粒径及送风方式对飞机座舱颗粒物分布的影响

通过合理简化波音737-200飞机的座舱,建立物理模型后,用计算流体力学(CFD)方法研究了粒径及送风方式对飞机座舱颗粒污染物分布的影响。用FLUENT软件计算分析了天花板送风和侧壁送风方式下飞机座舱内的流场;并在座舱中设置污染源,瞬态释放了1μm、10μm、20μm三种粒径的颗粒物,在机舱设置了不同的颗粒物浓度监测点并对整个机舱内颗粒物的浓度随释放后时间的变化情况进行比对,研究了这三种粒径的颗粒物在两种送风方式下的分布情况与排除速率。研究结果表明:粒径越小,颗粒物在机舱内扩散能力越强;天花板送风时,颗粒物更易集中于机舱中间过道及机舱后侧,且颗粒物排出速率与粒径成反比;侧壁送风时,颗粒物更易集中于机舱两边侧壁及机舱前侧,且粒径大小对排除速率的影响与释放后的时间有关。     

槽道内涡波流场的POD分析

对槽道内涡波流场的瞬态速度矢量场进行了2DPIV测量实验,将2DPIV测量的矢量场数据进行POD分析,根据POD分解的各阶模态的能量比确定了表征涡波流场主导结构的前15阶模态。结果表明,POD分解的前15阶模态发现槽道内涡波流场是由槽道壁面剪切层诱导的涡列以及伴随的波状主流组成;流场中大尺度的涡旋发展为涡对,对波状主流的脉动频率产生影响;根据涡波流场中的驻点和鞍点,获取了流场的大尺度涡对、平均流场以及Helmholtz涡环等明显特征;最后根据POD分解的前15阶模态对槽道内涡波流场进行重组,重组流场表征了槽道内层流状态下波状主流的形态和涡旋共存的涡波结构以及驻点和鞍点的位置处涡旋的变化等主要特征,有效地剔除了PIV测量流场中的随机信息,保留了PIV测量流场的主导特征。     

槽道内涡波流场的POD分析

对槽道内涡波流场的瞬态速度矢量场进行了2DPIV测量实验,将2DPIV测量的矢量场数据进行POD分析,根据POD分解的各阶模态的能量比确定了表征涡波流场主导结构的前15阶模态。结果表明,POD分解的前15阶模态发现槽道内涡波流场是由槽道壁面剪切层诱导的涡列以及伴随的波状主流组成;流场中大尺度的涡旋发展为涡对,对波状主流的脉动频率产生影响;根据涡波流场中的驻点和鞍点,获取了流场的大尺度涡对、平均流场以及Helmholtz涡环等明显特征;最后根据POD分解的前15阶模态对槽道内涡波流场进行重组,重组流场表征了槽道内层流状态下波状主流的形态和涡旋共存的涡波结构以及驻点和鞍点的位置处涡旋的变化等主要特征,有效地剔除了PIV测量流场中的随机信息,保留了PIV测量流场的主导特征。     

W型火焰锅炉炉内三维速度场数值模拟研究

W型火焰锅炉采用了煤粉浓缩、长火焰及分级送风等技术,有利于燃料的着火、火焰的稳定以及燃料的燃尽,在煤种适应性、低负荷稳燃能力、飞灰燃尽率等方面有很大的技术优势.本文通过数值模拟研究了W型火焰锅炉的三维速度场分布,得到了不同工况下炉内W型气流的流场图.通过比较数值结果和试验结果的流场图,结果表明:数值结果和试验结果基本吻合,W型火焰锅炉内的空气动力场取决于拱顶风与前后墙风的动量比,炉内气流形成两个明显的漩涡,延长了煤粉气流在下炉膛的停留时间,同时也增加了炉内气流充满度,有利于煤粉的完全燃烧.加大喉口风速,漩涡运动更加明显,在炉内形成γ型气流,煤粉气流在下炉膛的停留时间更长,炉内的一、二次风混合更加均匀.     

