求根传播算子方法及其在ARM抗诱偏中的应用

反辐射导弹（ARM）抗有源诱偏问题中,多源信号在空、频域的强相关性往往造成导引头对信源数目欠估计,从而导致传统超分辨算法的测向性能下降。针对这一问题,提出了一种求根的传播算子方法,该算法首先在信源数过估计情况下计算信号到达角,然后利用每个角度对应的信号功率来剔除虚假角度。求根传播算子方法不需要预先估计信号源数目,而且在信号高度相关的情况下具备很好的角度分辨性能,因此适用于解决ARM抗诱偏问题。仿真实验结果表明,求根传播算子方法在提高ARM抗诱偏能力方面的表现优于MUSIC算法。     

高可靠小条件数压缩感知叶尖定时信号辨识

为增强基于任意角度压缩感知(CS)叶尖定时信号(BTT)重构的稳定性,采用小生境微种群遗传算法提出了基于小条件数的高稳定性传感器安装布置方法。研究发现:任意角度CS的恢复矩阵条件数越小,不同信噪比下同步和非同步振动信号重构误差越趋于稳定在较低范围,优化后发现条件数为1的排布方案下,相邻传感器角度间隔趋向于均布2m取K的形式。利用条件数为1的矩阵冗余特性,设计了高可靠性的传感器排布方案,数值试验和有限元仿真验证表明叶尖定时系统在失效一个传感器的情况下仍可稳定得到准确的重构结果。在信噪比为5 dB时,冗余排布相比参考排布的主倍频幅值重构误差降低4.4%以上,验证了采用最小条件数排布的任意角度CS信号辨识方法在噪声及传感器失效情况下仍可保证BTT测量结果的有效性和可靠性。      

坡面浅层明流流态界定方法之商榷

为了探求坡面薄层水流流态界定方法,从流体力学与泥沙运动学观点出发,对4种不同粗糙尺度床面(光滑玻璃、人工加糙粒径分别为0.075、0.245和0.380mm)、5种不同坡度下坡面薄层水流放水进行试验研究,并对薄层水流阻力规律与明渠水流阻力规律进行了比较分析.在此基础上提出了粘性底层厚度与水深之比作为新的无量纲临界判数,结果表明该判数能更好地反映坡面薄层水流流动型态.     

超临界翼型低雷诺数流动分析及优化设计

以高空长航时无人机(UAV)翼型研究为背景,对超临界RAE2822翼型在高空高亚声速下的低雷诺数气动特性进行了数值模拟及优化设计研究。采用求解雷诺平均N-S方程的有限体积法,对典型低雷诺数下RAE2822翼型绕流进行数值模拟,验证了SST k-ω湍流模型的可靠性和准确性;基于不同高度不同雷诺数下RAE2822翼型的计算气动力对比分析,研究了高度增大所带来的低雷诺数效应;通过对低雷诺数下超临界翼型表面流场结构及流动机理的详细分析,提出了一种弱化激波的翼型设计思想,并通过优化算例验证了该思想的可行性。     

主流偏角对单排圆柱型气膜孔冷却特性的影响

数值模拟研究了主流偏角对单排圆柱型气膜孔冷却特性的影响,在气膜孔中心间距相等的计算条件下,在吹风比为1.0时,计算结果与主流和气膜孔都无偏角、主流无偏角而气膜孔有45°偏角这两种流动情况做了对比.结果显示:相对于主流和气膜孔都无偏角时,主流有45°偏角而气膜孔无偏角时气膜平均冷却效率更大,分布更均匀;相比于主流无偏角而气膜孔有45°偏角时,在气膜孔附近处,主流有45°偏角而气膜孔无偏角时气膜平均冷却效率更小,在远离气膜孔的下游位置处,气膜平均冷却效率更大.另外在吹风比为0.5和1.5条件下进行了数值模拟,结果也显示3种流动情况气膜冷却效率分布存在明显差距,有必要对主流偏角对单排气膜孔冷却特性的影响做进一步的实验和数值研究.      

