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Masakazu Shimooka, Makoto Iida, and Chuichi ArakawaThe University of Tokyo
Basic Study of Winglet Effects On Aerodynamics and Aeroacoustics Using Large-Eddy Simulation
European Wind Energy Conference & ExhibitionAthens, Greece, 27 February – 2 March 2006
Purpose of this work
To optimize the tip shape for increasing public acceptance of wind energy.
To clarify winglet effects on aerodynamic performance, loads, noise.
To investigate a possibility of application to the blade design tools.
Outline of this work
Simulate the whole blade including the tip shape effects, using LES (Large-Eddy simulation) with 300 million grid points.
Investigate effects of differences of tip shapes on aerodynamics and aeroacoustics (Direct Noise Simulation).
・ 2 types of winglets whose installation angle is 0, 50 degree.
Introduce our current work (Detached-Eddy simulation) based on our knowledge of LES.
Related research (WINDMELⅢ )
Oliver Fleig, Chuichi Arakawa23rd ASME Wind Energy SymposiumJanuary 5 – 8, 2004, Reno, Nevada
60
80
100
0 2000 4000 6000 8000 10000 12000Frequency (Hz)
SP
L [d
B],
ref:
2×10
-5 P
a
Actual tip shape
Ogee type tip shape
Simulation results
Actual tip shape
Ogee tip shape
What is winglet ?
Developed by Whitcomb
Diffuse tip vortices Reduce induced drag Increase thrust and lift
force
Examples of winglets for blades of rotation ・ Tip vane by van Holten ( Wind turbine ) ・ Mie vane by Shimizu ( Wind turbine ) ・ Bladelet by Ito ( Marine propeller )
Increase of rotor output as results of experiments and numerical analysis
such as ・ BEM (Blade Element Momentum method) ・ VLM (Vortex Lattice Method)
In this work, We use Navier-Stokes simulation to resolve complex structure of tip vortices in detail.
Numerical method(1) - Flow field
10
Rej jj
QF G
t x
0
, ,i
i j i j ij j ij
j kj k j
u
Q u F u u p G
E Hu u q
2
3ji k
ij t ijj i k
uu u
x x x
・ Governing equation: Compressible Navier-Stokes equation
・ Turbulence model : LES Smagorinsky model
1/ 222t s ij ijC S S SGS
Smagorinsky Model (Cs = 0.15)
1 exp / 26.0g y
Van Driest Wall damping function
・ 3rd order Upwind Finite Difference scheme in space
・ 1st order Implicit Euler scheme in time
Numerical method(2) - Acoustic field
Far field:Modeled By Ffowcs Williams-Hawkings (FW-H) equation
×
Near field:Direct noise simulation By compressible LES
Near field ( 1 to 2 chord lengths ) ・ Direct noise simulation ・ sufficiently fine grids ・ Accurate modeling of non-linear effects and wall reflectio
n, refraction, scattering in the near field
Far field ・ Ffowcs Williams-Hawkings equation ・ permeable integration surface whic
h does not need to correspond with the body surface
Boundary condition
Rotation axis
a
b
inflow
x
y
z
Uniform flow at inlet Convective boundary conditions at
outlet Wall: No-slip conditions; pressure and
density extrapolated Outer boundaries are very coarse to
prevent reflection of high frequency acoustic waves:
Large rate of grid stretching and extreme distance between blade and outer boundaries
・ Half-sphere ・ Periodic plane a-b ・ Radius of sphere is twice the blade
span
Computational domain
Computational grid
ξ
765 points , along the surface (ξ)193 points , perpendicular to the surface (η)2209 points , along the span direction (ζ)
Total number of grid points, 300million
Use 14 nodes (112 CPU) on Earth Simulator
ξ
η
ζ
xyz
Grid spacing of airfoil section (ζplane)
・ Single O-grid・ Minimum wall distance is 2×10-5
corresponding to y+=1 (wall resolved)・ High concentration of grid points in the
blade tip region
Direct noise simulation
25-30 grid points per wavelength
Simulation parameters and tip shapes
Re = 1.0x106
Reference is the chord length at tip c = 0.23(m) , and the effective flow velocity at tip Ueff = 61.74(m/s)
Mach = 0.18 at tip
Δt = 3.6x10-5c/Ueff
= 1.3x10-7(s)
Tip shape (top: 50deg., bottom: 0deg.)