流固耦合作用下真实人体上呼吸道呼吸流涡结构演化的数值仿真

通过构建真实人体上呼吸道三维规范模型,运用大涡模拟数值方法,对考虑流固耦合作用的低强度循环呼吸模式下人体上呼吸道内的呼吸流进行了数值仿真,研究分析了人体口喉模型及气管支气管内的气流涡结构及其演化过程。结果表明,循环吸气过程中,气流在口腔中部以及舌苔上部形成多个涡管,在声门部位形成强烈的射流,在气管前壁出现马蹄涡,到气管中部大尺度涡结构逐步消失,支气管中只剩下一系列小尺度涡结构;循环呼气过程中,气流在气管底部产生较为复杂的涡结构,随着气流在气管内的融合,涡强度逐步减弱,在咽喉后壁形成拱状涡,气流进入口腔后,涡结构破裂,涡量扩散,没有较大的涡结构产生。     

载人列车车厢内空气流场温度场数值模拟

采用稳态不可压缩雷诺时均N-S方程、k-ε湍流模型,计算了载人列车车厢内三维空气流场和温度场。将太阳辐射热和人体散热作为能量方程的附加源项,研究了在条缝送风条件下,乘客和太阳辐射对车厢内流场和温度场的影响。计算结果表明:现有的送风方式除车厢两端外,车厢内沿长度方向气流分布比较均匀;送风口的布置对车厢内流场温度场分布影响较大,送风气流在车厢两侧形成两股比较大的流动旋涡;人体散热和太阳辐射对车厢内流场温度场影响较大,非空载时车厢内流场分布与空载时有较大差别,太阳照射和人体产生的热气流使车厢内存在较大的温度梯度,靠窗处的温度较高,过道处温度较低。流场温度场的计算结果和实验数据吻合较好。     

低对流马赫数平面混合层的声波产生机理

为了详细揭示低对流马赫数下平面混合层的声波产生机理,基于高精度混合格式,对空间发展的平面混合层的流场结构及其声场特性进行了直接模拟.数值结果描述了对流马赫数为0.4时混合层失稳产生的涡串以及涡发展过程中所存在的各种声源,其中包括常规的单涡四极子声源、双涡以及多涡合并过程产生的四极子声源,另外,还发现因K-H不稳定引起混合层振动而产生的偶极子声源,声波以平面波的形式向周围传播.     

大型客机座舱混合送风形式的数值模拟

提出了一种新的四风口混合送风形式，并采用计算流体力学（CFD）对其送风效果进行评估。首先利用真实MD-82飞机实验平台的气流实验数据对所采用的非定常RNG k-ε模型进行了验证；然后针对某机型座舱的热天地面工况，用上述验证后的CFD模型分别对这种新的四风口送风形式及现行的两风口、三风口混合送风形式进行了数值仿真；最后对这三种送风形式营造的客舱环境从速度、温度、局部热舒适度等角度进行了分析比较。结果表明：非定常RNG k-ε模型能够准确合理地预测客机座舱内的空气流动；两风口送风形式在乘客周围形成较大风速，脚部吹风感达15%；三风口送风形式下走廊风速达到0.5m/s，会引起工作人员的热不舒适；而新的四风口送风形式在乘客周围大部分区域的风速低于0.1 m/s，垂直温差引起的不满意率（PD）平均值约为0.5%，吹风感引起的不满意率（DR）在身体周围大部分区域低于5%，其舒适度是三种送风形式中最优的，适合在客机上使用。     

湍流一般机理及其应用

本文综述了湍流机理发展中最重要的一些文章,包括:Brown-Roshko的混合剪切层中大尺度涡的发展;Perry和Chong的湍流边界层中A形涡结构的湍流机理;以及笔者提出的关于3维湍流场中涡结构的涡量脉动对流和扩散并存的一般机理。在一般机理基础上建立了判别流场的准则,列举了在固壁边界附近的猝发现象并展望它的未来应用。      

方孔障碍物对瓦斯火焰传播影响的实验与大涡模拟

为揭示置障管道内甲烷/空气预混火焰传播特性,运用高速摄影技术对甲烷/空气预混火焰的形状变化和火焰前锋的速度特性进行实验,并利用大涡模拟对管道内的流场结构进行数值分析。结果表明:置障管道内依次出现了球形火焰、指尖形火焰及“蘑菇”状火焰,且“蘑菇”状火焰出现之后,火焰开始反向传播;“蘑菇”状火焰是双涡旋结构与火焰前锋面相互作用的结果,而火焰的反向传播是由流场中出现逆流结构引起的;障碍物对火焰前锋有明显的加速作用;大涡模拟成功再现了实验中观察到的火焰形状、火焰前锋速度及流场结构,说明大涡模拟适用于置障管道内预混火焰传播特性的研究。     

