| This dissertation focuses on the study of airfoil flap for vertical axis wind turbine.By attaching flap on the trailing edge of symmetrical airfoil NACA0018,the research was carried out on both the effects of flap geometry on airfoil aerodynamic performance and the impact when flaps are applied on vertical axis wind turbine.A new flap control strategy was came up based on theory analyze of vertical axis wind turbine and static and dynamic performances research on airfoil.Flow field control was achieved at last.The main contents of this dissertation are listed below:1.Background and theory: first of all,the history of wind energy,the advantages of vertical axis wind turbine,history and development of flap are introduced.Then the methods and ideas used in research,numerical simulation method for CFD,governing equations,turbulence model and grid distribution are explained.2.Research was carried out on several geometry parameters including relative length of trailing edge flap,width of flap slot and flap angle based on basic airfoil NACA0018 using S-A turbulence model.Numerical simulation was applied to analyze its static aerodynamic performance.It concludes that first of all,flap could delay the appearance of stall when it has large angle of attack.However,before the appearance of stall,airfoil with flap always has lower lift ratio compared with basic airfoil.In addition,when the airfoil experiences large angle of attack,the pressure difference increases at leading edge and decreases at flap.What’s more,when flap swings to a large angle,high pressure area appearances on the above of trailing edge of flap.When the angle of attack is fixed,tail vertex enlarges with the increase of relative length of flap and moves towards to trailing edge.3.Several models with 0.2 c(c represents the length of wing chord)were built by setting different flap parameters,including relative flap slot width(),flap angle()and the models are all used for CFD numerical simulation to analyze the effect of flap swing on dynamic aerodynamic performance of airfoil.The results show that lift coefficient decreases with the increase of flap slot width when the amplitude of oscillation and swing angle keep the same.When the airfoil experiences same swing angle but different amplitude of oscillation,lift coefficient increases with lager amplitude of oscillation.During a period of flap oscillation,low pressure areas expand and shrink periodically onboth upside and downside of airfoil and as the area on one side falls,the another rises.When the flap keeps a positive angle,the low pressure area on lower surface of airfoil is smaller than that of upper surface while during one oscillate period,the sum of low pressure area on both sides keeps approximately the same.4.Based on the analysis on flap static and dynamic performance with different width of flap slot,the influence of flap control strategy on the aerodynamic performance of vertical axis wind turbine.The results indicates that when the width of flap slot increase,the wave crest of torque coefficient in every period decrease.When the flap angle is 10°,relative slot width is selected to be 1.5%c which could keep the torque coefficient relatively low at the same time keep it in the rated ranges so that it will not do negative work on motor. |
