (without duct)
comparison
between
theory
and
data
 Ducted turbine design
•
Effect of the addition of duct
•
Shape design of ducted turbine
 Conclusion and future perspectives
5
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Hydrodynamic design
3D effect
BEM
Blade Element
Momentum model
N
Limited
No
section data
Required
Required
Flow separation
and stall
Semiempirical
Cost
Very low
High
6
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Hydrodynamic design
3D effect
BEM
Blade Element
Momentum model
Panel Method
Boundary element Method
Limited
Yes
section data
Flow separation
and stall
Required
Semiempirical
Very low
Not
required
No
Medium
Cost
High
6
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Hydrodynamic design
3D effect
BEM
Blade Element
Momentum model
Panel Method
Boundary element Method
Limited
Yes
RANS
Reynolds-averaged
Navier-Stokes solution
Yes
section data
Flow separation
and stall
Required
Semiempirical
Very low
Not
required
No
Medium
Not
required
Yes
Cost
High
6
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Panel method
The panel methods are based on the potential flow theory.
We assume that the fluid is inviscid and non rotational (
).
The above assumption is equivalent to
To mimic the behavior of viscous fluid flow around a lifting body we force the flow to be
lined up with the trailing edge (Kutta-Joukowski condition) .
 Concerning the mesh, the panel method only requires a surface mesh of the solid objects.




Example of ducted marine current turbine mesh
7
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Panel method
The panel methods are based on the potential flow theory.
We assume that the fluid is inviscid and non rotational (
).
The above assumption is equivalent to
.
To mimic the behavior of viscous fluid flow around a lifting body we force the flow to be
lined up with the trailing edge (Kutta-Joukowski condition) .
 Concerning the mesh, the panel method only requires a surface mesh of the solid objects.




Propeller Terminology
Turbine Terminology
η
7
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Performance comparison between theory and data experiments
• The experimental results of the bare turbine, tested and described by Bahaj et al 1.
are used and compare with our numerical simulation.
• The turbine is three bladed with a Naca63-8xx hydrofoil.
• In the present work a 5° blade set angle is considered.
0.6
NACA 63-818
Power coefficient (Cp)
0.5
0.4
0.3
0.2
Panel Method 1.8m/s
Tow. Tank 1.46m/s Bahaj et al.
Cav. Tunnel 1.73m/s Bahaj et al.
0.1
0
1A.
4
5
6
TSR
7
8
9
S. Bahaj, W. M. J. Batten, G. McCann, “Experimental Verifications of Numerical Predictions for the Hydrodynamic
Performance of Horizontal Axis Marine Current Turbines”, Renewable Energy. 2007, Vol. 32, pp. 2479-2490.
8
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
The design of tidal turbine is imposed by:
 The cavitation occurrence.
 Flow separation has to be avoided.
where
NACA 63-415
α: Local angle of attack
ϕ: Local angle of the profile
θ: Local angle of the twist
a: Axial induction factor
a’: Tangential induction factor
Pressure coefficient min (Cp min)
Bare turbine design
-0.5
-1
-1.5
-2
-2.5
NACA 63-415
-3
-3.5
-4
-3
-2
-1
(Watt)
0
1 2 3 4 5
Angle of attack in °
6
7
Where:
Z: Number of blades
P/D: Average pitch (propeller pitch definition)
c/D: Chord
AER: Aspect ratio
Kq: Torque coefficient
Cp: Power coefficient
9
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
The design of tidal turbine is imposed by:
 The cavitation occurrence.
 Flow separation has to be avoided.
where
NACA 63-415
α: Local angle of attack
ϕ: Local angle of the profile
θ: Local angle of the twist
a: Axial induction factor
a’: Tangential induction factor
Pressure coefficient min (Cp min)
Bare turbine design
-0.5
-1
-1.5
-2
-2.5
NACA 63-415
-3
-3.5
-4
-3
-2
-1
(Watt)
0
1 2 3 4 5
Angle of attack in °
6
7
Where:
Z: Number of blades
P/D: Average pitch (propeller pitch definition)
c/D: Chord
AER: Aspect ratio
Kq: Torque coefficient
Cp: Power coefficient
9
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
The design of tidal turbine is imposed by:
 The cavitation occurrence.
