Erosion through synergetic effects between cavitation erosion and particle abrasion in silt-laden flow seriously affects the safe operations of hydroturbines. In this review, recent advances of cavitation inception on particles and microscopic interactions between bubbles and particles are reviewed and discussed. For cavitation inception, influences of several paramount parameters (e.g. types, sizes, shape and surface structure of particles, pressurization and memory effects) have been revealed and discussed. The interaction mechanisms between cavitation bubbles and particles are demonstrated using experimental data obtained with a single particle. Through the microscopic interactions, the particles can be accelerated by the collapsing bubbles up to 40 m/s and also be possibly split up by the cavitation, leading to deagglomeration of particle clusters.

A review of microscopic interactions between cavitation bubbles and particles in silt-laden flow

Erosion of material surface due to collision of solid particles has been a challenge to several fields of engineering. Despite of centuries of investigations and research, the exact phenomenon of erosion of surface by the solid particles has not been fully understood. Increasing number of hydropower plants are being built in the regions where rivers are heavily loaded with sediments. This induces material erosion in hydro turbines, leading to change in flow pattern, losses in efficiency, vibrations and even final breakdown of turbine components. To overcome sediment erosion related failures, development of erosion resistant alloys, coatings of the components, and optimization of hydraulic design of the components, are the important practices. In Francis turbines, erosion causes increase of clearance gap between guide vanes and facing plates and cross flow occurs from this increased gap. This cross flow together with other secondary flows disturbs the velocity profile at the runner inlet. Change in velocity profile at the inlet causes additional erosion damage and other undesired effects in the turbine runner. Most of the past studies in Francis turbine were focused to understand the flow phenomenon inside the turbine components and to analyze their effects on design improvements. There is still a need of further fundamental research to understand the effects of sediment erosion of turbine components on the flow phenomenon, and developing better designs of hydro turbines to minimize those effects.

Sediment erosion in hydro turbines and its effect on the flow around guide vanes of Francis turbine

Sediment erosion is caused by the dynamic action of sediment flowing along with water impacting against a solid surface. Hydraulic turbine components operating in sediment-laden water are subject t ...

B. Y. Cai

Papers

Design of Hydraulic Machinery Working in Sand Laden Water