Spanwise Wavy Trailing Edge Airfoil 1/ 31 NAWEA 2015
Aerodynamics and Aeroacoustics of Spanwise Wavy Trailing Edge Flatback Airfoils: Design Improvement
NAWEA 2015 SYMPOSIUM
Seung Joon Yang James D. Baeder
Department of Aerospace Engineering, University of Maryland Alfred Gessow Rotorcraft Center
Spanwise Wavy Trailing Edge Airfoil 2/ 31 NAWEA 2015
Outline
Wavy trailing edge design Wavy trailing edge modification
Conclusion
Introduction Flatback airfoil drag and noise emission Numerical methods
Results and discussions Aerodynamic Characteristics Aeroacoustic Characteristics
Spanwise Wavy Trailing Edge Airfoil 3/ 31 NAWEA 2015
Introduction and Motivation
* IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation” 2011
Higher power generation requires larger blades
Wind power generation is proportional to
square of rotor blade length!
Demands a structurally robust blade Thicker Airfoil at inboard sections (~40% of blade span!)
Spanwise Wavy Trailing Edge Airfoil 4/ 31 NAWEA 2015
Introduction: Flatback Airfoil Aerodynamics
* Baker,”Experimental Analysis of Thick Blunt Trailing Edge wind turbine Airfoils”, 2006
Advantages
Sharp TE Flatback TE
Flatback TE airfoil has superior lift performance; delayed stall on upper surface Structurally robust blade design compared to sharp TE airfoil
Spanwise Wavy Trailing Edge Airfoil 5/ 31 NAWEA 2015
Introduction: Flatback Airfoil Aerodynamics
Flatback TE
Sharp TE
Disadvantages
Flatback TE airfoil suffers from higher drag, lower max L/D Higher acoustical signature compared to sharp TE
Increase in drag
* Baker,”Experimental Analysis of Thick Blunt Trailing Edge wind turbine Airfoils”, 2006
Sharp TE Flatback TE
Spanwise Wavy Trailing Edge Airfoil 6/ 31 NAWEA 2015
Introduction: Flatback Airfoil Noise Emission
AoA 4°, Re = 3,000,000
* Dale E. Berg and M. Barone,”Aerodynamic and Aeroacoustic Properties of a Flatback Airfoil”, WINDPOWER 2008, Houston, 2008
Flatback TE
Sharp TE
Strong vortex shedding
Disadvantages
Flatback TE airfoil high tonal noise Generated by pressure fluctuations at TE because of strong nearly 2-D
spanwise coherent vortex shedding
Noise spectrum Vortex shedding pattern
Spanwise Wavy Trailing Edge Airfoil 7/ 31 NAWEA 2015
Introduction: Spanwise Wavy Trailing Edge Modification
Introduce streamwise vorticity to disintegrate/breakdown spanwise coherent vortex structure
Can the trailing edge geometry be modified to reduce drag and noise while maintaining aerodynamic efficiency?
Other solutions • Splitter plate, serrated TE add on devices …
* Seung Joon Yang and James D. Baeder,”Aerodynamic Drag and Aeroacoustic Noise Mitigation of Flatback Airfoil with Spanwise Wavy Trailng Edge”, 33rd Wind Energy Symposium at Scitech 2015, Kisimmee, FL, 2015
Baseline Proposed solution
Spanwise Wavy Trailing Edge Airfoil 8/ 31 NAWEA 2015
Numerical methods RANS – LES hybrid method (OVERTURNS, GPURANS3D) - Laminar – Turbulent transition modeling ; γ − 𝑅𝑒𝜃𝜃 transition model with S-A turbulence model - Delayed Detached Eddy Simulation (DDES) - Spatial reconstruction ; 5th order WENO - Time marching; Diagonal Alternating Direction Implicit (DADI) - GPU – accelerated computation ; Deepthought II cluster at UMD (40 gpu nodes) ; Nvidia Tesla K20m GPUs
* Deepthought II Cluster at UMD, College Park
Nvidia Tesla K20m
Processor core 2496
Processor core clock 706 MHz
Memory 5 GB
Memory clock 2.6 GHz
Band width 208 GB/sec
Spanwise Wavy Trailing Edge Airfoil 9/ 31 NAWEA 2015
Mesh Generation 271 x 141 x 61 ~ 2.33 milion grid points for each airfoil geometries 50C distance away in the normal to surface direction
resolution; Δy/c ~ 5.0µ (y+ ~ 0.8) 0.5C in span direction 104 grid points at the trailing edge
102 grid points upper/bottom surface near the trailing edge
Validation!
