Wind Modeling Studies by Dr. Xu at Tennessee State University
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Transcript of Wind Modeling Studies by Dr. Xu at Tennessee State University
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Wind Modeling Studies by Dr. Xu at Tennessee State University
Guanpeng Xu
Tennessee State University
Center of Excellence in Information System,
Engineering & Management
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Overview of Presentation
• Wind Projects
• Methodologies
• Results and Conclusions
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Wind Modeling Studies Computational Studies of Horizontal Axis Wind
Turbines Full NS Hybrid Methodology Overset Grid (CHIMERA)
2D/3D Icing Simulation 2D Icing 3D Icing
The first project is a part of my Ph.D. research. My advisor is Lakshmi Sankar at School of Aerospace Engineering,
Georgia Institute of Technology
Projects were supported by
National Renewable Energy Laboratory (NREL), DOE
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Mathematical FormulaReynolds Averaged Navier-Stokes Equations in Finite Volume Representation:
Where q is the state vector. E, F, and G are the inviscid fluxes, and R, S, and T are the viscous fluxes
•A finite volume formulation using Roe’s scheme is used.
•The scheme is third order or fifth order accurate in space and second order accurate in time.
t
qdV Eˆ i Fˆ j G ˆ k n dS Rˆ i Sˆ j T ˆ k
n dSt
qdV Eˆ i Fˆ j G ˆ k n dS Rˆ i Sˆ j T ˆ k
n dS
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The Hybrid Methodology The flow field is made of
– a viscous region near the blade(s)– A potential flow region that
propagates the blade circulation and thickness effects to the far field
– A Lagrangean representation of the tip vortex, and concentrated vorticity shed from nearby bluff bodies such as the tower
This method is unsteady, compressible, and does not have singularities near separation lines
N-S zone
Potential Flow Zone
Tip Vortex
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The Overset Grid Methodology
– Body-fitted grids are used for rotating blades and tower.
– Each grid block is simulated using either a Navier-Stokes or hybrid method.
– The flow fields among the grid sets are linked by 3-D interpolation.
•Inclusion of tower effects requires modeling non-rotating and rotating components.
•Georgia Tech CHIMERA methodology has been modified for tower shadow effects of HAWT :
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The Icing Simulation•Porous ice with liquid water content and air/vapor is assumed.
•The flow field and icing/melting are calculated using a modular approach.
•Grid is deformed with on-the-fly ice shape; NS solver is used for outer flow.
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Configuration Studied
NREL has collected extensive performance data for three rotor configurations:– A rotor with rectangular planform, untwisted blade and S-809
airfoil sections, called the Phase II Rotor
– A twisted rotor, with rectangular platform and S-809
sections, called the Phase III Rotor
– A two bladed, tapered and twisted rotor, called the Phase VI
Rotor. Best quality measurements (wind tunnel) are
available.
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Results and Discussion
Body fitted grid on Phase II rotor
•Size
11043402(380,000)•Viscous zone 6043202
(100,000)
--Sample Grid
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OVERSET GRID
A very coarse grid was used for Proof of Concept
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-10
-5
0
5
10
15
20
0 5 10 15 20 25Wind Speeds[m/s]
Gen
erat
or
Po
wer
[kw
]
NREL experimentN-S SolverHybrid CodeLifting Line results
Results for the Phase II Rotor
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Results for the Phase III Rotor
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Results for the Phase VI Rotor
Upwind Configuration, Zero Yaw
0
1000
2000
3000
4000
5000
5 10 15 20 25 30
Wind Speed (m/s)
Ro
ot
Fla
p B
end
ing
Mo
men
t (N
m)
NREL
Present Methodologies
Flap Bending Moment for One Blade
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8.0
8.5
9.0
9.5
10.0
10.5
11.0
11.5
0 2 4 6 8 10 12 14 16
Time(sec)
Me
asu
red
Win
d S
pe
ed
Inflow wind(3)inflow wind(4)
Typical Natural 10m/s Inflow Wind
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Measured Power v.s. Time at 20 degree Yaw
•Average values well predicted
•Higher harmonics are not captured well, because we only model the first harmonic of the wind.
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Wave Number Analysis for 10m/s Wind -20 deg Yaw
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0 5 10 15 20 25 30
Wave Number
Am
pli
tud
e
Harmonic Analysis of the Calculated Power
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The Upper Surface of the Phase II Rotor at 20 m/s
Flow Field May be Examined for Interesting Features
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Streamlines at a Typical Span Station of Phase II rotor at 20m/s
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Ice Shape after Half an Hour
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Tower Shadow Causes 15% Variation in Wind Speed
Portion of the Rotor Disk exposed to the tower wake
10m/s ~8.5m/s
•Code predicted this loss in dynamic pressure, but not the vortex shedding effects due to the sparse grid employed.
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Improvement to a Tip Loss Model and a Stall Delay Model Using CFD as a Guide
0
500
1000
1500
2000
0 5 10 15 20 25
wind speed
torq
ue
strip; no tip loss;no stall delayNREL NASA AmesNew Tip Loss ModelCorrigan Model; n = 1Corrigan Model; n = 1.85
Effects of Corrigan’s Model with Different values of n
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Conclusions• The Hybrid method, which solves the HAWT flow using a zonal approach, has been developed for efficiently simulating fully three-dimensional viscous fluid flow around an HAWT. Good results have been obtained.
• A full Navier-Stokes methodology has also been developed. Two turbulence models and two transition prediction models have been integrated into above solvers. Consistent results have been obtained for above two solvers. An overset grid based version that can model rotor-tower interactions has been developed.
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Conclusions
• The physics studied includes turbulence models, transition prediction models, yaw (unsteady) simulation, tower shadow, wind turbine flow states, stall delay, and tip losses.
• The complete research activities have been documented in Guanpeng Xu’s doctoral thesis, Journal of Solar Energy Engineering, and in AIAA papers, 1999-0042, 2000-0048, 2001-0682, 2001-7796, and are omitted here.