The free surface effects on the hydrodynamics of two-dimensional hydrofoils in tandem

摘要

The hydrodynamics of two dimensional tandem hydrofoils travelling below the water surface has been investigated numerically through potential flow theory. The boundary element method is adopted to solve the boundary value problem. The nonlinear free surface and vortex wake are tracked through time stepping schemes. The downstream hydrofoil is moving in the wake flow of the upstream hydrofoil. The wave induced by the upstream hydrofoil causes the variation of the flow field around the downstream hydrofoil. For tandem hydrofoils with finite longitudinal distance, the effective attack angle and the lifting force of the downstream hydrofoil are affected significantly when there is upwash/downwash flow. The longitudinal distance between the two hydrofoils dominates the hydrodynamic forces of the downstream hydrofoil. The downstream hydrofoil obtains higher lifting force when it is placed below the zero crossing with an upwash flow; a lower lifting force is found when it is placed below the zero crossing with a downwash flow.