3D calculations of aerofoil-turbulence interaction noise and the effect of wavy leading edges
3D calculations of aerofoil-turbulence interaction noise and the effect of wavy leading edges
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DOI：
10.2514/6.2014-2325
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发表时间：
2014-06
期刊：
影响因子：
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通讯作者：
S. Haeri;J. Kim;S. Narayanan;P. Joseph
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文献类型：
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作者：
S. Haeri;J. Kim;S. Narayanan;P. Joseph
本文用数值方法研究了波浪型前缘齿形对减小翼型-湍流相互作用噪声的影响。以平板翼型为研究对象，提出了一种通过流内边界条件综合产生湍流的先进方法，该方法特别适用于三维气动声学模拟。基于涡流叠加的合成流入湍流发生器几乎没有杂散噪声，并且可以优化生成任何所需的速度谱，如冯·卡门谱。定义了翼型前缘脉动压力的相关长度尺度，发现前缘齿形有效地减小了这一相关长度尺度。另外，假设通过增加锯齿幅值来提高降噪效果会达到最大值，超过此最大值后，再增加锯齿幅值就不能进一步提高锯齿的降噪特性。降噪机制进一步与锯齿前缘附近的涡旋结构变形有关，并与沿边缘计算的相位和相干谱相一致。
In this paper, wavy leading edge serrations for reduction of the aerofoil-turbulence interaction (ATI) noise are investigated numerically. A flat-plate aerofoil is considered and an advanced method is suggested to synthetically generate flow turbulence via an in-flow boundary condition that is particularly suitable for three-dimensional aeroacoustic simulations. The synthetic inflow turbulence generator which is based on superposition of eddies is practically free of spurious noise and can be optimised to generate any required velocity spectra such as the von Karman spectrum. A correlation length scale is defined for the fluctuating pressure on the leading edge of the aerofoil, and it is found that the leading edge serrations effectively reduce this correlation length scale. In addition, it is postulated that increasing the noise reduction by increasing the serration amplitude will reach a maximum beyond which, no further enhancement in noise reduction characteristics of the serration can be achieved by increasing the serration amplitude. The noise reduction mechanism is further related to the deformation of vortical structures near the leading edge of serrations which is explained in detail and is consistent with calculated phase and coherence spectra along the leading edges.