An aerodynamic/acoustic splitting technique for hybrid CAA applications
An aerodynamic/acoustic splitting technique for hybrid CAA applications
复制标题
用于混合 CAA 应用的空气动力学/声学分离技术
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
W. Desmet
中科院分区：
文献类型：
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作者：
W. D. Roeck;M. Baelmans;W. Desmet
混合CAA方法，其中的计算域分为一个气动源域和声传播区域，通常用于航空声学工程应用，并已被证明是可接受的效率和精度。不同的耦合技术往往会给一些应用程序，这主要是在密闭环境中遇到的错误的结果。声学类比是不准确的，如果声学变量是相同的数量级的流量变量和声学连续的源域模拟使用后一种解决方案作为声学边界条件是唯一可能的，如果没有涡流流出发生。这些不准确性可以通过使用适当的滤波技术来避免，其中源域解被分成声学和空气动力学波动部分。在本文中，这样的气动/声学分裂技术的开发和验证一些简单的测试用例。该滤波方法适用于低马赫数应用，假设所有可压缩性效应都是由无旋声场引起的，而不可压缩空气动力场则负责流场的旋涡运动。在这些假设下，它表明，在每个时间步的空气动力学和声场是通过求解由波动的膨胀比和涡量驱动的泊松方程系统，从源域模拟获得。对于混合CAA方法，这种滤波技术，一般适用于自由场和受限流应用，能够提供更准确的耦合信息，并提高了气动噪声产生机制的知识。
Hybrid CAA-approaches, where the computational domain is split into an aerodynamic source domain and an acoustic propagation region, are commonly used for aeroacoustic engineering applications and have proven to be of acceptable efficiency and accuracy. The different coupling techniques tend to give erroneous results for a number of applications, which are mainly encountered in confined environments. Acoustic analogies are inaccurate, if the acoustic variables are of the same order of magnitude as the flow variables and an acoustic continuation of the source domain simulation using the latter solution as acoustic boundary conditions is only possible if no vortical outflow is occurring. These inaccuracies can be avoided by using appropriate filtering techniques where the source domain solution is split into an acoustic and an aerodynamic fluctuating part. In this paper, such an aerodynamic/acoustic splitting technique is developed and validated for some simple test cases. The filtering method is valid for low-Mach number applications, assuming that all compressibility effects are caused by the irrotational acoustic field while the incompressible aerodynamic field is responsible for the vortical movement of the flow field. Under these assumptions, it is shown that the aerodynamic and acoustic fields at every time step are obtained by solving a system of Poisson equations driven by the fluctuating expansion ratio and vorticity, obtained form the source domain simulation. For hybrid CAA-approaches this filtering technique, general applicable for both free-field and confined flow applications, is able to provide more accurate coupling information and improves the knowledge of aerodynamic noise generating mechanisms.