【作者】 刘洁；

【导师】 翁培奋；

【作者基本信息】 上海大学 ， 流体力学， 2008， 博士

【摘要】 微型飞行器自20世纪90年代提出来以后,因为其尺寸小、不易被发现、便于携带等普通飞行器不具有的独特优势,在军用和民用等领域发挥重要作用。然而,由于微型飞行器在10~5量级的低雷诺数环境飞行,其气动力学特性和常规飞行器大不相同而成为国际上气动力学研究的热点和难点。本文以固定翼式微型飞行器的气动设计为研究背景,针对其小展弦比机翼低雷诺数流动的特点,数值研究了微型飞行器三维非定常流场的流动特征,以及机翼周围的层流/湍流分离现象。用三维不可压缩Navier-Stokes方程来描写薄翼附近的三维流动,数值模拟采用了人工压缩方法,湍流模型采用Baldwin-Barth一方程模型。考虑了微型飞行器机翼的展弦比、弯度、翼面形状、前缘形状等气动外形参数对流场的影响。研究结果表明:在-12°≤α≤12°的攻角范围内,使用齐默曼翼面、采用上斜的15°尖形前缘、或者翼型弯度在4%左右都能使微型飞行器机翼获得优良的升阻比。这些物理参数直接影响了沿薄翼的附面层发展,改变了薄翼表面附近的流场结构,改善了分离泡的形成与发展,从而使薄翼的升阻比提高了26%～68%。将遗传算法和Navier-Stokes方程数值模拟相结合,率先应用到微型飞行器机翼的三维气动布局优化分析中,编制了相关优化程序,得到了符合气动优化布局的三维机翼外形。遗传算法的小种群设计,大大减小了由反复求解三维Navier-Stokes方程带来的计算代价。多峰函数的测试结果表明,该优化模型能以较高的效率搜索到全局最优值。机翼的优化结果表明:8个设计点的升阻比均提高30%以上,尤其在2°攻角,升阻比提高2倍;优化翼型的前缘钝、尾缘弯,弯度增大,升力系数提高;优化机翼的展弦比为1.2左右;优化翼面为接近椭圆的齐默曼形状。成功实现了在低雷诺数下微型飞行器机翼附近三维非定常湍流流场的数值模拟,讨论了齐默曼薄翼的静态失速过程,揭示了翼面形状是影响小展弦比机翼三维非定常分离流动的重要因素。计算结果较准确地估算了失速附近的升阻力系数、捕捉到机翼的失速特征和升力系数的迟滞现象,发现翼面形状是影响升力系数迟滞类型的重要物理参数。其中,反齐默曼机翼具有较大的最大升力系数,没有明显的失速迟滞发生,失速攻角比椭圆机翼延迟约4°,可以作为微型飞行器机翼的理想翼面形状。更多还原

【Abstract】 A great deal of interest has emerged since micro air vehicle was put forward in 1990s. Its advantages of small size, invisibility, and portability make micro air vehicle broad prospects in both military and civilian fields. However, micro air vehicle flies at Reynolds number of 10~5, so classical aerodynamic theory that can accurately predict large-scale aircrafts is generally not applicable for it. In this paper, fixed wing of micro air vehicle is numerically studied to investigate the complicated three-dimensional unsteady aerodynamic characteristics and the laminar/turbulent separation phenomena at boundary layer.Flow around micro air vehicle is simulated by numerically solving three-dimensional incompressible Navier-Stokes equations by artificial compressibility method. Baldwin-Barth turbulence model is employed for turbulent flow calculations. Aerodynamic parameters such as aspect ratio, camber, wing planform, and leading-edge shape are selected to investigate their effects on wing’s aerodynamic performance. Results show that at small angles of attack between -12°to 12°, excellent parameters are Zimmerman wing planform, 4% camber, and sharp leading edge with 15°’up’ angles. These parameters directly affect the development of boundary layer close to the wing surface and determine the flow structure. As a result, separated bubble on the wing surface is weakened and lift-drag ratio is increased from 26% to 68%.Genetic algorithm code is developed with combination of Navier-Stokes equation simulation to obtain reasonable three-dimensional aerodynamic layout of micro air vehicle wing. In order to decrease huge computational cost generated from the repetitious calling of three-dimensional Navier-Stokes code, a real coded genetic algorithm is developed with small population. An optimization of a multimodal function indicates that present genetic algorithm can converge to the global value with high efficiency. Wing optimization results show that: (1) lift-drag ratios at eight design point are all increased by more than 30%. Especially at 2°angles of attack, double lift-drag ratio is obtained. (2) Optimal airfoils have large leading-edge radius and are cusped near the trailing edge, and have aspect ratios 1.2 and Zimmerman wing planforms.Unsteady Navier-Stokes equations code is developed in order to study the three-dimensional unsteady field of micro air vehicle especially close to the wing surface. Numerically, static stall of thin Zimmerman wing is discussed and wing planform is found to be an important parameter to affect the maximal lift coefficient, stall angle of attack, and hysteresis of lift coefficient. Results show that present numerical method can capture wing’s static stall and can comparatively accurately estimate lift coefficient near the stall. Inverse Zimmerman wing has higher maximal lift coefficient with no obvious hysteresis and stall delay of 4°angles of attack than elliptical wing, so it is a reasonable wing planform for micro air vehicle wing.更多还原