转子叶栅非同步振荡发声特性研究

轴流压气机转子叶片排振荡疲劳失效是常见的气动弹性失稳问题。当转子叶栅处于非同步振荡状态下时,压气机管道内部将伴随着异常噪声的产生,这类噪声的频率既不是分布在叶片通过频率及其谐波上,也不是分布在转子轴频率及其谐波上,同时也不满足简单多普勒效应。为了解释这种异常噪声现象,以三维升力面理论为基础,讨论叶片对其附近流体施加非定常载荷的发声问题,给出了转子叶栅振荡异常发声问题的物理解释,建立了声场频率及模态特性与转子声源特性的直接关系式,并给出了频率特性不同于叶片通过频率且不符合简单多普勒效应的完整解释。在此基础上,通过机理性实验研究证实了该模型的正确性。实验结果表明,理论预测声场的频率和周向模态特性与实验结果完全一致。     

基于放大因子与Spalart-Allmaras湍流模型的转捩预测

为了验证放大因子输运方程与Spalart-Allmaras(S-A)湍流模型耦合对转捩现象的模拟精度,选取Schubauer and Klebanoff(S-K)平板、S809低速翼型、30p30n多段翼型以及复杂的三维HiLiftPW-1构型进行自由转捩计算,并将计算结果与实验进行比较分析,其中针对S809算例,还与Langtry-Menter(L-M)转捩模型进行了比较.算例结果表明:放大因子输运方程与S-A湍流模型的耦合能够较好的捕捉转捩位置以及转捩发展过程,对分离泡诱导的转捩的模拟相比L-M转捩模型更精确,转捩位置的捕捉精度提升了10%;对比实验,多段翼转捩位置的捕捉误差最大为6.5%;针对三维高升力增升构型,以实验作为参考,全湍流计算与考虑边界层转捩的对比显示考虑边界层转捩能够更加精确的模拟气动力系数,升力和表面摩擦阻力系数的模拟精度精度提升1%.      

Instantaneous BeiDou–GPS attitude determination: A performance analysis

The advent of modernized and new global navigation satellite systems (GNSS) has enhanced the availability of satellite based positioning, navigation, and timing (PNT) solutions. Specifically, it increases redundancy and yields operational back-up or independence in case of failure or unavailability of one system. Among existing GNSS, the Chinese BeiDou system (BDS) is being developed and will consist of geostationary (GEO) satellites, inclined geosynchronous orbit (IGSO) satellites, and medium-Earth-orbit (MEO) satellites. In this contribution, a BeiDou–GPS robustness analysis is carried out for instantaneous, unaided attitude determination.     

航天器激光防护材料研究现状与发展趋势

根据激光防护的原理和途径,介绍了基于线性光学原理、基于非线性光学原理和基于相变原理的激光防护材料的特点及其国内外研究进展,讨论了激光防护材料的发展方向。     

An innovative navigation scheme of powered descent phase for Mars pinpoint landing

Pinpoint landing (within 100 m from the target) is essential for future Mars exploration missions. This paper deals with one aspect of the pinpoint landing architecture—the navigation performance improvement during the powered descent phase, and proposes an innovative navigation scheme to obtain the vehicle complete and accurate states. On the basis of dead reckoning relying on the Inertial Measurement Unit, measurements of the Integrated Doppler Radar are adopted to correct the vehicle velocity and altitude. Distance between the vehicle and one Mars Orbiter as well as their line-of-sight relative velocity is measured by a radio sensor, and integrated in the filter to correct the vehicle horizontal position. The innovative navigation system is based on an Extend Kalman Filter. Two observation schemes are developed. One considers measurements of the Integrated Doppler Radar and radio range measurement. Another further considers radio velocity measurement. The performance of the innovative navigation scheme is greatly influenced by the position of the Mars Orbiter with respect to the target. Stochastic analyses are performed to obtain optimal locations of Mars Orbiter. Finally, the innovative navigation scheme performances are assessed through stochastic simulations. Its performance improvements are demonstrated by comparison with the Integrated Doppler Radar only navigation scheme.     

