Abstract
The unsteady flow behavior and pressure fluctuations in the runner of a Francis turbine were predicted numerically for the middle-low head at three small guide vane openings. The unsteady Reynolds-averaged Navier-Stokes equations with the k–ω based SST turbulence model were solved to model the unsteady flow within the entire flow passage. The eddy characteristics inside the runner passage were discussed for various operating conditions, the shape of the blade channel vortex illustrate by the instantaneous iso-surfaces of the vorticity was similar with the experimental observation. This study investigates the characteristics of the unsteady flow dominant frequencies at different monitored points of the runner by spectrum analysis. At small guide vane opening conditions, the pulse in the runner flow passage are due to the rotor-stator interference between the runner and the guide vanes, the blade channel vortex in the runner blade passage. And the dominant frequencies of blade channel vortex were a low frequency. The unsteady flow behavior of blade channel vortex in the runner was classified numerically at part load of middle-low head.
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