In order to obtain the optimum fatigue performance, 35CrMo steel was processed by different heat treatment procedures. The microstructure, tensile properties, fatigue properties, and fatigue cracking mechanisms were compared and analyzed. The results show that fatigue strength and yield strength slowly increase at first and then rapidly decrease with the increase of tempering temperature, and both reach the maximum values at a tempering temperature of 200 °C. The yield strength affects the ratio of crack initiation site, fatigue strength coefficient, and fatigue strength exponent to a certain extent. Based on Basquin equation and fatigue crack initiation mechanism, a fatigue strength prediction method for 35CrMo steel was established.

The flow induced motion (FIM) of an elastically mounted trapezoid cylinder with different body shapes is numerically studied by solving two-dimensional unsteady Reynolds-averaged Navier-Stokes equations. The trapezoid cylinder is mounted on end-supporting linear springs constrained to oscillate normal to the direction of flow and the axis of cylinder. Numerical simulations were performed in Reynolds number(Re) range from 10 000 to 120 000. The ratio of the rear and front edge width of the cylinder, λ, varies from zero to one. Both vortex-induced vibrations (VIV) and galloping are observed for the cylinder in the tested cases. The VIV upper branch for trapezoid cylinder with λ=0.8 and square cylinder (λ=1) are clearly observed in the amplitude and frequency responses. Galloping are exhibited for trapezoid cylinder with different body shapes when Re90 000. The FIM responses of the square cylinder is obviously weaker than the triangle and trapezoid cylinders, since the interaction between the separated shear layers on the upper and lower sides of the cylinder becomes weak as λ increases. The maximum value of amplitude is achieved at 4.51D (D is the front edge width of the trapezoid cylinder) for λ=0.6 at U water * =22.21 (Re=120 000), where U water * =U/( f n,water D) and f n,water is the natural frequency of the oscillatory system in water. Up to 18 vortices are observed in the galloping branch. The displacement trend of the cylinder matches well with the lift forces, especially in the galloping branch.

Hydropower is a major renewable clean energy and is widely used worldwide. The reversible pump-turbine unit of the pumped-storage power station is able to work in two main operating modes as required by the power grid: turbine-mode for power generation and pump-mode for power storage. In order to absorb unstable energies such as wind and solar energy and improve the quality of the electricity, reversible pump-turbines need to frequently change operating conditions, and experience more start-stops under different operating modes in a short period. The unstable flow during these transient processes will lead to high-level stresses on the structural components of the pump-turbine units. Therefore, it is of great engineering and academic significance to study the flow characteristics and structural characteristics of the unit during the transient processes. This paper has established a numerical calculation model for a prototype reversible pump-turbine unit, has carried out the CFD calculations of the pump-turbine fluid domains during the pump shutdown transient process, and has analysed the corresponding structural dynamic characteristics of the stationary components of the unit with the fluid-structure coupling method. The pressure variation trend of the spiral case outlet during pump shutdown has the same trend as that of the spiral case domain, and the guide vane flow domain. The maximum flow-induced deformation and stress of the stationary structures have a strong correlation with the axial thrust values of the head cover. The maximum deformation occurs at the inner edge of the head cover, and the maximum stress appears in the fillet of the stay vane leading edge. An increase in the number of shutdowns will result in a higher real risk of fatigue damage to the stay vanes. The conclusions obtained are of great value for safe operation, field condition monitoring, fault diagnosis, and predictive maintenance of the pump-turbine units.