CFD based criteria of stall onset in centrifugal compressors

The determination of stall onset is very useful for the control and safety of centrifugal compressors which usually operate at high pressure ratios. This is an extremely intricate task since the details of the flow need to be acquired at several measuring planes. However, the state-of-the-art CFD tools have contributed substantially in the analysis of the flow structures and the design of centrifugal compressors. The present paper demonstrates the potentiality of numerical simulations to map the full flow field and assess some criteria used to predict the stall onset, typically those relating the boundary layer growth and stability. Through the entire impeller and diffuser, the quantification of the blockage factor in addition to the modified loading criteria (diffusion rate) which combines the blade-to-blade and hub-to-shroud Richardson numbers seem more suitable for predicting the stall onset and stall cells positions. The well-known models of centrifugal compressors operating at low-speed (LSCC) and high-speed (DLRCC) served for the validations. The present CFD based criteria are useful since they may easily integrate the design procedure of centrifugal compressors.