自维持合成双射流对超声速燃烧室凹腔质量交换特性影响研究

为了改善燃烧室凹腔与主流的掺混性能,提出了一种利用凹腔内压力差形成自维持合成射流的流场控制方法,在超声速冷流条件下,采用动网格技术对激励器的膜片振动过程进行模拟,详细分析了自维持合成双射流与凹腔相互作用的过程,研究了激励器出口位置、参数、凹腔构型以及来流Ma数等参数的影响。结果表明:加入自维持合成双射流激励器可以大幅提升凹腔的质量交换特性,减小气体在凹腔内的驻留时间;且激励器出口位置分布对控制效果影响较大,当激励器出口位于凹腔底部中间位置时,质量交换率最大能够提升49%。此外,凹腔构型以及来流条件都会影响自维持合成双射流对凹腔掺混的控制效果,在相同来流条件下,凹腔长深比越大,控制效果越显著,自维持合成双射流能使长深比L/D=7.76的凹腔质量交换率提升115%;对于同一凹腔,随着来流马赫数增加,激励器对凹腔质量交换特性控制效果提升更为明显,但改变振动膜片的振幅和频率对控制效果的改善不明显。     

Kelvin–Helmholtz instability in a twisting solar polar coronal hole jet observed by SDO/AIA

We investigate the conditions under which the fluting ($m=2$), $m=3$, and $m=12$ magnetohydrodynamic (MHD) modes in a uniformly twisted flux tube moving along its axis become unstable in order to model the Kelvin–Helmholtz (KH) instability in a twisting solar coronal hole jet near the northern pole of the Sun. We employed the dispersion relations of MHD modes derived from the linearized MHD equations. We assumed real wavenumbers and complex angular wave frequencies, namely complex wave phse velocities. The dispersion relations were solved numerically at fixed input parameters (taken from observational data) and varying degrees of torsion of the internal magnetic field. It is shown that the stability of the modes depends upon five parameters: the density contrast between the flux tube and its environment, the ratio of the external and internal axial magnetic fields, the twist of the magnetic field lines inside the tube, the ratio of transverse and axial jet’s velocities, and the value of the Alfvén Mach number (the ratio of the tube axial velocity to Alfvén speed inside the flux tube). Using a twisting jet of 2010 August 21 by SDO/AIA and other observations of coronal jets we set the parameters of our theoretical model and have obtained that in a twisted magnetic flux tube of radius of $9.8$ Mm, at a density contrast of $0.474$ and fixed Alfvén Mach number of $?0.76$, for the three MHD modes there exist instability windows whose width crucially depends upon the internal magnetic field twist. It is found that for the considered modes an azimuthal magnetic field of $1.3$–$1.4$ G (computed at the tube boundary) makes the width of the instability windows equal to zero, that is, it suppress the KH instability onset. On the other hand, the times for developing KH instability of the $m=12$ MHD mode at instability wavelengths between 15 and 12 Mm turn out to be in the range of $1.9$–$4.7$ min that is in agreement with the growth rates estimated from the temporal evolution of the observed unstable jet’s blobs in their initial stage.     

双基地角时变下的ISAR稀疏孔径自聚焦成像

针对双基地角时变下的逆合成孔径雷达（ISAR）成像分辨率低以及稀疏孔径存在相位误差引起图像散焦等问题,提出了一种基于贝叶斯压缩感知（BCS）的双基地ISAR稀疏孔径自聚焦高分辨成像算法。在平动补偿后回波数据的基础上,首先构造补偿相位将由双基地角时变引起的多普勒偏移补偿掉,然后构造随双基地角变化的稀疏基矩阵,建立基于压缩感知的双基地ISAR稀疏孔径观测模型,并将相位误差作为ISAR成像的模型误差,接着假设目标图像各像元服从Laplace先验、噪声统计特性服从Gaussian分布,利用贝叶斯推理进行"分布式"迭代求解,在高分辨成像的同时实现了相位自聚焦,仿真结果验证了算法的有效性和优越性。     

