Acoustic-structure interaction in disk-disk configurations in water for high head pump-turbines

Francis high-head pumps or pump-turbine runners often have speed and dimension ratios that make acoustic and structural natural frequencies, as well as rotor-stator excitation frequencies, approach each other. When compressibility effect becomes significant, it is not sufficient to only consider the incompressible added mass, which shifts the natural frequencies of the structure. The strong vibroacoustic coupling makes it difficult to distinguish the nature of each mode and the associated effect of the forced response amplification. The project’s main aim is to study a disk-disk system behavior in an acoustic cavity filled with water when the acoustic and structural frequencies are close, as a simplified model of a pump-turbine runner in its casing. It is demonstrated here that the compressibility significantly affects vibration modes of the system, particularly when individual acoustic and structural modes have similar frequencies and spatial coherence, resulting in an increase in energy transmission and a decrease in total natural frequency. Additionally, the system’s rigidity is affected by the cover’s stiffness; when the vibration frequencies of the cover and runner are similar, excitation transmission is divided between them.