Three-dimensional unsteady turbulent flow in a propylene centrifugal compressor stage was numerically studied in order to identify primary acoustic dipole sources. The investigated model is the last stage of a propylene compressor used in the megaton ethylene production. The leakage clearance between the impeller and diffuser was simplified and modeled to capture the rotor-stator interaction accurately. A series of sixth-order polynomials, the use of which significantly sped up the computation compared with directly using Helmholtz real gas equation as the gas model, were fitted with a relative error less than 0.03% based on the thermodynamic data of propylene obtained by the Helmholtz equation. According to Lowson’s equation, the root mean square of the partial derivative of static pressure with respect to time during two revolutions of the impeller was taken as the parameter to measure dipole source intensity. The spatial distribution and frequency characteristics of the dipole sources were also investigated intensively. As a result of the present study, the primary dipole source is located at the junction of the impeller and diffuser, and its intensity is dominated by the components at the impeller blade passing frequency (BPF) and its higher harmonics, which are induced by the strong rotor-stator interaction. The spectrum analysis downstream of the impeller indicates that the higher harmonic components of dipole sources attenuate faster than the BPF component along the streamwise direction, and it is the BPF that dominates the noise characteristic in the volute casing of the studied model.

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