熔喷双槽形喷嘴气体射流流场初探

在熔喷非织造布加工中,气体射流作为工作介质使聚合物熔体实现拉伸,气体射流流场的研究对熔喷气流拉抻数学模型研究非常重要。熔喷双槽形喷嘴形成的流场可以看作两股平面射流的合成。从单个点涡的性质出发,研究了涡偶的性质和涡偶代替射流的可行性。研究表明,在喷丝孔轴线附近,涡偶和射流的速度分布趋势相同,且有比较相近的速度分布,从而说明以涡偶代替射流是可行的。在此基础上,用两个涡偶分别代替两股射流,然后进行合成,推导出两股射流合成后速度分布的理论公式,该公式的计算结果与实验结果吻合较好。将该公式引入熔喷气流拉伸数学模型,预测出的纤维直径与采用经验公式时的预测结果几乎完全相同。结果表明,应用涡偶代替射流推导出的气流速度分布公式能够较好地描述熔喷双槽形喷嘴气体射流流场,可以用于完善熔喷气流拉伸数学模型。     

Forming and breaking the ceiling of inlet gas velocity regarding to separation efficiency of cyclone

The maximum-efficiency inlet velocity (MEIV) is a ceiling of inlet gas velocity that defines separation efficiency during cyclone design and operation. Experiment and computational fluid dynamics (CFD) simulation exhibited that an apex cone at the dust outlet can break the ceiling and improve the separation efficiency. The phenomenon is closely related to the effect of excessive high inlet gas velocity on the back-mixing escape of fine particles, which is the final result of back mixing, entrainment by the rapid upward airflow, and secondary separation of the inner vortex. In the center of the inner vortex, the airflow rotates slowly and moves rapidly upward. This elevator type of airflow delivers re-entrained particles to the vortex finder. A higher inlet gas velocity accelerates the elevator, causing more entrained particles to escape. This explains the decrease in efficiency at an excessively high inlet gas velocity. When an apex cone is installed at the dust outlet, the back-mixing is significantly weakened because the vortex core is bounded to the center of separator, while the transport effect of rapid upward airflow is weakened by the decrease in axial velocity in the center. Therefore, particle escape is weakened even at excessive high inlet gas velocities. Instead, the centrifugal effect is enhanced because of increased tangential velocity of the gas and particles. Consequently, the ceiling of inlet gas velocity is broken.     

气流特征对水平长管内石松子粉尘爆炸火焰结构的影响

为探索气流特征对水平长管内粉尘爆炸火焰结构的影响, 对采用加压送气传输方式形成的石松子粉尘云经静电引燃后其火焰在水平长管内的传播特性进行实验。利用热线风速仪测量不同气流条件下沿管径方向的速度分布和湍流强度分布, 采用高速摄像系统记录了火焰在水平管道内的传播过程。实验观察到, 即使管内石松子粉尘质量分数相同, 仍然会出现2种不同类型的火焰结构:一种类型火焰轮廓规则、清晰, 火焰中心为连续的黄色发光区并由红色边缘火焰包裹; 另一种类型火焰空间离散, 火焰发光区局部存在, 散乱地呈现不规则状态。详细分析不同气流条件对火焰结构的影响。     

Dynamics of interaction modes in excited annular jets

Evolution of coherent structures and their interaction dynamics are educed in the near field of an acoustically excited basic annular jet using conditional sampling technique based on a multiple triggering criterion to detect the two dominating modes of structure pattern. Acoustic excitation is applied with an aim to better organize the phase alignment of initial rolling and pairing process in the outer shear layer. Negligible modification of the time-averaged flow field results from the excitation. The educed coherent vorticities show that the two modes of evolution are due to the corresponding two modes of shedding pattern of the wake structures from the centerbody, namely the mode one wake and the mode zero wake. In both modes, the shear-layer mode jet vortex rings in the outer layer are perturbed by the shedding of wake structures in the inner region and interaction involving primary merging of three successive jet vortex rings or their partial circumferential sections is found. This results in the formation of wake-induced structures of the corresponding mode pattern, which possesses concentration of coherent vorticity and fluid circulation over a large spatial extent at 1 < x/D < 2. Secondary interactions, such as vortex tearing, are also observed.     

