Aerodynamic and Aeroacoustic characterisation of tip leakage flows

尽管对风扇噪声的研究已有五十多年的历史，但对叶片尖端产生的噪声的机理和理解仍然知之甚少。这主要是因为可能有许多不同的声源机制，也因为非定常流动，因此噪声源，被限制在叶片尖端周围的非常小的区域。该项目概述了一项综合的、以实验为主的工作，旨在更全面地了解、量化和表征导管风扇尖端产生的噪声的机理。为了详细了解翼型尖端附近的流动，将在开放式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。钻井平台的设计代表了该项目最具挑战性的方面之一，是充分了解这些微妙和复杂的流动特征的关键。几种互补的流速测量技术(HWA、LDA、PIV)将被用来全面描述叶片尖端附近的定常和非定常流动。结合这一流动和声学数据，可以从根本上了解与尖端泄漏噪声相关的噪声产生机理，这为制定噪声缓解措施提供了基础。

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.