Numerical analysis of Separate Vortex in the Diffuser

In order to simulate the flow structure accurately and find out the inducement of unstability in a centrifugal compressor with casing structure, three different cases of models were established.By contrasting the simulation result of Case1 and Case2 with experiment data, the accuracy of grids model and turbulence model was validated.Compared with utilized a "Mixing Plane" at the Rotor-Stator interface in Case1 and Case2, the flow in diffuser of Case 3 was solved in the rotating reference frame.Compared simulation result with Case1 and Case2, the accuracy of Case3 model was validated.By studying the flow structure in diffuser, the fusion and development of the ISV result in the scope of backflow extending to blade passage, which is inducement of compressor instability.A tracing back analysis was carried out with Case3 model to investigate the formation of ISV.The blade leakage flows and strong pressure variations at outlet of blade passage were the cause of ISV.