No name

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Basic Study of Winglet Effects On Aerodynamics
and Aeroacoustics Using Large-Eddy Simulation

• Masakazu Shimooka, Makoto Iida, and Chuichi
  Arakawa
• The University of Tokyo

European Wind Energy Conference
Exhibition Athens, Greece, 27 February 2 March
2006
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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.

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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.

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Related research (WINDMEL?)
Actual tip shape
Oliver Fleig, Chuichi Arakawa 23rd ASME Wind
Energy Symposium January 5 8, 2004, Reno, Nevada
Ogee tip shape
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What is winglet ?

• 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)

• Developed by Whitcomb
• Diffuse tip vortices
• Reduce induced drag
• Increase thrust and lift force

In this work, We use Navier-Stokes simulation to
resolve complex structure of tip vortices in
detail.
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Numerical method(1) - Flow field

• Governing equation Compressible Navier-Stokes
  equation
• Turbulence model LES Smagorinsky model

3rd order Upwind Finite Difference scheme in
space 1st order Implicit Euler scheme in time
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Numerical method(2) - Acoustic field

• Near field
• (1 to 2 chord lengths)
• Direct noise simulation
• sufficiently fine grids
• Accurate modeling of
• non-linear effects and wall reflection,
  refraction, scattering in the near field
• Far field
• Ffowcs Williams-Hawkings equation
• permeable integration surface which does not
  need to correspond with the body surface

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Boundary condition
inflow

• 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

a
b
y
x
z
Rotation axis
Computational domain
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Computational grid
765 points,along the surface (?) 193
points,perpendicular to the surface (?) 2209
points,along the span direction (?) Total number
of grid points, 300million Use 14 nodes (112
CPU) on Earth Simulator
?

• Single O-grid
• Minimum wall distance is 210-5 corresponding
  to y1 (wall resolved)
• High concentration of grid points in the blade
  tip region

Grid spacing of airfoil section (?plane)
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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
• ?t 3.6x10-5c/Ueff
• 1.3x10-7(s)

Ueff
Ueff
Tip shape (top 50deg., bottom 0deg.)
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Flow field - Tip vortex
50deg.
0deg.
Vorticity magnitude iso-surfaces
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Pressure contours at the trailing edge

0deg.
50deg.
trailing edge at the very tip (y/c1.0) Winglet
diffuses tip vortices.
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Vorticity magnitude contours at the near wake
y/c 2.0
y/c 1.8
y/c 1.6
50deg.
y/c 1.4
y/c 1.2
y/c 1.0
y
z
0deg.
x
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0deg.
50deg.
50deg
Vorticity magnitude contours and iso-surface
(?4.0)
Winglet reduces the strength of tip vortices .
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Spanwise velocity components contours

0deg.
50deg.
Spanwise velocity (w) component contours at
y/c0.7 Reduced downwash effect, and Spread of
wake in spanwise direction.
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Rotational torque and Flap moment
Winglet
Winglet
Main blade
Main blade
Hub side
Hub side
Tip side
Tip side
Increase of rotational torque at the winglet
and the main blade near the winglet. Reduction
of flap moment at the winglet.
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Pressure distribution
50deg.
0 deg.
Suction side
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Acoustic field Near field
SPL (dB), ref 210-5(Pa)
SPL (dB), ref 210-5(Pa)
Frequency (Hz)
Frequency (Hz)
Point A is where the tip vortex is developed.
Point B is slightly downstream from the trailing
edge of main blade near the winglet.
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Acoustic field Far field
Integration surface for FW-H equation (yellow
surface)
50deg.
0deg.
Far field overall sound pressure level
(OASPL) Integration from 1kHz to 12.5kHz (2.3m
downstream from rotor)
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Current Work Detached-Eddy Simulation
for NREL Phase VI
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Pressure distribution (U87.0m/s)
a10.1
a11.8
a12.2
a7.4
a8.3
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Flow field (U825.1m/s)
U8
Vorticity magnitude iso-surface (?0.2) and
contours
Streamlines
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Conclusions

• We succeeded in capturing winglet effects in
  detail, using 300 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.