基于支板燃烧室的喷管化学非平衡效应

采用有限体积法全隐式格式和代用燃料C₁₂H₂₃的10组元13步化学反应Arrhenius有限速率模型研究煤油燃料超燃冲压发动机单边膨胀喷管(SERN, Single Expansion Ramp Nozzle)内的化学非平衡流动,通过建立支板燃烧室——喷管模型有效解决了单边膨胀喷管模型的"入口薄层"问题.计算结果表明,整个单边膨胀喷管内,流动呈现化学非平衡效应,喷管入口附近区域尤其显著;非平衡流动喷管性能明显高于冻结流动,随发动机当量混合比 ε增加,非平衡流动的喷管推力系数和升力系数相对冻结流动的百分比增量 δ不断升高,当 ε=0.8时,推力系数百分比增量 δ_CF达到9.41%,升力系数百分比增量 δ_CY达到16.39%,化学非平衡效应对煤油燃料超燃冲压发动机尾喷管性能的影响不可忽略.     

热气防冰系统内表面弦向传热性能衰减规律

利用反向热流法实验研究了弦向3排射流喷口,且中央喷口正对前缘驻点结构下射流冲击热气防冰系统前缘内表面的局部传热特性。重点研究了喷孔射流出口雷诺数Re_j、笛形管相对于前缘的距离与孔径比Z_n/d、射流冲击驻点区弦向弧长与孔径比r/d对冲击前缘靶面的局部传热性能分布的影响。实验中Re_j范围为2.5×104~1×105,Z_n/d范围为1.736~27.5,r/d范围为13.21~61.5。结果表明,局部传热性能分布曲线为从驻点开始向两侧衰减的钟形曲线,包括稳定段、下降段和结束段3部分,其中稳定段只受参数r/d的影响,而参数Re_j、Z_n/d和r/d均能够明显影响下降段的下降速率,参数r/d则几乎不会改变下降段的总下降幅度。总结了此类喷口结构下射流冲击前缘换热性能衰减分布曲线的通用实验关联式,以指导防冰系统的设计和热性能的评估。      

基于Transition SST模型的高雷诺数圆柱绕流数值研究

为了研究高雷诺数下圆柱绕流边界层的转捩现象和圆柱尾迹近壁区的流动特征,首先通过在典型雷诺数下采用Transition SST四方程转捩模型模拟圆柱绕流得到的结果与实验结果及采用SST k-ω两方程湍流模型模拟结果的对比分析,验证了Transition SST模型在模拟高雷诺数下圆柱绕流的优越性,并较为准确地预测出了圆柱绕流边界层的转捩现象及尾迹近壁区的流动特征。然后分别对亚临界区、临界区、超临界区和过临界区的圆柱绕流问题进行了数值模拟,分析了不同雷诺数下圆柱绕流的流场结构及圆柱表面压力系数、摩擦力系数的变化规律,研究了圆柱绕流近壁区的流动特征、边界层转捩的流动机理、转捩位置及其随雷诺数的变化规律。结果表明,亚临界区二维圆柱绕流边界层发生层流分离,无分离泡和转捩现象;临界区和超临界区二维圆柱绕流边界层先产生了分离泡现象,之后流动发生了转捩并在转捩后发生湍流分离;过临界区二维圆柱绕流边界层流动在转捩之后发生湍流分离,无分离泡现象;在临界区、超临界区和过临界区,二维圆柱绕流边界层转捩位置随雷诺数增大向前驻点移动。     

激发跃迁速率对热力学非平衡氮气紫外辐射的影响

基于氮气的碰撞-辐射（CR）模型,计算了速度为6.2 km/s、初始压力为133 Pa的高超声速流动激波中N₂和N₂+分子电子能级的分布情况,分析了不同激发跃迁速率模型对电子能级分布及辐射光谱模拟的影响。针对流动中热力学非平衡区域和平衡区域,在300~440 nm的辐射光谱开展了逐线法的数值模拟,并与激波管实验测量光谱进行了对比。结果表明,目前的激发跃迁速率均存在偏差,综合Park模型的爱因斯坦系数和Johnston模型的碰撞激发速率可以得到与实验结果最为接近的辐射光谱。      

