散射对高温气体-碳黑颗粒混合物辐射传输的影响

基于全光谱k分布(Full spectrum k distribution,FSK)模型、MIE理论和有限体积法(Finite volume method,FVM),构建了均温、均质辐射参与性气体-碳黑颗粒混合物介质热辐射传输模型,并分析了碳黑不同尺寸、不同体积浓度以及介质不同路径长度和不同温度条件下,因忽略碳黑颗粒散射所导致的介质热辐射传输特性(如辐射热流、辐射源项)的计算误差。研究结果表明:体积分数不变,增大粒径,计算误差呈现出先增大后减小的趋势;数密度不变,增大粒径,或者粒径不变,增大体积分数,均将使得计算误差相应增大;粒径、体积分数不变,增大路径长度,或者升高介质温度,均将增大计算误差。通常对于含有大颗粒、高碳黑浓度的辐射参与性气体-碳黑颗粒混合物介质,碳黑颗粒散射不能忽略。     

钛合金表面抗激光涂层损伤特性及热效应影响研究

实验研究了钛合金和高反射型陶瓷涂层材料抗连续型激光烧蚀的损伤及温度分布特性，并从热效应影响角度对比分析了二者在抗激光损伤效果方面的差异性。研究结果表明：相比于钛合金，高反射型陶瓷涂层材料能有效增强钛合金基底抗激光损伤的能力；在同等激光功率密度辐照下，陶瓷涂层材料能有效提升钛合金基底耐受激光辐照的时间长度。实验结果表明该陶瓷涂层材料的激光损伤阈值比钛合金高约5.8倍。实验发现陶瓷涂层温升速率高于钛合金，但由于陶瓷材料具有较高的反射特性，以及良好的热吸收和热传导特性，因此能使由激光辐照产生的热量在其表面较快地扩散，而降低向基底方向传导的程度，最终提升陶瓷涂层的抗激光损伤阈值。     

Modeling the effects of green alternative on heat island mitigation of a meso level town,West Bengal,India

Urban heat island (UHI) is emerged as a ubiquitous phenomenon that affects the outdoor thermal comfort. Hence urban microclimatic studies using numeric simulation software to find out adaption strategies are attracting the great attention of researchers and policymaker. Number of scientists carried out their research on this topic using different tools and technique whereas ENVI-met model is the most widely used simulation tools. The present study intended to examine the implication of green infrastructure of the town on enhanced microclimatic condition and to evaluate the best suitable mitigation strategy modelling cool city with ENVI-met software (V4). Five greening condition such as existing UHI condition (C1), 100% greening of roof (C2), 100% greening of roof and walls (C3), 50% greening of roof and walls (C4) and: Plantation at suitable area with 50% greening of roof and walls (C5) have been taken into consideration for the microclimate simulation for all three selected sites. Among these five conditions, C3 for the open mid-rise and compact low-rise, C5 for the open low-rise are identified as one of the most suitable strategies which can reduce the air temperature of peak hours by 2.6 °C, 1.33 °C and 1.87 °C respectively. These models are validated by simple linear regression between simulated and existing air temperature in case of existing UHI condition (C1) and in all the cases coefficient of determination value is high such as for open mid-rise, compact low-rise and open low-rise, it is 0.92, 0.92 and 0.75 respectively. Therefore it can be concluded that the application of those strategies can improve the urban thermal environment as well as the outdoor thermal comfort of English bazaar Town and its surroundings.     

R141b在圆形微通道内的沸腾换热实验研究

为提高换热强度、解决设备内部高热流密度散热问题,采用实验方法研究R141b在不同直径(D=0.5mm和1.0mm)水平圆形微通道内的沸腾换热特性,分析了热流密度(q=2.0kW/m~2～47.6kW/m~2)、质量干度(x=0～0.6)、质量流速(G=111.11kg/(m~2·s)～333.33kg/(m~2·s))的变化对平均传热系数h的影响,探究不同情况下影响沸腾换热的主导因素。实验研究表明:平均传热系数h随热流密度q的增加而减小,在不同范围内减小速率有明显差异;热流密度q=2kW/m~2～5kW/m~2时质量流速G对平均传热系数h影响较明显,热流密度较高时质量流速G对换热影响很小;在质量流速G=111.11kg/(m~2·s)～333.33kg/(m~2·s),质量干度x0.3时,平均传热系数h随质量干度x增加而明显下降,在设计微通道换热器时应尽量使R141b处于初始沸腾阶段以获得更好换热效果,并采取一定措施预防干度过高引起的换热恶化。     

Variation of dayside chorus waves associated with solar wind dynamic pressure based on MMS observations

The whistler-mode chorus waves are one of the most important plasma waves in the Earth’s magnetosphere. Generally, the amplitude of whistler-mode chorus waves prefers to strengthen when the energetic fluxes of anisotropic electrons increase outside the plasmapause. This characteristic is commonly associated with the geomagnetic storms or substorms. However, the relationship between the solar wind dynamic pressure (P_sw) and the long-time variation of chorus waves during the quiet period of the geomagnetic activity still needs more detailed investigations. In this paper, based on MMS observations, we present a chorus event just observed in the inner side of magnetopause without obvious geomagnetic storms or substroms. Interestingly, during this time interval, some P_sw fluctuations were recorded. Both the amplitudes and frequencies of chorus waves changed as a response to the variation in P_sw. It proved that the enhancement of P_sw increases the energetic electrons fluxes, which provides free energies for the chorus amplification. Furthermore, the wave growth rates calculated using linear theory increases and the central frequency of the chorus waves shifts to a higher frequency when the P_sw enhancement is greater, which are also consistent well with the observations. The results provide a direct evidence that the P_sw play an important role in the long-time variation of whistler-mode chorus waves inside the magnetopause.     

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%。      

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.     

运载火箭推进剂复杂流动传热问题数值模拟中的模型简化方法

在运载火箭改进优化或新型运载火箭设计过程中,会遇到各种复杂的流动与传热问题。按照真实产品和物理过程直接建立的数值计算模型过于复杂,不同尺度的结构、流动与传热、长时间的飞行过程相互耦合,出现计算时间太长(数年)、收敛困难、程序调试困难等问题。针对初始条件复杂、飞行过程复杂、边界条件复杂3类具体问题,总结了3种相应的模型简化方法,分别是工程经验法、极限参数法、低维近似法,为推进剂复杂流动与传热的数值模拟提供参考。     

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。