期刊文献+
共找到7篇文章
< 1 >
每页显示 20 50 100
不稳定分层大气边界层中沙尘暴的无黏模型研究
1
作者 谢晨月 熊向明 +1 位作者 陶建军 刘炽杭 《气体物理》 2023年第4期63-72,共10页
实验观测表明,沙尘暴发生之前的大气边界层常常是不稳定分层的。沙尘暴可被视为处于超高Reynolds数的颗粒两相湍流异重流。为了研究异重流坍塌阶段的主控机制,建立了一个无黏模型,发现在重流体或环境流体或两者均存在不稳定密度分层时,... 实验观测表明,沙尘暴发生之前的大气边界层常常是不稳定分层的。沙尘暴可被视为处于超高Reynolds数的颗粒两相湍流异重流。为了研究异重流坍塌阶段的主控机制,建立了一个无黏模型,发现在重流体或环境流体或两者均存在不稳定密度分层时,表征异重流头部速度的Froude数都会变小。对不同的开闸高度和不稳定分层情况的开闸式异重流进行了数值模拟。尽管在密度界面存在混合,但是模拟所得的头部速度与高度关系同无黏模型的预测相符。另外,野外观测到的沙尘暴头部速度增量同该模型的预测基本一致,显示在该类高Reynolds数湍流中无黏机制的贡献不容忽视。 展开更多
关键词 异重流 无黏模型 不稳定分层 沙尘暴 头部速度 Froude数
下载PDF
不稳定分层海洋湍流对厄米-高斯光通信系统的影响 被引量:1
2
作者 丁桂璇 杜星 +3 位作者 杜浩 王生 敖磊 李崔春 《光学学报》 EI CAS CSCD 北大核心 2024年第6期105-112,共8页
推导了不稳定分层海洋湍流下厄米-高斯光束闪烁指数的理论公式,以及考虑海洋湍流和瞄准误差综合影响下UWOC系统信道系数的概率分布函数,进一步推导了系统主要性能参数即误码率、信道容量和中断概率的理论计算公式,并采用高斯-厄米正交... 推导了不稳定分层海洋湍流下厄米-高斯光束闪烁指数的理论公式,以及考虑海洋湍流和瞄准误差综合影响下UWOC系统信道系数的概率分布函数,进一步推导了系统主要性能参数即误码率、信道容量和中断概率的理论计算公式,并采用高斯-厄米正交积分近似方法求得3个性能参数的闭合表达式,仿真分析了不稳定分层和稳定分层湍流情况下,光束模数、传输距离、海洋湍流参数和瞄准误差对系统的平均误码率、平均信道容量和中断概率的影响。结果表明:相比于稳定分层,不稳定分层的系统计算误差更小;当盐度波动占主导时,系统性能更好;随着均方温度耗散率增大、湍流动能耗散率减小、瞄准误差增大,系统信道容量减小,中断概率增大。本研究结果可为厄米-高斯光在水下光通信领域的应用提供参考。 展开更多
关键词 海洋光学 厄米-高斯光束 不稳定分层 海洋湍流 水下光通信
原文传递
气辅共挤成型分层界面不稳定的数值模拟研究 被引量:3
3
作者 蔡奎 周国发 +1 位作者 钟序光 胡晨章 《塑性工程学报》 EI CAS CSCD 北大核心 2006年第2期97-102,共6页
提出了全新的气辅共挤成型工艺,基于气辅共挤成型特点建立了理论模型,通过数值模拟系统研究了聚合物流变性能和工艺参数对气辅共挤成型分层界面不稳定的影响规律,并揭示了其影响机理。研究结果表明,随着高粘层熔体与低粘层熔体粘度比的... 提出了全新的气辅共挤成型工艺,基于气辅共挤成型特点建立了理论模型,通过数值模拟系统研究了聚合物流变性能和工艺参数对气辅共挤成型分层界面不稳定的影响规律,并揭示了其影响机理。研究结果表明,随着高粘层熔体与低粘层熔体粘度比的增大,或温度比和速度比的减小,熔体分层界面不稳定性均会加剧,气辅共挤成型粘度比与传统共挤成型相比,其可调范围也更宽。 展开更多
关键词 气辅共挤成型 传统共挤成型 数值模拟 分层界面不稳定
下载PDF
PTX-3水平与不稳定心绞痛(UAP)危险分层的关系 被引量:1
4
作者 秦海斌 刘启明 +1 位作者 印茂峰 张利 《继续医学教育》 2010年第3期79-81,共3页
目的:对不同危险分层的不稳定心绞痛(UAP)患者进行长正五聚蛋白3(pentraxin-3,PTX-3)检测,探讨PTX-3在UAP危险分层中的价值。方法:采集并分析2008年8月~2009年12月在中南大学湘雅二医院住院的109位UAP患者,分为3组,低危患者27例,中危患... 目的:对不同危险分层的不稳定心绞痛(UAP)患者进行长正五聚蛋白3(pentraxin-3,PTX-3)检测,探讨PTX-3在UAP危险分层中的价值。方法:采集并分析2008年8月~2009年12月在中南大学湘雅二医院住院的109位UAP患者,分为3组,低危患者27例,中危患者42例,高危患者40例,测定血清PTX-3浓度,并进行统计分析,P<0.05为有统计学意义。结果:本研究通过对危险分层不同的UAP三组患者进行PTX-3检测,发现随着UAP患者临床危险分层的增加,PTX-3也随之升高,有统计学意义(P<0.05),且组间进行比较也有统计学意义(P<0.05)。结论:PTX-3的增高与UAP危险分层显著相关。 展开更多
关键词 长正五聚蛋白3 PTX-3 不稳定心绞痛危险分层
下载PDF
Emission Characteristics of Volatile Organic Compounds from Automobile Coating Industry in Chongqing City
5
作者 Zhou Zhi'en Fang Weikai +2 位作者 Luo Qian Wang Xiaochen Wu Liping 《Journal of Environmental Science and Engineering(B)》 2017年第11期543-552,共10页
To fully analyze emission characteristics of VOCs (Volatile Organic Compounds) from automobile coating industry in Chongqing city, related enterprises in the city were investigated in detail. The results show that t... To fully analyze emission characteristics of VOCs (Volatile Organic Compounds) from automobile coating industry in Chongqing city, related enterprises in the city were investigated in detail. The results show that the emission of VOCs from the automobile industry in Chongqing city was approximately 20,000 t in 2012, and the contribution rate of automobile coating was 83%. Most VOCs discharged from automobile coating industry were mainly from the use of coatings, diluents, curing agents and other materials containing VOCs. During the process of automobile coating, VOCs were mainly produced during the processes of spraying and drying. Besides, VOCs are partly produced during the processes of mixing paint, gluing, waxing and repairing. The major ingredients of VOCs discharged during the process of automobile coating were methylbenzene, dimethylbenzene, trimethylbenzene, cumene, ethyl acetate, butyl alcohol, n-butyl alcohol, isobutyl alcohol, formaldehyde, butanone, acetone, cyclohexanone and methyl ethyl ketone. Besides, the ingredients of naphtha and aromatic hydrocarbon in VOCs need to be determined. The maximum OFP (Ozone Formation Potential) of the above pollutants by the typical enterprises was 900-1,300 mg/m^3. The production of SOA (Secondary Organic Aerosol) was 3,636-11,073 t/a, which didn’t include the contribution of aldehydes, ketones, ethers and esters to SOA. This research could provide scientific reference for the establishment of emission standard, control technology and management methods of VOCs from automobile coating industry that accord with economic and social development in Chongqing city. 展开更多
关键词 Automobile coating VOCs environmental impact OZONE SOA.
下载PDF
Experimental Investigation of Flow Instabilities in a Laminar Separation Bubble 被引量:4
