Effect of bristle pack position on the rotordynamic characteristics of brush-labyrinth seals at various operating conditions

Over the last few decades, the research on the effect of bristle pack position on the rotordynamic characteristics of the brush-labyrinth seals is not sufficient. To this end, two kinds of brush-labyrinth seals for the bristle pack element installed upstream of the labyrinth teeth named BSU and installed downstream of the labyrinth teeth called BSD were used to investigate the effect of bristle pack position on the rotordynamic characteristics of the brush-labyrinth seals. Using the numerical model combining the porous medium model and the whirling rotor method, the rotordynamic characteristics of the BSU and BSD at various operating conditions including four kinds of pressure ratios, five kinds of inlet preswirl speeds and four kinds of rotor spinning speeds were conducted. The obtained results show that the effects of operating conditions on rotordynamic coefficients for the different seal configurations are different. The direct stiffness, cross-coupled stiffness and direct damping of the BSU are lower than those of the BSD. The rotordynamic coefficients of the BSU are more insensitive to the operating conditions variation. From the perspective of the seal stability, the BSU is a better brush-labyrinth seal configuration at high pressure ratio, high positive preswirl or high rotor spinning speed conditions. While in the case of low pressure ratio, low positive preswirl or low rotor spinning speed conditions, the BSD is a better choice.     

偏心撞击对撞击式喷嘴雾化特性的影响

为研究偏心撞击对撞击式喷嘴雾化特性的影响,建立了求解自燃推进剂冷态射流撞击雾化过程的数值模拟方案,计算了不同偏心度条件下的射流撞击雾化过程。采用树形自适应加密算法直接求解不可压Navier-Stokes方程组,由分段线性的流体体积(VOF)方法对流体界面进行捕捉。结果表明偏心撞击会导致雾场发生偏转,当无量纲偏心度E为1/8时,雾场偏转角度约为9.2°,应控制加工偏差小于该值。随着偏心度的增大,液膜的偏转角度增大,理论推导得到的液膜偏转角度要小于数值计算得到的液膜偏转角度。正心撞击时燃料与氧化剂流强峰值接近,雾场的流强分布呈单峰分布。当发生偏心撞击时,由于燃料与氧化剂部分射流未参与撞击导致流强峰值出现交错,雾场的流强分布呈双峰分布,混合比的空间分布发生较大改变。正心撞击时撞击点下游液滴的速度分布近似呈轴对称分布,而偏心撞击之后的速度分布则呈中心对称分布。偏心撞击导致的射流动量损失使得雾化性能变差,当无量纲偏心度E为1/8时,一甲基肼(MMH)的Sauter平均直径增大约4.8%,四氧化二氮(NTO)的Sauter平均直径增大约5.8%。      

亚超剪切混合层燃油雾化特性试验研究

为了摸清亚超大梯度剪切混合层内直射式喷嘴的燃油雾化特性，设计了用于向亚超剪切混合流中进行燃油喷射的直射式喷嘴，建立了亚超剪切混合层中燃油雾化试验系统。利用粒子图像测速系统（PIV），对亚超大梯度混合层中油雾场进行测量。通过改变喷嘴流量、喷射角度和喷嘴数量研究不同参数对雾化特性的影响，并应用图像处理技术对亚超大梯度剪切混合层内的油雾场进行分析，总结归纳其雾化规律。试验结果显示：随着流量增大，穿透深度会随之增大，破碎后的颗粒分布峰值所对应的液滴直径会逐渐变小，雾化效果提升；相同流量条件下，喷嘴的角度改变对雾化效果有影响，顺喷和逆喷的雾化效果均好于垂直喷射；逆喷的喷射高度最高，随着流量的增长，燃料将会碰壁；顺喷条件下，随着角度的增加，穿透长度会有所增加；综合燃油轨迹边界，逆喷的效果相对较好。相同流量条件下，喷孔个数的改变对雾化效果和穿透深度的影响不大。     

PBT弹性体微相分离及对其力学性能的影响研究

为了获得微相分离对宽温PBT叠氮聚醚弹性体力学性能的影响规律,用红外光谱分析法(FT-IR)和动态热力学分析法(DMA)研究了PBT叠氮聚醚弹性体产生微相分离的机理和影响因素。用调节硬段含量、交联参数的方法调控其微相分离,控制适当的微相分离程度可显著改善推进剂的力学性能。研究结果表明:在二元醇扩链的弹性体体系中,当硬段含量约为15%时,弹性体发生相对最大比例的微相分离,体现出较佳的综合力学性能。通过微相分离的调控可获得宽温范围内综合力学性能较好的叠氮聚醚推进剂用粘合剂基体材料。     

27-day variation in solar-terrestrial parameters: Global characteristics and an origin based approach of the signals

