Morphology Effects of Leading-edge Serrations on Aerodynamic Force Production: An Integrated Study Using PIV and Force Measurements
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While the leading-edge serration in owls’ wing is known to be responsible for low noise gliding and flapping flights, the findings on its aero-acoustic role have been diverse or even controversial. Here we present an experimental study of the morphological effects of leading-edge serrations on aerodynamic force production by utilizing owl-inspired, single-feather, clean and serrated wing models with different serration lengths and spacing, and by combining Particle Image Velocimetry (PIV) and force measurements. Force measurements show that an increase in the length and density of the leading-edge serrations leads to a reduction in the lift coefficient and lift-to-drag ratio at Angles of Attack (AoAs) < 15° whereas the clean and serrated wings achieve comparable aerodynamic performance at higher AoAs > 15°, which owl wings often reach in flight. Furthermore PIV visualization of the flow fluctuations demonstrates that the leading-edge serration-based mechanism is consistent in all serrated wing models in terms of passive control of the laminar-turbulent transition while at AoAs > 15° similar suction flow is present at leading edge resulting in a comparable aerodynamic performance to that of the clean wing. Our results indicate the robustness and usefulness of leading-edge serration-inspired devices for aero-acoustic control in biomimetic rotor designs.
Keywordsbiomimetic leading-edge serrations low-speed wind tunnel particle image velocimetry aerodynamic force laminar-turbulent transition
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This study was partially supported by an endowed project by Teral Inc., Japan. Hao Liu and Toshiyuki Nakata were partly supported by the Grant-in-Aid for Scientific Research on Innovative Areas (No. 24120007), the JSPS, and the Tough Robotics Challenge - Impulsing Paradigm Change through Disruptive Technologies Program (Cabinet Office, Government of Japan), JST. Chen Rao acknowledges the financial support from a Japanese Government MEXT scholarship. Special thanks are extended to the Yamashina Institute for Ornithology for providing the feathers of an Ural owl.
- Bachmann T, Blazek S, Erlinghagen T, Baumgartner W, Wagner H. Nature-Inspired Fluid Mechanics. Notes on Numerical Fluid Mechanics and Multidisciplinary Design, Springer, Berlin, Germany, 2012, 101–117.Google Scholar
- Lilley G M. A study of the silent flight of the owl. 4th AIAA/CEAS Aeroacoustics Conference, Toulouse, France, 1998, 1–6.Google Scholar
- Kopania J. Acoustics parameters the wings of various species of owls. Inter-Noise, Hamburg, Germany, 2016, 2868–2876.Google Scholar
- Schwind R G, Allen H J. The effects of leading-edge serrations on reducing flow unsteadiness about airfoils, an experimental and analytical investigation. NASA-CR-2344, 1973.Google Scholar
- Hersh A S, Hayden R E. Aerodynamic sound radiation from lifting surfaces with and without leading-edge serrations. NASA-CR-114370, 1971.Google Scholar
- Cranston B, Laux C, Altman A. Leading edge serrations on flat plates at low reynolds number. 50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, Nashville, USA, 2012, 1–14.Google Scholar
- Chen W, Qiao W, Wang X, Wang L, Tong F. An experimental and numerical investigation of airfoil instability noise with leading edge serrations. 22nd AIAA/CEAS Aeroacoustics Conference, Lyon, France, 2016, 1–23.Google Scholar
- Geyer T, Sarradj E, Fritzsche C. Silent owl flight: Acoustic wind tunnel measurements on prepared wings. 18th AIAA/CEAS Aeroacoustics Conference, Colorado Springs, USA, 2012, 1–17.Google Scholar
- Geyer T F, Claus V T, Sarradj E. Silent owl flight: The effect of the leading edge comb on the gliding flight noise. 22nd AIAA/CEAS Aeroacoustics Conference, Lyon, France, 2016, 1–12.Google Scholar
- Geyer T F, Wasala S H, Cater J E, Norris S E, Sarradj E. Experimental investigation of leading edge hook structures for wind turbine noise reduction. 22nd AIAA/CEAS Aeroacoustics Conference, Lyon, France, 2016, 1–13.Google Scholar
- Chaitanya P, Narayanan S, Joseph P, Vanderwel C, Kim J W, Ganapathisubramani B. Broadband noise reduction through leading edge serrations on realistic aerofoils. 21st AIAA/CEAS Aeroacoustics Conference, Dallas, USA, 2015, 1–29.Google Scholar
- Chaitanya P, Narayanan S, Joseph P, Kim J W. Leading edge serration geometries for significantly enhanced leading edge noise reductions. 22nd AIAA/CEAS Aeroacoustics Conference, Lyon, France, 2016, 1–19.Google Scholar
- Sakai M, Sunada Y, Rinoie K. Three-dimensional separated flow on a flat plate with leading-edge serrations. 53rd AIAA Aerospace Sciences Meeting, Kissimmee, USA, 2015, 1–13.Google Scholar
- Klän S, Klaas M, Schröder W. The influence of leading edge serrations on the flow field of an artificial owl wing. 28th AIAA Applied Aerodynamics Conference, Chicago, USA, 2010, 1–9.Google Scholar