NUMERICAL AND EXPERIMENTAL STUDY OF THE TONE NOISE GENERATION BY A TURBINE REAR FRAME

In a turbofan engine, the Turbine Rear Frame (TRF) is the component located downstream of the last turbine stage. Its function is mainly structural, but it is also devoted to de-swirl the hot flow within the turbine nozzle. For this reason the aerodynamic optimization of this component, basically aimed at increasing the overall turbomachinery efficiency, is commonly taken into account within the whole engine design loop. Recently, the request for a "green aviation" has introduced further requirements to be met during the component optimization, such as the reduction of the acoustic emissions. Consequently, low noise criteria have become necessary when designing a TRF and their identification implies the understanding of the physical mechanisms governing the noise generation and transmission across this row. In light of this, experimental investigation is fundamental to gain a deeper insight into the problem. In this context, this paper presents a numerical and experimental study focused on the tone noise generation due to a turbine rear frame installed downstream of an up-to-date Low Pressure Turbine (LPT) model. The aim of the paper is to assess the ability of two numerical methods, an already presented linearized CAA (Computational AeroAcoustics) procedure and a newly developed non-linear one, to correctly predict the TRF acoustic emissions at several operating conditions by comparing the numerical results with the experimental data acquired at the GE Avio cold flow facility in Turin.