Research on Noise Reduction of Air-conditioner based on the Acoustic Analysis using Large Eddy Simulation

基于大涡模拟声学分析的空调降噪研究

基本信息

批准号：
09555065
负责人：
MIYAKE Yutaka
金额：
$ 6.98万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
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

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09555065/
关键词：
Turbulent Flow Large-Eddy Simulation Direct Numerical Simulation Aeroacoustics Air conditioner Subgrid Scale Model Computational Fluid Dynamics 騒音

项目摘要

In order to simulate the complicated turbulence flow field concerning to the air-conditioner equipment, we developed a high-order finite difference scheme using the generalized coordinate system. By applying it to a direct simulation of turbulent flow in a wavy channel, we confirmed our scheme showed enough accuracy for our purpose. Furthermore using this DNS databases, a generalized normal stress model (GNS model) was found to be able to predict the flow separation on the wavy wall.To investigate the mechanism of generation of aerodynamic noise and to find an algorithm to reduce the broad band noise emitted from turbulent eddies ; we formulated suitable indices of sound source. In this study, acoustic fields from 2D Cavity flow and rotating vortex pair are reproduced with the direct method proposed by Hardin and Pope. As a result, the sources of propagated sound to the far field is identified by the second time derivative of pressure fluctuation. Based on this index, we examined the acoustic field emitted from wall turbulence. We revealed that the coherent structure of streamwise vortices and hair-pin-like vortices are responsible for turbulent noise. Also some coherent bubble-like structures of acoustic pressure were observed further away from the wall, while the frequency spectra of acoustic field is characterized to be broadband and disorder. Moreover, a numerical experiment to reduce the intensity and source of noise was examined by the control of the vortex structures in near-wall region. As a result, the attenuation of near-wall structure caused the reduction of sound pressure level in far field. Thus we confirmed that the turbulence control technique was also effective for noise reduction.

为了模拟空调设备所涉及的复杂湍流流场，我们开发了一种基于广义坐标系的高阶有限差分格式。通过将其应用于波状通道中湍流的直接模拟，我们确认我们的方案对于我们的目的显示出足够的准确性。此外，利用该DNS数据库，发现广义法向应力模型（GNS模型）能够预测波状壁上的流动分离。研究气动噪声的产生机制并找到一种降低宽带噪声的算法从湍流漩涡中发射出来；我们制定了合适的声源指标。在这项研究中，利用 Hardin 和 Pope 提出的直接方法再现了二维空腔流和旋转涡对的声场。结果，传播到远场的声源可以通过压力波动的二阶时间导数来识别。根据这个指标，我们检查了壁湍流发出的声场。我们揭示了流向涡流和发夹状涡流的相干结构是造成湍流噪声的原因。在远离壁面的地方还观察到了一些相干的气泡状声压结构，而声场频谱呈现宽带且无序的特征。此外，还进行了通过控制近壁区域涡流结构来降低噪声强度和噪声源的数值实验。结果，近壁结构的衰减导致远场声压级降低。因此，我们证实湍流控制技术对于降噪也是有效的。