COMPARISON OF DIFFERENT APPROACHES TO THE SELECTIVE SYNTHESIS OF DOMINANT DUCT MODES IN TURBOMACHINES USING LOUDSPEAKERS

Abstract

The dominant excitation of individual acoustic modes is a prerequisite for the in-depth analysis of sound propagation through installations, e.g. blade rows or acoustic liners, within turbomachinery flow ducts. A literature review yields various methods to synthesize dominant modes with loudspeaker arrays. In the present paper the most promising approaches are compared regarding their performance and accuracy. Tests are carried out by simulating experimental setups of increasing complexity levels. The setups range from the ideal case of a duct without installations and with anechoic terminations on both sides to a duct with blade-like obstacles and a reflecting termination. Included in the studies are the effects of practically relevant problems. These are superimposed reflections including scattered modes that arise at duct installations outside the actual test environment. Further considered is the impact of detuned speaker signals within the loudspeaker array and of tolerances in microphone transfer function measurements.