* Seung Joon Yang and James D. Baeder,”Aerodynamic Drag and Aeroacoustic Noise Mitigation of Flatback Airfoil with Spanwise Wavy Trailng Edge”, 33rd Wind Energy Symposium at Scitech 2015, Kisimmee, FL, 2015
Spanwise Wavy Trailing Edge Airfoil 10/ 31 NAWEA 2015
Wavy trailing edge design: Previous Designs
∆y = y𝑚𝑚𝑚 − y𝑚𝑚𝑚
local thickness =∆𝑦2
cos𝜔 ∗ 2𝜋𝜋
𝑙+ 1 + 𝑦𝑚𝑚𝑚
Wave formula
4 cyc/c better than 2 cyc/c or 8 cyc/c
1/2flatback-4cyc/C 3/4flatback-4cyc/C
* James D. Baeder and Seung Joon Yang,”Wavy Trailing-Edge Flatback Aerodynamics Using a GPU-Accelerated Navier-Stokes Solver”, EWEA Offshoer, Copenhagen, Denmark, 2015, March
Baseline
Spanwise Wavy Trailing Edge Airfoil 11/ 31 NAWEA 2015
Baseline Results Base-line cases A. FB3500-1750 (TE thickness 17.50% of C, flatback TE) B. FB3500-0462 (TE thickness 4.62% of C, sharp TE)
FB3500-1750 FB3500-0462
* Seung Joon Yang and James D. Baeder,”Aerodynamic Drag and Aeroacoustic Noise Mitigation of Flatback Airfoil with Spanwise Wavy Trailng Edge”, 33rd Wind Energy Symposium at Scitech 2015, Kisimmee, FL, 2015
Strong nearly 2-D spanwise vortex structure with flatback airfoil Weak spanwise vortex structure with sharp trailing edge airfoil
Spanwise Wavy Trailing Edge Airfoil 12/ 31 NAWEA 2015
Previous Wavy Trailing Edge: Flowfield
3/4 flatback – 4cyc/C 1/2 flatback – 4cyc/C
* James D. Baeder and Seung Joon Yang,”Wavy Trailing-Edge Flatback Aerodynamics Using a GPU-Accelerated Navier-Stokes Solver”, EWEA Offshoer, Copenhagen, Denmark, 2015
With shallow wavy pattern, still span-wise vortex structure With deeper wavy pattern, more stream-wise vortex structure However, relatively unstable flow at the wave troughs
Spanwise Wavy Trailing Edge Airfoil 13/ 31 NAWEA 2015
Previous Wavy Trailing Edge: Aerodynamic Performance
* James D. Baeder and Seung Joon Yang,”Wavy Trailing-Edge Flatback Aerodynamics Using a GPU-Accelerated Navier-Stokes Solver”, EWEA Offshoer, Copenhagen, Denmark, 2015
With shallow wavy pattern, higher lift and reduced drag With deeper wavy pattern, too much loss of lift
Spanwise Wavy Trailing Edge Airfoil 1/ 31 NAWEA 2015
Previous Wavy Trailing Edge: Potential Problems
Previous wavy TE
* Seung Joon Yang and James D. Baeder,”Aerodynamic Drag and Aeroacoustic Noise Mitigation of Flatback Airfoil with Spanwise Wavy Trailng Edge”, 33rd Wind Energy Symposium at Scitech 2015, Kisimmee, FL, 2015
Loss of blade volume at troughs weaken blade structural strength? Wavy modification make any difficulty during manufacturing stage?
Spanwise Wavy Trailing Edge Airfoil 2/ 31 NAWEA 2015
Design Improvements: Design #1 Can we remove wavy structure on upper surface?
Lower half way cut (only Bottom surface wavy TE )
Previous wavy TE
Lower half way cut wavy TE
Camber recovery helps aerodynamic performance
Larger blade volume with design #1 Better manufacturability
Spanwise Wavy Trailing Edge Airfoil 3/ 31 NAWEA 2015
Design Improvements: Design #2 Can we start wavy structure closer to TE?