The Earth and the near interplanetary medium are affected by the Sun in different ways. Those processes generated in the Sun that induce perturbations into the Magnetosphere-Ionosphere system are called geoeffective processes and show a wide range of temporal variations, like the 11-year solar cycle (long term variations), the variation of ～27?days (recurrent variations), solar storms enduring for some days, particle acceleration events lasting for some hours, etc.In this article, the periodicity of ～27?days associated with the solar synodic rotation period is investigated. The work is mainly focused on studying the resulting 27-day periodic signal in the magnetic activity, by the analysis of the horizontal component of the magnetic field registered on a set of 103 magnetic observatories distributed around the world. For this a new method to isolate the periodicity of interest has been developed consisting of two main steps: the first one consists of removing the linear trend corresponding to every calendar year from the data series, and the second one of removing from the resulting series a smoothed version of it obtained by applying a 30-day moving average. The result at the end of this process is a data series in which all the signal with periods larger than 30?days are canceled.The most important characteristics observed in the resulting signals are two main amplitude modulations: the first and most prominent related to the 11-year solar cycle and the second one with a semiannual pattern. In addition, the amplitude of the signal shows a dependence on the geomagnetic latitude of the observatory with a significant discontinuity at approx. ±60°.The processing scheme was also applied to other parameters that are widely used to characterize the energy transfer from the Sun to the Earth: F10.7 and Mg II indices and the ionospheric vertical total electron content (vTEC) were considered for radiative interactions; and the solar wind velocity for the non-radiative interactions between the solar wind and the magnetosphere. The 27-day signal obtained in the magnetic activity was compared with the signals found in the other parameters resulting in a series of cross-correlations curves with maximum correlation between 3 and 5?days of delays for the radiative and between 0 and 1?days of delay for the non-radiative parameters. This result supports the idea that the physical process responsible for the 27-day signal in the magnetic activity is related to the solar wind and not to the solar electromagnetic radiation.     

任意波发生器静态特性的评价

介绍了任意波发生器的主要静态特性指标、校准方法及实现过程。通过一组实验．获得了实际校准结果，并对校准中需要注意的问题进行了讨论。所述方法涉及的静态特性内容比较全面。具有足够的测量准确度、分辨力和稳定性。可用于任意波发生器的静态指标评价和计量。     

考虑辐射的化学平衡流驻点线解

本文用数值方法求解了化学平衡的高超声速粘性激波层驻点线流场。考虑了辐射和质量引射对流场的影响。辐射模型采用线和连续谱模型。文中讨论了引射率、头部半径、来流速度对壁面传热的影响。与有关文献结果比较表明,本文的方法是可行的。     

普郎克定律的一个新推论

根据热辐射基本定律———普郎克定律,推导出了一个新的推论。即对于任意温度T的黑体辐射源,总存在一对应波长λδ,该波长对应的黑体单色辐射亮度对温度T的偏导数最大,且λδT =2 4 10 .3μm·K。这一结论对于单波长辐射温度计设计中探测器波段的选择有重要参考价值,根据此结论可以推出温度测量灵敏度最高的波长。     

Obscured Activity: AGN, Quasars, Starbursts and ULIGs Observed by the Infrared Space Observatory

Some of the most ‘active’ galaxies in the Universe are obscured by large quantities of dust and emit a substantial fraction of their bolometric luminosity in the infrared. Observations of these infrared luminous galaxies with the Infrared Space Observatory (ISO) have provided a relatively unabsorbed view to the sources fuelling this active emission. The improved sensitivity, spatial resolution and spectroscopic capability of ISO over its predecessor Infrared Astronomical Satellite (IRAS) of enabled significant advances in the understanding of the infrared properties of active galaxies. ISO surveyed a wide range of active galaxies which, in the context of this review, includes those powered by intense bursts of star formation as well as those containing a dominant active galactic nucleus (AGN). Mid-infrared imaging resolved for the first time the dust enshrouded nuclei in many nearby galaxies, while a new era in infrared spectroscopy was opened by probing a wealth of atomic, ionic and molecular lines as well as broad band features in the mid- and far-infrared. This was particularly useful, since it resulted in the understanding of the power production, excitation and fuelling mechanisms in the nuclei of active galaxies including the intriguing but so far elusive ultraluminous infrared galaxies. Detailed studies of various classes of AGN and quasars greatly improved our understanding of the unification scenario. Far-infrared imaging and photometry revealed the presence of a new very cold dust component in galaxies and furthered our knowledge of the far-infrared properties of faint starbursts, ULIGs and quasars. We summarise almost nine years of key results based on ISO data spanning the full range of luminosity and type of active galaxies.     

Stellar infrared astronomy with EDISON

In this review the IR emission from circumstellar material is discussed, both of ionized gas and dust grains, and the astrophysical information that can be extracted from such observations. Some emphasis is placed on the possibilities of stellar IR astronomy using a large space-borne telescope, especially with respect to the much better spatial and spectral resolution of such a telescope compared to the current generation of ground-based and space IR telescopes.