The mechanical integrity of turbine blade rows might be compromised by transient aerodynamic effects that occur in interaction with the diffuser. Effectively addressing this issue requires the prediction of the effects and the creation of a basis for their evaluation. This paper focuses on the specific case of diffuser humming in steam turbines. The paper describes the results obtained from two turbine diffusers with different pulsation frequencies calculated and tested under identical conditions. One diffuser forced a resonance of the last-stage blade row, while the other diffuser ensured the absence of resonance. The basic principles are described that allow estimating and quantifying the pulsation frequencies of the fluctuating pressure. To evaluate the developed approach comprehensive test runs were conducted using a Siemens low-pressure turbine test rig. These measured results are shown to provide validation of the calculation method.

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