翼型后缘厚度对气动性能影响的数值分析

在研究DU系列翼型的空气动力特性时,发现DU97-W-300翼型的升阻力随时间变化。通过对比多种攻角和多种后缘厚度下的升阻力随时间变化曲线,发现该现象与边界层分离有关,而且后缘厚度对边界层分离有重要影响。最后得出结论:翼型后缘厚度存在一个临界值,当后缘厚度大于临界值时,受力不稳定,小于它时受力稳定。     

单通道测量条件下DORIS实时定轨方法研究

重点研究了单通道测量条件下的DORIS实时定轨方法。推导了实时定轨的扩展卡尔曼滤波（EKF）公式,仿真生成了47个测站的观测数据文件,分析了单通道测量条件下EKF滤波器的收敛性及其精度。仿真实验表明,仅有单个测站的观测数据时,滤波难以收敛;但在不同测站的观测数据切换时,滤波收敛效果显著。对于轨道高度为800km的卫星,初轨各轴位置误差小于500m、速度误差小于5m/s时,滤波平均收敛时间约55min;若各项系统误差能准确建模,实时轨道的位置精度将优于40cm。     

Flow Field Investigation in a Trapezoidal Duct with Swirl Flow Induced by Impingement Jets

An enlarged model of trapezoidal duct near the leading-edge in the blade is built up. The effects of impingement jets, swirl flow, cross flow and effusion flow are considered. Experiments are performed to measure flow fields in this confined passage and exit holes on one of its side walls. Cross flow and effusion flow are induced in the channel by the outflow of side exit hole (SEH) and film cooling hole (FCH), which are oriented on one end wall and bottom wall of the passage. Detailed flow structures are measured for two impingement angles of 35° and 45° with 6 combinations of outflow ratios. Results show that the small jets impinge the target wall effectively while the large jets contribute to inducing and impelling a strong counter-clockwise vortex in the upper part of the passage. Cross flow plays a dominate role for the flow structures in the passage and exit holes. It deflects jets, enhances swirl and deteriorates side exit conditions. Impingement angle is another significant factor for the flow characteristics. Its effect reveals more evidently with cross flow. Within the present test conditions, the mass flow rates and outflow positions of FCHs have no distinct effect on the main flow structures.     

Recent progress in flapping wing aerodynamics and aeroelasticity

Micro air vehicles (MAVs) have the potential to revolutionize our sensing and information gathering capabilities in areas such as environmental monitoring and homeland security. Flapping wings with suitable wing kinematics, wing shapes, and flexible structures can enhance lift as well as thrust by exploiting large-scale vortical flow structures under various conditions. However, the scaling invariance of both fluid dynamics and structural dynamics as the size changes is fundamentally difficult. The focus of this review is to assess the recent progress in flapping wing aerodynamics and aeroelasticity. It is realized that a variation of the Reynolds number (wing sizing, flapping frequency, etc.) leads to a change in the leading edge vortex (LEV) and spanwise flow structures, which impacts the aerodynamic force generation. While in classical stationary wing theory, the tip vortices (TiVs) are seen as wasted energy, in flapping flight, they can interact with the LEV to enhance lift without increasing the power requirements. Surrogate modeling techniques can assess the aerodynamic outcomes between two- and three-dimensional wing. The combined effect of the TiVs, the LEV, and jet can improve the aerodynamics of a flapping wing. Regarding aeroelasticity, chordwise flexibility in the forward flight can substantially adjust the projected area normal to the flight trajectory via shape deformation, hence redistributing thrust and lift. Spanwise flexibility in the forward flight creates shape deformation from the wing root to the wing tip resulting in varied phase shift and effective angle of attack distribution along the wing span. Numerous open issues in flapping wing aerodynamics are highlighted.     

