Aerodynamic and Aeroacoustic characterisation of tip leakage flows

尽管对风扇噪声的研究已经有50多年的历史，但对叶片尖端产生的噪声的机理和理解仍然知之甚少。这主要是因为可能存在许多不同的声源机制，还因为非定常流以及噪声源仅限于叶尖周围非常小的区域。该项目概述了一个综合的，主要是实验性的工作，旨在更全面地了解，量化和表征的机制产生的噪音在一个管道风扇。为了获得一个详细的了解在翼型尖端附近的流动，详细的流动和非定常表面压力测量将在一个开放的喷气风洞中的一个单一的，非旋转的翼型位于靠近刚性壁。钻机的设计代表了该项目最具挑战性的方面之一，是充分理解这些微妙而复杂的流动特征的关键。将采用几种互补的流速测量技术（HWA、LDA、PIV）来充分模拟叶尖附近的定常和非定常流。结合这些流量和声学数据，可以从根本上了解与叶尖泄漏噪声相关的噪声产生机制，从而为制定噪声缓解措施提供依据。

Despite more than fifty years of research into fan noise, the mechanism and understanding of the noise generated at the blade tip is still poorly understood. This is mainly because there are likely to be a number of different source mechanisms and also because the unsteady flow, and hence the sources of noise, are confined to the very small regions around the blade tip. This project outlines an integrated, predominantly experimental work aimed at understanding, quantifying and characterising more fully the mechanisms of the noise generated at the tip of a ducted fan.To gain a detailed understanding of the flow in the vicinity of the aerofoil tip, detailed flow and unsteady surface pressure measurements will be performed on a single, non-rotating aerofoil located close to a rigid wall in an open jet wind tunnel. The design of the rig, which represents one of the most challenging aspects of the project is key to fully understanding these subtle and complex flow features. Several complementary flow velocity measurement techniques (HWA, LDA, PIV) will be employed to fully characterise the steady and unsteady flow near the blade tip. Combining this flow and acoustic data provides a fundamental understanding into the noise generating mechanisms associated with tip leakage noise, which provides the bases for developing noise mitigation measures.