A numerical calculation method and experimental study on dynamic stress of steam turbine long blades with respect to vortex-induced effects

Aiming at the outstanding problems of flexibly operating the steam turbines' overall working conditions, a new dynamic stress numerical calculation method for the steam turbine long blades was proposed with respect to vortex-induced effects. The low-pressure last-stage blades of a 1000 MW air-cooled steam turbine were taken as the research object. The validity of the calculation method was demonstrated by the long blade dynamic test. The theoretical analysis shows that the vortex-induced effect on the blade surface caused by the flow separation is the key factor in increasing the dynamic stress of the blade at low-load operating conditions with constant back pressure. For the engineering application, it is feasible and effective to calculate and analyze the dynamic stress of the blade under different working conditions by taking the pressure fluctuation value on the blade surface of the aerodynamic flow field as the excitation factor for the structural field excitation force. By comparing several schemes, the simulation results are in good agreement with the test results. Both the simulation and dynamic test results show that, under constant back pressure, the maximum dynamic stress of the last-stage blade appears at about 20% load. It is found that the peak value of the dynamic stress of the tested blade is about 5% of the allowable value at the design back pressure, which has sufficient vibration resistance strength and safety margin, well meeting the requirements of flexible, safe, and reliable operation for the steam turbines' overall working conditions.