reynolds airfoil
DESCRIPTION
Airfoil Reynolds numberTRANSCRIPT
-
www.ecn.nl
High Reynolds Number Effects on
20MW Wind Turbine Rotor Design
zlem Ceyhan 11.10.2012
The science of making torque from wind conference, 9-11 October 2012, Oldenburg, Germany
-
Outline
Consequences of upscaling in rotor aerodynamics
Availability of high Reynolds numbers measurements for wind turbine airfoils
High Reynolds number effects on airfoils
High Reynolds number effects on rotor design
Geometry
Cp results
AEP
Modified designs (thicker airfoils)
Conclusions
Final Remarks
-
How large is a 20MW wind
turbine blade?
-
Consequences of Upscaling on
Aerodynamics
00,0E+00
4,0E+06
8,0E+06
12,0E+06
16,0E+06
20,0E+06
24,0E+06
0,0 0,2 0,4 0,6 0,8 1,0 1,2
Re
yno
lds
Nu
mb
er
r/R
20MW
5MW
0,0
1,0
2,0
3,0
4,0
5,0
6,0
7,0
8,0
9,0
10,0
0,0 0,2 0,4 0,6 0,8 1,0 1,2
Ch
ord
[m]
r/R
5MW (126m diameter; UPWIND Reference)
20 MW (252m diameter)
UPWIND project: Upscaling from 5MW reference turbine to 20MW wind turbine with Classical Similarity Rules:
Tip speed is constant Rotational speed is therefore inversely proportional to rotor diameter growth
Dimensions of the blades are scaled linearly Local velocities along the blade stay the same.
The only change in the aerodynamics is the increase in the local Reynolds numbers!
UcRe
U= local velocity c = chord length = kinematic viscosity
U=11.5m/s (rated wind speed)
-
Availability of Cl, Cd and Cm data of the wind
turbine airfoils for high Reynolds numbers
Up to Re=6x106, for NACA airfoils up to Re=9x109 (*) Up to
Re=3x106
Availability of the wind tunnel test data;
The effects of very high Reynolds numbers?
(*) Some tests are available for high Re numbers at low Mach numbers of thin NACA profiles coming from 1940s 1- Loftin, K.L.,Jr., Bursnall, W.J., Effects of Variations in Reynolds Number Between 3.0x106 and 25x106 upon the Aerodynamic Characteristics of a number of NACA 6-Series Airfoil Sections, NACA-TN-1773, 1948
-
High Reynolds numbers on aircrafts
0
10
20
30
40
50
60
70
80
90
0 0,2 0,4 0,6 0,8 1 1,2
Rey
nold
s N
umbe
r [m
illio
ns]
Mach Number
o A380
o o B747 C17 o A350
o B777 A340 o o B787
o B737 A320 o
Take off and Landing
10-20 MW Wind Turbines
Transport aircraft airfoils are for transonic, wind turbine airfoils for subsonic speeds. Wind turbine airfoils are thicker. During the take off and landing, flaps and/slots are extracted.
Source : http://www.etw.de; reproduced. Source of the image: http://en.wikipedia.org/
-
High Reynolds number effects on airfoils
-
Solution of BL equations for a flat plate suggests for laminar flows,
For turbulent flows,
Reynolds Number Effects: Background
2/1Re
91.4
x
x
5/1Re
37.0
x
x
: Boundary layer thickness (99% velocity thickness)
For airfoils;
-
00.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0.02
-1.6 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6
Cd
Cl
Re=9 mil.
Re=20mil.
Test Re=9mil
Test Re=20mil
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 5 10 15 20
Cl
Angle of Attack
Test Re=20mil.
Test Re=9mil.
rfoil Re=9mil
rfoil Re=20mil
0.002
0.004
0.006
0.008
0.01
-0.8 -0.4 0 0.4 0.8
Cd
Cl
Re=9 mil.
Re=20mil.
Test Re=9mil
Test Re=20mil
High Reynolds number effects on Cl and
Cd performace of (thick) airfoils
NACA 633018
0
0.1
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 1.4
Xtr
Cl
Suction Side Re=9 mil
Pressure Side Re=9 mil
Suction Side Re=20mil
Pressure side Re=20mil
-
-0.5
0
0.5
1
1.5
2
-10 -5 0 5 10 15 20
Cl
AoA
Re=7mil. Clean
Re=7mil. Rough
Re=20mil. Clean
Re=20mil. Rough
-0.5
0
0.5
1
1.5
2
-5 0 5 10 15 20
Cl
AoA
Re=7mil. Clean
Re=7mil. Rough
Re=20mil. Clean
Re=20mil. Rough
High Reynolds number effects on Cl and Cd
performance of thick airfoils (RFOIL predicted)
DU91-W2-250
DU97-W-300
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
Cl
Cd
Re=7mil. Clean
Re=7mil. Rough
Re=20mil. Clean
Re=20mil. Rough
-1
-0.5
0
0.5
1
1.5
2
0 0.01 0.02 0.03 0.04 0.05 0.06
Cl
Cd
Re=7mil. Clean
Re=7mil. Rough
Re=20mil. Clean
Re=20mil. Rough
-
High Reynolds number effects on 20MW wind
turbine rotor design:
-
Airfoil Data for high Re numbers Rotor Design
BEM coupled with gradient based optimization method.
