| The efficient development and utilization of water kinetic energy has important scientific merit and practical significance in solving resource shortage,reducing environmental pollution and promoting sustainable development of energy.Under the theoretical framework of the immersed boundary(IB)method,the lattice Boltzmann method(LBM)and the finite volume method are integrated to develop a numerical method for simulating the complex fluid-structure interaction under high Reynolds number.Taking the flapping hydrofoil as the research object,the influences of different geometric shape parameters,kinematic parameters,pitch motion attributes and wave drive system on the hydrodynamics characteristics,propulsion efficiency and energy harvesting performance of the hydrofoil are analyzed in detail.The main research contents and academic contributions are as follows:(1)Based on the implicit diffuse interface IB method,LBM and the subgrid stress model of large eddy simulation,a new strong coupled numerical method for fluid solid interaction under high Reynolds number was developed.For the large-displacement moving boundary problems,the translational velocity of the fluid grid same as the translational velocity of the solid is added to the governing equation to coupling solve the problems without enlarging the computational domain.The Smagorinsky sublattice stress term is added to the momentum equation to represent the small-scale motion of the flow.The predicted velocity field is solved quickly by LBM.The hydrodynamics characteristics of flow over a fixed airfoil,a flexible plate and a flexible cantilever beam under low Reynolds number,as well as flow over a cylinder and a flapping hydrofoil under high Reynolds number are analyzed.The reliability of this method are proved by comparing with the reliable experimental results and literature.(2)The hydrodynamic characteristics of hydrofoil with different heave or pitch motions,as well as the effects of symmetrical NACA hydrofoil shape on the energy harvesting performance were studied.The results show that pure heave motion can not obtain energy from the flow,and the pitch motion properties of the hydrofoil has a great influence on the hydrodynamics characteristics of the hydrofoil.When the ratio of the thickness of the hydrofoil,the distance between the center and the leading edge point,and the the distance between the rotation axis and the leading edge point to the chord length respectively are 0.12,0.4 and 0.35.The power harvesting efficiency of the flapping hydrofoil is optimal.The power harvesting efficiency can enhance about 3.71%compared with the hydrofoil in published literatures.(3)The effects of pitch motion on energy harvesting performance in the semi-active bionic flapping hydrofoil system were studied.The optimal initial phase angle under harmonic pitch motion is 0.5?,and under the optimal initial phase angle,the maximum energy harvesting efficiency of 44.22%was obtained at the amplitude of pitch angle of 60°,which was 12.04%higher than the sine pitch motion.Under the optimal pitch angle amplitude,the highest energy harvesting efficiency is 51.81%when the unharmonic pitch motion parameter?=2.0,and it is about 7.59%higher than that of the harmonic cosine pitch motion attribute.(4)The effects of Reynolds number,hydrodynamic motion parameters and pitch motion attributes on the energy harvesting performance of a semi-active energy collection and propulsion system,in which the heave motion is driven by wave,are studied.The results show that when the wave frequency and pitch motion frequency are equal,under the conditions of low pitch angle amplitude,high wave height and high frequency,the system can generate propulsion upstream,and the motion phase difference of 1.5?with the optimal propulsion performance is achieved.However,the unharmonic pitch motion is not beneficial to improve the propulsion.Under the conditions of high pitch angle amplitude,low motion frequency and the wave height is equal to the chord length of hydrofoil,propulsion can be generated downstream and considerable flow energy can be collected.The propulsion and energy harvesting efficiency are the highest at the phase difference of1.125?,but the net output power is the highest at the phase difference of 1.375?.At the phase difference of 1.125?,when the wave frequency and pitch motion frequency are equal,the energy harvesting efficiency is the highest.However,when the propulsion and net output power are the highest,the pitch motion frequency is about 21.43%higher than the wave frequency.When the parameters of unharmonic pitch motion of?are within the range of 1.25 to 1.5,the energy harvesting efficiency of the system is optimal,the maximum of87.38%is obtained,and the increment of output power and propulsion power are 18.03%and 14.83%,respectively,relative to the harmonic pitch motion.(5)The hydrodynamic characteristics of elastic hydrofoil are studied.It shows that the drag force and lift force are greatly reduced when the hydrofoil is slightly deformed.With the decrease of hydrofoil's deformation,the drag reduction effect is decreasing continuously,but the lift force is increasing greatly.The stiffness of the hydrofoil has a weak influence on the energy harvesting performance of the flapping hydrofoil.Increased Reynolds number from order 10~3 to order 10~4,the increment of energy harvesting efficiency is approximately 7%. |
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