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首页> 外文会议>AIAA 32nd Aerospace Sciences Meeting Exhibit January 10-13, 1994/Reno, NV >Laminar boundary layer aero-acoustic instabilities
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Laminar boundary layer aero-acoustic instabilities

机译：层流边界层气声不稳定性

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Instabilities which result from a coupling of aerodynamics and acoustics on isolated aerofoils are an importnat source of excess noise in several practical aeroacoustic problems. The effects are observed on a veriety of rotors, and are also important for fixed wing aircraft self noise. Previous experiments have shown that such instabilities can generate excess discrete frequency noise from the aerofil greater than 20dB. The two principal mechanisms are noise due to trailing edge thickness (TET) vortex shedding into the wake, and laminar boundary layer (LBL) instability noise. An analysis of these phenomena has provided new insights into the mechanisms involved. Previous theoretical descriptions of the LBL noise are shown to be incomplete. Analysis of the experimental data demonstrates that the LBL noise is controlled by an instability of a long laminar separation bubble on the aerofoil pressure surface. Simple new empirical formulas for predicting the occurrence of the TET noise have also been derived. Preliminary results from new experiments which capture the LBL noise in a wind tunnel are reported. These have shown several unexpected features. The results also have implications for the prediction of transition on aerofoils at moderate Reynolds numbers.
机译：在孤立的翼型件上将空气动力学和声学耦合在一起所导致的不稳定性是一些实际的空气声学问题中过量噪声的重要来源。可以在多种旋翼上观察到这种影响，这对于固定翼飞机的自噪声也很重要。先前的实验表明，这种不稳定性会从气雾剂中产生大于20dB的过量离散频率噪声。两种主要机制是由于后缘厚度（TET）涡旋脱落而进入尾流的噪声，以及层流边界层（LBL）的不稳定性噪声。对这些现象的分析为所涉及的机制提供了新的见解。 LBL噪声的先前理论描述显示不完整。对实验数据的分析表明，LBL噪声受机翼压力表面上较长的层流分离气泡的不稳定性控制。还推导了用于预测TET噪声发生的简单新的经验公式。报告了捕获风洞中的LBL噪声的新实验的初步结果。这些显示了一些意外的功能。该结果也对中等雷诺数的机翼过渡的预测具有影响。

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