基于壁面吹气的高超声速圆锥湍流边界层减阻控制研究
RESEARCH ON DRAG REDUCTION IN HYPERSONIC TURBULENT BOUNDARY LAYER OVER BLUNT CONE SUBJECT TO WALL BLOWING
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摘要: 在高超声速飞行条件下, 湍流摩阻相较于较层流状态增大3-5倍, 严重制约高超声速飞行器的航程与气动性能, 亟需发展有效的流动控制方法以实现高超声速湍流边界层减阻, 并深入揭示其物理机制. 本文采用直接数值模拟(Direct Numerical Simulation, DNS)方法, 以壁面吹气为控制手段, 针对三维高超声速钝锥背风面湍流边界层开展减阻控制研究, 并重点关注了控制区内的减阻机理. 结果表明, 在当前控制策略下, 壁面吹气能够有效降低钝锥背风面的摩阻系数, 控制区域内减阻率约为31.25%. 该减阻效果主要归因于平均粘性剪应力的减小. R-D(Renard-Deck)摩阻分解方法进一步表明, 壁面吹气通过增大法向速度( \tildeu_yn )从而减小了流向增长项(Cf,G1), 最终导致总摩阻减小. 针对边界层内层大尺度相干结构及频谱特性的分析表明, 吹气使以发卡涡为代表的大尺度相干结构的流向尺度减小. 通过小波变换得到边界层内密度脉动的时频谱, 表明吹气削弱了大尺度结构对密度脉动的贡献, 同时抑制了大尺度运动的间歇性, 导致大尺度结构在边界层内层出现的频率相对增加, 最终增大了内层的湍流强度. 该发现或可为在壁面吹气控制下抑制湍流脉动、进一步提升减阻效率提供可行方向.Abstract: Hypersonic vehicles hold immense strategic significance, occupying a pivotal position in modern aerospace development and representing a crucial frontier in contemporary technological competition. Under hypersonic flight conditions, the turbulent skin friction drag is typically three to five times greater than its laminar counterpart, thereby posing a severe constraint on the range and aerodynamic performance of hypersonic vehicles. Therefore, effective flow control methods are urgently required to achieve drag reduction in hypersonic turbulent boundary layers (TBLs), and it is equally essential to reveal the underlying physical mechanisms. In this study, direct numerical simulation (DNS) is employed to investigate the drag reduction performance of wall blowing on a hypersonic blunt cone, with particular attention paid to the drag reduction mechanism within the control region. The results demonstrate that, under the present control method, wall blowing effectively reduces the skin friction on the leeward side of the blunt cone by approximately 31.25% within the control region. This reduction is mainly attributed to the decrease in the mean viscous shear stress. To further uncover the underlying physics, the R–D (Renard–Deck) skin friction decomposition is utilized. It further reveals that wall blowing reduces the streamwise growth term (Cf,G1) by enhancing the wall-normal velocity ( \tildeu_yn ), ultimately leading to a reduction in the total skin friction. Analysis of large-scale coherent structures and spectral characteristics within the inner boundary layer reveals that wall blowing reduces the streamwise scale of hairpin vortices, which are representative large-scale coherent structures. Wavelet-based time–frequency analysis of density fluctuations reveals that wall blowing reduces the contribution from large-scale structures and suppresses their intermittent nature. Consequently, the frequency of large-scale structures in the inner boundary layer increases relatively, ultimately enhancing the turbulence intensity in this region. This finding may provide a feasible direction for suppressing turbulent fluctuations and further improving drag reduction efficiency under wall blowing control.
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