90%C cut (wavy TE at 90% of Chord)
Previous wavy TE
Wavy TE at 90% of chord
Can we get rid of 2-D spanwise vortex structure
With the New Designs??
Larger blade volume with design #2 Better manufacturability
Spanwise Wavy Trailing Edge Airfoil 4/ 31 NAWEA 2015
Improved Wavy Trailing Edge Designs
Structurally enhanced designs A. Lower half cut 3/4 flatback (min. TE thickness 15.38% of C) B. Lower half cut 1/2 flatback (min. TE thickness 13.12% of C) C. 90C cut 3/4 flatback (min. TE thickness 13.12% of C) D. 90C cut 1/2 flatback (min. TE thickness 8.75% of C)
B. Lower half cut 1/2 flatback A. Lower half cut 3/4 flatback
D. 90C cut 1/2 flatback C. 90C cut 3/4 flatback
Spanwise Wavy Trailing Edge Airfoil 5/ 31 NAWEA 2015
Results and Discussion: Flowfield (Iso-vorticity mag.)
Lower half cut 1/2 flatback Lower half cut 3/4 flatback
90C cut 3/4 flatback 90C cut 1/2 flatback
FB3500-1750 (flatback TE)
FB3500-0462 (sharp TE)
Lower half cut 3/4 flatback, still has spanwise coherent vortex structure Lower half cut 1/2 flatback, has more streamwise vorticity 90C cut designs work better to break up spanwise vortex
Spanwise Wavy Trailing Edge Airfoil 6/ 31 NAWEA 2015
Results and Discussion: Flowfield (Vorticity contours) • Aerodynamic characteristics; Trailing edge vortex shedding pattern
Lower half cut 1/2 flatback Lower half cut 3/4 flatback
Crest
Trough
Crest
Trough
Both Lower half cut airfoils have similar vortex shedding patterns along span. With shallow wave (3/4 flatback), strong 2-D coherent vortex structure. With deep wave (1/2 flatback), vortex strength now weaken and vortex core is
formed at further downstream.
Spanwise Wavy Trailing Edge Airfoil 7/ 31 NAWEA 2015
Results and Discussion: Flowfield (Vorticity contours) • Aerodynamic characteristics; Trailing edge vortex shedding pattern
Lower half cut 1/2 flatback Lower half cut 3/4 flatback
Crest
Trough
Crest
Trough
Both Lower half cut airfoils have similar vortex shedding patterns along span. With shallow wave (3/4 flatback), strong 2-D coherent vortex structure. With deep wave (1/2 flatback), vortex strength now weaken and vortex core is
formed at further downstream.
Spanwise Wavy Trailing Edge Airfoil 8/ 31 NAWEA 2015
Results and Discussion: Flowfield (Vorticity contours) • Aerodynamic characteristics; Trailing edge vortex shedding pattern
90C cut 3/4 flatback 90C cut 1/2 flatback
Crest
Trough
Crest
Trough
With 90%C cut designs, now entirely different vortex shedding patterns at the crest and trough.
Now vortex structure is more like 3-D, affected by streamwise vorticity.
Spanwise Wavy Trailing Edge Airfoil 9/ 31 NAWEA 2015
Results and Discussion: Flowfield (Vorticity contours) • Aerodynamic characteristics; Trailing edge vortex shedding pattern
90C cut 3/4 flatback 90C cut 1/2 flatback
Crest
Trough
Crest
Trough
With 90%C cut designs, now entirely different vortex shedding patterns at the crest and trough.
Now vortex structure is more like 3-D, affected by streamwise vorticity.
Spanwise Wavy Trailing Edge Airfoil 10/ 31 NAWEA 2015
Results and Discussion: Lift vs. AoA
Lower half cut 1/2 flatback
Lower half cut 3/4 flatback
90C cut 1/2 flatback
90C cut 3/4 flatback
Lower half cut 3/4 flatback, only small amount of lift loss. Lower half cut 1/2 flatback, 90C 3/4 flatback, some lift loss, but not a lot. 90C 1/2 flatback, too much loss of lift. (not eligible to be an improved design)
Spanwise Wavy Trailing Edge Airfoil 11/ 31 NAWEA 2015
Results and Discussion: Lift vs. Drag Polar
Lower half cut 1/2 flatback
Lower half cut 3/4 flatback
90C cut 3/4 flatback
Lower half cut 3/4 flatback, only little amount of lift loss, but too much drag (not eligible as a drag reduced design)
Lower half cut 1/2 flatback, 90C 3/4 flatback, some of lift loss, but not a lot and large drag reduction (down to 1/3 of the original flatback design)
Spanwise Wavy Trailing Edge Airfoil 12/ 31 NAWEA 2015
Results and Discussion: Lift / Drag Map
Lower half cut 1/2 flatback
90C cut 3/4 flatback
Lower half cut 1/2 flatback, 90C 3/4 flatback have better aerodynamic performance than the original flatback aifoil for both moderate and high angle of attack.