Prandtl tip loss corrections Turbulent wake state corrections Corrections for 3D effects due to rotation Airfoil data is read from an airfoil database Golden search optimization algorithm Cost function is maximizing the annual yield for the given wind conditions
High Reynolds number effects on rotor
design: Methodology
Existing airfoil Cl and Cd data is corrected for high Reynolds number effects by using RFOIL.
testRFOILlRFOILlRFOILl
RFOILltestll
CCC
CCC
Re,Re,
Re,Re,
,,,
,
A new airfoil database is generated by using max. Re number of 25 million.
rgrrcUPUpyield ,,,,max
-
High Reynolds number effects on rotor
design: Geometry
0
10
20
30
40
50
60
25
29
33
39
47
55
63
71
79
87
95
103
111
115
119
123
126
Blade Radius [m]
% C
ho
rd R
ed
ucti
on Design with UPWIND Airfoils (7 mil)
Design With 25mil Re Numbers
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
0 20 40 60 80 100 120 140
Ch
ord
[m]
Radius [m]
Classical Upscaled WT
Design With 25mil Re Numbers
-2.00
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
0 20 40 60 80 100 120 140
Twis
t an
gle
[]
Radius [m]
Classical Upscaled WT
Design With 25mil Re Numbers
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
0 20 40 60 80 100 120 140
Ab
solu
te T
hic
kne
ss [m
]
Radius [m]
Classical Upscaled WT
Design With 25mil Re Numbers
-
Performance: On and Off Design
Conditions
0,40
0,41
0,42
0,43
0,44
0,45
0,46
0,47
0,48
0,49
0,50
5,00 5,50 6,00 6,50 7,00 7,50 8,00 8,50 9,00 9,50 10,00 10,50 11,00 11,50 12,00 12,50 13,00
CP
Lambda
Design with Re=25x106 airfoils
pitch=0.0
pitch=0.5
pitch=-0.5
pitch=1.0
pitch=-1.0
0,40
0,41
0,42
0,43
0,44
0,45
0,46
0,47
0,48
0,49
0,50
5,00 5,50 6,00 6,50 7,00 7,50 8,00 8,50 9,00 9,50 10,00 10,50 11,00 11,50 12,00
CP
Lambda
Classical Upscaled - Re=7x106 airfoils
pitch=0.0
pitch=0.5
pitch=-0.5
pitch=1.0
pitch=-1.0
-
Performance in terms of AEP: Clean
and Rough Conditions
Significant improvement in operating in rough surface conditions. Can we translate this into an improvement in the rotor design?
Cle
an
Ro
ugh
-5% C
lean
Ro
ugh
Cle
an
Ro
ugh
-1.2%
-
Significant improvement in operating in
rough surface conditions:
How can we translate this improvement
into a better rotor design?
-
Significant improvement in operating in
rough surface conditions:
How can we translate this improvement
into a better rotor design?
Use of thick airfoils at the tip
-
Thick airfoils at the tip: 3 design
examples
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
0 20 40 60 80 100 120 140
Ab
solu
te T
hic
kne
ss [
m]
Radius [m]
Classical Upscaled WT
Design With 25mil Re Numbers
Modified design with DU 21% A/f at the tip
Modified design with DU 25% A/f at the tip
Modified design with DU 30% A/f at the tip
-2.00
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
0 20 40 60 80 100 120 140
Twis
t an
gle
[]
Radius [m]
Classical Upscaled WT
Design With 25mil Re Numbers
Modified design with DU 21% A/f at the tip
Modified design with DU 25% A/f at the tip
Modified design with DU 30% A/f at the tip
0.15
0.20
0.25
0.30
0.35
0.40
20 40 60 80 100 120 140
Re
lati
veTh
ickn
ess
[-]
Radius [m]
Original Airfoil Distribution
Modified design with DU 21% A/f at the tip
Modified design with DU 25% A/f at the tip
Modified design with DU 30% A/f at the tip
-
Thick airfoils at the tip: Results in terms
of AEP
Cle
an
Ro
ugh
5%
Cle
an
Ro
ugh
Cle
an
Cle
an
Cle
an
Ro
ugh
Ro
ugh
Ro
ugh
-
Thick airfoils at the tip: Improvement in
structural properties
Mod. Design with 21% af @ tip (from 80m to the tip)
Mod. Design with 25% af @ tip (from 63m to the tip)
Mod. Design with 30% af @ tip (from 50m to the tip)
With thick airfoils at the tip, it is possible to significantly improve the structural properties of the rotor blade with only minor reduction in the AEP. As a result, the total blade mass is also expected to be reduced.
-
Due to the growing sizes of the rotors, higher Reynolds numbers (up to 25 million) are introduced.
There is a lack of measurement data at high Reynolds numbers of the thick wind turbine airfoils.
RFOIL is used in order to predict the effects of Reynolds numbers together with some validations.
As a result of the effect of high Reynolds numbers, rotor blades get more slender and the optimum (Cp) operating conditions are improved.
Due to the improvement in performance of the thick airfoils both in clean and rough conditions it may be possible to use thick airfoils at the tip section of the blade which brings significant improvements in structural properties and the overall weight of the rotor.
Conclusions
-
Reynolds number is reduced with slender blades. It is increased again with higher tip speed operations.
Those effects can already be included in the existing or the next generation (7-10 MW) wind turbines.
More detailed design work is necessary to be performed in order to choose the right airfoils with right thickness. (stall, dynamic effects, stability etc.)
These results are based mainly on the numerical predictions that show a lot of improvement possibilities. However, wind tunnel tests of thick airfoils for high Reynolds numbers is required in order to understand the effects and afterwards apply these in real life problems!
Final Remarks
-
Herman Snel
Arne van Garrel
Special Thanks to
-
Questions...