Numerical investigation of a full load operation point for a low head propeller turbine

Abstract

The performance of low head turbines heavily depends on the draft tube. In the design process of hydraulic machines the geometry is often simplified, meaning gaps between runner and shroud and, if occurring, gaps at the trailing edge of the guide vanes are often neglected. The gap flow can however lead to a stabilization of the draft tube flow. In order to investigate this, a numerical analysis of a 4-blade runner with tip clearance is carried out. For the investigated operating point a full load vortex in the draft tube develops. The numerical results are evaluated against experimentalmeasurements of integral quantities head, torque and discharge according to IEC 60 193 standard. Additionally to the investigations of the integral quantities, an evaluation of the vortex rope shape, turbulence quantities and velocity profiles in the draft tube are compared for the different numerical approaches.