Analysis of internal flow in the Kaplan turbine with the Triangle Acute Clearance

Analysis of internal flow in a Kaplan turbine runner with the Triangle Acute Clearance has been conducted in this paper. The flow fields at big opening conditions of the guide vane have been obtained by numerical simulations, with and without the consideration of the vane tip clearance and the runner blade triangle acute clearance near the hub. The analysis shows the following results: (1) At big opening conditions of the guide vane, the acute angle clearance and the shaft neck have some influence on the flow status in the passage bending area of the guide vane. At the same guide vane opening condition, the pressure gradient at the bottom ring decreases gradually from the inlet to the outlet, with the peak pressure in the high pressure area decreasing. (2) The triangle acute clearance of the runner blades near the hub is decreasing with the increase of the runner blade angle. The main flow in triangle acute clearance is characterized by two kinds of flow structures: a water jet flow near the leading edge of the hub, and a vortex strip flow near the trailing edge of the hub. These two kinds of triangle acute clearance have some certain effects on the cavitation performance.