Numerical Simulation Of Wake Flows And Coupled Aero-hydro Dynamic Analysis Of Floating Offshore Wind Turbines

Wind energy is one of the most promising renewable energy.As an important part of ocean exploiting equipment,the offshore wind turbine has a great potential space to develop.Compared to land-based wind turbines,offshore wind turbines are more large-scaling and bear more complex environmental load.Due to vast space and more abundant wind energy resources at deep-water area,the exploitation of offshore wind energy develops towards the deep sea inevitably.The increasing demand of wind turbines mounted in deep water will lead the usage of floating foundation.For the floating wind turbine system,there are many problems waiting to be solved: how to effectively modeling the unsteady aerodynamics of the rotor,how to modeling the wake flows for the sake of reducing wake loss and the lake of coupled aero-hydro dynamic simulation codes.The open source CFD toolbox OpenFOAM is used as basic tool in the study.This dissertation first has a study on aerodynamic performance and wake flows of wind turbines,and then investigate the effects of platform surging and pitching motion on the aerodynamics of rotor,finally conduct fully coupled dynamic analysis of floating offshore wind turbines(FOWT).Firstly,this paper investigate the actuator line model in detail.The actuator line model(ALM)provides a means of effectively displacing the real blade surfaces with virtual actuator lines,in consequence,has a benefit of saving computational time.This paper investigates the aerodynamic loads and wake flows of wind turbines using ALM.This paper also validate the ALM model and reveal some characteristics of wind turbine wake flow field using the “Blind Test 1” experimental data.Sequentially,this paper makes an attempt to develop an unsteady actuator line model(UALM)by considering the platform motion in the initial actuator line model.In order to validate the UALM,the results of this new model are compared to that of unsteady blade element-momentum theory and CFD.Then,this new model is used to investigate the effects of platform surging and pitching motion on the aerodynamic loads and wake flows of rotor.Finally,this paper embed the UALM code into the CFD solver naoeFOAM-SJTU,and then performed two kind of full-system simulations with different complexity using the coupling analysis code.First,the wind forces are simplified into a constant thrust in the simplified model;second,the fully coupled dynamic simulation with wind and wave excitation is conducted by utilizing the UALM.The results of two method with different complexity are compared and the aero-hydro coupled effects are investigated in this paper.