The effect of unsteady vortex behavior on noise characteristics in a centrifugal compressor

Abstract

The effect of diffuser width on the noise level of a centrifugal compressor equipped with vaneless diffusers was investigated through experiments and numerical techniques. In this regard, two diffusers with different widths were installed in the compressor. In case the wider diffuser was used, there was the bandwidth (800 to 900 Hz) noise and pressure fluctuation which was closed to 1/2BPF (700 Hz). This fluctuation occurred because the leakage vortices were of two different frequencies. Type 1 vortices are the ones that were discharged from the main blade and covered Passage 1. Type 2 vortices had the same length as Type 1, but they were discharged from the splitter blade. Type 3 vortices covered both Passages 1 and 2; these were discharged from the main blade. Type 3 vortices were generated predominantly at 270°, and their frequency was approximately 700 Hz at 1/2 BPF frequency. The former two types of vortices occurred occasionally, and their frequency was approximately 1400 Hz. Type 3 vortices grew with the wider diffuser because of the higher pressure-recovery, which caused the serous loading to the impeller blades. The broadband noise fluctuation occurred by the coexistence of the two frequency vortices.