ANALYSIS OF THE INLET RECIRCULATION PHENOMENON IN A HIGH-SPEED INDUSTRIAL CENTRIFUGAL COMPRESSOR: EXPERIMENTAL AND COMPUTATIONAL STUDY

This research paper presents an investigation of the local flow instability known as inlet recirculation in a high-speed industrial centrifugal compressor. This phenomenon might appear when a compressor operates at a lower than the design mass flow rate and approaches the surge line. The study combines experimental measurements with a 3D steady-state Reynolds-Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) model using the k-omega Shear Stress Transport turbulence model. The single-passage CFD model was validated against the experimental data for the design speed line. A detailed mesh independence study was conducted to estimate the discretization uncertainty and evaluate grid refinement at the design point. The results indicate that as the mass flow rate decreases and approaches the surge line, the inlet recirculation phenomenon is observed. The inlet recirculation is quantitatively analyzed, and the blockage it causes is determined. It was found that inlet recirculation can account for approximately 9% of the compressor mass flow rate and can block up to 38% of the flow area at the impeller inlet. Also, the expansion of the inlet recirculation zones was growing in two phases, showing significant radial and streamwise growth as the inlet blockage increased. For lower inlet blockage, the radial growth dominated the streamwise growth. While the streamwise growth increased significantly with relatively constant radial expansion at the higher inlet blockage.