Abstract: The tubular turbine is a main type of the hydraulic turbines for low head hydropower development, but its tip clearance flow is the key factor controlling its cavitation and stability performances. Using CFD simulations, this paper examines the mechanism of the initial location variation and shape variation of the tip leakage vortices (TLVs) that are induced by a variation in the operating condition, and evaluates the vortices’ influence on the cavitation and stability of the turbine. Results support the major conclusion that a variation in guide vane opening alters the angle of attack at the leading edge of runner blades and further affects the initial locations and three-dimensional shapes of TLVs. And we find these variations are the cause of variations in runner cavitation performance, and verify TLVs can increase the amplitude of pressure fluctuations over the regions they swept, leading to the amplitudes doubled or more.

Key words: tubular turbine, tip clearance, tip leakage vortex, pressure fluctuation