Acoustic resonance in vaneless radial diffusers with swirling flows

Generation of complex sound waves by impeller rotation in centrifugal compressors is examined, and characteristics of certain combinations of compressor geometry and operating conditions are shown to increase the likelihood of generation of high levels of noise due to resonance. Results are expressed in terms of a nondimensional frequency and for either volume sources or pressure sources. It is demonstrated that geometrically perfect impellers of centrifugal compressors do not excite resonance in vaneless diffusers during operation in axisymmetric inlet and outlet flow fields. Causes of flow nonuniformities and identification of the lobe number are considered.