Understanding sediment erosion on hydropower turbines

Fifteen percent of the world’s electrical energy comes from hydropower, making it the leading source of renewable energy. But due to the vast amount of abrasive sediment carried in rivers, hydropower turbines are constantly being eroded.

To understand the degradation of hydropower turbines by sediment erosion, Shrestha et al. studied the erosion effects on a Francis turbine. These turbines use a runner, which produces power, and a set of guide vanes, which directs the flow of the water. For a guide vane to operate, a small gap is maintained towards its axial sides. These gaps, called clearance gaps, enlarge due to high pressure or due to erosion of the guide vanes. Using numerical modeling, the researchers compared guide vanes with increased gaps to study water flow and erosion of the runner.

The authors found this pressure difference on guide vane sides to cause a flow from the high pressure side to the low pressure side, resulting in leakage. Their results showed that as the gap was widened, leakage increased and caused more turbulence that accelerated erosion at the leading edge of the inlet of the runner. This highlights the cascading effect of erosion inside the turbine system and the importance of focusing maintenance efforts on preventing clearance gap erosion.

The researchers’ simulations also showed increased erosion on the side of the runner that experienced higher pressure from the flow of water. They validated this previously unobserved finding with an experimental study.

“It is now clearly demonstrated that the erosion in guide vanes could also cause erosion in runners,” said author Kushal Shrestha. “That it was proven experimentally was really exciting.”

Source: “Effect of leakage flow from guide vanes on erosion of the runner of Francis turbine,” by Kushal Shrestha, Bhola Thapa, Sailesh Chitrakar, Zhiwei Guo and Zhongdong Qian, International Journal of Fluid Engineering (2026). The article can be accessed at https://doi.org/10.1063/5.0298836 .