Ueff
Ueff
50deg.
0deg.
Pressure contours at the trailing edge
・ trailing edge at the very tip (y/c=1.0)
・ Winglet diffuses tip vortices.
0deg. 50deg.
Smaller but more complex structure
Vorticity magnitude contours at the near wake
y/c =1.0y/c =1.2
y/c =1.4y/c =1.6
y/c =1.8y/c =2.0
50deg.
0deg. x
y
z
50deg0deg.
Vorticity magnitude contours and iso-surface (|ω|=4.0)
・ Winglet reduces the strength of tip vortices .
50deg.
Spanwise velocity components contours
・ Spanwise velocity (w) component contours at y/c=0.7・ Reduced downwash effect, and Spread of wake in spanwise direction.
0deg.
50deg.
x
z
x
z
Rotational torque and Flap moment
30 32 34 36 38
0
0.01
0.02
Spanwise position (z/c)
Rot
atio
nal t
orqu
e (n
on-d
imen
sion
)
0deg 50deg
Hub
sid
e
Tip
sid
e
30 32 34 36 380
0.1
0.2
Spanwise position (z/c)
Flap
mom
ent (
non-
dim
ensi
on)
0deg 50deg
Tip
sid
e
Hub
sid
e
Winglet WingletMain blade Main blade
・ Increase of rotational torque at the winglet and the main blade near the winglet.
・ Reduction of flap moment at the winglet.
Pressure distribution
0 0.2 0.4 0.6 0.8 1
-5
-4
-3
-2
-1
0
y/chord
Cp
0deg 50deg
0 deg.
50deg.
Suction side
Larger suction peak at the leading edge
More sufficient recovery of pressure at the trailing edge
Acoustic field – Near field
1000 5000 10000100
120
140
160
180
1000 5000 10000100
120
140
160
180
Point A Point B
Frequency (Hz) Frequency (Hz)
SP
L (d
B),
ref
: 2×
10-5(P
a)
SP
L (d
B),
ref
: 2×
10-5(P
a)
0deg.50deg.
・ Point A is where the tip vortex is developed.
・ Point B is slightly downstream from the trailing edge of main blade near the winglet.
0deg.50deg.
Acoustic field – Far field
Integration surface for FW-H equation
(yellow surface)
(dB) (dB)
Far field overall sound pressure level (OASPL)
Integration from 1kHz to 12.5kHz(2.3m downstream from rotor)
Blade
50deg.0deg.Smaller but more complex vortices
caused by winglet emit strong noise
In high frequency.
Pressure distribution (U∞=7.0m/s)
0 0.5 1-2
0
2
4
6
y/chord
-Cp
calc. exp.
r/R=0.30
0 0.5 1-2
0
2
4
6 calc. exp.
y/chord
-Cp
r/R=0.47
0 0.5 1-2
0
2
4
6
y/chord
-Cp
calc. exp.r/R=0.63
0 0.5 1-2
0
2
4
6
y/chord
-Cp
calc. exp.
r/R=0.80
0 0.5 1-2
0
2
4
6
y/chord
-Cp
calc.r/R=0.95
α=7.4°α=8.3°
α=10.1°α=11.8°α=12.2°
Conclusions We succeeded in capturing winglet effects in detail, using 30
0 million grid points in Earth Simulator.- Diffuse and reduce tip vortices.- Reduce downwash effect, and Spread wake in spanwise direction.
This simulation will be very useful for designing optimal tip shapes.
We have performed Detached-Eddy simulation as the first step for less computational costs
This simulation is based on our knowledge of grid dependence in LES.