Studies On The Characteristics Of Aerodynamic And The Design Methods For Wind Turbine Blades With Vortex Generators

Variable Pitch wind turbine blades easily occur flow separation at inner span during the wind turbine normal operating,and effect the wind rotor absorbing more wind energy.Study show that add an additional device on the blade is a flow control method to improve the blade aerodynamic performance.Vortex generators with the simple structure and easy installing,are often used for flow control,and gain more attention by scholars and wind power enterprises.However,there exist many unsolved scientific problems which effect the vortex generators applied in the blade flow control.The problems include the vortex generator size selection,the better VGs shape,the better position to place the VGs on the blade surface,the optimal combination of VGs and the rule about the blade intensity by the VGs to the blade aerodynamic performance etc.For these reasons,firstly,take vortex generators on the flat plane as model,use CFD method,and investigate the influence of vortex-generator height H(H=0.18,0.2?,0.5?,1.0? 1.5?,2.08(8 is the boundary layer thickness)),vortex generators setting angle ?(?=10°15°,20°,25°,30°),and vortex generators step ?(?=3 H,5 H,7 H,9 H)influences on the disturbed flow characteristics of vortex generator.Results show that vortex intensity and vortex core radius is proportional to vortex generator height,and the same characteristics law between them and the average kinetic energy at the vortex generator height.And vortex generator shape resistance is also proportional to the height,when H?1.0?,boundary sublayer fluid kinetic energy remains unchanged,while vortex generators shape drag increases with the height raises;Vortex generator installation angle show the proportion law to the vortex intensity,while vortices dissipation speed along the downstream of the vortex generators is just reversed.Vortex generator fluid boundary sublayer kinetic energy is inversely proportional to the step of vortex generators.However,shorten the step of VGs,the vortex core center distance from the wall will be lifted,and the span-wise vortex development will be restrained.Further more,the influence rule of vortex generators disturbed characteristic under the three different kinds of VGs shape(triangle,trapezoid,rectangle)is investigated.Results show that rectangle vortex generator has the highest boundary sublayer fluid kinetic energy,followed by trapezoid,triangular minimum.However,triangular vortex generators cause less wall friction deficit and pressure deficit,followed by the trapezoid,rectangle maximum.So triangular vortex generator is best for the separation flow control among the three different shapes.Then take the classical wind turbine airfoil DU93-W-210 as test case,using wind tunnel experiments,study focus on the airfoil aerodynamic characteristic influence law of VG height H(H=4mm,6mm,8mm),VGs installation angle ?(?=10°15°,20°,25°,30°),VGs step ?(?=5H,7 H,13 H,19 H)and VGs spacing S(S=3 H,5 H,7 H,9 H).Results show that airfoil lift coefficient is not proportional to vortex generator height,while the drag coefficient has a direct correlation with vortex generator height.Vortex generators installation angle is smaller,the airfoil lift drag ratio is higher,but the airfoil lift coefficient show an inverse proportional relation to the setting angle.There exist the optimal step of vortex generators,when ? =5H,airfoil lift coefficient reach the peak.And when ? ?13H,the overall effect of airfoil lift coefficient and lift drag ratio works better.Vortex generator spacing has the same characteristics with the step,namely when S?5H,airfoil lift coefficient is the highest.while S?13H,the total effect of airfoil lift coefficient and lift drag ratio is better than other spacing situation.More in detail,take eight typical thickness airfoils along the span-wise of the wind turbine as model,using CFD method,study the different thickness straight airfoil segment influence law by the vortex generator.Results show that the thicker the airfoil is,the smaller stall angle turns,and the smaller the maximum lift coefficient.When airfoil do not occur flow separation,VGs will reduce airfoil lift force and lift drag ratio.When a small flow separation of the airfoil occurs,VGs can effectively delay flow separation,increase the stall attach angle,promote the lift drag ratio.Finally,take a typical megawatt wind turbine blade as model,based on the BEM method,study the aerodynamic performance of VGs.Results show that,when place vortex generator along the full span(0-1.OR)?rotor power increase by 6.6%at most,axial thrust increase by 7%.While place vortex generator along the inner span(0-0.3R),rotor power increase up to 6%,axial thrust up to 3%.Under the great majority of annual average wind speed,VGs placing along the full span is better than only placing along the inner span.Furtherly,using CFD method,study the vortex chord-wise installation position influence law to the blade aerodynamic performance.Results show that where to set the vortex generator is very important.When VGs is placed in the transient zone,the separation point of blade surface will be moved in advance,down the blade aerodynamic performance.While placing in the laminar flow zone and turbulent flow zone,VGs will restrain the flow separation at some extent,and add the blade aerodynamic performance.In addition,the effect of VGs placing in the turbulent flow zone is much better than that in the laminar flow zone.On this base,study the combination relation of the vortex generator's four key parameters(height H,installation angle ?,step ?,spacing S)?found that the step ?,is the most important factor,then installation angle,height H,and the smallest is the spacing S.Furtherly,based on CSD and CFD coupling method,study the blade intensity effect of vortex generators.Results show that vortex generators will increase the quantity of blade flap-wise deformation and strain deformation.However,deformation amplitude is so slow that it can be ignored.The blade load factor with vortex generator decreases slightly,which means vortex generators will reduce the blades strength.Similarly,the impact is also very low,so it will not cause the structure unsafety of the blades.