Numerical simulation of the relationship between steam flow excitation characteristics and coverage on the governing stage of marine steam turbine

“Coverage” refers to the disparity between the inlet height of the rotor blade and the outlet height of the nozzle blade in the governing stage of steam turbines. The adoption of partial admission operating mode exacerbates the instability of the internal flow field. Therefore, investigating the influence of coverage on the governing stage's internal flow field is of paramount importance. In this regard, numerical simulations are conducted to analyze the internal flow field of the governing stage under partial admission operation, aiming to explore the impact of coverage variation. The results show that coverage significantly affects the excitation characteristics. The steam flow excitation force of the governing stage rotor blades under partial admission will fluctuate periodically in the flow zone of the steam flow. There will be a sudden increase in pressure at the rotating outlet end, particularly at the rotation frequency, two times the rotation frequency, and the blade pass frequency, exhibiting substantial amplitude. Adjusting the coverage to reduce the amplitude of the excitation force at the rotation frequency will result in an increase in the amplitude at the blade pass frequency. This study provides a reference for the design of the coverage of marine steam turbines.