Discharge Characteristics of Axial Flow Turbomachines with Plane-Symmetric Rotor and Stator

Flow pattern in the rotor of turbomachines changes discontinuously when flow rate decreases beyond a critical limit. Typical examples are seen in reverse flow at the suction flow at the suction of axial and centrifugal impellers, in the reversal of discharge direction of centripetal impellers, etc. The purpose of this study is to find a clue to the criteria which initiate the transition from one pattern to the other. Non-staggered rotor was installed in an annulus between two stators with plane-symmetric configurations, so that the flow condition became perfectly symmetric. The flow pattern took either discharge or recirculation mode according to the geometry of rotor and stator. Transition criteria were discussed based on the measured driving torque and discharge flow.