The Investigation of the Flow Characteristics Inside the Vaned Diffuser at Small Flow Rate

For the components of the centrifugal compressor, the deterioration inside vaned diffuser usually restricts the regular operation of the whole machine. Aiming at investigating the flow structure inside the vaned diffuser at the small flow rate, the paper conducted the transient measurement, whose results are compared with the numerical results, to present the transient phenomena under this condition. The results point out that the blade passing disturbance from the impeller enhances prominently as the mass flow decreases, especially for the disturbances triggered by the non-uniformity between the main and splitter blades. Meanwhile, the performance of the region from the semi-vaneless to the throat appears to be critical during the process of the instability inside the vaned diffuser. It has been found that the considerable throat blockage caused by the large-scale corner separation on the suction side, combined with the blade passing disturbance, directly leads the initiation of the rotating stall cell at the front part of the diffuser.