Experimental Investigation of Leading Edge Hook Structures for Wind Turbine Noise Reduction

Geyer, Thomas; Wasala, Sahan; Cater, John; Norris, Stuart; Sarradj, Ennes

doi:10.2514/6.2016-2954

Cited by 8 publications

(10 citation statements)

References 15 publications

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“…Recent interest in silent owl flight has led to research in a number of aerofoil adaptations as a way to reduce aerofoil-turbulence interaction noise as discussed by Lilley (1998). The leading-edge comb (Graham 1934) appears as a serration to the leading edge of the wing, and through experimental (Geyer et al 2016;Chaitanya et al 2016) and numerical investigations (Haeri et al 2015;Kim et al 2016) has been seen as an effective way to reduce leading-edge noise. Despite these results, it is still not fully understood why the serrated edge is such an effective way to reduce leading-edge noise, therefore analytic 2 solutions for simple leading-edge interaction noise models are sought to illuminate the physical noise-reduction mechanisms within the flow, and hence aid in designing optimal leading-edge geometries for silent blade operation.…”

Section: Introductionmentioning

confidence: 99%

An analytic solution for the noise generated by gust–aerofoil interaction for plates with serrated leading edges

Ayton

Kim

2018

J. Fluid Mech.

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This paper presents an analytic solution for the sound generated by an unsteady gust interacting with a semi-infinite flat plate with a serrated leading edge in a background steady uniform flow. Viscous and nonlinear effects are neglected. The Wiener–Hopf method is used in conjunction with a non-orthogonal coordinate transformation and separation of variables to permit analytical progress. The solution is obtained in terms of a modal expansion in the spanwise coordinate; however, for low- and mid-range incident frequencies only the zeroth-order mode is seen to contribute to the far-field acoustics, therefore the far-field noise can be quickly evaluated. The solution gives insight into the potential mechanisms behind the reduction of noise for plates with serrated leading edges compared to those with straight edges, and predicts a logarithmic dependence between the tip-to-root serration height and the decrease of far-field noise. The two mechanisms behind the noise reduction are proposed to be an increased destructive interference in the far field, and a redistribution of acoustic energy from low cut-on modes to higher cut-off modes as the tip-to-root serration height is increased. The analytic results show good agreement in comparison with experimental measurements. The results are also compared against nonlinear numerical predictions where good agreement is also seen between the two results as frequency and tip-to-root ratio are varied.

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Section: Introductionmentioning

confidence: 99%

An analytic solution for the noise generated by gust–aerofoil interaction for plates with serrated leading edges

Ayton

Kim

2018

J. Fluid Mech.

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“…In other work, Geyer et al [50] found that serrations mounted to the leading edge of a NASA/Langley LS(1)-0314 aerofoil led to a noise reduction at low frequencies (less rsfs.royalsocietypublishing.org Interface Focus 7: 20160078 than 1.6 kHz), while the noise at high frequencies increased slightly. In contrast with other results [47][48][49], no change in aerodynamic performance was observed by these authors.…”

Section: Serrationsmentioning

confidence: 99%

Features of owl wings that promote silent flight

et al. 2017

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Owls are an order of birds of prey that are known for the development of a silent flight. We review here the morphological adaptations of owls leading to silent flight and discuss also aerodynamic properties of owl wings. We start with early observations (until 2005), and then turn to recent advances. The large wings of these birds, resulting in low wing loading and a low aspect ratio, contribute to noise reduction by allowing slow flight. The serrations on the leading edge of the wing and the velvet-like surface have an effect on noise reduction and also lead to an improvement of aerodynamic performance. The fringes at the inner feather vanes reduce noise by gliding into the grooves at the lower wing surface that are formed by barb shafts. The fringed trailing edge of the wing has been shown to reduce trailing edge noise. These adaptations to silent flight have been an inspiration for biologists and engineers for the development of devices with reduced noise production. Today several biomimetic applications such as a serrated pantograph or a fringed ventilator are available. Finally, we discuss unresolved questions and possible future directions.

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“…Apart from studying natural serrations, the influence on the airflow of simplified artificial serrations was examined (Arndt 1972, Schwind 1973, Klän et al 2010, Hansen et al 2012, Gharali et al 2014, Narayanan et al 2015, Agrawal and Sharma 2016, Geyer et al 2016a. For example, acoustic measurements made in turbulent airflow suggested that artificial serrations reduce noise generation (Narayanan et al 2015, Geyer et al 2016a. Gharali et al (2014) reported a load increment for a serrated case in comparison to a case without serrations and a delay in dynamic stall at high angles of attack.…”

Section: Introductionmentioning

confidence: 99%

Interaction of barn owl leading edge serrations with freestream turbulence

Midmer,

Brücker,

Weger

et al. 2024

Bioinspir. Biomim.

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The silent flight of barn owls is associated with wing and feather specialisations. Three specialfeatures are known: a serrated leading edge that is formed by free-standing barb tips whichappears as a comb-like structure, a soft dorsal surface, and a fringed trailing edge. We useda model of the leading edge comb with 3D-curved serrations that was designed based on 3Dmicro-scans of rows of barbs from selected barn-owl feathers. The interaction of the flow withthe serrations was measured with Particle-Image-Velocimetry in a flow channel at uniform steadyinflow and was compared to the situation of inflow with freestream turbulence, generated fromthe turbulent wake of a cylinder placed upstream. In steady uniform flow, the serrations causedregular velocity streaks and a flow turning effect. When vortices of different size impacted theserrations, the serrations reduced the flow fluctuations downstream in each case, exemplifiedby a decreased root-mean-square value of the fluctuations in the wake of the serrations. Thisattenuation effect was stronger for the spanwise velocity component, leading to an overall flowhomogenization. Our findings suggest that the serrations of the barn owl provide a passive flowcontrol leading to reduced leading-edge noise when flying in turbulent environments.

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Experimental Investigation of Leading Edge Hook Structures for Wind Turbine Noise Reduction

Cited by 8 publications

References 15 publications

An analytic solution for the noise generated by gust–aerofoil interaction for plates with serrated leading edges

An analytic solution for the noise generated by gust–aerofoil interaction for plates with serrated leading edges

Features of owl wings that promote silent flight

Interaction of barn owl leading edge serrations with freestream turbulence

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