Stability of the seasonal variations in diurnal and semidiurnal components of mid-latitude F2 layer parameters

We report work utilizing 15-min resolution ionospheric data obtained with DPS-4 digisonde in 2003–2011 to study the seasonal variations in amplitudes and phases of the most powerful spectral components of the F2 layer critical frequency (foF2) and peak height (hmF2) fluctuations over Irkutsk (52.5°N, 104.0°E). We show that fluctuations of both parameters contain quasi-harmonic components with periods of T_n = 24/n h (n = 1–7). The number of distinct spectral peaks varies from 3 in summer to 7 in winter. Amplitude and phase characteristics of the diurnal (n = 1) and semidiurnal (n = 2) components is studied using the data sets extracted from the original data sets with band-pass filter. It has been found that the amplitudes of diurnal/semidiurnal foF2 and diurnal hmF2 components are maximum in winter and minimum in summer. Amplitudes of the diurnal components vary gradually; those of the foF2 semidiurnal one, abruptly, thus forming a narrow winter maximum in November–January. The phase (local time of maximum) of the diurnal foF2 component increases gradually by 4–6 h from winter to summer. The phase of the semidiurnal foF2 component is nearly stable in winter/summer and sharply decreases (increases) by 2–3 h near the spring (autumn) equinox. The phase of the diurnal component of hmF2 (local time of minimum) varies slightly between 1130 and 1300 LT; that of the semidiurnal one decreases (increases) by 4–6 h from January to March (from September to November). The results obtained show that the main features of seasonal variations in the diurnal and semidiurnal components of the mid-latitude F2 layer parameters recur consistently during the solar activity growth and decline phases.     

载波相位辅助的GPS动态单点定位算法综述

对载波相位辅助条件下应用于全球定位系统（Global Positioning System,GPS）动态单点定位的各种算法进行了综合分析与比较。首先简要介绍定位算法中的基本公式与观测模型;然后分别对周跳修复与滤波解算两部分所应用的各种算法进行详细介绍并比较其性能与适用范围;最后对尚待解决的问题及可能的发展方向进行了总结。     

液态水相变发散冷却的实验

以液态水为冷却介质,采用高温合金粉末烧结多孔材料制造平板实验件,实验研究了具有液态水相变的发散冷却特性.用远红外热像系统记录实验平板热端表面温度分布,通过热电偶及压力传感器监控冷却腔内温度和压力变化,从而分析液态水的相变过程.实验表明:随着液态水注入率的增大,平均冷却效率不断提高;当液态水在暴露于高温主流的平板表面发生气液相变时,平均冷却效率趋于稳定且不再大幅上升;主流温度与液态水注入率决定了液态水的相变位置,并对冷却腔内压力变化产生影响.      

离散广义Markov跳变系统的镇定性

针对转移概率部分未知情况下的离散时间广义Markov跳变系统,研究了系统的稳定性和镇定性。转移概率部分未知的情况包含了转移概率完全已知和完全未知两种特殊情况,具有更广泛的实际意义。首先利用线性矩阵不等式方法,将离散Markov跳变系统的结论推广到离散广义Markov跳变系统,提出了使开环系统随机稳定的充分条件;在此基础上,进一步提出了闭环系统可镇定的判据,并表示为线性矩阵不等式形式;最后,通过仿真算例验证了所提方法的有效性。     

吹吸扰动控制猝发过程中雷诺应力的实验

采用热线测速技术和双丝边界层热线探针,在风洞中以高于对应最小湍流时间尺度的分辨率,精细测量了平板湍流边界层施加不同频率周期性质量引射前后,不同流向和法向位置的瞬时流向、法向和展向速度分量的时间序列信号.采用流向脉动速度局部平均结构函数模极大值法检测了壁湍流猝发过程中拟序结构不同速度分量和雷诺应力分量的条件相位平均波形.发现在扰动源下游一定范围内,摩擦因数和雷诺应力幅值有所减小,扰动改变了法向或展向脉动速度与流向脉动速度的条件相位平均波形的相位差,使其保持在π/2的奇数倍左右,此时雷诺应力几乎为0,改变了湍流边界层原有雷诺应力的产生和扩散输运机制,抑制了湍流雷诺应力的产生和输运.