Numerical Evaluation of the Unsteady Flow in a Centrifugal Compressor With Vaned Diffuser via URANS Approach

The three dimensional, compressible, unsteady Navier-Stokes equations are solved to investigate the flow field of a centrifugal compressor with high compression ratio. Computational domain is consisted of an inlet bell and impeller with splitter blades followed by a two dimensional wedge vaned diffuser. The numerical method is validated by comparing the computational results with the experiments in terms of pressure ratio and compressor efficiency. The present study focuses on the unsteady pressure fluctuations and entropy production within the impeller and diffuser passages at the compressor design point. It is shown that the interaction between the impeller and diffuser blades leads to unsteadiness at the interface region and a pulsating behavior within the diffuser passages. Pressure waves with different convective velocities, generated by the impeller-diffuser interaction and pseudo-periodic unsteady separation bubbles, are captured in time/space domain along the diffuser blade surfaces. The pressure fluctuation spectra captured at the impeller-diffuser interface is evaluated to analyze the noise characteristics of the centrifugal compressor as a main source of blade passing frequency noise.