Presented here are the numerical calculations of the 3D transonic flow of an ideal gas through an LP steam turbine last stage with exhaust hood, taking into account blade oscillations. The approach is based on a solution to the coupled aerodynamic-structure problem for 3D flow through a turbine stage using the partially integrated method. The blade oscillations and loads acting on the blades are a part of the solution. An ideal gas flow through the stator and moving rotor blades with periodicity on the whole annulus is described by unsteady Euler conservation equations, integrated with the Godunov-Kolgan explicit monotonous finite-volume difference scheme and a moving hybrid H-H rotor blade grid. The structural analysis uses the modal approach and a 3D finite element model of a blade. The proposed algorithm allows for the calculation of turbine stages with an arbitrary pitch ratio of stator and rotor blades, taking into account unsteady-load induced blade oscillations. The pressure distribution behind the rotor blades was non-uniform on account of the exhaust hood. As a result of the fluid-structure interaction and exhaust hood induced nonsymmetrical pressure distribution behind the rotor blades, the first blade mode was no longer bending but bending-torsion.

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