Numerical Investigation into the Noise Emission of Integrated Contra-Rotating Open Rotors

该项目的目的是扩展气动和气动声学数值过程链，包括CFD求解器和声学后处理，用于研究集成对旋开放式转子(CROR)的噪声屏蔽和反射，并利用安装在空气动力学和气体动力学研究所的CROR模型试验台的实验数据进行详细验证。尽管CRR效率很高，但到目前为止，它还没有在民航中被接受。造成这一现象的主要原因是高噪声排放，这是最近许多研究项目的主题。除了避免产生噪音外，在飞机尾部集成CROR还显示出极大的降噪潜力。为了在定性和定量上可靠地预测这种积分效应的降噪效果，必须对气动和气动声学现象有一个准确的理解。孤立CROR的噪声产生流动机制确实是初步了解的，然而，对集成CROR的声音扩展的深入了解还不存在。集成CRR的实验数据不能免费供研究使用。因此，有了数值研究，但没有经过验证的模拟工具。为此，目前正在建立一个CROR试验台，用于产生CROR与塔式尾翼集成的CROR的空气动力学和声学实验数据。因此，与数值过程链一起，可以第一次比较集成CROR的实验数据和数值数据。在这个项目中，数值过程链将扩展到计算综合CRR，并通过测量数据进行验证。为此，将使用当前版本的CFD求解器以及具有更高阶格式的修改后的版本，两者都与现有的Ffowcs Williams-Hawking求解器一起使用。此外，声学后处理将结合边界单元法(BEM)和射线追踪法(RTM)展开。边界元将用于计算屏蔽声和反射声的音调部分，而RTM将用于模拟更高的频率。这两种方法通过覆盖不同的频域来相互补充，这是这些不同方法组合的优势。由于这种方法需要对波长进行最小离散化，因此可以用边界元法计算低频的展开。相反，对于RTM，波长必须相对于几何形状很小，因此这种方法覆盖了高频域。新开发的模块将用测量数据进行验证，并随后用于全尺寸集成CROR的模拟。

The aim of the project is the expansion of the aerodynamic and aero-acoustic numerical process chain, consisting of a CFD solver and acoustic post-processing for the investigation into the noise shielding and reflection of an integrated contra-rotating open rotor (CROR) and its detailed validation with experimental data of a CROR model test bench installed at the Institute of Aerodynamics and Gas Dynamics. Despite its high efficiency, the CROR has not become accepted in civil aviation so far. The main reason for this is the high noise emission, which is the topic of many recent research projects. In addition to the avoidance of noise development, the integration of a CROR at the empennage of the aircraft shows great potential for noise reduction. In order to reliably predict the noise reducing impact of such integration effects qualitatively and quantitatively, an accurate comprehension of the aerodynamic and aero-acoustic phenomena is necessary. The noise generating flow mechanisms of an isolated CROR are indeed rudimentary understood, however, an in-depth knowledge of the expansion of sound of an integrated CROR does not exist. Experimental data of integrated CRORs are not freely accessible for research. Hence, there are numerical investigations but no validated simulation tools. Thus, currently a CROR test bench generating experimental data of aerodynamics and acoustics of a CROR integrated into an empennage with a pylon is built up. Thereby together with the numerical process chain, experimental and numerical data for an integrated CROR can be compared for the first time. Within this project, the numerical process chain will be expanded to calculating integrated CRORs and validated by the measured data. For this purpose, the current version of the CFD-solver will be used as well as a modified one with a higher order scheme, both together with the existing Ffowcs Williams-Hawkings solver. In addition, acoustic post-processing will be expanded with a combination of boundary-element method (BEM) and ray-tracing method (RTM). BEM will be executed for the calculation of the tonal part of the shielded and reflected sound, whereas RTM will be used for the simulation of higher frequencies. Both methods complement one another by covering different frequency domains, which is the advantage of the combination of these different methods. The expansion of low frequencies can be calculated with BEM because for this method a minimal discretization of the wavelength is necessary. In contrast to this, wavelengths have to be small against geometry for RTM, therefore the high frequency domain is covered with this method. The newly developed modules will be validated with measured data and subsequently used for the simulation of a full-scale integrated CROR.