Abstract: The turbine impeller was simplified to a disk immersed in fluid， and the vibration differential equation of the disk was established with considering the effect of boundary conditions on natural frequency of the disk. The influence of different disk speed， fluid depth and fluid density on the natural frequency was studied. The results show that the natural frequency of the disk immersed in fluid decreased comparing with the natural frequency of the disk in vacuum. When the disk in fluid is rotated， the mode of the disk is changed from standing wave to traveling wave. Different rotation directions correspond to two different natural frequencies. As the fluid depth reduces， the value of natural frequency decreases. The higher the fluid density is， the lower the natural frequency is.

Key words: turbine, impeller, natural frequency, fluid depth, fluid density