Concave serrations on broadband trailing edge noise reduction

Abstract

The far-field noise and flow field of a novel curved trailing-edge serration (i.e. iron-shaped) are investigated. Spectra of the far-field broadband noise, directivity plots and the flow-field over the iron-shaped serration are obtained from numerical computations performed using a compressible Lattice-Boltzmann solver. The new design is compared to a conventional trailing-edge serration with a triangular geometry retrofitted to a NACA 0018 airfoil at zero degree angle of attack. The iron-shaped geometry is found to reduce far-field broadband noise of approximately 2 dB more than the conventional sawtooth serration for chord-based Strouhal numbers St c < 15. It is found that the larger noise reduction achieved by the iron-shaped trailing-edge serration is due to the mitigation of the scattered noise at the root, effect obtained by mitigating the interaction between the two sides of the serration, by delaying toward the tip both the outward and the downward flow motions present at the root.

Comparison between analog and digital phased microphone arrays for aeroacoustic measurements

“…The experiment focuses on the measurement of the turbulent boundary layer trailing-edge (TBL-TE) noise of an airfoil in wind-tunnel tests, which is the dominant noise source for modern wind turbines in normal operational conditions [21,22]. Trailing-edge serrations [23][24][25][26][27][28][29][30][31] are one of the most effective passive noise-reduction measures for turbulent-boundary-layer trailing-edge (TBL-TE) noise, currently being applied by wind turbine industry [21,[25][26][27][28]32]. Therefore, the current object of study is the TBL-TE noise of two different airfoil models (NACA 0012 and NACA 0018) equipped with two different serration geometries, as well as of the straight trailing edge case as a baseline.…”

A semi-analytical noise prediction model for airfoils with serrated trailing edges

“…E-mail addresses: yannick.mayer@bristol.ac.uk (Y. Mayer), hasan.kj@bristol.ac.uk (H. Kamliya Jawahar), bl362@cam.ac.uk (B. Lyu), m.azarpeyvand@bristol.ac.uk (M. Azarpeyvand). sinusoidal and sawtooth serrations, more recently, novel serrations such as slitted, slittedsawtooth and sawtooth-sinusoidal serrations [8] as well as concave serrations [9,10] were examined in order to further increase the noise reduction capabilities of the serration technology. Several experimental studies by Dassen et al [11], Moreau et al [12], Gruber [13] and Leon et al [14], Oerlemans et al [15] among others have also examined the sound reduction potential of serrated trailing edges, while Liu et al [16] and Chong et al [17] have investigated the aerodynamic changes due to the presence of serrations.…”