超临界翼型尾缘噪声影响因素研究

使用大涡模拟(LES)和FW-H相结合的方法对超临界翼型尾缘噪声进行了研究。针对超临界翼型后缘的不同设计参数(后缘厚度、后缘角和几何形状)对尾缘噪声的影响,使用ANSYS FLUENT的LES湍流模型计算声源,采用FW-H积分方法求解远场噪声总声压级。首先完成二维非定常流圆柱绕流的流场及其噪声的验证计算,计算结果与实验值符合,证明了求解器设置和网格生成的合理性。然后基于此正确的求解器设置和网格生成,使用LES/FWH对比了典型超临界翼型的不同后缘设计参数对远场总声压级的影响,所得结论对低噪声超临界翼型优化设计有参考意义,同时为进一步的噪声控制优化设计提供了基础。     

复合材料布带缠绕智能纠偏控制技术

智能纠偏是复合材料缠绕成型的关键技术之一,其焦点问题是如何实现布带跑偏量的精确检测控制.在分析布带跑偏机理及纠偏可行性的基础上,针对布带跑偏量检测问题,提出了基于线阵电荷耦合(CCD)的布带边缘检测方法,并对其检测原理进行了分析.在此基础上,建立了智能纠偏控制系统的数学模型,分析了系统的稳定性,并采用Fuzzy-PID...     

基于提升小波和形态学的图像边缘检测算法

基于提升小波变换和形态学的基本理论,提出了一种提升小波和形态学相结合的图像边缘检测算法,算法充分利用了提升小波变换相对于传统小波变换快速而有效的完成小波分解和重构的算法优势。形态学运算在图像处理中具有独特的优势,利用其对图像膨胀和腐蚀的差运算来获取图像的边缘,取得了很好的效果。实验结果表明,算法边缘定位准确,抗噪能力强,检测出的图像边缘连续、平滑,是一种有效的边缘检测方法。     

带自适应流通处理机匣的轴流压气机全通道数值研究

采用全通道数值模拟方法研究了两种自适应流通装置数目的处理机匣对亚声速轴流压气机性能及流场的影响,非定常数值计算结果表明两种自适应流通处理机匣分别获得了6.3％,9％的失速裕度改进量,通过详细地分析压气机叶顶流场表明,高速喷射气流能抑制前缘溢流现象的产生,有效地改善了叶顶通道的流动状况.随着自适应流通装置数目从10增加到15,喷射气流对转子叶顶间隙泄漏流的影响频率也随着提高,因此增强了处理机匣抑制叶顶间隙泄漏流负面影响的能力.     

曲率连续的压气机叶片前缘设计方法

为优化压气机叶片前缘形状以改善叶型性能,提出了一种曲率连续叶片前缘的设计方法。前缘设计过程基于三次Bezier曲线,只需引入三个设计变量。使用该方法对可控扩散叶型前缘进行了重新设计,并采用计算流体力学方法比较了不同前缘形状对于叶型气动性能的影响。计算结果表明新型前缘在来流马赫数0.2和0.6两种下均能够有效抑制前缘分离泡的产生和发展,与圆弧形和椭圆形前缘相比叶型攻角范围分别扩大约1.2°和2.5°。对跨声转子叶片的前缘进行重新设计后,提高了动叶效率,扩大了稳定工作范围。      

考虑应力梯度的轮盘疲劳寿命预测

考虑应力梯度和尺寸效应对寿命的影响,通过引入应力梯度影响因子,将缺口试件与光滑试件的疲劳寿命相关联,建立了基于Walker平均应力修正的缺口试件寿命预测模型,进而结合三维弹性有限元分析对发动机涡轮盘进行了寿命预测.结果表明:所发展的寿命模型能较好地反映影响疲劳寿命的多种因素,尤其是应力集中对试件疲劳寿命的影响,综合考虑平均应力、应力梯度和尺寸效应的轮盘寿命预测结果更接近试验值,对GH901标准试件和轮盘的疲劳寿命预测结果都在2倍分散带以内.