Abstract
Owls are widely known for their silent flight, which is attributed to their unique wing morphologies comprising leading-edge (LE) serrations, trailing-edge (TE) fringes, and a velvety surface. The aeroacoustic characteristics of owl-inspired TE fringes have been widely investigated through two-dimensional (2D) modeling, but remain yet poorly studied in association with their three-dimensional (3D) effects. Here, we present a numerical study of the 3D aeroacoustic characteristics of owl-inspired TE fringes in which we combined large-eddy simulations (LES) with the Ffowcs Williams‒Hawkings analogy. We constructed a clean wing model and three wing models with TE fringes that were distributed differently spanwise. The aerodynamic forces and 3D acoustic characteristics reveal that, like the 2D results of our previous studies, the 3D TE fringes enable remarkable sound reduction spatially while having aerodynamic performance comparable to the clean model. Visualizations of the near-field 3D flow structures, vortex dynamics, and flow fluctuations show that TE fringes can robustly alter the 3D flow by breaking 3D TE vortices into small eddies and mitigating 3D flow fluctuations. Particularly, it is verified that TE fringes alter spanwise flows, thus dominating the 3D aeroacoustic characteristics in terms of passive flow control and flow stabilizations, whereas the fringes are inefficient in suppressing the acoustic sources induced by wingtip vortices. Moreover, the TE fringes distributed at midspan have better acoustic performance than those in the vicinity of the wingtip, indicating the importance of a spanwise distribution in enhancing aeroacoustic performance.
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The data that support the findings of this study are available from the corresponding author upon reasonable request.
References
Gruschka, H. D., Borchers, I. U., & Coble, J. G. (1971). Aerodynamic noise produced by a gliding owl. Nature, 233, 409–411.
Kroeger, R. A., & Gruschka, H. D. (1972). Low speed aerodynamics for ultra-quiet flight. Tullahoma: University of Tennessee Space Institute.
Sarradj, E., Fritzsche, C., & Geyer, T. (2011). Silent owl flight: Bird flyover noise measurements. AIAA Journal, 49, 769–779.
Chen, K., Liu, Q. P., Liao, G. H., Yang, Y., Ren, L. Q., Yang, H. X., & Chen, X. (2012). The sound suppression characteristics of wing feather of owl (Bubo bubo). Journal of Bionic Engineering, 9, 192–199.
Wagner, H., Weger, M., Klaas, M., & Schroder, W. (2017). Features of owl wings that promote silent flight. Interface Focus, 7, 20160078.
Karabasov, S., Ayton, L., Wu, X. S., & Afsar, M. (2019). Advances in aeroacoustics research: Recent developments and perspectives. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 377, 20190390.
Jaworski, J. W., & Peake, N. (2020). Aeroacoustics of silent owl flight. Annual Review of Fluid Mechanics, 52, 395–420.
Bachmann, T., & Wagner, H. (2011). The three-dimensional shape of serrations at barn owl wings: Towards a typical natural serration as a role model for biomimetic applications. Journal of Anatomy, 219, 192–202.
Narayanan, S., Chaitanya, P., Haeri, S., Joseph, P., Kim, J. W., & Polacsek, C. (2015). Airfoil noise reductions through leading edge serrations. Physics of Fluids, 27, 025109.
Ayton, L. J., & Chaitanya, P. (2019). An analytical and experimental investigation of aerofoil–turbulence interaction noise for plates with spanwise-varying leading edges. Journal of Fluid Mechanics, 865, 137–168.
Turner, J. M., & Kim, J. W. (2019). On the universal trends in the noise reduction due to wavy leading edges in aerofoil–vortex interaction. Journal of Fluid Mechanics, 871, 186–211.
Polacsek, C., Cader, A., Buszyk, M., Barrier, R., Gea-Aguilera, F., & Posson, H. (2020). Aeroacoustic design and broadband noise predictions of a fan stage with serrated outlet guide vanes. Physics of Fluids, 32, 107107.
Wang, L., Liu, X. M., & Li, D. (2021). Noise reduction mechanism of airfoils with leading-edge serrations and surface ridges inspired by owl wings. Physics of Fluids, 33, 015123.
Bachmann, T., Wagner, H., & Tropea, C. (2012). Inner vane fringes of barn owl feathers reconsidered: Morphometric data and functional aspects. Journal of Anatomy, 221, 1–8.
Zhu, W. J., & Shen, W. Z. (2016). LES tests on airfoil trailing edge serration. Journal of Physics: Conference Series, 753, 022062.
Vad, J., Koscsó, G., Gutermuth, M., Kasza, Z., Tábi, T., & Csörgo, T. (2006). Study of the aero-acoustic and aerodynamic effects of soft coating upon airfoil. JSME International Journal Series C, 49, 648–656.
Ayton, L. J., Colbrook, M. J., Geyer, T. F., Chaitanya, P., & Sarradj, E. (2021). Reducing aerofoil–turbulence interaction noise through chordwise-varying porosity. Journal of Fluid Mechanics, 906, A1.
