Numerical simulation of unsteady flow phenomena and excitation force in control stage of steam turbine

The prominently unsteady effect of the control stage in a steam turbine will result in strong flow excitation force. On the basis of the software ANSYS CFX, a 3-D unsteady viscous model for the control stage of a steam turbine with a partial admission room and a reinforced rib was constructed with the RNG k-ε turbulence model, the dual time step method, the sliding interface model and the structural hexahedron mesh. The simulation results show that the time-averaged unsteady wheel efficiency is lower than steady wheel efficiency. There are greater unsteady axial and circumferential forces in the inlet and outlet blocked areas of the rotor blades. Spectrum analysis indicates that the typical low frequency of the exciting force is 50 Hz. The circumferential distributions of pressure and static entropy are nonuniform and the nonuniformity decreases gradually towards the downstream sections. The mixing and windage losses are larger in the blocked channel, leading to the decrease in the blade work. In addition, the suction pressure of the rotor blade is affected significantly earlier than that of pressure side when the flow passes the blocked channel.