冲击-多斜孔复合冷却中冲击孔与多斜孔面积比对换热特性的影响研究

用数值计算的方法研究了冲击-多斜孔壁复合冷却方式的冷却特性,在保证当量开孔面积相同且压降相同的前提下,研究了冲击孔壁与多斜孔壁开孔面积比 变化对冷却特性的影响。研究发现,随着冲击孔与多斜孔开孔面积比减小,多斜孔壁气膜出流速度降低,气膜覆盖增强,冲击换热系数呈增大趋势,使得模型冷却效果增强;多斜孔壁热侧、冷侧与多斜孔孔内换热量随开孔面积比减小而减小,多斜孔内换热量在模型总体换热量中所占比例逐渐增加。     

小管径冷凝管的数学模型

基于环状流流型建立了小管径冷凝管的数学模型.模型考虑了气液界面表面张力的作用,在同一横截面上气相与液相存在压力差.对两相压降的计算,考虑了气液两相间的相互作用,包括摩擦切应力和动量转移切应力.应用该模型,可考察气相与液相压降、液膜厚度、气相与液相平均速度、气液界面切应力以及管内壁换热系数等的沿程变化情况.根据模拟结果可得:两相压降沿管长呈近似线性增加;气相平均速度沿管长先增大后逐渐减小,但变化范围很小,且远大于液相平均速度;动量转移切应力随液膜厚度增加而增大,同摩擦切应力相比不可忽略;管内壁对流换热系数随液膜厚度增加而减小,由于冷凝管的管径很小,即使蒸气冷凝趋于完毕,气液界面接近冷凝管中心线,换热系数仍较大.     

低Weber数射流撞击雾化的数学模型

通过分析低Weber数无粘射流撞击形成液膜雾化的特征, 由质量守恒和动量守恒, 并借鉴前人的理论和实验结果, 推导出Taylor心形波作用下计算液膜厚度和形状的近似解析式, 数值计算结果与文献所给实验数据基本吻合一致。结合矩形喷孔形成的扇形液膜的破碎理论, 进一步计算了不同撞击角下雾化形成液滴尺寸的大小及分布。      

Study of thermo-fluidic characteristics for geometric-anisotropy Kagome truss-cored lattice

The aim of this paper is to provide a comprehensive comparison of the thermal insulation and heat transfer performance for Kagome truss-cored lattice along two perpendicular orientations OA and OB. Three test conditions are conducted under forced air convection for the titanium sandwich panel fabricated by 3 D printing technology. The thermo-fluidic characteristics are further explored by numerical simulation to reveal the underlying mechanisms of heat transfer enhancement.The results indicate that the orientation OB exhibits better thermal insulation than orientation OA under the identical temperature loading, while the latter outperforms the former by up to 20% higher overall heat transfer performance. In particular, the endwalls and lattice core in orientation OA achieve 9.7% and 22.5% higher area-averaged Nusselt number respectively than that in orientation OB for a given Reynolds number. The heat transfer superiority of orientation OA comes from the unique topology which induces the large scale spiral primary flows, facilitating the heat exchange between the cooling air and the surfaces of sandwich panel. However, the complex flow mixing leads to a maximum of 20% higher friction factor in orientation OA than that in orientation OB.     

内埋武器机弹分离相容性研究进展综述

为满足新型有人或无人作战飞机高隐身、高速和高机动性等要求，作战飞机普遍采用武器内埋挂载方式。当高速气流流过内埋武器舱的空腔时，将引发边界层分离、舱口附近会存在复杂的剪切流动、舱内会产生极为恶劣的噪声环境等非定常流动现象，这些复杂的非定常流动现象严重影响内埋武器机弹分离相容性（ASSC）。首先，给出内埋武器机弹分离相容性的重要研究意义；接着，重点介绍内埋武器机弹分离相容性的研究进展；最后，论述和总结了国内外采用4种方法（理论分析与建模、风洞试验、数值模拟和飞行试验）研究内埋武器机弹分离相容性及其流动控制方法的进展，指出内埋武器机弹分离相容研究存在的主要问题，并给出几点建议。     

