Free Rotating Vaneless Diffuser of Diffuser Diameter Ratio 1.30 with Different Speed Ratios and its Effect on Centrifugal Compressor Performance Improvement

Free rotating vaneless diffuser is one of the novel methods in the design of radial diffuser for reducing the energy losses associated with diffusion. In the present study, the impeller with a stationary vaneless diffuser of diffuser diameter ratio 1.40 and impeller with a free rotating vaneless diffuser of diffuser diameter ratio 1.30 along with stationary vaneless diffuser at downstream for the remaining radius ratio, running at speed ratios 0.25 and 0.75 times the impeller rotational speed are analyzed. A higher static pressure rise with reduced losses is achieved by free rotating vaneless diffuser configuration, Free RVD30 SR0.75. The static pressure recovery coefficient increased by 23 to 80%, by rotating the diffuser independently over the entire flow range. Also, losses are lesser due to reduced shear between the through flow and independently rotating walls of the diffuser. The efficiency of both Free RVD30 SR0.25 and Free RVD30 SR0.75 are marginally lesser by 3.5 to 5.3% with SVD. This clearly reveals that the diffusion rate is higher in the free rotating vaneless diffuser configuration.