Effect of steel spiral case cushion layer on excitation characteristics of pulsating pressure in turbine flow passage

Embedding the steel spiral case (SSC) with a cushion layer has become a popular design choice in hydropower stations. However, under the excitation of pulsating pressure in turbine flow passage, the influence of the SSC cushion layer on vibration energy transfer characteristics remains unclear. Therefore, based on Wudongde Hydropower Station in China, this paper established a dynamic finite element model for a standard unit section, then applied pulsating pressure of flow passage in different zones according to model test data of hydraulic turbine, so the influence of cushion layer range and elastic modulus on vibration response of powerhouse structure and hydraulic turbine metal structure were studied. The results showed that the SSC cushion layer had definite vibration isolation effect for the superstructure of the powerhouse. The vibration response of the slab beam-column structure of the powerhouse decreased with the extension of the cushion layer′s plane range and the meridian section range. There are two issues worth noting: ① the vibration amplitude is no longer sensitive when the plane angle exceeds 180°; ② the vibration isolation effect is not significant when the meridian section extends 15° downward from the waist line. Reducing the elastic modulus of the cushion layer can enhance its vibration isolation effect. However, within the conventional elastic modulus range of 2 to 5 MPa, the benefits obtained are relatively limited. The vibration response of the SSC under the cushion layer area is significantly greater than that of the SSC without the cushion layer. The cushion layer has little effect on the stay ring′s vibration response.