Autor: Norbert Schönwald

Due to the need to reduce noise emissions, aeroacoustic issues are becoming increasingly important alongside aerodynamic and economic requirements in the design of aircraft engines. In the context of industrial aerodynamic design, computational fluid dynamics (CFD) is already established as a robust and reliable tool. The simulation of aeroacoustic processes with such CFD methods is however extremely expensive due to the inherent properties of sound waves and therefore unsuitable for industrial application. A variety of specialised computational aeroacoustics (CAA) methods exist in the academic environment, which are specifically optimized for the simulation of acoustic processes with an acceptable computational expense. However, the applicability of each such approach is limited to very specific configurations and conditions. In this work therefore, a selection of different CAA strategies are combined to form a hybrid zonal approach, which offers an efficient simulation methodology for sound propagation and radiation including mean flow effects in complex industrial applications. An optimized high-order finite difference method is applied as a component of the hybrid CAA approach, which requires high-quality computational meshes. The generation of these becomes more and more challenging as the geometric complexity increases, eventually encountering the well-known limitations of pure block-structured grid strategies. In order to overcome this problem and to enable the generation of high-quality grids for complex, three-dimensional configurations, the overset grid technique is adopted. This is an established technique in CFD, which is adapted to the requirements of CAA approaches and implemented in the employed methodology. Using various configurations of increasing complexity, the hybrid simulation procedure is validated and its accuracy and limitations are assessed. The feasibility of the procedure for the prediction of tonal engine noise in practical application configurations is then demonstrated and evaluated. For this purpose, simulations of the sound propagation through a selection of scarfed engine intakes with varying incident flow as well as through bypass ducts with different installed components are conducted. The generic configurations employed are chosen to reflect the requirements of real engine simulations.