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An Investigation of the Genaration Mechanism of Discrete Frequency Noise Relating to the Large Scaled Turbulent Organized Structures and Its Noise Control

大型湍流组织结构离散频率噪声产生机制及其噪声控制研究

基本信息

批准号：
09650210
负责人：
TANAKA Shuji
金额：
$ 2.11万
依托单位：
Toyota Technological Institute
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

项目摘要

Flow fields around a two-dimensional flat plate aerofoil emitting discrete frequency noise in a uniform flow have been determined, and the generation mechanism of the noise has been studied.Frequency analysis as well as phase-locked averaging technique were used for determination of flow fields. The wake velocity fields were obtained with I-type and X-type hotwire probes and the fluctuating pressure on the aerofoil surface was measured with small-sized semiconductor pressure transducers mounted in the aerofoil, whereas the sound level of emitted noise were artificially modified by inserting a circular cylinder with a small diameter in the near wake region. The flow details, such as organized structures in a turbulent wake flow as well as fluctuating pressures on the aerofoil surface, have been analyzed quantitatively, from which the generating mechanism of discrete frequency noise has been studied relating to the larged scaled organized structures in a turbulent wake.Clear coherent organized structures in a turbulent wake are confirmed in every case. The sound source of discrete frequency noise are distributed in a narrow region restricted near the traihing edge of the aerofoil. It has been quantitatively confirmed that the sound sources are generated from the fluctuating pressures due to the fluctuating velocities on the aerofoil induced from the turbulent organized structures in the wake. The span-wise correlations of the organized structures in the turbulent wake have a dominant effect on the sound pressure level of the discrete frequency noise.The calibratrion of the sound intensity mesuring system has been made, which shows that the location of the sound source can be determined within the accuracy of 1mm in the three-dimensional space.

本文采用频率分析和锁相平均技术，测量了均匀流场中二维平板翼型的离散频率噪声流场，研究了噪声的产生机理。尾流速度场由I型和X型热线探针获得，翼型表面的脉动压力由安装在翼型中的小型半导体压力传感器测量，而发射噪声的声级通过在近尾流区插入小直径的圆柱体来人为地修改。定量分析了湍流尾流中的组织结构和翼型表面脉动压力等流动细节，研究了与湍流尾流中大尺度组织结构相关的离散频率噪声的产生机理，证实了湍流尾流中清晰的相干组织结构。离散频率噪声的声源分布在机翼后缘附近的一个狭窄区域内。定量地证实了声源是由尾流中的湍流有序结构引起的翼型上的脉动速度引起的脉动压力产生的。湍流尾流中有组织结构的展向相关性对离散频率噪声的声压级有着重要的影响，本文对声强测量系统进行了标定，结果表明，在三维空间中可以确定声源的位置，精度在1mm以内。