Study Of Flow Around Airfoil With Bionic Structure Based On Vortex Theory

As a passive control technology with simple structure,remarkable flow control and outstanding drag reduction effect,transverse bionic groove is an effective means to improve the performance of airfoil.Due to the unclear mechanism of the transverse groove structure on the airfoil surface,its reasonable design and wide application are limited.Therefore,it is of clear theoretical significance and engineering application value to investigate the effect of transverse groove structure on airfoil and reveal the control mechanism of transverse groove.In this paper,the transverse bionic groove structure with 5% chord length is proposed to improve the airfoil aerodynamic performance at different positions of the suction surface of NACA0012 airfoil;the three-dimensional unsteady flow field around various bionic groove airfoils is calculated by using large eddy simulation;the influence of the transverse bionic groove structure on the airfoil aerodynamic performance,flow field and separated eddies is investigated.Firstly,the aerodynamic performance of different grooved airfoils under different working conditions is analyzed.The results show that: the transverse groove airfoil aerodynamic performance increases and then decreases with the backward position of the groove;the groove position of the best aerodynamic performance is forward with the forward position of the separation;the main source of drag reduction of the groove airfoil is the reduction of differential pressure drag.The effect of the groove structure on the flow field of the airfoil bypass was investigated.The results show that: the transverse groove structure can significantly delay the boundary layer separation and reduce the low pressure area in the separation section of the airfoil;the setting of the groove structure reduces the local friction of the groove,and the more backward the location of the groove,the more significant the increase of the frictional resistance in the turbulent region;in the velocity field,the velocity curves of the laminar and turbulent regions of the groove airfoil are shifted downward,and the velocity in the local location of the groove shows a slip velocity,which reduces the upper velocity gradient;in addition,the turbulent state before the turning point of the groove airfoil The turbulent state before the turning point is weakened by the weakened velocity fluctuation and reduced Reynolds stress,but the turbulent state after the turning point is enhanced.The vortex definition parameter Liutex and the Liutex-Omega vortex identification criterion are applied to analyze the effect of the groove structure on the surface separation vortex of the airfoil.The results show that the lateral groove structure can significantly delay the position of the separating vortex and weaken the low-pressure pulsation zone caused by the spreading vortex.Before the turning point,the vortex intensity of the grooved airfoil is lower,and the spreading fluctuation of the separated vortex is weakened;while the vortex intensity of the grooved airfoil increases at the turning point and in the turbulent region,which shows that each vortex component of the grooved airfoil has a higher vortex intensity peak at the spreading vortex fragmentation,and the more the location of the grooves is backward in the turbulent region,the more significant the increase of the flow direction vortex intensity.The spreading vortex rotates in different directions and has different effects on flow separation when the lateral grooves are placed at different locations,and the grooves only have a normal full-section weakening effect on the pre-turn region;the spread to correlation of the spreading vortex generation and evolution of the groove wing type increases,and the interference between the front and back vortices decreases,but the fragmentation of the spreading vortex and the generation of the streamwise vortex increase.The research approach and related conclusions in this paper provide an important basis for the design and application of transverse trench structures.