Theory and Application of an Analytical Approach for the Determination of the Transmission of Sound Waves through a Turbomachinery Stator

Abstract

The application of the two-dimensional aeroacoustic blade row model of Smith [1] to stators of axial turbomachines is investigated in detail. The study is part of an on-going research project including the verification of the model by comparison with data from experiments and from CFD/CAA codes. The overall objective is the accurate prediction of the transmission and reflection of sound waves, which is of large interest with regard to the pre-design of turbomachinery blade rows. The underlying concepts, related to the wave number, the phase velocity and the group velocity of the incoming 2D plane waves, are examined thoroughly. The 2D blade row model is applied to predict the sound transmission and reflection through a 3D stator and outcomes are compared with results of the CFD code Lin3D provided by MTU Aero Engines. For the approximation of the sound waves and the geometry using the 2D model parameters different approaches are developed and discussed. It is shown that the accuracy of the prediction can be improved by incorporating the effect of the impedance jump that corresponds to the change in cross-sectional area due to the stator blades.