Sediment erosion of hydraulic turbine is the major problem from the perspective of operation and maintenance in power plants of Himalayan and Andes region. The effects of sediment erosion on turbine components need to be predicted in advance during the design phase so that the best design with better sediment handling can be installed in real power plants. In this paper, comparison of performance and erosion of two different designs of Francis turbine i.e. design I and design II are carried out. Full turbine steady state numerical simulations are carried out for 8 different guide vane openings using shear stress transport (SST) k-ω turbulence model. Sediment erosion analysis is carried out using Tabakoff erosion model for both the designs, numerical hill charts are constructed using Ned and Qed values for all the operating conditions. Comparison of pressure distribution along pressure and suction side of GV surface between design I and a similar measurement in a previous experiment is carried out, which shows a good agreement between numerical and experimental results. Hydraulic efficiency and the sediment erosion rate density on the runner blades of design I for all operating conditions is higher than that of design II. The difference in efficiency is less than 1.85%for all operating conditions while sediment erosion rate density is much less in design II, which shows that design II is a better option for this turbine.
Clearance gap in guide vanes of Francis turbine induces the leakage vortex. This vortex flow interacts with the main flow and leads to the instability in the fluid flow pattern and eventually deteriorates the performance of the turbine. In this study, the detailed numerical examination of the unsteady flow due to leakage vortex and influence of this in the performance of turbine is carried out using time dependent numerical analysis. The numerical simulation is carried out using SST turbulence model with numerical validation. The development of leakage vortex is studied within the clearance gap region. Time dependent numerical simulation is carried out to investigate the growth and vortex propagation considering five revolutions of the runner. Results shows that the leakage vortex travelling form the guide vane clearance gaps influence the performance of the runner. On analysing the leakage vortex path, it is seen that the vortex travels from the pressure side of runner blade to the suction side of adjacent blade opposite to the runner rotation. Furthermore, this leakage vortex is carried down to the draft tube where the vortex rope seems to grow up to 50% geometric progression of draft tube cone and gradually decreases before reaching the elbow. Upon investigation of resulting torque and head during runner rotation, the periodic variation of torque and head can be seen, however with different phase. This is inferred to be the influence of leakage vortex that travels along with the main flow.
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