Zhou, P., Zhong, S. Y., & Zhang, X. (2021). On the effect of velvet structures on trailing edge noise: Experimental investigation and theoretical analysis. Journal of Fluid Mechanics, 919, A11.
Graham, R. R. (1934). The silent flight of owls. The Aeronautical Journal, 38, 837–843.
Lilley, G. (1998). A study of the silent flight of the owl. In 4th AIAA/CEAS aeroacoustics conference, Toulouse, France.
Bachmann, T., Klan, S., Baumgartner, W., Klaas, M., Schroder, W., & Wagner, H. (2007). Morphometric characterisation of wing feathers of the barn owl Tyto alba pratincola and the pigeon Columba livia. Frontiers in Zoology, 4, 23.
Choi, H., Park, H., Sagong, W., & Lee, S.-I. (2012). Biomimetic flow control based on morphological features of living creatures. Physics of Fluids, 24, 121302.
Celik, A., Mayer, Y. D., & Azarpeyvand, M. (2021). On the aeroacoustic characterization of a robust trailing-edge serration. Physics of Fluids, 33, 075120.
Hasheminasab, S. M., Karimian, S. M. H., Noori, S., Saeedi, M., & Morton, C. (2021). Experimental investigation of the wake dynamics for a NACA0012 airfoil with a cut-in serrated trailing-edge. Physics of Fluids, 33, 055122.
Wei, Y. L., Qian, Y. J., Bian, S. Y., Xu, F., & Kong, D. Y. (2021). Experimental study of the performance of a propeller with trailing-edge serrations. Acoustics Australia, 49, 305–316.
Howe, M. S. (1991). Aerodynamic noise of a serrated trailing edge. Journal of Fluids and Structures, 5, 33–45.
Howe, M. S. (1991). Noise produced by a sawtooth trailing edge. The Journal of the Acoustical Society of America, 90, 482–487.
Jones, L. E., & Sandberg, R. D. (2012). Acoustic and hydrodynamic analysis of the flow around an aerofoil with trailing-edge serrations. Journal of Fluid Mechanics, 706, 295–322.
Gruber, M., Joseph, P., & Azarpeyvand, M. (2013). An experimental investigation of novel trailing edge geometries on airfoil trailing edge noise reduction. In 19th AIAA/CEAS Aeroacoustics Conference, Berlin, Germany, Paper No. AIAA-2013–2011.
Azarpeyvand, M., Gruber, M., & Joseph, P. (2013). An analytical investigation of trailing edge noise reduction using novel serrations. In 19th AIAA/CEAS Aeroacoustics Conference, Berlin, Germany, Paper No. AIAA-2013-2009.
Avallone, F., Pröbsting, S., & Ragni, D. (2016). Three-dimensional flow field over a trailing-edge serration and implications on broadband noise. Physics of Fluids, 28, 117101.
Ragni, D., Avallone, F., van der Velden, W. C. P., & Casalino, D. (2018). Measurements of near-wall pressure fluctuations for trailing-edge serrations and slits. Experiments in Fluids, 60, 6.
Avallone, F., van der Velden, W. C. P., Ragni, D., & Casalino, D. (2018). Noise reduction mechanisms of sawtooth and combed-sawtooth trailing-edge serrations. Journal of Fluid Mechanics, 848, 560–591.
Prigent, S. L., Buxton, O. R. H., & Bruce, P. J. K. (2017). Coherent structures shed by multiscale cut-in trailing edge serrations on lifting wings. Physics of Fluids, 29, 075107.
Thomareis, N., & Papadakis, G. (2017). Effect of trailing edge shape on the separated flow characteristics around an airfoil at low Reynolds number: A numerical study. Physics of Fluids, 29, 014101.
Zhou, P., Liu, Q., Zhong, S. Y., Fang, Y., & Zhang, X. (2020). A study of the effect of serration shape and flexibility on trailing edge noise. Physics of Fluids, 32, 127114.
Rong, J. X., & Liu, H. (2022). Aeroacoustic interaction between owl-inspired trailing-edge fringes and leading-edge serrations. Physics of Fluids, 34, 011907.
Gelot, M. B. R., & Kim, J. W. (2020). Effect of serrated trailing edges on aerofoil tonal noise. Journal of Fluid Mechanics, 904, A30.
Turner, J. M., & Kim, J. W. (2020). Effect of spanwise domain size on direct numerical simulations of airfoil noise during flow separation and stall. Physics of Fluids, 32, 065103.
Rao, C., & Liu, H. (2020). Effects of Reynolds number and distribution on passive flow control in owl-inspired leading-edge serrations. Integrative and Comparative Biology, 60, 1135–1146.
Rao, C., Ikeda, T., Nakata, T., & Liu, H. (2017). Owl-inspired leading-edge serrations play a crucial role in aerodynamic force production and sound suppression. Bioinspiration & Biomimetics, 12, 046008.