 Flow separation has to be avoided.
where
NACA 63-415
α: Local angle of attack
ϕ: Local angle of the profile
θ: Local angle of the twist
a: Axial induction factor
a’: Tangential induction factor
Pressure coefficient min (Cp min)
Bare turbine design
-0.5
-1
-1.5
-2
-2.5
NACA 63-415
-3
-3.5
-4
-3
-2
-1
(Watt)
0
1 2 3 4 5
Angle of attack in °
6
7
Where:
Z: Number of blades
P/D: Average pitch (propeller pitch definition)
c/D: Chord
AER: Aspect ratio
Kq: Torque coefficient
Cp: Power coefficient
2.24E+06
9
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Bare turbine design
(Watt)
Where:
Z: Number of blades
P/D: Average pitch (propeller pitch definition)
c/D: Chord
AER: Aspect ratio
Kq: Torque coefficient
Cp: Power coefficient
2.24E+06
Bare turbine performance
0.5
Pressure coefficient
Power Coefficient
0.6
0.4
0.3
0.2
0.1
0
Local pressure coefficient (r/R=0.7)
-1
-0.5
0
0
0.2
0.4
0.6
0.8
1
x/c
0.5
1
1.9
2.9
TSR
3.9
4.9
5.9
6.9
10
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Bare turbine design
(Watt)
Where:
Z: Number of blades
P/D: Average pitch (propeller pitch definition)
c/D: Chord
AER: Aspect ratio
Kq: Torque coefficient
Cp: Power coefficient
2.24E+06
r/R
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0.95
1
c/D
0.07142857
0.07142857
0.07142857
0.07142857
0.07142857
0.07142857
0.07142857
0.07142857
0.07142857
0.07142857
t/c
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
f/c
-0.02
-0.02
-0.02
-0.02
-0.02
-0.02
-0.02
-0.02
-0.02
-0.02
Bare turbine performance
0.5
0.4
0.3
0.2
0.1
0
Pitch°
P/D
0.28865064
0.35359894
0.38177779
0.39604095
0.4041486
0.40916662
0.41247731
0.41477209
0.41566306
0.41642619
Pressure coefficient
Power Coefficient
0.6
P/D
0.28865064
0.35359894
0.38177779
0.39604095
0.4041486
0.40916662
0.41247731
0.41477209
0.41566306
0.41642619
1.9
2.9
TSR
3.9
4.9
5.9
6.9
α°
7.065007473
5.135647948
4.076894047
3.37465628
2.87237177
2.496218928
2.204816355
1.972929877
1.873990238
1.784312468
24.67413332
20.56509281
16.89925935
14.15091209
12.10142785
10.53991319
9.320266606
8.345515542
7.92877136
7.550685995
1.5
Pressure coefficient (Cp ITTC at TSR=4)
0.5
(r/R)
-0.5 0
0.2
0.4
Pressure side
0.6
0.8
1
-1.5
-2.5
-3.5
Suction side
10
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
 Objective
Boundary Element Method (Panel Method)
•
Reynolds Averaged Navier-Stokes Solution
•
Performance
experiments
•
Bare turbine design (without duct)
comparison
between
 Ducted turbine design
•
Effect of the addition of duct
•
Shape design of ducted turbine
 Conclusion and future perspectives
theory
and
FLOW
data
Duct
Hub
•
20 m
Blade Element Momentum Theory
Yaw system
Rotor
Column
10 m
•
10-15 m
 Hydrodynamic design
11
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Ducted turbine design
Theoretical performance of ducted
turbine according to Werle et al.²
Power
coefficient
Duct Drag
coefficient
Rotor thrust
coefficient
The power coefficient reaches 1.2, but it is defined according to
the rotor area and not according to the overall area.
² M. J. Werle and W. M. Presz, Ducted Wind/Water Turbines and Propellers
Revisited. Journal of Propulsion and Power.2008,Vol.24, PP.1146-1150.
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International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Effect of the addition of duct
Theoretical performance of ducted
turbine according to Werle et al.²
Duct Drag
coefficient
Rotor thrust
coefficient
Power coefficient (Cp)
0.7
Cp : duct 0010
Cp: duct 0020
Cp: duct 0024
0.6
0.4
Power coefficient (Cp*)
1.9
0.36
² M. J. Werle and W. M. Presz, Ducted Wind/Water Turbines and Propellers
Revisited. Journal of Propulsion and Power.2008,Vol.24, PP.1146-1150.
•Evolution of the power
coefficient (Cp) versus TSR for
ducted turbine when Cp is
computed from the rotor
diameter.
0.5
0.3
The power coefficient reaches 1.2 but it is defined according to
the rotor are and not according to the overall area.
Comparison between the
rotor in the symmetrical duct
section and the bare rotor
with the same overall cross
section of 20m.
 The length of the duct is
equal to the radius of the
overall cross section (10m).
