Segmented ROSI method: Beamforming method for investigating turbomachinery noise sources along segmented trajectories

Abstract

The rotating source identifier (ROSI) beamforming method is a method designed for localizing rotating noise sources in a uniform flow based on out-of-flow acoustic pressure field measurement data. It has been developed for sources moving along a circular trajectory, such as turbomachinery blades. The original ROSI method processes the measured acoustic signals over a long time segment to reconstruct the noise sources, providing time-averaged results for each noise source. By doing so, it does not take into consideration certain features of the noise sources, such as the directivity of the trailing edge and leading-edge noise sources. A further development of the ROSI method is presented herein, which separates the sound-pressure signal of one revolution into multiple segments. In this way, the beamforming maps can provide one with a better understanding of the differences between the noise sources as a function of angular position. This method will be referred to herein as the segmented ROSI method. The goal of this further development is to improve the capability of the method in identifying the position-dependent modulations of the various noise sources as they are moving along their trajectories, rotating around the axis. The investigation presents the theory behind the new segmented ROSI method along with simulation and measurement-based test cases which help in comparing the new method to the original ROSI method. The results show that the novel method provides a strong tool for investigating turbomachinery noise sources that vary along segments of their trajectories. It is therefore expected that the tool will be useful in cases that look at turbomachinery from an angle and cases where the loading of the blades changes as a function of angular position.