Influence of Spanwise Boundary Conditions on Slat Noise Simulations
Influence of Spanwise Boundary Conditions on Slat Noise Simulations
复制标题
展向边界条件对缝翼噪声模拟的影响
DOI：
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
P. Buning
中科院分区：
文献类型：
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作者：
D. Lockard;Meelan Choudhari;P. Buning
30 P/30 N增升系统的缝翼噪声是通过用OVERFLOW代码结合Ffowcs Williams-Hawkings声学解算器进行计算流体动力学模拟来研究的。本文采用两种不同的展向网格来研究展向长度和周期性对近场非定常结构和辐射噪声的影响。具有周期性边界条件的基线网格具有等于收起弦的1/9的短跨度，而另一个长跨度网格在核心基线网格的两侧添加拉伸网格，以允许两端的无粘性表面边界条件。结果表明，使用两种网格获得的近场平均统计是彼此相似的，是辐射噪声的方向性和频谱形状。然而，周期性迫使跨越跨度的所有具有小于一个波长的声波是二维的，而跨度没有任何变化。声波的展向相干性是对实际跨度长度辐射的噪声进行估计所需要的。周期性条件下的模拟需要至少六个缝翼弦的跨度，以允许与宽带缝翼噪声峰值相关的低频的展向变化。即使这样，周期性的全部影响是不清楚的，所以采用网格与精细，中心区域和高度拉伸网格，去滑壁可能是一个更有效的手段捕捉展向去相关的低频声学现象。
The slat noise from the 30P/30N high-lift system is being investigated through computational fluid dynamics simulations with the OVERFLOW code in conjunction with a Ffowcs Williams-Hawkings acoustics solver. In the present study, two different spanwise grids are being used to investigate the effect of the spanwise extent and periodicity on the near-field unsteady structures and radiated noise. The baseline grid with periodic boundary conditions has a short span equal to 1/9th of the stowed chord, whereas the other, longer span grid adds stretched grids on both sides of the core, baseline grid to allow inviscid surface boundary conditions at both ends. The results indicate that the near-field mean statistics obtained using the two grids are similar to each other, as are the directivity and spectral shapes of the radiated noise. However, periodicity forces all acoustic waves with less than one wavelength across the span to be two-dimensional, without any variation in the span. The spanwise coherence of the acoustic waves is what is needed to make estimates of the noise that would be radiated from realistic span lengths. Simulations with periodic conditions need spans of at least six slat chords to allow spanwise variation in the low-frequencies associated with the peak of broadband slat noise. Even then, the full influence of the periodicity is unclear, so employing grids with a fine, central region and highly stretched meshes that go to slip walls may be a more efficient means of capturing the spanwise decorrelation of low-frequency acoustic phenomena.