Aeroacoustics and Aerodynamic Performance of a Rotor with Flatback Airfoils
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Transcript of Aeroacoustics and Aerodynamic Performance of a Rotor with Flatback Airfoils
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
Matthew Barone, Josh PaquetteSandia National Laboratories, Albuquerque, NM
Eric SimleyUniversity of Colorado, Boulder, CO
Monica ChristiansenPenn State University, State College, PA
Aeroacoustics and Aerodynamic Performance of a Rotor with Flatback Airfoils
2010 European Wind Energy ConferenceWarsaw, Poland
23 April 2010
Outline
Flatback Airfoils: Motivation and Introduction Flatback Airfoil Wind Tunnel Tests
Field Tests of the BSDS Rotor
Modeling of Flatback Rotor Noise
Motivation Wind turbine blade design is a multi-disciplinary optimization
problem• Cost of Energy is the ultimate objective function• Optimal aero-structural design may differ markedly from the
optimal aerodynamic and optimal structural designs Basic Design Question
• Blade aerodynamics dominate the outboard design• Structural requirements dominate the inboard design• What inboard blade shape provides an optimal structural
design without sacrificing too much aerodynamic performance?
Sandia Blade System Design Study (BSDS) Employed a multi-disclipinary, iterative design process
• Integrated blade design for aerodynamic performance, low weight, and manufacturability
Innovative blade design features• Flatback airfoils• Optimal design of a carbon fiber spar cap
9 m blades were fabricated by TPI Composites for testing
Flatback Airfoils Structural Advantages
• Structural benefit of larger sectional stiffness for given chord and thickness.
• Results in higher blade strength, lower blade weight.
Aerodynamic Advantages/Disadvantages• Sensitivity of lift to leading edge soiling is
reduced.• Drag is increased (although L/D may still
increase).• Increased aerodynamic noise due to blunt
trailing edge.
Flatback Airfoil Research at Sandia
Wind Tunnel TestsField Tests
Computational Modeling
Goal: Predict and
Quantify Noise and Drag of
Flatback Airfoils
Flatback Airfoil Wind Tunnel Tests
Wind Tunnel Experiments
• Virginia Tech Stability Wind Tunnel• Aeroacoustic test section• Beamforming microphone array• Airfoil surface pressure taps• Pitot tube wake surveys
• DU97-W-300 and DU97-flatback (10% trailing edge thickness)
• Flatback tested with/without splitter plate• Chord Reynolds numbers from 1.5 to 3.2
million• Several angles of attack
Facilities and Instrumentation
Tests Performed
Wind Tunnel Noise Measurements
U = 56 m/s
Findings from the wind tunnel tests• Flatback noise generated a
prominent tone• Tonal frequency and amplitude is
relatively insensitive to• Angle of attack• Boundary layer transition location
• Simple splitter plate attachment reduced noise by ~12 dB
Field Tests of the BSDS Rotor
c
h
BSDS Blade Geometry
flatback
34-m Pad
CTL B
RESERVOIR
ROAD
N0 100 200
Scale, ft
Prevailing Wind
2.5 Dia Lateral Spacing
Turbine
Anemometer Tower
Test Turbine and Instrumentation
• Site• 8.7 m/s average wind speed
at 80 m•Turbine
•Modified Micon 65•19 m Rotor Diameter•23 m Hub Height
• Instrumentation• Inflow
• Center and off-axis met towers, and nacelle
• Wind speed and direction• Power• Loads
• Tower, hub, and blade• Noise
• 32-microphone array centered one hub height upwind
USDA/SNL Micon Test Turbine
Acoustic Instrumentation
Microphone Array Schematic45 Total Sensor Locations, configurable to either a low-frequency or high-frequency array.
High-frequency Microphone Ellipse
Low-frequency Microphone Ellipse
Tower
Acoustic Measurements
Averaged Noise Maps at Different Blade Azimuth Positions
250 Hz – Entire Rotor 1250 Hz – Single Blade
Modeling of Flatback Rotor Noise
Rotor Performance ModelWTPerf Performance Model with CFD-
generated airfoil tables
Modeling of Flatback Noise SourceObserver• Brooks, Pope, and Marcolini (BPM) model
for blunt trailing edge noise
• Empirical model based on wind tunnel measurements
• Peak amplitude depends on the ratio of blunt trailing edge thickness to boundary layer thickness, h/d* .
• BPM only had data for h/d* < 1.
• Modified BPM model
• Scaling with flow velocity and blade dimensions unchanged
• Spectral shape function unchanged• Amplitude function modified based on
Virginia Tech wind tunnel data – more applicable to large h/d*
• Low-frequency directivity function used
Trailing Edge
Boundary Layer
Turbulent Wake
h
d*
Modeling of Rotor Noise
Blunt Trailing Edge Noise• Blade divided into span-wise sections• Local relative flow velocity obtained
from WTPerf model• Modified BPM model applied for each
section with a flatback airfoil Inflow Turbulence Noise
• Empirical model of Hubbard and Shepherd
Other airfoil self-noise sources are not currently considered
• Turbulent boundary layer trailing edge• Laminar vortex-shedding• Separation
Flatback Noise Source
Low-frequency
noise
BSDS Rotor Noise Predictions
Rotor-averaged Noise spectra for a ground observer one hub height upwind
Wind Speed = 8 m/s Wind Speed = 12 m/s
Utility-Scale Rotor Noise Predictions
WindPACT 1.5 MW Reference Turbine
• Rotor Diameter = 72 m• Hub height = 85.3 m• Wind Speed = 11 m/s• Blade Pitch = 2.6 deg.• Rotational Speed = 20 RPM
Rotor-averaged Noise spectra for a ground observer one hub height upwind
Summary Flatback airfoil technology can lead to lighter, more efficient
rotors Flatback rotor noise is being measured in a subscale field test
• Challenging due to competing hub noise Noise associated with the blunt trailing edge of flatbacks has
been studied using models informed by wind tunnel data• Existing BPM model may be over-conservative for flatback airfoil noise• Flatback airfoil noise is predicted to be lower than inflow turbulence
noise for both the subscale BSDS rotor and a reference 1.5 MW rotor with flatbacks
Ongoing Work Acoustically absorbing foam
panels will be added to the test turbine nacelle
• Attenuate hub noise• Isolate inboard blade noise
Splitter plate trailing edge attachment will be added to the BSDS blades.
• Examine effects on performance and noise.
BSDS blade with trailing edge splitter plate