Influence of Trailing Edge Serrations on Flow Topology December 6, 2014 EWEA Workshop on Wind Turbine Sound By Carlos Arce
AGENDA Introduction and background Experiment setup Findings Wrap-up References Trailing Edge Serrations 2/18
Trailing Edge Serrations As sound reduction devices Play in external viewer B Trailing Edge Serrations 3/18
Trailing Edge Serrations Previous research Source: Gruber et al. [2013] Source: Moreau and Doolan [2013] Source: Oerlemans et al. [2009] Source: Arina et al. [2012] Trailing Edge Serrations 4/18
Trailing Edge Serrations Theoretical background Howe [1991], non-dimensional frequency spectrum of a serrated trailing edge 1 : Ψ (ω) Ψ 0 (ω) 1 + (2 2h/λ) 2 (1) 1 1 For ωδ/u c 1 where U c 0.7U ( f 100 Hz in the case tested) Trailing Edge Serrations 5/18
Trailing Edge Serrations Theoretical background Howe [1991], non-dimensional frequency spectrum of a serrated trailing edge 1 : Ψ (ω) Ψ 0 (ω) 1 + (2 2h/λ) 2 (1) 2h λ 1 1 For ωδ/u c 1 where U c 0.7U ( f 100 Hz in the case tested) Trailing Edge Serrations 5/18
Trailing Edge Serrations Theoretical background Howe [1991], non-dimensional frequency spectrum of a serrated trailing edge 1 : Ψ (ω) Ψ 0 (ω) 1 + (2 2h/λ) 2 (1) γ cot γ = 4h/λ (2) 1 1 For ωδ/u c 1 where U c 0.7U ( f 100 Hz in the case tested) Trailing Edge Serrations 5/18
Trailing Edge Serrations Theoretical background Howe [1991], non-dimensional frequency spectrum of a serrated trailing edge 1 : Ψ (ω) Ψ 0 (ω) 1 + (2 2h/λ) 2 (1) θ γ γ cot γ = 4h/λ (2) 1 cot γ = γ ± θ (3) 1 For ωδ/u c 1 where U c 0.7U ( f 100 Hz in the case tested) Trailing Edge Serrations 5/18
AGENDA Introduction and background Experiment setup Findings Wrap-up References Trailing Edge Serrations 6/18
Experiment Setup Play in external viewer Trailing Edge Serrations 7/18
Experiment Setup Measurement locations y, v z, w x, u y, v z, w x, u y, v z, w x, u 6 cm Trailing Edge Serrations 8/18
AGENDA Introduction and background Experiment setup Findings Wrap-up References Trailing Edge Serrations 9/18
Findings [surface parallel measurements, explanation] θ γ γ Trailing Edge Serrations 10/18
Findings Surface parallel measurements, pressure side Trailing Edge Serrations 11/18
Findings Surface parallel measurements, pressure side Variation Angle of attack Flap angle Free stream velocity Sensitivity Trailing Edge Serrations 11/18
Findings Surface parallel measurements, pressure side Variation Angle of attack Flap angle Free stream velocity Sensitivity Sensitive Trailing Edge Serrations 11/18
Findings Surface parallel measurements, pressure side Variation Angle of attack Flap angle Free stream velocity Sensitivity Sensitive Trailing Edge Serrations 11/18
Findings Surface parallel measurements, pressure side Variation Angle of attack Flap angle Free stream velocity Sensitivity Sensitive Very sensitive Trailing Edge Serrations 11/18
Findings Surface parallel measurements, pressure side Variation Angle of attack Flap angle Free stream velocity Sensitivity Sensitive Very sensitive Trailing Edge Serrations 11/18
Findings Surface parallel measurements, pressure side Variation Angle of attack Flap angle Free stream velocity Sensitivity Sensitive Very sensitive Not sensitive Trailing Edge Serrations 11/18
Findings Surface parallel measurements, suction side Pressure side Suction side Trailing Edge Serrations 12/18
Findings Crossflow measurements α = 0 α = 3 α = 6 ϕ = 0 ϕ = 3 ϕ = 6 U = 40 m/s A serration tip is approximately in the center of each frame Adjacent tips are on the edge of the frames Suction side is on the top Trailing Edge Serrations 13/18
Findings A more complete view from RANS Play in external viewer Trailing Edge Serrations 14/18
AGENDA Introduction and background Experiment setup Findings Wrap-up References Trailing Edge Serrations 15/18
Wrap-up 1. Flow was studied near the serration surface and its wake in order to establish how incidence affects it. 2. Flow complexity increases considerably because of incidence and departs from the assumptions made in the theory of sound generation by serrated trailing edges. 3. Experimental and numerical results show that the flow is particularly sensitive to the serration flap angle. 4. This should have an impact on the way we consider designing serrations for industrial applications. Trailing Edge Serrations 16/18
Thanks you for your time Contact details: Co-authors: Carlos Arce 1 caar@lmwindpower.com C.A.ArceLeon-2@tudelft.nl Daniele Ragni, PhD 2 d.ragni@tudelft.nl Stefan Pröbsting 3 s.probsting@tudelft.nl Carlos is supported by the Industrial PhD Programme of the Danish Ministry of Higher Education and Science. 1 PhD Candidate, Faculty of Aerospace Engineering, Delft University of Technology and LM Wind Power A/S 2 Assistant Professor, Faculty of Aerospace Engineering, Delft University of Technology 3 PhD Candidate, Faculty of Aerospace Engineering, Delft University of Technology Trailing Edge Serrations 17/18
References R Arina, RDR Rinaldi, A Iob, and D Torzo. Numerical Study of Self-Noise Produced by an Airfoil with Trailing-Edge Serrations. In 18th AIAA/CEAS Aeroacoustics Conference, number June, pages 4 6, Colorado Springs, US, 2012. AIAA. URL http://arc.aiaa.org/doi/pdf/10.2514/6.2012-2184. M Gruber, P Joseph, and M Azarpeyvand. An experimental investigation of novel trailing edge geometries on airfoil trailing edge noise reduction. In 19th AIAA/CEAS Aeroacoustics Conference, Reston, Virginia, May 2013. American Institute of Aeronautics and Astronautics. ISBN 978-1-62410-213-4. doi: 10.2514/6.2013-2011. URL http://arc.aiaa.org/doi/abs/10.2514/6.2013-2011. MS Howe. Noise produced by a sawtooth trailing edge. The Journal of the Acoustical Society of America, 90 (July):482 487, 1991. doi: 10.1121/1.401273. URL http://link.aip.org/link/?jasman/90/482/1. DJ Moreau and CJ Doolan. Noise-Reduction Mechanism of a Flat-Plate Serrated Trailing Edge. AIAA journal, 51 (13):2513 2522, September 2013. ISSN 0001-1452. doi: 10.2514/1.J052436. URL http://arc.aiaa.org/doi/abs/10.2514/1.j052436. S Oerlemans, M Fisher, T Maeder, and K Kögler. Reduction of wind turbine noise using optimized airfoils and trailing-edge serrations. AIAA Journal, 47(6):1470 1481, June 2009. ISSN 0001-1452. doi: 10.2514/1.38888. URL http://doi.aiaa.org/10.2514/1.38888. Trailing Edge Serrations 18/18