R141b在矩形微尺度通道中的两相流传热特性

设计搭建水力直径分别为1mm和0.5mm的矩形微尺度通道实验台,研究了以R141b型制冷剂作为工质的两相流沸腾传热特性。实验取热流密度为1～16kW/m2、质量流速为111.1～333.3kg/(m2·s)和质量干度为0～1,分析了三者对平均传热系数的影响,探究影响换热的主导因素。结果表明:热流密度较高时,平均传热系数随热流密度增加而减小,流动换热主要受到沸腾传热的影响;当质量流速较大且热流密度较低时,平均传热系数随热流密度增加而有所增长;热流密度较低时,平均传热系数随质量流速变化明显,热流密度升高到一定值后,质量流速对平均传热系数的影响很小;当质量流速处于111.1～333.3kg/(m2·s)时,平均传热系数随质量干度的增加而减小。      

基于雷诺平均Navier-Stokes方程的表面传热系数计算

采用有限体积法数值求解控制二维绕流的雷诺平均Navier-Stokes(RANS)方程组,计算了光滑和粗糙NACA0012翼型以及圆柱表面的局部表面传热系数.分析了近壁面网格间距、湍流模式和表面粗糙度模型对数值计算结果的影响.结果表明:切应力输运(SST)湍流模型能够区分层流和湍流边界层的对流传热特性,并能预测转捩的发生;采用Spalart-Allmaras(S-A) 扩展模型能够计算粗糙壁面的对流传热系数,但采用忽略转捩函数的S-A模型不能有效计算层流边界层的传热系数.当近壁面网格间距接近10-5量级的黏性子层时,在光滑和粗糙壁面都能得到准确的传热系数分布.结合合适的近壁面网格间距,湍流模式和表面粗糙度模型可以得到与实验数据十分接近的表面传热系数曲线.通过与求解不可压缩RANS方程得到的结果比较后发现,不可压缩RANS方程主要忽略了压缩和黏性耗散效应,这种效应可以通过绝热升温项的形式并入总体热分析.      

汽雾两相流强化冷却燃气轮机叶片内冷通道

实验研究了方形通道这一重型燃气轮机中常用叶片强制对流冷却通道结构.分析了雷诺数、壁面热流密度以及水雾质量流量比等关键参数对汽雾冷却通道的传热特性的影响,并建立了考虑离散相水雾的流动工况和通道壁面加热条件的实验关联式.结果表明:相对于纯蒸汽,汽雾两相流的传热系数显著提高,且传热性能提高的幅度随热流密度的增大而减小,随雷诺数和水雾质量流量比的增大而增大;通道上壁面平均传热系数低于下壁面,在高热流密度和低水雾质量流量比下,两者相差约13%,而在低热流密度与高水雾质量流量比的情况下,该比值增加到约25%.      

Probing the origin of the iron Kα line around stellar and supermassive black holes using X-ray polarimetry

Asymmetric, broad iron lines are a common feature in the X-ray spectra of both X-ray binaries (XRBs) and type-1 Active Galactic Nuclei (AGN). It was suggested that the distortion of the Fe Kα emission results from Doppler and relativistic effects affecting the radiative transfer close to the strong gravitational well of the central compact object: a stellar mass black hole (BH) or neutron star (NS) in the case of XRBs, or a super massive black hole (SMBH) in the case of AGN. However, alternative approaches based on reprocessing and transmission of radiation through surrounding media also attempt to explain the line broadening. So far, spectroscopic and timing analyzes have not yet convinced the whole community to discriminate between the two scenarios. Here we study to which extent X-ray polarimetric measurements of black hole X-ray binaries (BHXRBs) and type-1 AGN could help to identify the possible origin of the line distortion. To do so, we report on recent simulations obtained for the two BH flavors and show that the proposed scenarios are found to behave differently in polarization degree and polarization angle. A relativistic origin for the distortion is found to be more probable in the context of BHXRBs, supporting the idea that the same mechanism should lead the way also for AGN. We show that the discriminating polarization signal could have been detectable by several X-ray polarimetry missions proposed in the past.     

Accelerating NLTE radiative transfer by means of the Forth-and-Back Implicit Lambda Iteration: A two-level atom line formation in 2D Cartesian coordinates

State-of-the-art methods in multidimensional NLTE radiative transfer are based on the use of local approximate lambda operator within either Jacobi or Gauss–Seidel iterative schemes. Here we propose another approach to the solution of 2D NLTE RT problems, Forth-and-Back Implicit Lambda Iteration (FBILI), developed earlier for 1D geometry. In order to present the method and examine its convergence properties we use the well-known instance of the two-level atom line formation with complete frequency redistribution. In the formal solution of the RT equation we employ short characteristics with two-point algorithm. Using an implicit representation of the source function in the computation of the specific intensities, we compute and store the coefficients of the linear relations J=a+bS$J=a+\mathit{bS}$ between the mean intensity J and the corresponding source function S. The use of iteration factors in the ‘local’ coefficients of these implicit relations in two ‘inward’ sweeps of 2D grid, along with the update of the source function in other two ‘outward’ sweeps leads to four times faster solution than the Jacobi’s one. Moreover, the update made in all four consecutive sweeps of the grid leads to an acceleration by a factor of 6–7 compared to the Jacobi iterative scheme.     

基于XML的EtherCAT工业以太网协议解析技术

重点研究了基于可扩展标记语言(XML,eXtensible Markup Language)的EtherCAT工业以太网协议解析器技术和实现方法.介绍了EtherCAT协议报文格式和特点,分析了以太网数据侦听器和协议解析器的结构,针对通用以太网解析器在工业以太网领域应用的局限性,提出使用XML语言描述协议报文的方法,在此基础上开发出一种开放式、可重构的EtherCAT协议解析器.实验结果表明基于XML的协议报文描述方法及解析器能够有效地描述和解析EtherCAT协议报文,使用者可以根据解析对象格式使用XML语言自定义、修改和扩展协议解析规则,获得清晰、直观的解析结果.      

含湿气流单缝冲击冷却数值模拟

对饱和湿空气夹带液滴的含湿气流单缝冲击冷却进行了数值模拟,比较研究了含湿气流中液滴相变换热/液滴载量比和单缝射流几何参数对强化换热效果的影响,研究发现:气流中液滴的加入对冷却效果的影响十分显著,热流密度为8000W/m2的条件下,空气中注入5%的液滴会比饱和湿空气对驻点区的冷却效果提高90%,当液滴载量比从1%提高到5%,冲击驻点区局部传热系数提高了32%;而合适的缝宽和冲击高度也是影响冷却效果的重要因素,在该条件下冲击高度与缝宽的比值为4.55时冲击冷却效果最佳.      

火星气囊气体发生器充气过程稳压仿真研究

文章对低温和常温环境下的气囊稳压充气过程的参数进行了仿真计算。主要分析计算了气囊内外壁的对流换热、囊内气体与囊壁间辐射以及水蒸气液化等传热方式的传热量。同时,计算了在不同环境温度下,气囊内气体温度、充气质量以及充气质量流率随时间的变化关系。分析结果可以为工程研制提供参考和数据支持。     

5kN再生冷却发动机推力室传热研究

5 kN摇摆发动机推力室采用再生冷却身部,为检验推力室冷却方案设计的合理性,对5 kN再生冷却发动机推力室进行传热计算,分析了再生冷却的影响因素,并针对发动机设计提出了相应的改进措施,改进后的发动机热试车工作正常,表明了改进工作的有效性。