Abstract: Based on the average N-S equation, adopting Reynolds stress differential models and unstructured mesh technology, numerical simulation is performed on the 3D turbulent flow of Kaplan turbine’s flange clearance. The research of flow consists analyzing the velocity distributing rules of blade surface inside Kaplan turbine flange clearance and leakage flow of flange clearance under different conditions. The result indicates that the leakage flow through the clearance isn’t a single flow type but can be divided into four regions (Ⅰ, Ⅱ, Ⅲ, Ⅳ) according to the direction of leakage flow in the flange clearance: Ⅰregion is at leading edge of the blade’s flange, some parts lie in pressure side which form low pressure region affected by a fraction water leakage flowing from suction side to the pressure side, the other lie in suction side; Ⅱ region is the middle region of blade flange within tip clearance where the leakage flow change it’s direction; Ⅲ region is tip leakage flow that direction of blade flange clearance turn to suction side; Ⅳ region is trailing edge vortex region of tip near the flange of blade. The produce and the development of runner tip clearance flow and leakage vortex core at different operation point and the interaction of main flow and leakage vortex and make further study on mechanism of second flow caused by main flow and leakage vortex, are investigated. The effect on interior flow structure of hydraulic turbine and explain cavitations as well as cavitations abrasion of Kaplan turbine caused by flange clearance, is revealed. The flow rule in hydraulic turbine is improved, which provides gist for safe operation of Kaplan turbine and designing Kaplan turbine with excellent performance.

Key words: Flange clearance flow, Kaplan turbine, Reynolds stress differential models, Unstructured mesh