Vortical and Separated Flow Structures in a Centrifugal Compressor Impeller with Splitter Blades at Off-Design Condition

The objective of the present paper is to identify vortical and separated flow structures in a transonic centrifugal compressor impeller with splitter blades at an off-design condition. Steady state single passage RANS and time-accurate full annulus DES calculations are used to investigate the flow field inside the centrifugal impeller. In order to clearly show distinctive flow structures in the unsteady flow field at the off-design condition, the time-averaged flow field from the DES calculation is investigated by being compared with the RANS result. It is observed that a horseshoe vortex is generated in front of the splitter blade tip due to a reversed flow inside the impeller near the casing, being integrated with leading-edge separation vortex, tip leakage vortex and secondary flow vortex out of the full blade to form one large-scale vortical flow structure.