Large eddy simulation of turbulent statistical and transport properties in stably stratified flows

Three dimensional large eddy simulation （LES） is performed in the investigation of stably stratified turbulence with a sharp thermal interface. Main results are focused on the turbulent characteristic scale, statistical properties, transport properties, and temporal and spatial evolution of the scalar field. Results show that the buoyancy scale increases first, and then goes to a certain constant value. The stronger the mean shear, the larger the buoyancy scale. The overturning scale increases with the flow, and the mean shear improves the overturning scale. The flatness factor of temperature departs from the Gaussian distribution in a fairly large region, and its statistical properties are clearly different from those of the velocity fluctuations in strong stratified cases. Turbulent mixing starts from small scale motions, and then extends to large scale motions.     

在β-环糊精存在下2-(5-溴-2-吡啶偶氮)-5-二乙氨基酚与钴显色反应的研究及应用

本文研究了β-环糊精(β-CD)对Co(Ⅱ)与5-Br-PADAP显色反应的增溶、增敏、增稳作用,实验表明1%β-CD的用量为3.0—7.0ml,适宜酸度范围为pH5.0—7.8,最大吸收波长为585nm,配合物组成为CO(Ⅱ):5-Br-PADAP=1:2,表现摩尔吸光系数8.84×10~4L·mol~(-1)·cm~(-1),Co(Ⅱ)含量0—15μq/25ml范围内符合比尔定律.采用EGTA-NH_4F-焦磷酸钠联合掩蔽剂可消除Fe~(3+)、Cu~(2+)、Al~(3+)、Zn~(2+)、Mn~(2+)、Cd~(2+)、Hg~(2+)等离子的干扰,该方法操作简便、快速、稳定,并用此法直接测定人发样品中微量钴,获得了满意的结果.     

Coherent structures over riblets in turbulent boundary layer studied by combining time-resolved particle image velocimetry(TRPIV),proper orthogonal decomposition(POD),and finite-time Lyapunov exponent(FTLE)

Time-resolved particle image velocimetry(TRPIV) experiments are performed to investigate the coherent structure's performance of riblets in a turbulent boundary layer(TBL) at a friction Reynolds number of 185. To visualize the energetic large-scale coherent structures(CSs) over a smooth surface and riblets, the proper orthogonal decomposition(POD) and finite-time Lyapunov exponent(FTLE) are used to identify the CSs in the TBL. Spatial-temporal correlation is implemented to obtain the characters and transport properties of typical CSs in the FTLE fields. The results demonstrate that the generic flow structures, such as hairpin-like vortices, are also observed in the boundary layer flow over the riblets, consistent with its smooth counterpart. Low-order POD modes are more sensitive to the riblets in comparison with the high-order ones,and the wall-normal movement of the most energy-containing structures are suppressed over riblets. The spatial correlation analysis of the FTLE fields indicates that the evolution process of the hairpin vortex over riblets are inhibited. An apparent decrease of the convection velocity over riblets is noted, which is believed to reduce the ejection/sweep motions associated with high shear stress from the viscous sublayer. These reductions exhibit inhibition of momentum transfer among the structures near the wall in the TBL flows.     

Hilbert-Huang变换方法在Duffing方程和圆柱尾迹流分析中的应用

本文采用N．E Huang最近提出的Hilbert-Huang变换方法分析了使用三阶Runge-Kutta方法数值求解的Duffing方程的性质和圆柱绕流尾流特性,分解得到了有限阶经验模态（Empirical Modes）,给出了相应的Hilbert谱。结果表明,Hilbert-Huang变换得到的主要含能模态物理意义清晰,相应的瞬时频率存在着明显的波内频率调制,很好地刻画了信号的时空局部特性。     

稳定分层流动中湍流统计特性和输运特性的数值研究

采用大涡模拟方法研究了上下两层温度不同的稳定分层湍流,主要对其中的湍流尺度特性、统计特性和湍流输运特性,以及标量场的时空演化进行了分析研究.研究结果表明:浮力尺度沿流动方向先增加然后趋于某个稳定值,剪切越强,浮力尺度越大;翻转尺度沿流向也是逐渐增大,剪切越强,翻转尺度越大;统计特性的分析发现,在较大的区域内温度脉动的平坦因子都偏离Gauss分布,强分层条件下温度脉动的统计特性与速度脉动的统计特性有较明显差别;湍流混合的过程开始于小尺度运动,最后扩展到大尺度运动.     

在β环糊精存在下2-(5-溴-2-毗咤偶氮)-5一二乙氨基酚与钻显色反应的研究及应用

本文研究了介环糊精(刀-CD)对Co( I)与5一Br-PADAP显色反应的增溶、增敏、增稳作用,实验表明1 } }-CD的用量为3 , 0-7. 0m1,适宜酸度范围为pH5.0-7.8 ,最大吸收波长为585nm,配合物组成为Co( I ):5-Br-PADAP=1:2,表现摩尔吸光系数8.84x10'L"mol-1"cm-1, Co( I)含量。-15}aq/25m1范围内符合比尔定律.采用EGTA一NH, F-焦磷酸钠联合掩蔽剂可消除Fe’十、Cu二十、A1,十、Zn'“、Mn二十、Cd习十、Hg'+等离子的干扰,该方法操作简便、快速、稳定,并用此法直接测定人发样品中微量钻,获得了满意的结果