6
作者 Simoni D. Ubaldi M. Zunino P. 《Journal of Thermal Science》 SCIE EI CAS CSCD 2014年第3期203-214,共12页
The present paper reports the results of a detailed experimental study aimed at investigating the dynamics of a laminar separation bubble, from the origin of separation up to the breakdown to turbulence of the large s... The present paper reports the results of a detailed experimental study aimed at investigating the dynamics of a laminar separation bubble, from the origin of separation up to the breakdown to turbulence of the large scale co- herent structures generated as a consequence of the Kelvin-Helmholtz instability process. Measurements have been performed along a fiat plate installed within a double contoured test section, designed to produce an adverse pressure gradient typical of Ultra-High-Lift turbine blade profiles, which induces the formation of a laminar separation bubble at low Reynolds number condition. Measurements have been carried out by means of comple- mentary techniques: hot-wire (HW) anemometry, Laser Doppler Velocirnetry (LDV) and Particle Image Veloci- metry (PIV). The high accuracy 2-dimensional LDV results allow investigating reverse flow magnitude and both Reynolds normal and shear stress distributions along the separated flow region, while the high frequency response of the HW anemometer allows analyzing the amplification process of flow oscillations induced by instability mechanisms. PIV results complement the flow field analysis providing information on the generation and evolu- tion of the large scale coherent structures shed as a consequence of the separated shear layer roll-up, through in- stantaneous velocity vector maps. The simultaneous analysis of the data obtained by means of the different meas- uring techniques allows an in depth view of the instability mechanisms involved in the transition/reattachrnent processes of the separated shear layer. 展开更多
关键词 Ultra-High-Lift turbine profiles separated flow transition mode STREAKS Kelvin-Helmholtz instabil- ity linear stability theory
原文传递
Unsteady Inflow Effects on the Wake Shed from a High-Lift LPT Blade Subjected to Boundary Layer Laminar Separation 被引量:1
7
作者 Francesca Satta Marina Ubaldi Pietro Zunino 《Journal of Thermal Science》 SCIE EI CAS CSCD 2012年第2期97-108,共12页
An experimental investigation on the near and far wake of a cascade of high-lift low-pressure turbine blades subjected to boundary layer separation over the suction side surface has been carried out, under steady and ... An experimental investigation on the near and far wake of a cascade of high-lift low-pressure turbine blades subjected to boundary layer separation over the suction side surface has been carried out, under steady and unsteady inflows. Two Reynolds number conditions, representative of take-off/landing and cruise operating conditions of the real engine, have been tested. The effect of upstream wake-boundary layer interaction on the wake shed from the profile has been investigated in a three-blade large-scale linear turbine cascade. The comparison between the wakes shed under steady and unsteady inflows has been performed through the analysis of mean velocity and Reynolds stress components measured at midspan of the central blade by means of a two-component crossed miniature hot-wire probe. The wake development has been analyzed in the region between 2% and 100% of the blade chord from the central blade trailing edge, aligned with the blade exit direction. Wake integral parameters, half-width and maximum velocity defects have been evaluated from the mean velocity distributions to quantify the modifications induced on the vane wake by the upstream wake. Moreover the thicknesses of the two wake shear layers have been considered separately in order to identify the effects of Reynolds number and incoming flow on the wake shape. The self-preserving state of the wake has been looked at, taking into account the different thicknesses of the two shear layers. The evaluation of the power density spectra of the velocity fluctuations allowed the study of the wake unsteady behavior, and the detection of the effects induced by the different operating conditions on the trailing edge vortex shedding. 展开更多
关键词 Wake-wake unsteady interaction high-lift blade profiles low-pressure turbine blade wake.
原文传递
上一页 1 下一页 到第
使用帮助 返回顶部