空间站乘员睡眠区二氧化碳聚集现象

为了分析乘员在没有良好通风的压力舱内停留时,呼出CO₂的聚集过程并评估其可能导致的医学危害,建立了乘员在特定空间站睡眠舱的计算流体动力学模型,对乘员在睡眠区的呼吸过程进行了非稳态模拟.模拟中乘员的CO₂呼出浓度和肺通气量根据生理实验随CO₂吸入浓度变化.通过模拟给出了睡眠区典型位置处CO₂分压随时间的变化规律.最后提出了无通风条件下乘员在睡眠区停留的最大容许时间,睡眠区CO₂浓度监测仪的布置原则和类似情况下为保障乘员生命安全可采取的一些措施.      

改进SA模型对翼型分离流动的数值模拟

采用(CFD,Computational Fluid Dynamics)软件Fluent,选取(SA,Spalart-Allmaras)模型,对风力机翼型S825进行了二维数值模拟,并与实验数据进行比较.针对SA模型不能准确预测翼型尾部流动分离的情况,分析了分离区域内湍流的强非平衡输运特性.研究表明,SA模型中系数C_b1与湍流的非平衡输运特性密切相关,进而提出了修正模型系数C_b1改进SA模型的方法,结果表明该方法能够更准确地模拟风力机翼型分离流动.     

含泡沫镍中间层陶瓷/不锈钢接头微观组织和性能

连接温度850℃,保温时间60 min,用泡沫镍金属作为中间层真空钎焊Al₂O₃陶瓷与1Cr18Ni9Ti不锈钢,利用扫描电子显微镜（SEM）、能谱（EDS）分析钎焊接头的微观组织,利用剪切实验检测接头的力学性能。实验结果表明,不添加中间层时,接头平均剪切强度只有7.7 MPa,断裂位置发生在陶瓷侧;添加泡沫镍中间层时,接头平均剪切强度达到101.7 MPa,断裂位置发生在陶瓷与泡沫镍金属连接界面处。不添加中间层时,Ti元素主要分布在钎料与陶瓷以及钎料与不锈钢反应界面处;添加中间层后钎焊接头中Ti元素主要分布在中间层,与Ni元素形成TiNi₃,Ag、Cu和Ti元素分布更加均匀。      

用时域法EIS技术研究LY12CZ 铝合金的局部腐蚀

通过周期浸泡腐蚀实验和时域法电化学阻抗谱(EIS)技术研究了LY12CZ铝合金的腐蚀损伤,用金相法测量最大腐蚀深度,用统计分析方法处理实验数据.结果表明,LY12铝合金经周期浸泡腐蚀试验后,低频阻抗倒数1/R_d符合Gumbel分布,1/R_d随腐蚀时间变化的动力学曲线呈S形,该曲线分成点蚀和剥蚀两个阶段,点蚀阶段符合Sigmoidal曲线关系,剥蚀阶段符合线性关系.1/R_d与最大腐蚀深度在空间统计分布和腐蚀动力学规律两个方面都有一致性,因此可以用1/R_d表征腐蚀损伤程度.由此可见,时域法EIS技术可作为一种快速、无损、定量的腐蚀评估手段.      

基于分数阶Maxwell模型的振荡流传热特性分析

经求解基于分数阶Maxwell模型的粘弹性流体在周期性振荡压力梯度下,圆直管内的运动方程和能量方程,得到了振荡管流换热的速度分布、温度分布以及热扩散系数的解析解形式.通过对无量纲热扩散系数的分析可知,影响粘弹性流体管内振荡流轴向换热的无量纲参数有:Womersley数Wo、Deborah数De、无量纲振幅Δx/R和流体普朗特数Pr.分数阶Maxwell模型振荡流传热也存在粘弹性流体流动中存在的共振现象,且共振峰的数量随De数的减小而增加,发生共振的起始频率随De数的减小而降低.共振峰值出现的位置即频率值与Pr和无量纲振幅Δx/R无关.     

