Influence of Operational Geometry Changes on Turbine Acoustics

Abstract

Due to the fact that noise emitted by aero engines became a very important issue especially during the last few years, acoustic measurements were carried out downstream of the lowpressure turbine in a two-stage two-spool test turbine. The aim of these analyses was to determine the influence of small geometry changes in the flow path of the rig under enginerelevant conditions, which usually occur during the operation of an engine. These geometry changes include steps in the flow path and different rotor tip gaps, both generated by a nonuniform warming of different parts of the engine. In order to evaluate the noise emissions, the outflow duct downstream of the second rotor was instrumented with an acoustic measurement section, which uses a circumferentially traversable microphone array located at the outer endwall. The acoustic field is characterized by azimuthal modes gained by traversing the microphone array over 360 degrees. Therefore, the spectra and emitted sound pressure levels are compared regarding different geometry changes.