合成射流大攻角非对称涡控制的试验研究

利用合成射流对细长旋成体大攻角非对称涡控制进行了研究,基于合成射流激励器设计了一频率高达1kHz的非定常小扰动控制机构,并将其成功应用于大攻角非对称涡主动流动控制。应用天平测力和七孔探针流场测试技术,研究了合成射流非定常小扰动电压和频率对非对称涡的控制特性和规律。结果表明,采用合成射流能够完全消除背涡的非对称性,扰动频率是影响非对称涡控制的一个关键参数,高频扰动下模型背风区非对称涡结构趋于无控制流态。且文中结果发现,当攻角α=57.5°、非定常小扰动频率fs=150Hz时,即可将非对称涡完全控制成为对称涡。     

模糊综合评判法在信息技术对传统产业贡献的综合效果评价中的应用

根据全面性、可测性、客观性、层次性以及定量分析与定性分析相结合的原则,经过调查研究和专家讨论,建立评价信息技术对传统产业贡献的综合效果的指标体系,并对模糊综合评判法在其评价中的应用问题进行了研究。     

一种适于机载SAR系统的高效快视成像方法

提出了一种适于机载ＳＡＲ成像处理的快视方法（ＱＬＦＭ）及其实现。该方法的高效、实用性主要表现在以下几个方面：①成像处理流程中的运算单元较少,即二维去调频之后,一次二维的逆付立叶变换即可以完成快视功能;②该算法的全息特性使得成像积累不必满足一个合成孔径时间的要求,采用少量有限的回波数据即可获得较大测绘区域内的图像;③ＱＬＦＭ可对被测区域中心进行灵活地选择,且测绘中心处可获得高分辨率完全聚焦的图象;④该算法实现的主要功能模块为复乘和ＦＦＴ,可通过灵活地旁路控制完成其在传统条带ＳＡＲ处理机中的嵌入。计算机仿真及原始数据成像结果验证了ＱＬＦＭ算法的快视功能。     

高精度星载SAR多普勒参数估算方法

提出了一种基于空间坐标转换,利用卫星位置、速度参数精确估算星载SAR(Synthetic Aperture Radar)全观测带多普勒参数的方法.利用卫星速度、位置,通过星载SAR空间几何模型和坐标转换关系,建立SAR图像中斜距同卫星下视角之间的四次方程,解出下视角并进一步计算出该斜距处的多普勒参数值.仿真结果表明,该方法在无卫星位置、速度误差情况下估算精度达到0.02Hz(多普勒中心频率)和2×10-4Hz/s(多普勒调频率);存在卫星位置测量误差(300m)以及速度测量误差(0.3m/s)的情况下,估算精度达到0.8Hz(多普勒中心频率)和0.07Hz/s(多普勒调频率).该方法适用于单星SAR以及分布式SAR高精度多普勒参数的估算.      

基于模糊理论的军用飞机系统维修保障能力评估

介绍了国内外装备保障性及维修保障能力评估方法研究现状;依据全面性、合理性、科学性原则,建立了军用飞机系统维修保障能力评估指标体系;应用基于层次分析法（AHP）的模糊多级综合评判方法,建立了评判模型,对两型飞机实施其维修保障方案时维修保障系统的能力进行了评估。结果表明,应用该方法解决保障系统维修保障能力评估问题具有较好的准确性和有效性。     

Sum-difference Reduced-dimensional Processing in SAR Image Domain and Statistical Analysis for Ground Moving Target Indication

In this article, a new reduced-dimensional adaptive processing algorithm based on joint pixels sum-difference data for clutter rejection is proposed. The sum-difference data are obtained by orthogonal projection of the joint pixels data of different synthetic aperture radar (SAR) images generated by a multi-satellite radar system. In the sense of statistical expectation, the sum-differ- ence data contain the common and different information of the SAR images. Therefore, the objective of clutter cancellation can be achieved by adaptive processing. Moreover, based on the residual image after clutter rejection, statistical analysis of constant false-alarm rate (CFAR) detection of moving targets is also presented. Simulation results demonstrate the effectiveness and robustness of the proposed algorithm even with heterogeneous clutter and image co-registration error.