Experimental Study of Airfoil Leading Edge Combs for Turbulence Interaction Noise Reduction

Geyer, Thomas; Wasala, Sahan; Sarradj, Ennes

doi:10.3390/acoustics2020014

Cited by 11 publications

(11 citation statements)

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“…In this respect it seems important that we have carefully rebuilt the natural shape of the serrations, characterized by twisting and tilting and taper, which Bachmann and Wagner [19] called a first order approach and not used the zero order approach, i.e. use simply-shaped, often symmetric serrations as is done in most studies [5,11,12,15]. The focus of the study was to demonstrate the basics of the novel turning effect.…”

Section: Methodological Considerationsmentioning

confidence: 99%

“…These authors could show that the sources of higher noise levels for high angles of attack stem from the wing tip. Jaworski and Peake [14] speculated that the leading edge comb may play a role in reducing spanwise flow variations due to separation at high angles of attack (α = 24 • , in [5]), thereby reducing the strength of the tip vortex and the associated tip noise [14]. If so, it would, however, not be relevant for the gliding phase.…”

Section: Introductionmentioning

confidence: 99%

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Flow turning effect and laminar control by the 3D curvature of leading edge serrations from owl wing

Muthuramalingam¹,

Talboys²,

Wagner³

et al. 2020

Bioinspir. Biomim.

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This work describes a novel mechanism of laminar flow control of straight and backward swept wings with a comb-like leading edge device. It is inspired by the leading-edge comb on owl feathers and the special design of its barbs, resembling a cascade of complex 3D-curved thin finlets. The details of the geometry of the barbs from an owl feather were used to design a generic model of the comb for experimental and numerical flow studies with the comb attached to the leading edge of a flat plate. Due to the owls demonstrating a backward sweep of the wing during gliding and flapping from live recordings, our examinations have also been carried out at differing sweep angles. The results demonstrate a flow turning effect in the boundary layer inboards, which extends downstream in the chordwise direction over distances of multiples of the barb lengths. The inboard flow-turning effect described here, counteracts the outboard directed cross-span flow typically appearing for backward swept wings. This flow turning behavior is also shown on SD7003 airfoil using precursory LES investigations. From recent theoretical studies on a swept wing, such a way of turning the flow in the boundary layer is known to attenuate crossflow instabilities and delay transition. A comparison of the comb-induced cross-span velocity profiles with those proven to delay laminar to turbulent transition in theory shows excellent agreement, which supports the laminar flow control hypothesis. Thus, the observed effect is expected to delay transition in owl flight, contributing to a more silent flight.

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Section: Methodological Considerationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Flow turning effect and laminar control by the 3D curvature of leading edge serrations from owl wing

Muthuramalingam¹,

Talboys²,

Wagner³

et al. 2020

Bioinspir. Biomim.

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“…In the recent years, a lot of work has been devoted to studying noise reduction achieved by single-wavelength, sinusoidal leading-edge serrations, optimization of their serrationgeometry parameters and inlet conditions to achieve the best noise reduction, and identification of the key non-dimensional parameters and their dependence on the achieved noise reduction. [16][17][18][19][20][21][22][23][24][25] More recently, the idea has been extended to using doublewavelength serrations 26 and more sophisticated serration geometries 27,28 such as chopped-peak and slitted-root, which are shown to provide enhanced noise reduction than the single-wavelength serrations.…”

Section: Introductionmentioning

confidence: 99%

On the use of leading-edge serrations for noise control in a tandem airfoil configuration