第2级径向旋流器旋流数对燃烧室点火和贫油熄火性能的影响

双级旋流器是航空发动机燃烧室头部产生回流区所采用的主要形式,研究主要考察第2级径向旋流器的旋流数对点火与燃烧稳定性能的影响,数值模拟结果能够较好地匹配第2级径向旋流器设计参数.试验研究表明:第2级径向旋流器旋流数的改变对燃烧室点火性能无影响;但减小该旋流数会对贫油熄火性能产生明显地改善,旋流卷吸效果会影响回流区火焰稳定.减小第2级径向旋流器旋流数,使下游卷吸量增加,回流区流动与火焰匹配更好,更有利于燃烧稳定性的提高.      

旋转通道内流阻特性实验的实现与验证

针对涡轮叶片的蛇形内冷通道内流阻特性的研究,在北京航空航天大学航空发动机气动热力国家级重点实验室的旋转涡轮叶片内冷通道换热实验台上构建了旋转工况的测压系统.该测压系统具有高精度、多路选通、高压高旋转数等特点.在通道进口雷诺数从20000~70000,旋转数从0~1.025的范围内,实验研究了旋转状态下,冷态与热态流场下方形截面光滑U形通道流阻系数.实验结果与国外同类实验对比验证了构建的实验系统的可靠性和优越性.实验结果表明:低雷诺数下静止工况的流阻随雷诺数增大而增大,并在雷诺数增大到一定值后转而减小.冷态下流阻随旋转数增大而增大,低旋转数下旋转对热态流阻影响并不显著,高旋转数下热态流阻随旋转数增大而显著增大.      

Aerodynamic performance of owl-like airfoil undergoing bio-inspired flapping kinematics

Natural flyers have extraordinary flight skills and their prominent aerodynamic performance has attracted a lot of attention. However, the aerodynamic mechanism of birds' flapping wing kinematics still lacks in-depth understanding. In this paper, the aerodynamic performance of owl-like airfoil undergoing bio-inspired flapping kinematics extracted from a free-flying owl wing has been numerically investigated. The overset mesh technique is used to deal with the large range movements of flapping airfoils. The bio-inspired kinematics consist of plunging and pitching movement. A pure sinusoidal motion and a defined motion composed of plunging of sinusoidal motion and pitching of the bio-inspired kinematics are selected for comparison. The other two NACA airfoils are also selected to figure out the advantages of the owl-like airfoil. It is found that the cambered owl-like airfoil can enhance lift during the downstroke. The bio-inspired kinematics have an obvious advantage in lift generation with a presence of higher peak lift and positive lift over a wider proportion of the flapping cycle. Meanwhile, the bio-inspired motion is more economical for a lower power consumption compared with the sinusoidal motion. The sinusoidal flapping motion is better for thrust generation for a higher peak thrust value in both upstroke and downstroke, while the bio-inspired kinematics mainly generate thrust during the downstroke but produce more drag during the upstroke. The defined motion has similar lift performance with the bio-inspired kinematics, while it consumes more energy and generates less thrust. The unsteady flow field around airfoils is also analyzed to explain the corresponding phenomenon. The research in this paper is helpful to understand the flight mechanism of birds and to design a micro air vehicle with higher performance.     

基于参数优化的脉冲轨道设计

基于参数优化设计了一种可处理各类脉冲轨道优化的一般方法,并给出了两种确定最优脉冲数的方法。以脉冲矢量与脉冲施加时刻为未知参数,将脉冲轨道优化设计转为非线性参数优化,用合适的非线性规划算法求解。主矢量理论对所得解最优性的验证表明该方法可行。     

A linear stability analysis of large-Prandtl-number thermocapillary liquid bridges

A linear stability analysis is applied to determine the onset of oscillatory thermocapillary convection in cylindrical liquid bridges of large Prandtl numbers (4  Pr  50). We focus on the relationships between the critical Reynolds number Re_c, the azimuthal wave number m, the aspect ratio Γ and the Prandtl number Pr. A detailed Re_c–Pr stability diagram is given for liquid bridges with various Γ. In the region of Pr > 1, which has been less studied previously and where Re_c has been usually believed to decrease with the increase of Pr, we found Re_c exhibits an early increase for liquid bridges with Γ around one. From the computed surface temperature gradient, it is concluded that the boundary layers developed at both solid ends of liquid bridges strengthen the stability of basic axisymmetric thermocapillary convection at large Prandtl number, and that the stability property of the basic flow is determined by the “effective” part of liquid bridge.