Aerodynamic and Aeroacoustic characterisation of tip leakage flows

尽管对风扇噪声的研究已经进行了50多年，但人们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噪声源机制，也因为非定常流，因此噪声源，被限制在叶尖周围非常小的区域内。该项目概述了一个综合的，主要是实验性的工作，旨在理解，量化和更全面地描述管道风扇尖端产生的噪音机制。为了详细了解翼型尖端附近的流动情况，将在开放射流风洞中对靠近刚性壁面的单个非旋转翼型进行详细的流动和非定常表面压力测量。钻机的设计是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）来全面表征叶尖附近的定常和非定常流动。将这些流动和声学数据结合起来，可以对与叶尖泄漏噪声相关的噪声产生机制有一个基本的了解，这为制定降噪措施提供了基础。

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.