Non-Reflective Boundary Conditions for Computational Fluid Dynamics of External Flows

在声传播的数值预测中经常使用非反射边界条件，以防止来自区域边缘的虚假数值反射污染感兴趣的结果。在气动CFD，特别是工业标准RAN CFD代码中的应用一直是零散的，重点是管道内声学预测。最近与罗尔斯-罗伊斯联合开展的工作表明，将非反射边界条件应用于气动和声学应用的外部流动CFD计算可能具有显著的优势。拟开展的研究包括：1.考察CFD和声学规范中使用的非反射边界条件的范围。2.筛选和测试最有希望应用于气动CFD的候选对象，考虑到复杂的几何形状和网格、非均匀平均流动以及(在区域出口处)涡流扰动的存在等问题。3.提出、开发、实现和验证了工业CFD程序中新的非反射边界条件。本课程的主要应用目标是计算喷气发动机的进气和排气空气动力学和空气声学性能，但稍后可能会有机会考虑其他应用程序(如海洋CFD)。该项目由劳斯莱斯提供支持，他将就行业要求提供指导，并就实施提供支持和建议。关键词：非反射边界条件、本征模、波分裂、完全匹配层、海绵层、无限元、卡尔德隆投影器

Non-reflective boundary conditions are regularly used in numerical predictions of sound propagation to prevent spurious numerical reflections from the edges of the domain contaminating the results of interest. Application to aerodynamic CFD, and to industrial standard RANS CFD codes in particular, has been patchy, with an emphasis on in-duct acoustic prediction. Recent work in conjunction with Rolls-Royce suggests there may be a significant advantage in applying non-reflecting boundary conditions to external flow CFD calculations for both aerodynamic and acoustic applications. The research envisaged will include the following: 1. Survey the range of non-reflecting boundary conditions used in CFD and acoustics codes. 2. Shortlist and test most promising candidates for aerodynamic CFD application, taking into account issues related to complex geometry and mesh, non-uniform mean flow and the presence (at domain exit) of vortical disturbances. 3. Propose, develop, implement and validate a new non-reflecting boundary condition in an industrial CFD code. The primary application objective is the calculation of jet engine inlet and exhaust aerodynamic and aeroacoustic performance, though there may be opportunity later in the programme to consider other applications (such as Marine CFD). The project is supported by Rolls-Royce, who will provide guidance as to the industrial requirements and also provide support and advice on implementation. KeyWords: Non-Reflective Boundary Conditions, Eigenmodes, Wave-Splitting, Perfectly Matched Layers, Sponge Layers, Infinite Elements, Calderon Projectors