Numerical Investigation of Three-dimensional Aeroacoustic Characteristics of Owl-inspired Trailing-edge Fringes

Rong, Jiaxin; H, Liu

doi:10.1007/s42235-022-00311-z

Cited by 1 publication

(24 citation statements)

References 54 publications

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“…Furthermore, the TE fringes were modeled ideally with a uniform distribution aligned with the incoming airflow without consideration of the complexity of the 3D features. Such simplifications have been confirmed to be reasonable in previous studies [29,30,[38][39][40][41], allowing us to focus on the essential aeroacoustic mechanisms of TE fringes. Furthermore, the length, width, and interval of the fringes (table 1) were identical to those employed in our previous studies [30], determined by the values of real fringes, and it has been shown that the fringes with this set of parameters are effective in reducing aerodynamic noise induced by single-feather models.…”

Section: Owl Wing-based Models With and Without Te Fringessupporting

confidence: 72%

“…We found that TE fringes can passively control three-dimensional (3D) turbulent fluctuations in the vicinity of the TE, resulting in remarkable sound reductions throughout the space (e.g. 5-6 dB in the dominant directions of sound propagation [30]).…”

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

“…The TE fringes of the three owl wing morphologies have been recently recognized as a promising biomimetic device for reducing aerodynamic noise caused by fluid machinery [27,28], as well as providing a solution to the trade-off between aerodynamic force production and sound reduction [29,30]. The TE fringes are microstructures observed on the TEs of owl feathers (figures 1(a) and (b)) and can control TE flows in terms of vortical features and flow fluctuations [30]. In 1991, Howe [31,32] conducted theoretical investigations of the aerodynamic noise induced by fringes with two different geometries, serrated [31] and sawtooth [32], and derived formulas of sound reductions for the two types of fringes.…”

Section: Introductionmentioning

confidence: 99%

“…The mechanism for flexible fringes was thought to be associated with the mitigation of cross-flow intensity [35] and suppression of TE vortices [36]. In our previous work [29,30], we extensively investigated the aeroacoustic mechanisms of TE fringes using owl-inspired singlefeather models [37] at a low Reynolds number (Re) of 6000. We found that TE fringes can passively control three-dimensional (3D) turbulent fluctuations in the vicinity of the TE, resulting in remarkable sound reductions throughout the space (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Trailing-edge fringes enable robust aerodynamic force production and noise suppression in an owl wing model

Rong,

Jiang,

Murayama

et al. 2023

Bioinspir. Biomim.

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As one of the unique owl-wing morphologies, trailing-edge (TE) fringes are believed to play a critical role in the silent flight of owls and have been widely investigated using idealized single/tandem airfoils. However, the effect of TE fringes and associated mechanisms on the aeroacoustics of owl wings, which feature curved leading edges, wavy TEs, and several feather slots at the wingtips, have not yet been addressed. In this study, we constructed two 3D owl wing models, one with and one without TE fringes, based on the geometric characteristics of a real owl wing. Large-eddy simulations and the Ffowcs Williams‒Hawkings analogy were combined to resolve the aeroacoustic characteristics of the wing models. Comparisons of the computed aerodynamic forces and far-field acoustic pressure levels demonstrate that the fringes on owl wings can robustly suppress aerodynamic noise while sustaining aerodynamic performance comparable to that of a clean wing. By visualizing the near-field flow dynamics in terms of flow and vortex structures as well as flow fluctuations, the mechanisms of TE fringes in owl wing models are revealed. First, the TE fringes on owl wings are reconfirmed to robustly suppress flow fluctuations near the TE by breaking up large TE vortices. Second, the fringes are observed to effectively suppress the shedding of wingtip vortices by mitigating the flow interaction between feathers (feather-slot interaction). These complementary mechanisms synergize to enhance the robustness and effectiveness of the TE fringe effects in owl wing models, in terms of aerodynamic force production and noise suppression. This study thus deepens our understanding of the role of TE fringes in real owl flight gliding and points to the validity and feasibility of employing owl-inspired TE fringes in practical applications of low-noise fluid machinery.

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