Experimental and Numerical Investigation of a Draft Tube Cone at Lower Runner Speeds

The variable demand on the energy market enforces that hydraulic turbine to operate at different regimes, far from the best efficiency point. An experimental test rig was developed in our laboratory in order to reproduce these regimes. As a result, the investigated flow regimes allow us to quantify the flow behavior from part load operation to full load operation. The paper focuses on experimental and numerical investigations of mean velocity profiles and of stagnant region developed in the centre of draft tube cone. First the numerical results are validated against experimental results. At the end a qualitative analysis of the streamline pattern is complemented, giving us an evaluation of the stagnant region from the draft tube cone at different runner speeds.