Aeroacoustic testing for sound propagation through turbine vanes

摘要

A strong focus in the development of modern aircraft engines is the reduction of the tonal noise of the core engine. The dominant tonal noise is generated by rotor-stator interactions at blade-passing frequency (BPF) and its harmonics. Each engine component produces a set of spinning modes over a wide range of frequencies. Depending on the acoustic wave characteristics, these modes can propagate to the neighboring row. In particular, for the low pressure turbine (LPT), some of the tonal noise is refracted and dissipated internally, while a large part of its power is transmitted through the blade rows down to the outlet duct and consequently radiated into the environment. A variety of methods can be employed to reduce the noise emission. Currently, the main approach to limit tonal noise radiation is to limit blade passage transmission. This design method (also called modal design) however requires accurate predictive capabilities, in order to be included in an engine's design process of engine manufacturers. High quality experimental data are therefore needed to validate the design tools. The designer usually relies on two-dimensional analytical sound transmission models in the preliminary design phase and three-dimensional numerical noise propagation simulations during design validation. While some of the analytical transmission models are excessively mathematically complex to implement (e.g. the Koch 2D-Sound Transmission Model), other are mathematically simpler but struggle to capture important features of the sound transmission adequately (e.g. LINSUB 2D-Sound Transmission Model) [6]. Empirical acoustic sound transport models which are based solely on experimental correlations are not known in the open-literature. The goal of the present study is to describe the aeroacoustic optimization process applied to an Aeroacoustic Wind Tunnels (AWT), in order to generate high-quality experimental data for analytical sound transmission model development and validation of 3D numerical CAA-methods. The obtained characteristics of the AWT are then presented (i.e. quality of the inflow, stability of the design point, no flow separation on the Stator vanes, the diffusor and the duct walls, quality of the synthetic sound generation for various acoustic modes and frequencies). Results from the extensive aerodynamic and aeroacoustic measurements will also be discussed.