亚临界雷诺数细长体绕流流态随迎角的变化和分区

通过在北航1.2m水洞中利用染色液显示和激光片光技术的显示实验以及在西工大NF-3风洞中进行的表面测压实验,对拱形头部细长旋成体在无侧滑条件下的流场结构和流动特性随着迎角的变化进行了实验研究。在流动显示和测压结果分析的基础上,对迎角从0°到90°范围内绕细长体的流动进行了流态分区,即细长体绕流经历6种流态:极小迎角下(0°≤α≤3°)物面附着绕流流态、小迎角下(3°<α≤25°)背部对称旋涡流态、中等迎角下(25°<α≤40°)背部2个非对称旋涡流态、大迎角下(40°<α≤60°)的非对称多涡系复杂流态、特大迎角下(60°<α<75°)背部多个旋涡依次破裂的流态、极大迎角下(75°≤α≤90°)背部类卡门涡街(或随机尾迹)流态。阐述了不同区域的流动特性和气动特性。     

低速振荡三角翼气动特性研究

对后掠角７０°尖前、后缘三角翼进行了低速风洞试验。用五分量内式应变天平测量了静、动态气动力。考核了动态试验装置、测试系统和数据采集／处理方法。模型静态法向力测量结果跟文献［１］实验符合;在一定折合频率范围内作大振幅动态运动时,法向力和俯仰力矩出现过冲量;动态失速延迟;上仰和下俯运动产生的气动载荷形成滞后环。用俯仰气动阻尼表示滞后度并确定振荡稳定特性。文中还对实验结果用傅里叶分析作了预测,二者趋势一致。     

悬挂式跷跷板旋翼桨叶拉力载荷的一种工程算法

在一阶诱导速度分布,一阶周期变距,三阶挥舞运动的基本假定下,提出了一种悬挂式跷跷板旋翼桨叶挥舞面内拉力载荷的工程算法。为此,首先推导了含有悬挂高度和桨叶预锥角影响的这类桨叶的挥舞运动方程。并用“法方程法”及“共轭斜量法”求解了一种属于矛盾方程的挥舞运动系数方程组,取得一致结果。随后,导出了气动拉力载荷表达式。最后,以××无人驾驶直升机悬挂式跷跷板旋翼桨叶为算例,计算了拉力载荷并分析了悬挂高度和预锥角对挥舞运动系数的影响关系。     

共轴式双旋翼气动特性的固定尾迹分析

对经典的儒氏旋翼涡系模型作了一些修正，建立了悬停状态下共轴式旋翼的固定尾迹模型，对双旋翼之间的气动干扰问题开展了理论研究和实验研究，最后，将理论结果与实验结果进行了比较、分析，证明了理论方法的正确性，并获得了一些重要结论。     

空气耦合式超声波无损检测技术的发展

空气耦合式超声波无损检测技术具有完全非接触、无损伤的特点,可用于传统超声检测手段难以适应的场合。本文介绍了空气耦合式超声检测技术的发展历程和主要难点,总结了该技术近几年的实际应用情况,分析了该技术的局限性。     

OPTIMIZED STRAPDOWN CONING CORRECTION ALGORITHM

Traditional coning algorithms are based on the first-order coning correction reference model. Usually they reduce the algorithm error of coning axis （z） by increasing the sample numbers in one iteration interval. But the increase of sample numbers requires the faster output rates of sensors. Therefore, the algorithms are often lim- ited in practical use. Moreover, the noncommutivity error of rotation usually exists on all three axes and the in- crease of sample numbers has little positive effect on reducing the algorithm errors of orthogonal axes （x, y）. Considering the errors of orthogonal axes cannot be neglected in the high-precision applications, a coning algorithm with an additional second-order coning correction term is developed to further improve the performance of coning algorithm. Compared with the traditional algorithms, the new second-order coning algorithm can effectively reduce the algorithm error without increasing the sample numbers. Theoretical analyses validate that in a coning environ- ment with low frequency, the new algorithm has the better performance than the traditional time-series and fre- quency-series coning algorithms, while in a maneuver environment the new algorithm has the same order accuracy as the traditional time-series and frequency-series algorithms. Finally, the practical feasibility of the new coning al- gorithm is demonstrated by digital simulations and practical turntable tests     

GAS PATH ELECTROSTATIC SENSOR MONITORING AND COMPARISON EXPERIMENT ON TURBOJET ENGINE

A monitoring and comparison experiment with two types of sensors on a turbojet engine is carried out. Compared with a probe-typed sensor, which is designed successfully before, signals are collected to verify the va- lidity and better feasibility of the circular sensor. According to the signals monitored over 131 h, the typical signals of 125--129 phases are analyzed. The results show that the unusual exhaust particles are carbon depositions from fuel spray nozzle. Therefore, with the electrostatic sensor, early warning can be provided for initial fault condition, as well as real-time reference for the condition-based maintenance.     

OLEOPHOBIC AND HYDROPHOBIC FEATURE EXPERIMENTS OF FLUORINATED HIGH DENSITY POLYETHYLENE

The surface performances of directly fluorinated high density polyethylene （HDPE） are studied with Fourier transform infrared （FT-IR） spectra, scanning electron microscopy （SEM） and contact angle （CA） system. The SEM images show that there is a three-layer structure called the reaction, virgin and boundary layer structure. The depth of fluorinated layer is 5.75 ~m with 1 h fluorination time and 7.86 b~m with 2 h. The depths are 5.46 /~m and 5.07 /~m when fluorine density is 2G and 1~/0, respectively. CA indicates that the HDPE surface property becomes more hydrophobic with the increasing water contact angle from 78.5~ to 104.5~. Oleophobic and hydrophobic features of HDPE are identified by comparison of mass change experiments. It is shown that the in- crement rate of fluorinated HDPE is much lower than that of un-fluorinated HDPE filled in neither distilled water nor jet fuel.     

导管内塞式量热计热流测量实验及数值模拟研究

对电弧风洞中超声速湍流导管内塞式量热计进行改进,采用测热端与校测件线接触的量热计和测热塞块边缘与校测件有0.4mm 缝隙的量热计。与传统的塞式量热计热流测量值进行对比,实验结果表明,在低压、低冷壁热流条件下3个量热计输出特性较接近;而随着压力、冷壁热流的增加,线接触量热计测量值略有降低,而测热端与校测件有缝隙的量热计测量值大幅增加。最后,通过数值研究了缝隙内的流动对热流测量的影响,同时,模拟了其它来流条件不变时来流马赫数对缝隙内流动的影响。     

跨声速翼型风洞开孔壁的简化模型数值模拟

以开孔壁翼型风洞为研究对象,构建简化的仿真模型,模拟开风洞孔壁附近及小孔内的流动,研究开孔壁对风洞试验的影响。研究了开孔壁流动的主要特征参数并建立多孔板模型,为进一步建立数值风洞模型及研究洞壁干扰提供参考。通过简化的孔壁模型,研究了开闭比等特征参数对风洞流场和翼型绕流的影响。构建了二维简化孔壁模型和多孔介质孔壁模型,并验证了以多孔板模型模拟孔壁风洞流场的可行性。本文建立了一种研究跨声速孔壁风洞的孔壁效应的数值方法,为跨声速孔壁风洞流场的模拟研究提供参考,为进一步构建可靠的风洞孔壁数值模拟数学模型提供一种研究思路。