Sliding grid and dual-time step method-based unsteady flow simulation on the final two stages of a steam turbine is performed without geometry scaling. The behavior and characteristic of unsteady pressure fluctuations on the blade surfaces of stator and rotor blades are investigated in details. FFT is performed on the blade surface pressure fluctuation to estimate the region covered by the unsteady flow perturbation from upstream and downstream. Results show that for long blade turbine stage investigated, pressure loading fluctuation is significant, with the maximum amplitude being equivalent up to level of 61% pressure loading. The loading fluctuation follows the trend of increasing from hub to shroud in stator while contrary trend is followed by the rotor. Among the unsteady perturbation sources causing the significant pressure fluctuations in long blade turbine stage, trailing edge shock is the dominating one, leading significant pressure distortion along circumferential direction, which induces strong interaction on downstream blade row.

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