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采用高精度大涡模拟方法,对5°来流迎角、马赫数0.4、三个不同雷诺数(55 000、100 000和150 000)的NACA 0025翼型进行仿真,研究低雷诺数条件下翼型的气动特性。通过对比分析3种工况的计算结果,发现翼型绕流存在两种不同的分离流态:Re=55 000和100 000时,翼型上表面出现大尺度的开式分离,形成宽的尾迹区;Re=150 000时,上表面边界层分离后再附到翼型表面,形成时均化的闭式分离泡,尾迹宽度明显减小。无论哪种流态,Kelvin-Helmholtz(K-H)不稳定性均对层流分离诱导转捩过程起重要作用,雷诺数的增加导致转捩过程加速,时均化的分离区也从开式变为闭式。
A high-precision large-eddy simulation method was used to simulate the NACA 0025 airfoil at a flow angle of attack of 5 °, a Mach number of 0.4 and three different Reynolds numbers (55 000, 100 000 and 150 000) Type of aerodynamic characteristics. Comparing the calculation results of three kinds of operating conditions, it is found that there are two different flow regimes around the airfoil: Re = 55 000 and 100 000, large-scale open separation occurs on the upper surface of the airfoil to form a wide wake At Re = 150 000, the boundary layer on the upper surface is separated and then attached to the airfoil surface to form a closed closed-cell separation bubble, the width of the wake is obviously reduced. Regardless of the flow regime, the Kelvin-Helmholtz (KH) instability plays an important role in the process of laminar flow-induced transition. The increase of Reynolds number leads to the acceleration of transition and the time-averaged separation zone changes from open to Closed