Dynamic response of a NACA0009 hydrofoil under cavitation conditions

The dynamic response of an hydraulic machine is greatly affected by the water due to the added mass effect . However, the presence of cavitation can change the modal response of the coupled fluid - structure system because it modifies the properties of the surrounding fluid, i.e. the speed of sound and density. In this paper, a FEM - based acoustic - fluid model has be en used to simulate the dynamic response of a NACA0009 hydro foil with attached leading edge cavitation . The n atural frequencies and the corresponding mode shapes have been compared for the hydrofoil in air, in still water and in cavitation conditions. The numerical predictions show a good agreement with the experimental results obtained in a high - speed cavitation tunnel. They confirm that different fluid conditions can modify the mode shapes in comparison with the modes in air. The nodal lines of the torsio n and the second bending modes are slightly shifted with water and cavitation. Furthermore, the third mode of vibration under cavitation conditions appears as a combination of the torsion and the second bending shapes. The results indicate that such altera tions are mainly induced by the value of the speed of sound inside the cavit