基于伪寿命的加速退化机理一致性边界检验

根据寿命型随机变量的加速机理一致性条件,提出一种基于伪寿命的加速退化机理一致性边界检验方法,通过由低到高逐一对各个加速应力水平下的退化机理一致性进行检验,来确定加速退化机理一致性的边界应力水平.针对工程常用的两类寿命型分布——对数正态分布和Weibull分布,分别以对数标准差和形状参数为退化机理表征量,在产品伪寿命估计的基础上建立了退化机理表征量齐性检验的F统计量,导出了退化机理一致性检验拒绝域的解析式,给出了退化机理一致性边界检验的具体步骤.该方法能够充分利用多个应力水平下表征产品退化机理一致的横向信息,有效提高了检验的精度.以某镀膜平板玻璃热退化机理一致性边界温度的确定为例,分析说明了该方法的合理性与有效性.     

Geomagnetic effects on mid-latitude railways: A statistical study of anomalies in the operation of signaling and train control equipment on the East-Siberian Railway

Intense geomagnetically induced currents (GIC) can hamper rail traffic by disturbing signaling and train control systems. GIC threats have been a concern for technological systems at high-latitude locations due to geomagnetic disturbances driven by substorm expansion electrojet or convection electrojet intensifications. However, other geomagnetic storm processes such as storm sudden commencement (SSC) and geomagnetic pulsations can also cause GIC concerns for technological systems. We present in this paper the first evidence based on statistical data for links between geomagnetic disturbances and faulty operations (anomalies) in the functioning of railway automatics and telemetry. We analyze anomalies of automatic signaling and train control equipment which occurred in 2004 on the East-Siberian Railway (corrected geomagnetic latitude _m = 46–51°N and longitude λ_m = 168–187°E). Our results reveal a seasonal effect in the number of anomalies per train similar to the one observed in geomagnetic activity (Kp, Ap, Dst indices). We also found an increase by a factor of 3 in the total duration of daily anomalies during intense geomagnetic storms (local geomagnetic index specific to Siberian Observatory A_max > 30), with a significant correlation between the daily sum of durations of anomalies with geomagnetic activity. Special attention was paid to failures not related to recognized technical malfunctions. We found that the probability of these failures occurring in geomagnetically disturbed periods was 5–7 times higher than the average anomaly occurrence.     

A southern hemisphere error in the IRI

I would like to call attention to the fact that the IRI computes erroneously the F2-layer semithickness parameter B₀ at southern hemisphere locations. The values of B₀, based on northern latitude observations, have a seasonal variation which must be preserved at southern latitudes.The error was found in the course of a study to develop a new ionospheric model for radio-propagation predictions. We observed at southern latitudes major discrepancies between the IRI and the Bradley-Dudeney (1973) model in relation to the F2-layer semithickness. This is estimated in the latter model as the difference between the height of maximum electron concentration (hmF2) and the ionospheric characteristic h′F,F2, the minimum observed virtual height of reflection from the F2-layer, corrected taking into account underlying ionization. The profiles for both models were drawn using the same values of foF2 and hmF2. Then, our analysis served also to test the IRI model with h′F,F2 data obtained from CCIR maps but not used as primary inputs by the IRI.     

发动机进气道水滴撞击特性分析

针对某发动机进气道的防冰系统设计,对进气道的水滴撞击特性进行了研究.在对进气道流场进行计算的基础上,采用差分法对水滴运动方程进行了数值求解,得到了水滴运动轨迹,从而确定了水滴的撞击极限、总收集系数和局部水收集系数等水滴撞击特性参数;此外,还研究了飞行高度、飞行速度及水滴半径对水滴撞击特性的影响;研究发现水滴撞击极限、总收集系数和局部水收集系数随飞行速度的减小、飞行高度的增加或者水滴半径的增加而增大.这些为进气道的防冰系统设计奠定了基础.     

