The flow characteristics of the draft tube of a Francis turbine have a significant influence on turbine stability. Numerical simulations were performed for a Francis turbine under three different output conditions of 20%, 100%, and 120% at the rated and maximum heads. Laser Doppler velocimetry (LDV) tests were conducted to test the flow characteristics of the draft tube of the Francis turbine model. The flow characteristics in the draft tube, the mechanism of the flow characteristics change, and the effect of the opening on the vortex rope were analyzed. The results showed that the large and invisible vortex in the conical cross-section at the inlet of the draft tube gradually changed to a tangible vortex rope as the guide vane opening (GVO) increased. The pressure and velocity are significantly influenced by the GVO, and the flow characteristics in the draft tube improve as the GVO increases. Simultaneously, the influence range of the vortex rope increased as the head increased.

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In this paper, in order to study the wear of the guide vane of the hydraulic turbine, a test bench was built according to the actual internal flow of the hydraulic turbine of the power station. The value of the wear of the surface of the guide vane after polishing was reduced by 18.1 μm compared with that before polishing of P = 30.9 MW and by 12.5 μm at P = 42.8 MW. In order to reduce the influence of sediment wear on the guide vane, a 0.3 mm thick tungsten carbide coating was sprayed on its surface, and the wear of the guide vane after spraying tungsten carbide was obtained. The wear of the guide vane was reduced by about a factor of three to four times compared with that before spraying. In addition, according to the pH value of 6.73 of the river where the power station is located, the change of dissolved oxygen in the water body will affect the wear of the metal material on the surface of the guide vane, and the dissolved oxygen varies with the change of the water body temperature, so we simulated the temperature of the water body in the flood and the dry period of the power station, and got the wear amount of the polished guide vane in the flood period under the two working conditions of 28.1 μm and 47.3 μm, respectively. The wear amounts of the guide vane in the dry period were 25.2 μm and 43.9 μm, respectively. In addition, the service life of the guide vane before and after polishing and after tungsten carbide spraying was estimated based on the wear data obtained from the test, which provides a basis for power plant maintenance.

This paper describes three-dimensional unsteady simulations of sand–water flow within a turbine passage. Sand abrasion of a movable guide vane made from ZG06Cr13Ni4Mo is tested before and after tungsten carbide spray-coating. ZG06Cr13Ni4Mo forms medium- and high-strength stainless steel castings for engineering structures. Different sand particle sizes produce different wear forms on the guide vane. For 0.4-mm sediment particles, the guide vane head is more seriously worn by impact; for 0.058-mm sediment particles, the guide vane tail is more seriously worn by sediment scouring. Spray-coating the guide vane with tungsten carbide produces significant anti-sand-wear performance. Before tungsten carbide spraying, the total guide vane wear at the maximum position reached 45 μm after 90 h of testing, but after spray-coating, the guide vane wear at the maximum position was only 2.6 μm after 136 h of testing. Sand abrasion test results before and after tungsten carbide treatment are used to derive a calculation formula that provides a basis for anti-silt-abrasion hydraulic turbine design and operation. The movable guide vane’s life expectancy in a power plant was estimated. Before spraying, the guide vane had to be replaced after 22.7 months of operation at P = 11.4 MW, but it operated for 44.2 months after spray-coating.

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