90C 3/4 flatback has broader performance coverage than lower halfway cut 1/2 flatback.
Spanwise Wavy Trailing Edge Airfoil 13/ 31 NAWEA 2015
Results and Discussion: Acoutic Measurement Details • Aeroacoustic characteristics; measurement details
- 3 pressure fluctuation measurement points at 3C distance from TE - 0.5C distances between 3 locations - Freestream M = 0.3, Re = 666,000, AoA = 12°
SPL dB = 10 log10( 𝑝′2
𝑝𝑟𝑟𝑟2 ) , 1kHz sampling rates for 1 sec
Spanwise Wavy Trailing Edge Airfoil 14/ 31 NAWEA 2015
Results and Discussion: Sound Pressure Level
Lower half cut 1/2 flatback
Lower half cut 3/4 flatback
90C cut 1/2 flatback
90C cut 3/4 flatback
Noise emissions reduced about 20 dB by the improved wavy trailing edge. Regarding aerodynamic performance, the lower half cut 1/2 and 90C 3/4
flatback may be the best designs acoustic-wise.
Spanwise Wavy Trailing Edge Airfoil 15/ 31 NAWEA 2015
Results and Discussion: Noise Spectrum (by FFT)
peak [dB] peak [dB] peak [dB] peak [dB]
Const. thickness flatback TE: Tonal noise at low frequency range Noise peak is alleviated by the improved designs.
Spanwise Wavy Trailing Edge Airfoil 16/ 31 NAWEA 2015
Results and Discussion / Overall • Overall (AoA 12°)
Min. TE thickness Cl Cd Cl/Cd Acoustics
15.38% of C 1.9789 0.0820 24 118
13.12% of C 1.8252 0.0475 38 103
13.12% of C 1.8283 0.0483 37 105
8.75% of C 1.6757 0.0490 34 99
Lower half cut 1/2 flatback
Lower half cut 3/4 flatback
90C cut 1/2 flatback
90C cut 3/4 flatback
Best Performance: 90%C cut ¾ flatback & Lower half cut ½ flatback!
High Drag High noise
Low Lift
Best Performance!
Spanwise Wavy Trailing Edge Airfoil 17/ 31 NAWEA 2015
Conclusions
Aerodynamic Performance ▪ Larger blade volume with the lower half cut and 90%C cut wavy trailing edges
▪ 90%C cut wavy TE more effective to break down spanwise vortex compared to the lower half cut
▪ Lower half cut wavy TE 1/2 flatback: small lift loss & large drag reduction, consequently high L/D
▪ 90%C cut wavy TE 1/2 flatback: although dramatic drag reduction, too much lift loss, consequently low L/D
▪ 90%C cut wavy TE 3/4 flatback: small lift loss & large drag reduction, consequently high L/D
Acoustic Noise Reduction ▪ Strong magnitude tonal noise peaks at low frequency (100~170 Hz) with const. Flatback airfoil, was reduced up to 20 dB (mitigated down to the sharp TE noise level) by the improved designs
▪ Although best acoutic noise reduction design is the 90%C cut wavy TE 1/2 flatback, however, relatively worse aerodynamic performance.
Best aerodynamic and aeroacoustic performance: Lower half cut wavy TE 1/2 flatback / 90%C cut wavy TE 3/4 flatback
Future work
Combine to investigate lower half 90%C cut wavy TE 1/2 flatback
Spanwise Wavy Trailing Edge Airfoil 18/ 31 NAWEA 2015
NAWEA 2015 SYMPOSIUM
THANK YOU
Acknowledgements UMD supercomputing resources – Use of Deepthought II computing cluster
Research sponsored by State of Maryland (MHEC/MEA)
Top Related