Rao, C., & Liu, H. (2018). Aerodynamic robustness in owl-inspired leading-edge serrations: A computational wind-gust model. Bioinspiration & Biomimetics, 13, 056002.
Li, D., Liu, X. M., Hu, F. J., & Wang, L. (2020). Effect of trailing-edge serrations on noise reduction in a coupled bionic aerofoil inspired by barn owls. Bioinspiration & Biomimetics, 15, 016009.
Ikeda, T., Ueda, T., Nakata, T., Noda, R., Tanaka, H., Fujii, T., & Liu, H. (2018). Morphology effects of leading-edge serrations on aerodynamic force production: An integrated study using PIV and force measurements. Journal of Bionic Engineering, 15, 661–672.
Liu, H., & Aono, H. (2009). Size effects on insect hovering aerodynamics: An integrated computational study. Bioinspiration & Biomimetics, 4, 015002.
Winzen, A., Roidl, B., Klän, S., Klaas, M., & Schröder, W. (2014). Particle-image velocimetry and force measurements of leading-edge serrations on owl-based wing models. Journal of Bionic Engineering, 11, 423–438.
Nicoud, F., & Ducros, F. (1999). Subgrid-scale stress modelling based on the square of the velocity gradient tensor. Flow, Turbulence and Combustion, 62, 183–200.
ANSYS Fluent: Theory guide, release 16.0. (2015). ANSYS, Inc., Canonsburg, PA.
Lighthill, M. J., & Newman, M. H. A. (1952). On sound generated aerodynamically I. General theory. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 211, 564–587.
Lighthill, M. J. (1954). On sound generated aerodynamically II. Turbulence as a source of sound. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 222, 1–32.
Curle, N., & Lighthill, M. J. (1955). The influence of solid boundaries upon aerodynamic sound. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 231, 505–514.
Ffowcs Williams, J. E., & Hawkings, D. L. (1969). Sound generation by turbulence and surfaces in arbitrary motion. Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences, 264, 321–342.
Ffowcs Williams, J. E., & Hawkings, D. L. (1969). Theory relating to the noise of rotating machinery. Journal of Sound and Vibration, 10, 10–21.
Garcia-Sagrado, A., & Hynes, T. (2012). Wall pressure sources near an airfoil trailing edge under turbulent boundary layers. Journal of Fluids and Structures, 30, 3–34.
Shi, Y. J., & Kollmann, W. (2021). Wall-modeled large-eddy simulation of a trailing-edge serration–finlet configuration. AIP Advances, 11, 065222.
Wang, L., & Liu, X. M. (2022). Aeroacoustic investigation of asymmetric oblique trailing-edge serrations enlighted by owl wings. Physics of Fluids, 34, 015113.
Liu, X., Kamliya Jawahar, H., Azarpeyvand, M., & Theunissen, R. (2017). Aerodynamic performance and wake development of airfoils with serrated trailing-edges. AIAA Journal, 55, 3669–3680.
Brooks, T. F. (1989). Airfoil self-noise and prediction. NASA-RP-1218.
Lee, S., Ayton, L., Bertagnolio, F., Moreau, S., Chong, T. P., & Joseph, P. (2021). Turbulent boundary layer trailing-edge noise: Theory, computation, experiment, and application. Progress in Aerospace Sciences, 126, 100737.
Bachmann, T., Emmerlich, J., Baumgartner, W., Schneider, J. M., & Wagner, H. (2012). Flexural stiffness of feather shafts: Geometry rules over material properties. The Journal of Experimental Biology, 215, 405–415.
Talboys, E., Geyer, T. F., & Brücker, C. (2019). An aeroacoustic investigation into the effect of self-oscillating trailing edge flaplets. Journal of Fluids and Structures, 91, 102598.
Anyoji, M., Wakui, S., Hamada, D., & Aono, H. (2018). Experimental study of owl-like airfoil aerodynamics at low Reynolds numbers. Journal of Flow Control, Measurement and Visualization, 06, 185–197.
Aono, H., Kondo, K., Nonomura, T., Anyoji, M., Oyama, A., Fujii, K., & Yamamoto, M. (2020). Aerodynamics of owl-like wing model at low Reynolds numbers. Transactions of the Japan Society for Aeronautical and Space Sciences, 63, 8–17.
Acknowledgements
This work was partly supported by a Grant-in-Aid for Scientific Research of KAKENHI, Japan Society for the Promotion of Science (Grant No. 19H00750). J.R. acknowledges financial support from the Japanese Government through a MEXT scholarship.
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Rong, J., Liu, H. Numerical Investigation of Three-dimensional Aeroacoustic Characteristics of Owl-inspired Trailing-edge Fringes. J Bionic Eng 20, 1103–1120 (2023). https://doi.org/10.1007/s42235-022-00311-z
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DOI: https://doi.org/10.1007/s42235-022-00311-z