Direct numerical simulation of supersonic boundary layer transition induced by gap-type roughness

IF 2.9 3区 工程技术 Q2 ENGINEERING, MECHANICAL
Hongkang Liu, Kehui Peng, Yatian Zhao, Qian Yu, Zhiqiang Kong, Jianqiang Chen
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Abstract

The transition of the supersonic boundary layer induced by roughness is a highly intricate process. Gaining a profound understanding of the transition phenomena and mechanisms is crucial for accurate prediction and control. In this study, to delve into the flow mechanisms of a transition in a supersonic boundary layer induced by the medium gap-type roughness, direct numerical simulation is employed to capture and analyze the transition process. Research indicates that as the flow over the flat plate passes the gap, the spanwise convergence effect leads to the formation of both upper and lower counter-rotating vortex pairs. As the flow progresses, these counter-rotating vortex pairs in the central region exhibit attenuation, with streamwise vortices developing on both sides. At a certain downstream distance, the boundary layer becomes unstable, triggering the formation of streamwise vortex legs. These streamwise vortex legs undergo further evolution, transforming into hairpin vortices and leg-buffer vortices. The formation of the central low-speed zone downstream of the roughness element is mainly attributed to the lift-up effect of the low-speed flow propelled by the central counter-rotating vortex pairs. The low-speed streaks on both sides are primarily influenced by the streamwise vortices. Through a meticulous analysis of the turbulent kinetic energy distribution and its generation mechanisms during the transition phase, this study infers that the primary sources of turbulent kinetic energy are the hairpin vortices, leg-buffer vortices, and their consequent secondary vortices. Combined with modal analysis, the study further elucidates the generation and breakdown of hairpin and leg-buffer vortices.
间隙型粗糙度诱发超音速边界层过渡的直接数值模拟
粗糙度引起的超音速边界层过渡是一个非常复杂的过程。深刻理解过渡现象和机制对于准确预测和控制至关重要。在本研究中,为了深入探讨介质间隙型粗糙度诱导的超音速边界层过渡的流动机制,采用了直接数值模拟来捕捉和分析过渡过程。研究表明,当流过平板的气流通过间隙时,跨向收敛效应会导致上下反向旋转涡对的形成。随着气流的前进,中心区域的这些逆旋转涡对出现衰减,两侧形成流向涡。在下游一定距离处,边界层变得不稳定,引发流向涡腿的形成。这些流向涡腿进一步演变,变成发夹涡和涡腿缓冲涡。粗糙度元件下游中央低速区的形成主要归因于中央反向旋转涡对推动的低速流的抬升效应。两侧的低速条纹则主要受到流向涡的影响。通过对过渡阶段湍流动能分布及其产生机制的细致分析,本研究推断湍流动能的主要来源是发夹涡、腿缓冲涡及其随之产生的次级涡。结合模态分析,该研究进一步阐明了发夹涡和腿缓冲涡的产生和分解。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
CiteScore
4.50
自引率
4.30%
发文量
35
审稿时长
11 weeks
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