Hydrodynamic Investigation Of Three-Dimensional Oscillating Hydrofoil Near The Free Surface

The oscillating hydrofoil device design is comes from the observation of fish tail and bird wing. The oscillating hydrofoil has the higher propulsion efficiency and can provide a larger transient lifting force. The hydrofoil fin device is widely used in the area of propulsion, low speed maneuvering and ship attitude control. Based on the theory of flapping wing device ship motion in waves, ship speed and ship moving stability may be improved. The development and research of flapping wing device has a widely application in the design of high performance vehicle.In the present research, the 3-D hydrofoil has steady forward speed with heavy motion, pitch motion or heave-pitching couple motion. The paper investigates the unsteady hydrodynamic performance of 3-D hydrofoil with large amplitude motion. The theoretical formulation, mathematical method and numerical examples are provided in the present paper.At the first, the paper introduced the basic theory of steady boundary element method. The singularity integral in the computing influence coefficient matrix can be performed by analytical method. The flow computation around a sphere is carried out to verify the analytical method. The hydrodynamic force computation results are presented for a hydrofoil in unbounded fluid.For the moving hydrofoil near the free surface, the effects of the free surface on the hydrofoil can not be ignored. The present paper provided a time-domain numerical method based on the Green's theorem. The Rankine sources and dipoles are distributed on boundary surfaces including the hydrofoil body surface and free surface. The dipoles are also placed on the wake surface. The Kutta condition is satisfied. A time-stepping panel method is employed in the present paper. The effects of the free surface on the hydrodynamic force are presented for the hydrofoil with different moving speed, span length and depth.Configuration hydrofoil model test is carried out to analyze the hydrodynamic performance of hydrofoil near the free surface. The nonlinear free surface boundary condition is introduced to deal with the interaction between the hydrofoils. The results of (?)tion and model test havr been compared and good agreements are (?)(?)the oscillation hydrofoil (?)steady. The hydrodynamic performance (?) time very vortex surface at the tail edge of the foil. The Rankine sources and (?) on the hydrofoil body (?)face and free surface. The dipoles are also (?)wake surface. The Kutta condition is satisfied. Newton-Raphson method is used. The hydrodynamic forces are computed for the hydrofoil with heavy motion, pitch motion and heavy-pitching couple motion in unbounded fluid. The effects of appropriate on the hydrofoil performance are presented.(?)unsteady boundary element method is employed to deal with the hydrodynamic (?)of hydrofoil moving near the fr(?) surface. The computation formulation is (?)The Rankine sources and dipoies are distributed on boundary surfaces (?)the hydrofoil body surface and free surface. The Kutta condition is satisfied. A (?)ping panel method is employed to simulate the flow field around the hydrofoil (?)surface profile. The linear free sirface is utilized. The dipoles are also placed (?)the wake surface. The hydrodynamic forces are computed for the hydrofoil with heavy motion, pitch motion and heavy-pitching couple motion in unbounded fluid. The effects of appropriate parameter on the hydrofoil performance are presented.