A Numerical Investigation on the Volute/Impeller Steady-State Interaction due to Circumferential Distortion

To understand the volute/impeller interaction at off-design conditions, the steady-state interaction between volute and impeller is investigated in this paper using CFX-TASCflow’s frozen rotor model. This model is applicable to the compressor flow where the acoustic Strouhal number is close to zero. The gentle circumferential pressure distortion is confirmed at the exit of the vaneless diffuser; but the radical pressure distortion is found around the tongue, resulting from the incidence to the tongue. The circumferential pressure distortion, which is lagged in phase to the total pressure distortion, is predicted to propagate upstream over the vaneless diffuser without significant decay. It is found that the impeller exit flow pattern depends on the slope of the circumferential variation of the static pressure at exit. This explains why the impeller efficiency is reduced at off-design conditions. Therefore, this study suggests that the undersized volute is beneficial to the impeller.