On the acoustic optimality of leading-edge serration profiles
On the acoustic optimality of leading-edge serration profiles
Leading-edge serrations are studied extensively as a way of reducing leading-edge noise and have been shown to be able to reduce leading-edge noise significantly. Previous experiments showed that different serration geometries have different noise reduction capabilities. However, the optimal serration geometry has not been known. Consequently, there are no guides that can be used at the design stage of serrations. In this paper, by performing an asymptotic analysis, we show that in order to achieve greater noise reduction in the high frequency regime (k1h >> 1, where k1 denotes the streamwise hydrodynamic wavenumber and h half of the root-to-tip amplitude of serrations), the serration profile cannot have stationary points. Therefore, piecewise smooth profiles free of stationary points are more desirable. Moreover, we show that greater noise can be achieved in the high frequency regime by using serrations that are sharper around the non-smooth points. The underlying physical mechanisms of these findings are discussed. Based on these findings, a new type of serration profile is proposed, and analytical model evaluations confirm its improved acoustic performance in the frequency range of interest. At low frequencies, a slight deterioration may be expected, but this is often negligible. To verify the conclusion drawn from the analysis, we perform an experimental study to investigate the acoustic performance of this new serration design. The results show that it is indeed superior than conventional sawtooth serrations. For example, a remarkable 7 dB additional noise reduction is observed in the intermediate frequency range with no perceivable noise increase elsewhere. The trends predicted by the analysis are well validated by the experiment. It is expected that these findings can serve as an essential guide for designing serrations, and lead to more acoustically optimized serration geometries.
1-17
Lyu, Benshuai
6de4a23e-c663-48f9-97ad-ffe2a84e3e52
Ayton, Lorna
e38b13c1-fd88-4b3e-9115-f9fa80c8b538
Paruchuri, Chaitanya
5c1def64-6347-4be3-ac2d-b9f6a314b81d
8 December 2019
Lyu, Benshuai
6de4a23e-c663-48f9-97ad-ffe2a84e3e52
Ayton, Lorna
e38b13c1-fd88-4b3e-9115-f9fa80c8b538
Paruchuri, Chaitanya
5c1def64-6347-4be3-ac2d-b9f6a314b81d
Lyu, Benshuai, Ayton, Lorna and Paruchuri, Chaitanya
(2019)
On the acoustic optimality of leading-edge serration profiles.
Journal of Sound and Vibration, 462, , [1149223].
(doi:10.1016/j.jsv.2019.114923).
Abstract
Leading-edge serrations are studied extensively as a way of reducing leading-edge noise and have been shown to be able to reduce leading-edge noise significantly. Previous experiments showed that different serration geometries have different noise reduction capabilities. However, the optimal serration geometry has not been known. Consequently, there are no guides that can be used at the design stage of serrations. In this paper, by performing an asymptotic analysis, we show that in order to achieve greater noise reduction in the high frequency regime (k1h >> 1, where k1 denotes the streamwise hydrodynamic wavenumber and h half of the root-to-tip amplitude of serrations), the serration profile cannot have stationary points. Therefore, piecewise smooth profiles free of stationary points are more desirable. Moreover, we show that greater noise can be achieved in the high frequency regime by using serrations that are sharper around the non-smooth points. The underlying physical mechanisms of these findings are discussed. Based on these findings, a new type of serration profile is proposed, and analytical model evaluations confirm its improved acoustic performance in the frequency range of interest. At low frequencies, a slight deterioration may be expected, but this is often negligible. To verify the conclusion drawn from the analysis, we perform an experimental study to investigate the acoustic performance of this new serration design. The results show that it is indeed superior than conventional sawtooth serrations. For example, a remarkable 7 dB additional noise reduction is observed in the intermediate frequency range with no perceivable noise increase elsewhere. The trends predicted by the analysis are well validated by the experiment. It is expected that these findings can serve as an essential guide for designing serrations, and lead to more acoustically optimized serration geometries.
Text
1-s2.0-S0022460X19304857-main
- Accepted Manuscript
More information
Accepted/In Press date: 21 August 2019
e-pub ahead of print date: 29 August 2019
Published date: 8 December 2019
Identifiers
Local EPrints ID: 433818
URI: http://eprints.soton.ac.uk/id/eprint/433818
ISSN: 0022-460X
PURE UUID: 5e0bc918-c0fe-496a-a57d-a72e81729fec
Catalogue record
Date deposited: 04 Sep 2019 16:30
Last modified: 16 Mar 2024 08:10
Export record
Altmetrics
Contributors
Author:
Benshuai Lyu
Author:
Lorna Ayton
Download statistics
Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.
View more statistics