Study on three dimensional flow of last stage with lashing wire and tip clearance in steam turbine

In order to obtain the detailed information of the three-dimensional viscous flow in the last stage with lashing wire and tip clearance, the numerical model and calculation method was developed by adopting the renormalization group turbulence model (RNG k-ε), wall-function method, structure grid and mixing plane approach. Numerical results indicate that the spanwise static pressure of blade and the streamline near the lashing wire change significantly, especially on the suction surface. It is shown that there are vortices system on the blade tip and suction surface as flow separation appears. Meanwhile, the static pressure on pressure surface near the blade tip reduce as the existence of tip clearance, and it was lower than the static pressure of suction surface in some region. Furthermore, for the isentropic efficiency of last stage, the model with lashing wire, the another model with lashing wire and tip clearance compared with the model without lashing wire and tip clearance show reduction of 0.36% and 1.14%, so the leakage loss is larger than that created by lashing wire. The numerical results obtained in this paper has the engineering application value and it can be used to improve the aerodynamic performance and reliability of turbine stage.