Since there is a large difference in geometrical scale in the side chamber and comb-labyrinth seal of Francis turbine runner, the fractional step method is used to solve the unsteady, three-dimensional, incompressible Navier-Stokes equations for the flow in the chamber and tortuous path of the seal. In order to capture vortex structure more exactly, the hexahedral mesh with refinement near the wall boundaries are adopted. The Quick upwind and second-order central difference schemes are selected for convection and diffusion terms, respectively. The velocity and vorticity profiles in the path of labyrinth seal are obtained at different Reynolds numbers; meanwhile the pressure distribution in the side chamber, axial thrust on the runner and torque on the shaft are estimated. It is turned out that a vortex structure can be developed as soon as the fluid enters the path of the labyrinth seal to consume a certain amount of kinetic energy, and a pressure drop is established to prevent the leakage. Note that the vortex structure is largely affected by Reynolds number. The results may be helpful in understan-ding the physical mechanism of complex flow in the path of comb-labyrinth seal and the influence of the seal on rotordynamics of Francis turbine.
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