各级差异化多级刷式密封级间压降均衡性数值与实验研究

分析多级刷式密封级间压降分配特性理论,提出新型各级差异化多级刷式密封结构,基于流固耦合方法建立新型多级刷式密封三维实体计算模型,设计搭建新型多级刷式密封泄漏流动特性实验装置,数值与实验研究在不同工况条件下,结构参数对新型结构多级刷式密封级间压降均衡性和泄漏特性的影响规律。研究结果表明：传统结构多级刷式密封各级级间压降占比均衡性标准差为8.41,新型结构各级级间压降占比均衡性标准差最大为4.69,最小为2.07。相较传统各级相同结构,增大下游级有效流通面积的新型各级差异化多级刷式密封可有效改善级间压降的不均衡性。提高后挡板保护高度使得新型结构各级级间压降占比均衡性标准差最小,各级级间压降占比较接近,可明显改善新型结构多级刷式密封级间压降均衡性。减少刷丝束厚度和增大刷丝束与转子面间隙使新型结构多级刷式密封的泄漏量增大明显。     

串列双U型管束换热器压降与回热效率模型实验

为了研究串列双U型管束换热器的流动和传热特性,开展了模型实验,得到了串列双U型管束换热器布置方式对喷管通道流动压降和换热器回热效率的影响。结果表明:喷管通道流动压降随着换热器安装角的增大而增加,邻近喷管收敛状出口位置的换热器安装角对流动压降的影响最为显著,进口附近的换热器影响次之;相对通道内置单个换热器的情形,串列换热器中前置换热器安装角的变化对流动压降的影响有所减弱;较小的前置换热器安装角度导致其回热效率过低,从而导致平均回热效率难以改善;在本文研究的几种布置方式下,安装角为30°-17°-13°的串列换热器布置方式的流动和传热综合性能相对较优。     

Variation of rain drop size distribution with rain rate at a few coastal and high altitude stations in southern peninsular India

Rain drop size distribution (DSD) was measured at four places in Southern India {Thiruvananthapuram, Kochi, Munnar and Sriharikota (SHAR)} using a Joss–Waldvogel (JW) impact type disdrometer. The data for each minute were corrected for dead time errors and rain rate was computed from the corrected data. The data for a whole month were then sorted according to rain rate (R) into several classes ranging from 0.1 to >100 mm/h. The average DSD in each class was computed, and the lognormal distribution function was fitted to the average. In all the cases, the function fitted the data very well. The fit parameters were found to have dependence on rain rate. The total number of drops (N_T), the geometric mean diameter (D_g) and the standard geometric deviation (σ) were also computed from the fit parameters. The standard geometric deviation (σ) was found to be more or less constant with rain rate at all the sites and in all months. The other two parameters (N_T and D_g) were found to vary exponentially with rain rate except in Munnar, a high altitude station. At Thiruvananthapuram, in most of the months, N_T increased exponentially with rain rate up to some value of R, which was different in different months, and then remained more or less constant or decrease slightly. In all cases, the variation of N_T and D_g was such that N_TD_g³ increased linearly with rain rate.     

双级轴向旋流杯气量比对雾化性能影响的试验

为探索小状态下改善雾化性能的途径,从调节旋流杯气量分配的角度出发,对不同一、二级气量比的双级轴向旋流杯开展了试验研究,获得了气量比对液滴平均直径、液滴尺寸分布指数以及喷雾锥角的影响规律。试验结果表明:气量比的增大不仅降低液滴平均直径,而且使得旋流杯在较宽的供油压差范围内都具有良好的雾化品质,可实现小状态下雾化性能的改善。旋流杯喷雾锥角随气量比的增大而增大,随供油压差的增大而增大并逐渐趋于稳定。旋流杯总气量恒定时,气量比接近1时的综合雾化性能最佳。      

某歼击机前起落架着陆瞬间有关参数的试验研究

 以某歼击飞机前起落架为例, 用落震试验的方法, 通过分析起落架有关参数随机轮转速变化的情况,来研究飞机着陆瞬间起落架的状况。研究结果表明, 在飞机着陆过程中, 当起转水平载荷达到最大值时, 起落架逆航向的弹性变形还未结束; 当起落架逆航向的弹性变形达到最大值时, 机轮从滑动转为滚动。