# Active Stall Control for Offshore HAWT

```The Science of Making Torque from Wind - 2012
Active Stall Control for Offshore HAWT
a study considering different actuation methods
Ricardo Pereira
10-10-2012
Delft
University of
Technology
Challenge the future
Basic Idea
The Research Question
‘Can the pitch system
of HAWT be replaced
by “modern” active
stall control? Which is
the best actuation
method? ‘
2
Approaches
•
Boundary Layer Transpiration
•
Trailing Edge Jets
•
Plasma Actuators
3
Question of Authority – NREL 5 MW
•
BEM model (Sheng Tip Correction)
•
Generic Actuator
•
Changes on Cl, Cd remains constant
4
Question of Authority – NREL 5 MW
U=21 m/s
18
13
16
12
10
9
L=21m
L=29m
L=37m
no actuation
rated
10*DeltaCl / alpha [deg]
Power [MW]
11
8
7
14
12
alpha
10*DeltaCl
10
8
6
6
5
0.4
0.5
0.6
0.7
Cl
0.8
0.9
1
35
40
45
50
55
60
5
Boundary Layer Transpiration
- Aerodynamic Tool
Rfoil_suc (Panel
method + integral
boundary Layer)
- Blowing at the
Region x/c ϵ [0.05;
0.2]
- Similar behaviour
for different airfoils
6
Trailing Edge Jets
- Few Mechanisms
(compared to Flaps)
than LE
- Not effective at large
angles of attack
- 25 times the mass of
7
Plasma Actuators - DBD
•Dielectric Barrier Discharge
•No moving parts
•KV, Khz … 40 W/m
•F=0.2 N/m
•Must be placed exactly
8
DBD Separation - Laminar
• Thwaites Laminar
Separation Criterion
• DBD as a point force
 2 dU e
  0.09 
 dx
F  U e
2
• Rfoil_suc data for BL parameters
• NACA64618 at Re=10 million, alpha= 8, 11, 14, 17 deg
9
DBD Separation - Laminar
alpha=11 deg
0.25
0.2
lambda [-]
0.15
•no separation
for any alpha
Fact=0.2
Fact=0.5
0.1
Fact=0.8
Fact=1.1
0.05
Fact=0
0
-0.05
-0.1
0
0.002
0.004
0.006
0.008
0.01
chord [-]
0.012
0.014
0.016
0.018
10
DBD Separation - Turbulent
- Stratford Turbulent
Separation Criterion
dC p '
 Re x 
C p ' x'
 k 6 
dx
 10 
k  0.35;0.39
0.1
-h=5 mm &amp; l= 25 mm
 x    y 
 sin

- Body Force Distribution F ( x, y )  A sin
 l   h 
dp
3
- F ( x)  N / m  Pa / m 
dx
11
DBD Separation - Turbulent
alpha=14 deg
0.5
0.45
0.05c
0.1c
0.2c
0.3c
clean
separation
Separation Criterion [-]
0.4
0.35
0.3
•no separation
for any alpha
0.25
0.2
0.15
0.1
0.05
0
0
0.05
0.1
0.15
0.2
0.25
Chord [-]
0.3
0.35
0.4
0.45
0.5
12
Future Work-DBD Experiment
DBD Actuator designed to provoke separation
Usually interest
is in maximizing
Thrust
Intermediate steps
Large Re &amp; against
the flow
decreasing electrode length
Separation ???
13
The Big Picture
Stall Controlled
Pitch Controlled
•
•
•
•
•
•
•
Known Technology
1.3% of ICC
5 % COE of OM &amp; Replace
Power Regulation
Fatigue alleviation if IPC
Aerodynamic brake
No power used above rated
•
•
•
•
•
•
•
Known Technology
2.4% of ICC for Gen &amp; PE
1.8% COE for Gen &amp; PE
Power Regulation
No Fatigue alleviation
No aerodynamic brake
No power used above rated
Active Stall Controlled
•
•
•
•
•
New Technology
Power Regulation
Fatigue alleviation?
No aerodynamic brake
Power used above rated ?
14
The Big Picture
Pitch Controlled
•
•
•
•
•
•
•
Stall Controlled
• Known Technology
Known Technology
• 2.4% of ICC for Gen &amp; PE
1.3% of ICC
Hybrid Solution
• 1.8% COE for Gen &amp; PE
5 % COE of OM &amp; Replace
• Active
Power Stall
Regulation
Power Regulation
• Design from scratch with
• No Fatigue alleviation
Fatigue alleviation Control
if IPC
• No aerodynamic brake
Aerodynamic brake
• No power) used above rated
No power used •above
rated
Airfoil
optimization ( Transpiration
Active Stall
• ControlDBD
strategy
• New Technology
• Power
Control
Design
combined with Passive
• Fatigue alleviation?
Stall
• No aerodynamic brake
• Power used above rated ?
15
Suggestions? Questions?
16
Power for Actuation and Practical
Issues
Boundary Layer
Transpiration
• Air Pump required
• More Mechanisms
• Power required to
operate the pump
• Unknown maintenance
Plasma Actuators
• Wet Environment –
Electric Arcs
• 1.5% power above
rated