15 years of experience with the Triple Plane Pressure Mode Matching technique

The so-called Triple-Plane-Pressure-Mode-Matching technique (TPP for short) is a method used to isolate and quantify the acoustic part in numerical simulations of turbomachinery. Nowadays, simulations such as Harmonic Balance are commonly applied during the design phase of new turbomachinery components for both aeroacoustic and aeroelastic analyses. The TPP method was first published 20 years ago by Ovenden and Rienstra. The principle is to match the periodic pressure data from three or more neighbouring analysis planes with a subset of acoustic eigenmodes. The original method assumes that the flow in the channel section is potential so that the eigenmodes can be determined analytically. This approach can also be applied in slowly varying ducts. The TPP method is a powerful technique that is used at DLR and MTU Aero Engines. For nearly 15 years, constant joint efforts have been made to improve its applicability in industrial environment. Targeted applications are turbine stages, where the mean flow is complex and vortical wakes contaminate the results. In this paper, the latest developments of the method are presented, including the extension to curved extraction surfaces to enable its application to small blade-row spacing. The utility of the technique is illustrated by an industrial application.