Investigations on unsteady flow excitation and mechanical performance of last turbine stage long blade using fluid-structure interaction method

Detailed numerical investigations on the unsteady flow excitation characteristics and mechanical performance under unsteady surface pressure of last turbine stage long blade are conducted by applying sliding interface method and fluid-structure interaction approach. Unsteady aerodynamic performance of turbine stage is analyzed through solving the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solution and k-ε turbulent model using commercial CFD software ANSYS-CFX. The computational domains include last stage stator domain, rotor domain, shroud domain and curved diffusor. Unsteady pressure on long blade surfaces in every time step is transferred to the mechanical grids of long blade after interpolated in the fluid-solid interface. The mechanical performance of long blade with damper shroud and part-span connector (PSC) is obtained using finite element method (FEM) while considering the unsteady aerodynamic load and nonlinear contact between adjacent damping tip-shroud and PSC. The numerical results show that static pressure on long blade surface presents obvious periodic fluctuation; with the decrease of mass flow, blade loading reduces obviously and separation vortex appears in the diffusor and extends to the rotor passages; the frequency of separation vortex is about 126 Hz; the maximum displacement and maximum Von-Mises stress of long blade both show periodic features.