64. Numerical Three-Dimensional Turbulent Flow Analysis Through a Pump-Turbine Draft Tube in the Turbine Mode

The simulation of three-dimensional turbulent flow through a Pump-Turbine draft tube at turbine mode, as a part of the complete pump-turbine calculation is presented in this paper. Four cases were calculated based on the Computational Fluid Dynamics – CFD Methodology (Navier-Stokes equations and the k-e turbulent model). Those four cases were: 1. Optimal mode, 2. Mode at maximal discharge, 3. Mode near minimal discharge, 4. Mode between minimal and optimal discharge. The mesh discretization, boundary conditions and calculated results are presented and they shall be useful for development, optimisation, refurbishment or rehabilitation projects, because the draft tube behaviour can be a major criterion for increasing the performances of the Pump-Turbines. This work describes new computational approaches for modern development of radial type single stage pump-turbine. A pumpturbine with specific speed nS = 89 was calculated, as an example of the applicability of this methodology. The work presented in this paper coincides with the current trend of improvement in the CFD field, as a faster and less expensive way of testing and development of hydraulic machinery. The results are promising, but a lot of experiments are still necessary for the completion of the validation process. The influence of the cavitation on the total efficiency is calculated for the pump mode. The results presented in figure 5 show some discrepancies between the numerically obtained calculations and the experimental results. The numerical anaysis of the flow field in the pumpturbine in the turbine mode showed the velocity vectors, pressure distributions, vortex positions and intensity in the draft tube and the streamline behaviour. Using these results, conclusions regarding the exploitation and design processes can be achieved.