A new calculation model is proposed to simulate flows in the steam turbine stages with balance holes in this paper. The model describes the flows in a 2.5 stage turbine with focus on the second stage and the corresponding seals, balance holes and disk cavities. The aerodynamic performance of the turbine stages is predicted by using a three-dimensional Reynold-Averaged Navier-Stokes (RANS) solver. The Spalart-Allmaras one equation turbulence model is adopted, and the RANS solver is run in steady mode using the mixing plane approach. In order to analyze the impact of leakage flow on main flow, the aerodynamic performance of the ideal flow path turbine stages (without balance holes and seals) is also calculated. The numerical results show that the total-total efficiency of the turbine stages with balance holes is 1.81% lower than that of ideal flow path turbine stages. The flow characteristics in the seals, disk cavities and balance holes and their influence on the mainstream are described. Finally, the influence of the balance hole diameter and radius crossing the balance hole axis on the turbine stage performance is studied. The variations of the torque, axial thrust and relative efficiency with the diameter and radius are presented respectively.

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