不同雷诺数下翼型气动特性及层流分离现象演化
收稿日期: 2016-04-20
修回日期: 2016-09-19
网络出版日期: 2016-09-21
基金资助
国家自然科学基金（11672282，91216116）；国家“973”计划（2014CB744100）
Aerodynamic characteristics of airfoil and evolution of laminar separation at different Reynolds numbers
Received date: 2016-04-20
Revised date: 2016-09-19
Online published: 2016-09-21
Supported by
National Natural Science Foundation of China (11672282, 91216116); National Basic Research Program of China (2014CB744100)
低雷诺数下空气黏性效应突出，翼型表面普遍存在层流分离现象，相比常规雷诺数情况气动特性显著恶化。采用带预处理的Roe方法求解非定常可压缩Navier-Stokes方程的数值模拟技术和低雷诺数低湍流度风洞油流显示试验技术，对FX63-137翼型不同雷诺数下气动特性和流动结构展开深入研究。通过风洞油流显示试验可以清晰获得低雷诺数层流分离流动的两道油流汇集线。数值模拟结果表明其分别为时均化主分离线和二次分离线，两种结果定性定量均吻合较好，证明了本文的研究方法有效可靠；雷诺数从500 000降至20 000，翼型气动特性和层流分离流动结构均发生显著的变化，伴随阻力系数剧增和升力系数剧降，时均化流动结构从附体至出现经典的长层流分离泡，并最终演化为后缘层流分离泡，相应的两种分离泡的非定常流动结构也存在显著差异；对于阻力系数和升力系数而言，存在不同的临界雷诺数，因为导致阻力系数剧增的机理在于经典长层流分离泡的产生使翼型压差阻力大增，而造成升力系数剧降的主要原因在于后缘层流分离泡使得等效翼型后部弯度减小；非定常结果显示正是由于翼型表面漩涡周期性的生成与脱落，才造成了低雷诺数下升力系数的周期性波动。翼型上表面主分离涡即将脱落时，流线在后缘附近再附，升力系数达到峰值；而当流体从下表面向上卷起二次分离涡时，尾部流线大尺度分离，升力系数降至谷值。
刘强 , 刘强 , 白鹏 , 李锋 . 不同雷诺数下翼型气动特性及层流分离现象演化[J]. 航空学报, 2017 , 38(4) : 120338 -120338 . DOI: 10.7527/S1000-6893.2016.0257
Due to the outstanding air viscosity at low Reynolds number, laminar separation is common on airfoil surface, resulting in the deterioration of aerodynamic characteristics compared with those at general Reynolds number. The numerical simulation technology for solving the unsteady compressible Navier-Stokes equations with the preconditioning Roe method and oil flow visualization in the low Reynolds number low turbulence wind tunnel is used to investigate the aerodynamic characteristics and flow structures of the FX63-137 airfoil at different Reynolds numbers. The main conclusions are described in the following. Two clear oil accumulation lines are captured in laminar separation flow through oil flow visualization. Numerical results show that the lines are the primary and secondary separation lines respectively. The qualitative and quantitative results of the two technologies are in good agreement, showing the effectiveness and credibility of the research method in this paper. Airfoil dynamic characteristics and laminar flow separation structures change significantly with the decrease of Reynolds numbers from 500 000 to 20 000. With the sharp increase of drag coefficient and reduction of lift coefficient, the time-average flow structure develops from attachment to classical long laminar separation bubble, and eventually evolves into trailing-edge laminar separation bubble. Correspondingly, two types of separation bubbles are significantly different in unsteady flow. There are different critical Reynolds numbers for the drag coefficient and lift coefficient. The reason is that the drag coefficient increases as the long laminar separation bubble can increase the pressure drag, while the lift coefficient sharply decreases as the appearance of trailing-edge laminar separation bubble can cause the decrease of equivalent airfoil camber. Unsteady results display that it is because of the generation and shedding of periodic vortex on airfoil surface, the lift coefficient has periodic fluctuation. When the main vortex is about to shed, the streamlines are near the trailing edge, and the lift coefficient reaches the peak. When the fluid is rolled up to generate the secondary vortex, the streamlines separate significantly, and the lift coefficient reduces to the valley.
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