单窄条控制件对横向振荡柱体尾流 2P模式 旋涡脱落的改变

横向强迫振荡柱体尾流控制是柱体涡激振动控制的基础,在海洋、土木等工程中具有重要意义. 横向强迫振荡柱体尾流中存在一种锁频旋涡脱落模式,即在一个振荡周期内柱体上、下侧各脱落旋转方向相反的一对涡,称为2P模式. 本文将相对宽度b/D=0.32的窄条控制件置于横向强迫振荡柱体下游,对振幅比A/D=1.25, 无量纲振频f_e D/V_∞=0.22,雷诺数Re=1 200的2P模式旋涡脱落进行干扰,并通过改变控制件位置,研究旋涡的变化规律. 采用二维大涡模拟和实验验证方法进行研究,在控制件位置范围0.8≤X/D≤3.2, 0.4≤Y/D≤3.2内,得到了2P, 2S, P+S和另外6种新发现的旋涡脱落模式,并对各模式旋涡的形成过程作了详细描述. 在控制件位置平面上给出了各旋涡模式的存在区域,画出了旋涡脱落强度的等值线图,并发现在一个相当大的区域内,旋涡脱落强 度可减小一半以上,尾流变窄. 发现柱体大幅振荡引起的横向剪切流在旋涡生成中起关键作用. 探讨了控制件对横向剪切流的影响,分析了控制件在每种旋涡模式形成中的作用机制.      

水蚀性岩层中的渗流和无机污染物的迁移

介绍水蚀性岩层中的渗流及金属和无机污染物迁移问题．通过对含有污染物的某些蓄水系统中的物理和化学过程的分析得出一些结论，并对这些过程不仅作了详细的说明，而且采用恰当的数学和化学方程加以讨论．在水蚀性岩层中无机污染物的迁移用高渗透率多孔介质中流动的基本方程近似地描述，而对流、水动力学扩散、稀释等影响可作为物理过程来阐述．总的说来，控制裂隙岩体中地下水流动与污染物输运的物理和化学机理是建立水蚀性岩层中无机污染物输运近似方法的基础．     

Effect on flow field characteristics in methane–air non-premixed flame with steam addition

The present paper reports on an experimental study to determine the effect of humidity on the flow field and the flame stability limit in turbulent non-premixed flame, and examines the dynamical behavior of the unsteady aerodynamic flow structures observed on a bluff-body burner at both humid and non-humid air combustion states. Particle image velocimetry (PIV) is used to capture the instantaneous appearance of vortex structures and obtain the quantitative velocity field. Streamlines and velocity contours analysis are used to identify specific flame structures and reveal the effect of steam added on the vortex structure. The results show both central fuel penetration limit and partially quenching limit in the humid air case reduce. The decrease in the critical penetration limit is primarily attributed to a reduction in momentum of the humid air. The flamelet concepts are applied to discuss the partially quenching limit in the blue neck region. The analysis reveals that the large decrease in the partially quenching limit is due to the increase in chemical reaction time of the humid air combustion.     

Vortex dynamics and scalar transport in the wake of a bluff body driven through a steady recirculating flow

The air ventilation system in wide-body aircraft cabins provides passengers with a healthy breathing environment. In recent years, the increase in global air traffic has amplified contamination risks by airborne flu-like diseases and terrorist threats involving the onboard release of noxious materials. In particular, passengers moving through a ventilated cabin may transport infectious pathogens in their wake. This paper presents an experimental investigation of the wake produced by a bluff body driven through a steady recirculating flow. Data were obtained in a water facility using particle image velocimetry and planar laser induced fluorescence. Ventilation attenuated the downward convection of counter-rotating vortices produced near the free-end corners of the body and decoupled the downwash mechanism from forward entrainment, creating stagnant contaminant regions.     

Effects of supply air temperature and inlet location on particle dispersion in displacement ventilation rooms

The effects of supply temperature and vertical location of inlet air on particle dispersion in a displacement ventilated (DV) room were numerically modeled with validation by experimental data from the literature. The results indicate that the temperature and vertical location of inlet supply air did not greatly affect the air distribution in the upper parts of a DV room, but could significantly influence the airflow pattern in the lower parts of the room, thus affecting the indoor air quality with contaminant sources located at the lower level, such as particles from working activities in an office. The numerical results also show that the inlet location would slightly influence the relative ventilation efficiency for the same air supply volume, but particle concentration in the breathing zone would be slightly lower with a low horizontal wall slot than a rectangular diffuser. Comparison of the results for two different supply temperatures in a DV room shows that, although lower supply temperature means less incoming air volume, since the indoor flow is mainly driven by buoyancy, lower supply temperature air could more efficiently remove passive sources (such as particles released from work activities in an office). However, in the breathing zone it gives higher concentration as compared to higher supply air temperature. To obtain good indoor air quality, low supply air temperature should be avoided because concentration in the breathing zone has a stronger and more direct impact on human health.