Experiments on the aerodynamic noise sources in centrifugal turbomachinery

Flow induced noise generation mechanisms in a centrifugal turbomachine are investigated in this study. To isolate the noise generation mechanisms of interest, a simplified discharge configuration was selected. The unsteady flowfield discharging from the rotating impeller has been measured with stationary hot-wire sensors. A space and time cross-correlation technique using two stationary hot-wire sensors was developed to simulate a rotating hot-wire measurement. The simulated auto-spectrum of the discharged velocity shows a similar pattern to that observed in the spectrum from an impeller mounted rotating pressure sensor. Experimental results demonstrate how the unsteady flow in the impeller passages, modulated by a mild rotating stall pattern, interacts with the trailing edge of the impeller blades, and generates noise.