To investigate the performances of the last stage of a huge power and half-rotation speed nuclear steam turbine, a 3-stage wet steam turbine performance test rig is designed. Experiments are carried out to test the performances of the modeled turbine at design and off-design operating points. Frozen-rotor steady-state computations are performed on design point as well as off-design operating points. The calculated massflow rate, power and efficiency are validated with the experimental data and the flow details are discussed. Steam humidity, temperature and pressure are compared with the tested results. With the detailed 3D flow results derived with numerical simulations, it is found that for the investigated steam turbine, the performances of the first two stages only changes slightly when turbine operation point changes, meanwhile, the aerodynamic quantity distribution characteristics also keep nearly almost the same. However, for the last stage, both efficiency and flow details changes significantly when operating point changes. It is also found that for the last stage, flow region with maximum steam humidity is located at downstream of stator near hub and downstream of blade near tip, where water droplets mostly likely to be formed and accumulated.

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