Noise Generation and Its Control of Discrete Frequency Noise Emitted from Aerofoils in Consideration of Flow Transition and Large Scaled Coherent Structures

考虑流动过渡和大规模相干结构的翼型离散频率噪声的产生及其控制

基本信息

批准号：
14550163
负责人：
TANAKA Shuji
金额：
$ 1.73万
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：
2002
资助国家：
日本
起止时间：
2002 至 2003
项目状态：
已结题

项目摘要

It is well known that a discrete frequency noise is emitted even from the well-designed aerofoils for practical use in a uniform flow under some specific conditions, but the mechanism of the noise generation is not clear yet. In this research, coherent flow structures near conventional aerofoils have been investigated to study the mechanism of the noise generation as well as to obtain useful informations for its control. The following three coherent flow structures are considered : (a)a coherent flow due to transition from the laminar to the turbulent in a boundary layer, (2)a coherent flow due to a local separation on an aerofoil surface, (3)a large scaled turbulent coherent flow structure formed in the wake region of an aerofoil. The velocity fields around and behind test aerofoils were obtained and analyzed with FFT. They were also analyzed with phase-locked averaging technique using the reference signal made from the noise itself. The procedure allows us to identify the coherent flow which causes the discrete frequency noise. The results obtained can be summarized as follows ;1.Any flow separation or any coherent wake flow is not formed for the aerofoil from which discrete frequency noise is emitted. Then, a coherent flow due to a local separation and a coherent wake flow are not the cause of the discrete frequency noise.2.When a discrete frequency noise is emitted, a flow transition appears in the baoudary layer on the pressure surface near the trailing edge of an aerofoil and a coherent flow with clear correlation to the noise occurs there.3.Coherent flow fields appearing near the trailing edge on the pressure surface obtained with the phase-locked averaging technique, which are the cause of a discrete, frequency noise, are similar for many cases with different aerofoil sections, angles of attack and velocities.

众所周知，即使在某些特定条件下均匀的流动中，即使是从设计良好的空气机构中发出离散的频率噪声，但是噪声产生的机理尚不清楚。在这项研究中，已经研究了传统架空层附近的相干流结构，以研究噪声产生的机制，并为其控制获得有用的信息。考虑以下三个相干流结构：（a）由于边界层中从层流到湍流的过渡而引起的连贯的流，（2）由于在空气机层表面上的局部分离而导致相干流，（3）在空气机尾部区域中形成的较大缩放的湍流相干流量。获得了测试钢制周围和后面的速度场并用FFT进行分析。还使用噪声本身制成的参考信号对它们进行分析平均技术分析。该过程使我们能够识别导致离散频率噪声的相干流。所获得的结果可以汇总如下； 1.任何流量分离或任何相干唤醒流量都不会用于发出离散频率噪声的空气机。然后，由于局部分离和连贯的唤醒流引起的连贯的流量并不是导致离散频率噪声的原因。2。当发出离散的频率噪声时，在空气层的尾压边缘附近的压力表面上出现了流动过渡，并在噪声上出现了与噪声相关的相关性，而落后的阶段则是落后的。对于许多具有不同气管段，攻击角度和速度的情况的情况，技术是离散频率噪声的原因。