Optimization of trailing-edge serrations with and without slits for broadband noise reduction

摘要

The single-objective surrogate-based optimization study of the trailing-edge serrations is performed using Ayton's analytical model. The parametric study of the model is provided, and the main effect of the serration amplitude, wavelength and the shape curvature are investigated. The spanwise coherence length of the wall-pressure fluctuations is found to act as a filter for cut-on modes. The surrogate-based optimization problem is solved for serrations with and without slits. For three increasing values of serration wavelength, the optimal shape of serrations smoothly changes from ogee to sawtooth and to sinusoidal or iron-shaped. The noise reduction margin between the best and the worst shape decreases with increasing wavelength. For all the optimal shapes, the noise reduction is largely uniform for f delta/U-0 > 0.63. The effect of slits is found to be additive to the effect of the main shape. It appears mostly after 1000 Hz. For all the cases, the optimum size of slits tends to maximum slit amplitude and minimum slit wavelength. The frequency of maximum noise reduction with slits decreases with an increase in the main serration wavelength. The current study represents a practical approach towards further development of trailing-edge serrations. (C) 2020 Elsevier Ltd. All rights reserved.