Page - 1375 - in Book of Full Papers - Symposium Hydro Engineering

1.3. CFD ANALYSIS Numerical computation was also carried out to verify the experimental model testing with CFD-analysis. Distinct water waves appear in the tail water especially in the region around the draft tube outlet. The flow rate dependent change of the wave structure in the tail water is presented by the following Figure. Fig. 14 Water Volume Fraction plotted on a cross sectional area for Q1 = 87.5 to Q5 = 250 l/s [4] On the one hand it turns out that the ejector is capable of increasing the hydraulic power available at the turbine by a maximum of 18 %. On the other hand an analysis of the presented data shows that the positive effect of the ejector does not only depend on the ejector flow rate but also on the tail water level with respect to the level of the ejector nozzle. If the tail water level is too high even a comparably high ejector flow rate does not cause an increase of power output. 1375