Performance Analysis Of Tower Wake Vortex Tidal Current Energy Capture System With Swing Oscillating Hydrofoil

The total area of the earth's oceans is about 360 million square kilometers,accounting for about 71%of the earth's surface area.Ocean energy has abundant reserves including tidal energy,wave energy,ocean current energy etc.As compared with other renewable energy sources,such as wind energy,ocean energy has the advantages of higher power density and better predictability.On the other hand,large scale ocean energy as well as wind energy projects may damage natural currents,tides and ecosystems.Therefore,this paper explores a way to utilize wind energy and ocean energy jointly,puts forward a swinging motion model of oscillating hydrofoil.Combines the swinging oscillating hydrofoil device with the underwater tower of offshore wind turbine,and designs a tower wake vortex tidal current energy capture system with swing oscillating hydrofoil.Based on the existing offshore wind field,the system can acquire tidal current energy,so as to improve the overall efficiency of offshore wind field.Research also shows that the existence of oscillating hydrofoil can also effectively reduce the fatigue load of the tower,and it is friendly to the aquatic environment in the offshore wind field.The main work of this paper is as follows:At first,the motion mode and energy harvesting mechanism of oscillating wing are introduced,the motion models of traditional oscillating wing and pendulum oscillating wing are established,and the expressions of main performance parameters of oscillating wing in different motion modes are analyzed and derived.Combined with the previous scholars'research conclusions,the scheme of combining pendulum oscillating wing with underwater tower of offshore wind turbine is put forward,and the physical model of tidal current energy capture system of pendulum oscillating wing is established.Then,the lattice Boltzmann method and the related theories of large eddy simulation are introduced,and the numerical model of the vortex tidal current energy capture system in the tail of the pendulum oscillating wing tower is established and verified.The NACA0015 airfoil is taken as the research object,according to the pressure distribution and attached vortex on the hydrofoil wing surface with different parameters,the hydrodynamic performance of the pendulum oscillating wing placed in uniform incoming flow and tower wake at Reynolds number of 400 was analyzed,and the concrete effects of the heave motion parameters,pitch motion parameters and hydrofoil chord length on the pendulum oscillating wing were explored.It reveals the influence mechanism of tower wake effect on the energy capture performance of pendulum oscillating hydrofoil,summarizes the characteristic law of motion parameters of pendulum oscillating hydrofoil capturing tidal energy,and finds that there is a high efficiency range of pendulum oscillating hydrofoil around 80 degrees of pitching amplitude.Due to the vortex behind the tower,the synchronization between the lift coefficient and the heave speed of the pendulum oscillating wing is better,it takes longer to do positive work,and it can generate more power,which has a significant effect on the improvement of the energy capture efficiency of hydrofoil.Especially when the pitch amplitude is 70 degrees and other parameters are the same,the energy capture efficiency of hydrofoil increases from 26.2%to 32.2%.Meanwhile,after the pendulum oscillating wing is added to the wake vortex area of the tower,the hydrodynamic load of the tower is reduced by about 3%,and the vortex shedding of the tower is also slowed down,thus reducing the fatigue load of the tower caused by the flow around the blunt body,which can enhance the anti-fatigue performance of the tower to a certain extent.At last,the anharmonic pitching motion model of the pendulum oscillating wing and the trailing edge flap swing model are established.Preliminary analysis of the influence of nonsinusoidal oscillation and trailing edge flap on the energy capture performance of the system lays a foundation for further optimization design of the pendulum oscillating wing.