Cause specification of performance curve instability in mixed-flow pump by LES

A technique for high-accuracy predicting performance curve instability in pumps and clarification of the phenomenon in order to control the instability is required for designing high performance pumps. We analyzed internal flow of a test mixed-flow pump by using Large Eddy Simulation (LES) and clarified that Euler's head drop caused by stall near the tip of impeller blade is a dominant factor of this test pump's instability. We looked carefully at internal flow of impeller before and after the head drop, and also in the middle of the head drop. When the Euler's head drops, recirculation on the leading edge of the tip of impeller blade extends towards trailing edge. Angular momentum between tip and mid span decreases, and angular momentum near the tip is high. Work drop of the impeller on the side of leading edge caused by the stall on leading edge exceeds angular momentum increment caused by decreasing in flow rate on trailing edge, and so the angular momentum on the trailing edge drops. At that situation, the impeller blade load on the tip side shows state of stall. And, the stall fields occurred on the trailing edge cover whole impeller blade passages near the tip. When the head is in the middle of drop, only some impeller blade passages are covered with the stall fields.