et al. 2020

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Passive noise control for a tandem NACA 65-710 airfoil configuration is experimentally investigated by applying leading-edge serrations on the rear airfoil. With a sliding side-plate mechanism that allows the rear airfoil to move in the vertical direction relative to the front airfoil, the position of maximum turbulence interaction noise is first identified from the far-field noise measurements. Subsequently, detailed static surface pressure distribution and unsteady surface pressure fluctuations are acquired to shed more light on the physical phenomenon and underlying noise-reduction mechanism of the leading-edge serrations. The far-field noise measurements confirm that a notable turbulence interaction noise reduction can be achieved from 600 Hz < f < 3000 Hz, agreeing well with the previous literature on the effectiveness of the leading-edge serrations. The near-field hydrodynamic analyses obtained using remote-sensing techniques of the fluctuating pressure fields over the airfoil show that a significant reduction in the surface pressure fluctuation levels up to 20 dB/Hz can be observed at the serrated-tip plane of the rear serrated airfoil close to the leading-edge regions, over the range of frequencies investigated. Although reduction can also be observed on the serrated-root plane, the magnitude is much less significant. The present results suggest that the modification of the unsteady loading on the rear airfoil by the leading-edge serrations plays a crucial role in the reduction of turbulence interaction noise in the tandem airfoil configuration, which may find practical application for noise reduction in aerodynamic systems involving rows of airfoils, such as contra-rotating open rotors and outlet guide vanes.

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“…Also another striking feature observed with dual-wavelength serrations is that as the serration amplitude increases the reductions in noise levels are shifted towards the low frequency regions as marked in Figure 4 followed by an increase in the high frequency range. The shift in the frequency arises due to the earlier disintegration of large incoming turbulent structures into small structures or moves them away from the surface of the airfoil by the amplitude of the multi-wavelength leading edge serrations, thus minimizing the pressure fluctuations on the airfoil surface as reported in Geyer et al 16 Thus, it clearly reveals that by increasing the maximum amplitude of the dual-wavelength serrations, improvement in the broadband noise reductions are possible even at low frequencies, which are difficult to achieve with singlewavelength serrations alone. The acoustic power level spectra of dual-wavelength LE serrations for the same maximum amplitudes are compared with the constituent single ones at various U values in Figure 5.…”

Section: Frequency Characteristicsmentioning

confidence: 89%

On the reductions of aerofoil-turbulence interaction noise through multi-wavelength leading edge serrations

Narayanan

Singh

2020

Proceedings of the Institution of Mechanical Engineers, Part G:

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This paper provides an experimental study into the use of multi-wavelength sinusoidal leading edge ( LE) serrations for enhancing the aerofoil-broadband noise reductions. The noise reduction performances of multi-wavelength serration profiles introduced on a flat plate are compared against those generated by single-wavelength profiles when applied separately. The multi-wavelength leading edge serration is made in such a way that its maximum amplitude is kept same as that of each single-wavelength ones to be compared. The present study reveals that the dual-wavelength serrations provide higher noise reductions over a narrow band of frequencies as compared to single and triple wavelength ones. Further, it reveals that the noise reduction characteristics of dual-wavelength serrated airfoils are similar to the flat plates. It shows that the baseline plate generate higher noise radiations for all emission angles as compared to leading edge serrated plates, but the common feature among them is the downstream directivity. For the range of frequencies 0.9 to 5 kHz, the highest directivity is seen at an emission angle of 55° for the baseline, while it occurs at 75° for the serrated plates. The dual wavelength serrations generate lowest acoustic radiations as compared to single and triple ones for all the emission angles. Also, it is noticed that the radiation levels of the dual serrations decrease with increase in amplitude of the serration, which shows that the longer dual serrations generate lowest acoustic radiations. Thus, the present study illustrates that the dual wavelength leading edge serrations act as the best passively modified serration profiles for achieving the highest noise reductions over a wide range of frequencies as compared to single and triple wavelength ones.

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Experimental Study of Airfoil Leading Edge Combs for Turbulence Interaction Noise Reduction

Cited by 11 publications

References 44 publications

Flow turning effect and laminar control by the 3D curvature of leading edge serrations from owl wing

Flow turning effect and laminar control by the 3D curvature of leading edge serrations from owl wing

On the use of leading-edge serrations for noise control in a tandem airfoil configuration

On the reductions of aerofoil-turbulence interaction noise through multi-wavelength leading edge serrations

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