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首页> 外文期刊>Aerospace science and technology >Non-modal stability analysis of low-Re separated flow around a NACA 4415 airfoil in ground effect
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Non-modal stability analysis of low-Re separated flow around a NACA 4415 airfoil in ground effect

机译：地面效应中NACA 4415机翼周围低Re分离流的非模态稳定性分析

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In this numerical-theoretical study, we perform a linear non-modal stability analysis of the separated flow around a NACA 4415 airfoil over a no-slip ground at low Reynolds numbers (300 = Re = 500) and high angles of attack (12 degrees = alpha = 20 degrees). We find that: (i) the strength of the recirculation zone behind the airfoil is a key parameter controlling the absolute/convective nature of the instability in the boundary layer downstream; (ii) when Re, alpha or the ground clearance increases, the energy gain also increases, with the optimal perturbations switching from being three dimensional to two dimensional; and (iii) classical hairpin vortices, or Klebanoff modes, can be produced by three-dimensional optimal perturbations on a two-dimensional steady base flow containing a laminar separation bubble. Knowledge of the spatiotemporal features of the optimal mode could aid the design of advanced strategies for flow control. This study offers new insight into the transient growth behavior of airfoil-ground flow systems at low Re and high alpha, contributing to a better understanding of the ground-effect aerodynamics of small insects and micro aerial vehicles. (C) 2019 Elsevier Masson SAS. All rights reserved.
机译：在此数值理论研究中，我们对在低雷诺数（300 <= Re <= 500）和大迎角（）时在防滑地面上围绕NACA 4415机翼的分离流进行线性非模态稳定性分析12度<= alpha <= 20度）。我们发现：（i）翼型后面的回流区的强度是控制下游边界层不稳定性的绝对/对流性质的关键参数； （ii）当Re，α或离地间隙增加时，能量增益也增加，最佳扰动从三维转换为二维； （iii）经典的发夹式涡旋或Klebanoff模式，可以通过对包含层流分离气泡的二维稳定基流进行三维最佳扰动来产生。了解最佳模式的时空特征可以帮助设计先进的流量控制策略。这项研究提供了对低Re和高α值的机翼-地面流动系统的瞬态生长行为的新见解，有助于更好地理解小型昆虫和微型飞行器的地面效应空气动力学。 （C）2019 Elsevier Masson SAS。版权所有。

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