【作者】 刘敏；

【导师】 黄志伟（Chi Wai Wong）；

【作者基本信息】 哈尔滨工业大学 ， 动力工程， 2020， 硕士

【摘要】 大部分高速运输机的空气阻力来自于表面摩擦阻力,其表面摩擦阻力又与湍流边界层内涡旋以及条带等相干结构密不可分。因此,抑制湍流边界层内涡旋与条带等相干结构的产生与发展则成为了有效减小表面摩擦阻力的核心问题。据此,本文以减少空气摩擦阻力为目标,将展向狭缝吹气技术应用于控制湍流边界层。本课题研究在三种不同信号模式（包括稳态,非稳态和时间周期的非对称吹气,不对称度γ_s=T_a/T_p,其中T_a和T_p分别表示一个周期内信号幅值增加的时间和一个周期的时间,下标s表示输入信号）下不同的射流频率f⁺（=fν/u_τ²,其中ν和u_τ分别是空气的运动粘度和摩擦速度）和不同的射流角度β（=37°～143°,相对于流向）对减阻量的影响。本实验将利用热线和高精度(10^-4)测力天平技术测量在不同控制工况下采用对局部和空间减阻量的影响,利用流动显示和粒子图像示踪实验对比有无控制下湍流边界层内速度分布和流场结构变化以解释相关减阻机理。研究发现在非稳态（E=12 k V,DC=80%）和非对称信号（E=6～12 k V,γ_s=0.3）激励下,在狭缝下游x⁺=66.7的局部减阻量均随着控制频率f⁺（=0.0134～0.286）的增加先增大（f⁺<0.143）后减小（f⁺>0.143）,在f⁺=0.143下分别达到最大局部减阻量56%和58%。在静风状态的非稳态和非对称吹气（f⁺=0.0143～0.143）控制下,在狭缝近壁面处产生两列涡结构,沿壁面法线方向移动,且涡结构的流向直径d_x⁺和涡心间距D⁺会随着频率的增加而减小,在f⁺=0.286时无法产生连续的涡结构。涡结构的空间分辨率d_x⁺/D⁺与控制频率f⁺呈正相关,在非对称吹气（E=6～12k V,γ_s=0.3,f⁺=0.143）时达到最大值0.603。单狭缝展向吹气产生该展向涡流,在近壁面形成反向流动,从而降低了壁面附近的速度,因此获得更优的减阻。本文在最佳控制频率f⁺（=0.143）的非稳态、非对称吹气和稳态吹气模式的不同吹气角度（β=37°～143°）下进行了局部（x⁺=66.7）和空间减阻量（x⁺=113.3～780）研究。研究发现,无论在何种吹气模式下,空间减阻量均随着射流角度β的增大先增大（β<123°）后减小（β>123°）。稳态,非稳态和非对称吹气模式分别在β=118°,120°和123°时获得28%,35%和37%空间减阻量。在不同射流角度β吹气（尤其在非对称吹气中β=123°）控制湍流边界层时,黏性底层增厚导致转移内外层能量和动量的缓冲层变薄,从而减小表面摩擦阻力。更多还原

【Abstract】 In the era of rapid development of transportation,the air-friction drag accounts for40%to 50%of the total drag of high-speed transport aircraft,and most of the air-friction drag comes from skin-friction drag.The skin-friction drag of high-speed transport aircraft is inseparable from coherent structures such as vortices and trips in the turbulent boundary layer（TBL）.Therefore,how to suppress the coherent structure in the turbulent boundary layer has became the key to reducing skin-friction drag.In this project,a dielectric barrier（DBD）plasma actuator induced blowing jets with different frequencies and different angles in the spanwise slit are used to control the turbulent boundary layer,thus reduce skin-friction drag.This work presents an experimental investigation on the TBL control using DBD plasma-induced blowing through a spanwise slot.Under three blowing modes,including steady,unsteady and periodical with dissymmetric in time（dissymmetric ratioγ_s=T_a/T_p,where T_a and T_p denote the time period with signal amplitude increase and the time period for one cycle,respectively.The subscript s denotes the actuation signal）,different blowing frequencies f⁺（=0.0143～0.286,f⁺=fν/uτ²,whereνand uτare the kinetic viscosity of air and friction velocity,respectively）and jet anglesβ（=37°～143°,with respect to the longitudinal axis）have been invesigated with a view to maximize the friction drag reduction（DR）.A hot-wire measurement technology and a high-resolution(10^-4)floating-element force balance have been adopted to measure the local-and spatial-averaged DR with control.The mechanism of drag reduction is explained by comparing the velocity flow profile and flow structure changes in the turbulent boundary layer with and without control through flow visualization and partical image velocity measurement technique.It has been found that for unsteady（E=12 k V,DC=80%）)and dissymmetrical blowing（E=6～12 k V,γ_s=0.3）modes the drag reduction（DR）increases with increasing f⁺until f⁺reaches about 0.143,and decreases with further increase in f⁺.At the optimum f⁺of 0.143,the unsteady and dissymmetrical blowing can achieved DR of 56%and 58%,repectively.In quescient air,two rows of vortex structures are generated near the blowing slit and moving along the normal direction under unsteady and dissymmetric blowing of f⁺=0.0143～0.143.The streamwise-diameter of vortex d_x⁺and the center-to-center spacing between two adjacent vortices in the same row D⁺decrease with the increasing frequency.When f⁺=0.286,there is no continuous vortices generated.Under dissymmetrical blowing of f⁺=0.143 andγ_s=0.3,the spatial fraction d_x⁺/D⁺of the vortex structure is positively correlated with the f⁺,which is found to be 0.603,the highest among all cases.It is indicated that the vortices adjacent to the wall influence a large portion of the TBL over the entire forcing period.The spanwise vortices form a reverse flow near the wall,thereby reducing the velocity near the wall,thus achieving better drag reduction.In this study,local（x⁺=66.7）and spatial-averaged DR（x⁺=113.3～780）are studied at different blowing anglesβ（=37°～143°）under steady,unsteady and dissymmetric blowing at the optimal f⁺（=0.143）.It has been found that for any given blowing modes the drag reduction（DR）increases with increasingβuntilβreaches about 123°,and decreases with further increase inβ.The steady,unsteady and dissymmetric blowing obtain the space drag reduction of 28%,35%and 37%atβ=118°,120°and 123°,respectively.Mean streamwise velocity profiles indicated that the sublayer would thickened at blowing control with various jet angles.The thickened sublayer leads to a thinner buffer layer（especially atβ=123°in dissymmetrical blowing）where the energy and momentum transfer between the inner and outer layer,as well as the turbulence production,take place mostly.更多还原