20 m
Power
coefficient
Effect of the addition of duct to the rotor design
2.9
TSR 3.9
4.9
5.9
0.35
•Evolution of the power
coefficient (Cp*) versus TSR for
ducted turbine when Cp is
computed using the same overall
cross section.
0.34
0.33
0.32
0.31
Cp*: duct 0010
Cp*: duct 0020
Cp*: duct 0024
0.3
0.29
1.9
2.9
3.9 TSR 4.9
5.9
6.9
12
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Shape design of ducted turbine
 Effect of the addition of symmetrical duct profile to the rotor design
Duct profile
NACA 0010
NACA 0020
NACA0024
18
16
15.2
Cp max
Cp* max
TSR
Power output (MWatts)
0.4362
0.3525
4
1.5311
0.5507
0.3515
4.5
1.5267
0.6174
0.3556
5
1.5446
Loss relative to bare turbine
-31.76%
-31.95%
-31.16%
Rotor diameter (m)
 The addition of symmetrical duct at the same overall cross
section is not advantageous because we get a loss in energy
close to 32%.
 Effect of the addition of camber duct profile to the rotor design
0
0
0.2
0.4
-0.2
0.6
Cp max
Cp* max
TSR
Power output
(MWatts)
Loss or gain
relative to bare
turbine
2.4E+06
1
2.2E+06
naca 0020
EMB20 & 12% camber
X/c
-0.4
EMB20
camber%
Rotor diameter
(m)
0.8
0%
4%
8%
10%
12%
16.00
15.80
15.55
15.15
14.75
0.5507
0.3515
4.5
0.6501
0.4047
4.0
0.7577
0.4568
4.0
0.9019
0.5174
5.0
0.9826
0.5344
5.0
1.5267
1.7576
1.9841
2.2474
2.3222
-31.95%
-21.67%
-11.57%
+0.16%
+3.5%
Power (Watts)
Y/c
0.2
2.0E+06
1.8E+06
1.6E+06
1.4E+06
EMB20 &12% camber
1.2E+06
EMB20 & 10% camber
1.0E+06
Bare turbine
0.1
0.2
RPS
0.3
0.4
0.5
Power produced by the bare turbine and the camber
ducted turbine versus RPS at the same overall cross
section of 20m
13
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Shape design of ducted turbine
The effect of the chord length has been tested for the EMB 20 and 12% camber
0.5
0.375
0.250
0.125
Rotor diameter (m)
14.75
16.3
17.38
18.53
Cp max
Cp* max
TSR
0.9826
0.5344
5
0.8152
0.5414
5
0.5966
0.4505
4
0.5126
0.4400
4
Power output (MW)
2.3210
2.3516
1.9567
1.9111
Gain or Loss relative
to bare turbine
+3.5%
+4.80%
-12.80%
-14.83%
Where:
L: The length of the duct
D: The overall cross section
1.8E-02
Torque coefficient (Kq)
L/D
1.6E-02
1.4E-02
1.2E-02
1.0E-02
TSR=5
8.0E-03
6.0E-03
4.0E-03
1
3
5
7
Iterations
9
11
13
15
Power coefficient max for duct
profile EMB20 & 12% camber
1.2
1
0.8
0.6
0.4
Cp max
Cp* max
0.2
0
0.1
0.2
L/D 0.3
0.4
0.5
0.6
Ducted turbine design: 2.35Mega Watts (naca63-415
rotor, 12% max camber duct, L/D=0.375 and 20m
overall diameter)
14
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Conclusion and future perspectives
• A design method involving BEM and Panel method code was developed and used to obtain the
geometry of an horizontal axis marine current turbine for the Race of Alderney.
• A bare turbine was designed which can attain up to 90% of the Betz limit.
• The addition of an accelerating duct at the same overall diameter with bare turbine was investigated.
• It was found that, to obtain a sufficient acceleration capable to compensate the loss of blade
diameter, the section has to be seriously cambered when there is no flaring of the duct profile at the
exit.
• The effect of the flaring of the duct exit is currently being studied.
• The obtained ducted water turbine has a potential power output of 2.35MW, 5% more than the bare
turbine with the same overall diameter.
• The device is designed for uni-directional flow.
• Adding a duct will not only increase the total weight but also the manufacturing cost.
• In this study only the hydrodynamics aspects have been taken into account.
• Our future line of investigation will concern the composite materials and the structural behavior of
the ducted water turbine.
• Materials and layup optimization.
15
International Conference on Ocean Energy ICOE2014, November 4-6, Halifax, NS Canada
Questions
16

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