Investigation On Flow-induced Vibration Characteristics Of Flexible Hydrofoil In Unsteady Cavitating Flow

Caviation occurs in many fields such as hydraulic machinery and underwater weapons. Cavitating flow is a complex and multiphase phenomenon which has strong unsteady characteristics. As the application of flexible materials, the unsteady hydrodynamic loads will cause significant flow–induced vibration, which may change the structural performance and the flow field. The unsteady cavitating flow will enhance this effect, so it’s important to study the flow-induced vibration in unsteady cavitating flow.The present thesis is devoted to the flow-induced vibration characteristics of flexible hydrofoil in unsteady cavitating flow. The variation characteristics and their effects are investigated. Principle results are as follows.A set of research method which combines experimental measurement and numerical calculation has been built up. A multi-field synchronous measuring system is used to measure the cavity shape and hydrofoil vibration. A fluid-structure coupling method is developed to simulate the flow field and structure response.The results showed that for the inception cavitation, the cavities develop randomly with vortexes shedding periodically in the weak reagion. The flow leads to the bending and twisting deformation as well as flow-induced vibration. The vibration velocity and displacement vary in high frequency. The vibration contains first three natural vibration and vortex-induced vibration. The lift coefficient characteristics change when compared with rigid hydrofoil.In the sheet cavitation stage, the cavity attaches to the hydrofoil with small-scale cavities shedding from rear end of the cavity. The magnitude of flow-induced vibration increases and it contains first natural vibration and cavity shedding induced vibration. The vibration state varies as the development of sheet cavitation. The lift coefficient of flexible hydrofoil oscillates when small-scale cavities shedding.In the cloud cavitation stage, more acute cavitation development process along with the periodic characteristics can be observed.. One cycle can be divided into three stages which are attached cavity development, cavity fluctuation and cavities shedding. The flow-induced vibration is mainly influenced by the development of cloud cavitation and the main vibration frequency is corresponding to the cavity shedding frequency. The vibration velocity and displacement have different characteristics in three stages. The hydrodynamic characteristics and the flow structure change when compared with rigid hydrofoil.