No abstract

Estimation of sediment erosion in hydraulic turbines is limited by the broad range of dependent parameters, such as characteristics of sediment, base materials and flow conditions. Some mathematical models have been proposed in the past literatures and some of them has been incorporated in a CFD tool for predicting the erosion together with the flow conditions. Rotating Disc Apparatus is a simplified experimental setup that was initially developed targeting on erosion studies in Francis turbines. However, the closeness of the results obtained from this apparatus with the actual turbine remains uncertain. This paper focuses on investigating the flow phenomena inside the region of guide vanes using RDA and comparing with the actual turbine. A reference case of Jhimruk hydropower plant has been taken in this study, which has been scaled down with a factor of 1.6 from its original size. The numerical fluid domain consists of four rotating blades distributed around the disc uniformly. The pressure distribution around the guide vanes inside RDA along with development of the tip-vortices have been compared with the results from the past research works. The experiment consists of a qualitative analysis of the wear pattern, which has been compared with the results of the CFD. It is found that flow field around guide vanes inside RDA matches closely with that of the real turbine. The stagnation point and development of the pressure and suction sides are similar to the actual guide vanes, which makes the apparatus suitable for investigating the erosion after including the sediment particles. However, more investigations might be needed for using the same apparatus for the runner blades, or guide vanes at different operating conditions.

The sediment loads originated from Run-off-river reaches to the turbines as suspended particles, causing wear and tear of the mechanical components. In the case of power plants under Himalayan Rivers, the turbines need to undergo repair and maintenance in a regular basis, due to a substantial loss of material from the turbine components. Past research works have focused on minimizing the erosion in turbines by changing the design of runner and guide vanes, strategically operation of the power plant during the monsoon season, as well as application of the coating materials over the susceptible regions. This paper studies the suitable coating technologies that could be implemented for hydro turbines, in the context of hydro power plants exposed to sediment particles. The review has shown numerous materials and approaches of applying the coating, their performance evaluation using experiments and important findings. This paper also discusses on different methods of characterizing the coating, mechanical integrity as well as the tribological behavior of the coated material.