管道内有流声阻抗边界条件的对比研究
首发时间:2014-12-29
摘要:管道声衬是一种十分重要的噪声传播控制技术,广泛应用于航空发动机和其它各种流体机械。针对如何考虑气流边界层对声衬作用影响这一问题, 研究分析了2种等效声阻抗边界条件,即薄边界层假设下的Ingard-Myers边界条件和一种新近提出的引入边界层名义厚度的阻抗边界条件。方法是在给定的点声源入射条件下,对比使用等效声阻抗边界条件和求解线化欧拉方程的管内声场解,后者在给定速度型下能直接包含边界层对于声传播的影响。结果表明:与直接考虑边界层的计算相比,Ingard-Myers边界条件会引起明显的声场计算偏差; 而另一种等效声阻边界条件在经过适当修改后, 即以边界层位移厚度取代名义厚度, 从而在相同位移厚度下进行对比则能给出一致相符的结果。
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A comparative invesigation of impedance boundary conditions with flow in a duct
Abstract:Acoustic liners are widely used in ducts with flow in order to reduce noise emission of the aero-engine and many other turbomachineries. In this paper, a comparative investigation is carried out to evaluate two equivalent impedance boundary conditions for describing the acoustic liner function in presence of flow: the Ingard-Myers boundary condition based on thin boundary layer assumption and that newly proposed to include the effect of finite boundary layer thickness. The acoustic pressures in the duct outlet obtained with the equivalent boundary conditions are compared with the results from solving the linearized Euler equations (LEEs) by the finite element method. The later approach can directly incorporate the boundary layer profile. It is shown that the Ingard-Myers boundary condition gives the sound pressure results that are in obvious dicrepancy with the results of the LEEs. When using the displacement thickness instead of the norminal thickness as the characteristic length scale of the boundary layer, the newly-proposed equivalent impedance boundary condition leads to consistent results with the predictions from the LEEs.
Keywords: boundary layer impedance boundary condition linearized Euler's equations finite element model
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