Effects of tailward stretching geomagnetic field on drift motion of plasma particles in the magnetospheric equatorial plane

Drift paths of electrons and protons are calculated in the equatorial plane of the superquiet (SQ) and superdisturbed(SD) Mead-Fairfield magnetospheric models in order to study effects of tailward stretching geomagnetic field on drift motion of plasma particles. Magnetospheric electric fields in the equatorial plane are given by vector sums of uniform dawn-dusk electric field of 0.1 mV/m or 0.4 mV/m and corotation electric field projected onto the equatorial plane from the earth's surface along the MF geomagnetic field lines. All particles start from a geocentric circle of 17 earth radii (R_E) in the tail equatorial plane. The late-evening stagnation point for zero-energy particles and low-energy electrons is produced by the anticlockwise corotation drift larger than the sunward electric-field drift in the outer magnetosphere. The late-morning stagnation point for energetic protons and the late-afternoon stagnation point for energetic electrons result from small radial gradient of the MF geomagnetic field in the late-morning and the late-afternoon outer magnetosphere respectively.     

Model calculation of hydrogen balmer emissions under various modes of proton precipitation

A theoretical model is developed to study the H_α and H_β volume emission rates in proton auroras. The H_α and H_β photon yields are deduced by using the recent experimental cross-sections. These photon yields are then coupled with the primary proton fluxes to get the altitude profiles of the emissions. The prediction of the altitude profiles are found in good agreement with the auroral measurements. The effects of various modes of proton precipitation on the emission intensities (IH_α and IH_β) are discussed and a comparison is made with the earlier theoretical models. It is also found that the intensity ratio IH_α/IH_β varies between 5 and 6.     

PANS方法在双圆柱绕流数值模拟中的性能分析

PANS方法以传统的雷诺平均Navier-Stokes(RANS)方程为模板,引入控制参数对原方程进行修改,是一类能够有效模拟分离湍流流动的混合方法.采用基于Menter 剪切应力输运(SST)湍流模型的PANS方法,选取双圆柱绕流作为研究对象, 分析双圆柱流动结构,验证方法的准确性与可靠性,考察PANS方法中模型参数选取对于计算结果的影响,评估不同类型PANS方法的性能.研究表明:模化湍动能比例这一模型参数对计算结果有显著影响,且计算域内统一的模型参数取值难以处理复杂流动问题.在此基础上使方法中模化湍动能比例取值随流场物理信息和网格尺度变化,所得结果与SST DES计算结果及实验结果吻合较好,表明该方法适用于复杂湍流数值模拟.      

Human adaptation to simulated gravitational fields

We present the results of manned studies in which test subjects were exposed to simulated zero $\text{g}$ (water immersion or head-down tilt at ?6°) and head-to-feet acceleration. The findings give evidence that humans have different individual tolerances to an acceleration of +3 G_z after exposure to zero $\text{g}$, whether simulated by immersion or by head-down tilt. The paper discusses the functional relationship between water balance and cardiac output in the establishment of adaptive reactions to simulated zero $\text{g}$.     

Ion beams at oblique shocks

Using a mixture of hybrid simulations and test particle techniques we investigate the relative importance of two local mechanisms, direct reflection and local leakage, for the production of field-aligned beams at oblique collisionless shocks. For direct reflection, between θ_Bn=40° and 60° the reflected density decreases with increasing M_A and, most strongly, with increasing θ_Bn. As θ_Bn increases the reflected ions increasingly come from the wings of the distribution, and their density becomes dependent on β_i and the form of the incident distribution. We next examine local leakage of the transmitted gyrating particles, assuming they are pitch angle scattered behind the shock. We find such leakage considerably less likely than expected from simple considerations. We also present results for a case where the downstream ions receive extra energization.