Unsteady Flow in a Centrifugal Compressor Stage Equipped With a Vaned Diffuser and Cavities

Abstract

The purpose of this work is to present the Computational Fluid Dynamics (CFD) transient flow simulations of a centrifugal compressor stage with cavities. The cavities are included in the CFD model for several reasons. First the leakage flows and the windage effects are important to predict the absolute level performance of the stage (efficiency). Secondly the cavities also play an important role in the generation of the aerodynamic forcing on the impeller as well as in the prediction of the aerodynamic damping. As the compressor stage contains unequal numbers of blades and vanes, the Time Transformation method, an extension of the time inclining method is used in this work. This method which requires only a few passages per row is employed to reduce computational load and accurately model the full wheel. The numerical procedure is applied at design point firstly and then extended to the off-design operating conditions, permitting to compare and understand the transient flow behavior. The ability of the method to predict the impeller/diffuser interactions and cavity unsteady pressure response is discussed. The respective contributions of the diffuser, impeller blade passages and side cavities in terms of impeller forcing amplitude and frequency content are studied. In addition to this, comparisons between the experiment, the reduced model and the equivalent part wheel periodic solution are made to demonstrate the accuracy and computational efficiency of the considered transformation method.

Influence of rotor–stator component partition structure on the aerodynamic performance of centrifugal compressors

“…During actual operation, a gap exists between the partition and wheel cover and the wheel disk of the impeller, which can easily lead to airflow leaks. Leaking flow and cavity are important when predicting stage efficiency (Younsi, Corneloup, Moyroud, & Baldacci, 2017). These subtle flow phenomena interact with the main flow and can threaten the efficiency and stable operation of centrifugal compressors (Qin, Sun, Wang, Ju, & Zhang, 2016).…”