Credibility of Rotating Disc Apparatus for investigating sediment erosion in guide vanes of Francis turbines

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.