AN EXPERIMENTAL INVESTIGATION TO IMPROVE THE PERFORMANCE OF CENTRIFUGAL COMPRESSORS OPERATING AT OFF-DESIGN CONDITIONS

Experiments to investigate the feasibility of controlling (delaying/or suppressing) the stall in the radial diffuser of a low speed centrifugal blower were carried out. The mass flow rate of air through the blower could be gradually reduced until stall inception is accomplished. The static and dynamic pressures in the diffuser were measured along a radial or a circumferential path using static and dynamic pressure transducers. The technique was very simple and involved changing the flow area at the diffuser exit with the use of throttle rings to either diffuser shroud, or the diffuser hub. Simultaneous attachment of the throttle rings to both the diffuser shroud and the hub was also made. The diffuser exit blockage ratio varied between 0 % and 75 % when throttle rings were attached to the diffuser walls to reduce its exit flow area. The results showed that the flow instability in the diffuser (stall) was delayed to a lower flow coefficient (the critical mass flow rate could be reduced to 55 % of its value without the blockage). The experimental data also confirmed that the throttle rings could be an effective way to control the stall in the vaneless radial diffuser.