Numerical investigation on the effects of leakage flow from Guide vane-clearance gaps in low specific speed Francis turbines

Abstract

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.

Numerical Prediction of Erosion of Francis Turbine in Sediment-Laden Flow under Different Heads

“…(2) The main areas where erosion occurs are irregular boundary areas, including the According to the existing research results on friction in hydraulic machinery, it can be seen that the sediment erosion on the wall can be divided into impact sediment erosion and frictional sediment erosion, which are mainly determined by the impact angle of sediment particles [19]. The default impact angle of sediment particles set in the Tabakoff sediment erosion model is 25 • [20], indicating that the impact angle of sediment particles when frictional sediment erosion occurs on the blade wall is below 25 • . The impact speed mainly affects the degree of sediment erosion.…”

Study on the Effect of the Guide Vane Opening on the Band Clearance Sediment Erosion in a Francis Turbine

“…In the Lagrangian framework, the main force on the particles comes from the velocity difference between the particles and the fluid, which contain gravity, resistance, virtual mass force, pressure gradient force, Basset force, Saffman force, Magnus force, etc. [19,20]. The particle track model is as follows:…”

Leakage Vortex Progression through a Guide Vane’s Clearance Gap and the Resulting Pressure Fluctuation in a Francis Turbine

“…Transient simulations were carried out for total time corresponding to three runner revolutions, and at a time step of 1 • of angular rotation for runners. The turbulence model selected for this study was the shear stress turbulence model developed by Meter [27], which was determined based upon the literature [28][29][30]. The details of the simulation settings are listed in Table 1.…”