湍流的确定性与随机性

本文讨论和证实了近代被人称作湍流流动“相干结构”确定性方面的积极兴趣。可以证明,通过实验研究已经得列了一些重要的新的结果,对流动的随机特征提出了新的见解并为进一步的实验和理论探索提出了新的方向。     

热射流拟序结构中混沌现象的实验研究

就开放流体系统中的热射流拟序结构的混沌现象进行了实验研究．发现流场在绝对不稳定情况（S＜0.72）下,环涡模式控制了整个流场．此时相空间中对应的动力系统发生倍周期和Hopf分岔,说明动力系统可通过Feigenbaum和RTN途径进入混沌．相关维、相关熵和Lyapunov指数的计算表明：在一定Re数下,动力系统的时间渐近行为已呈混沌态,表现为奇异吸引子,相关维数D2约为3．80．     

实验研究具有周向抽吸轴对称射流的拟序结构

基于实验研究具有周向抽吸轴对称射流拟序结构的动力学行为,定义了临界出口主速度以及超临界工况（低速工况）和亚临界工况。提出了超临界工况下,拟序结构的空间演化特征。基于功率谱确定了超、亚临界工况流动系统发生自激励振荡的速度比范围。     

亚音速湍流再附着研究述评

引言在大量的实际工程构件中,包括扩散器、有分离气流区的机翼、建筑物和燃烧室湍流,剪切层的再附着是一个重要的过程。为能预测这些复杂的流动,需要研究再附着剪切层的特性。目前对剪切层再附着过程的了解很少,还无法预测大范围变动参数时的简单的再附着流动,甚至还没有列出影响再附着的完整的参数表。在二维流动中,后向台阶是最简单的再附着流动。分离线是直线,固定在台阶边缘,只     

以二羧酸二苯甲醚和吡啶基三唑为配体构筑的钴(Ⅱ)配合物的合成、结构、热稳定性及DFT计算

基于V型配体4,4’-二羧酸二苯甲醚(H₂oba)和刚性配体3-(3吡啶基)-5-(4’吡啶基)-1-H-1,2,4三唑(3,4’-Hbpt),在水热条件下与醋酸钴制备了一种新的配位聚合物[Co(oba)(3,4’-Hbpt)]·H₂O,并对其进行X-射线单晶衍射、热重分析、元素分析和红外光谱表征。配合物为单斜晶系,P2₁/c空间群,完全脱质子的oba^2-配体的2个羧基连接Co(Ⅱ)离子形成八元环,3,4’-Hbpt配体和H₂oba桥连2个Co(Ⅱ)形成二十五元环。相邻的八元环和二十五元环进一步通过oba^2-作支柱连接,形成了二维的层-孔结构。采用密度泛函理论(DFT)方法,在B₃LYP/6-31*G(d)和6-31**G(d,p)水平上对配体H₂oba结构进行优化计算,探讨了其稳定性,前线轨道以及最优构型,计算结果与化合物1中H₂oba的构象一致。     

流体中的湍流

运动的流体,无论是气体还是液体,在人类的许多事务中,如在气动装置和船舶的性能方面;在通过管线从阿拉斯加北坡流来的石油里;在我们的空气和河流的污染方面;在我们的活动范围受到限制以及有时因大气和海洋的难以预测的变化给我们的生活带来威胁方面;甚至在漂移着的大陆当它们刺激并激发起圣·海伦山的喷发中,都扮演着一个极为重要的角      

Coherent structures in countercurrent axisymmetric shear flows

The dynamical behaviors of coherent structures in countercurrent axisymmetric shear flows are experimentally studied.The forward velocity U1 and the velocity ratio R=(U1-U2)/(U1+U2),where U2 denotes the suction velocity,are consldered as the control parameters.Two kinds of vortex structures,i.e.,axisymmetric and helical structures,were discovered with respect to different reginmes in the R versus U1 diagram .In the case of U1 rangjing from 3 to 20m/s and R from 1 to 3,the axisymmetric structures plan an important role.Based on the dynamical behaviors of axisymmetric structures,a critical forward velocity U1cr=6.8m/s was defined,subsequently,the subcritical velocity regime:U1>U1cr and the supercritical velocity regime:U1<U1er,In the subcritical velocity regine,the flow system contains shear layer self-excited oscillations in a certain range of the velocity ratio with respect to any forward velocity.In the supercritical velocity regime,the effect of the velocity ratio could be explained by the relative movement and the spatial evolution of the axisymmetric structure undergoes the following stages:(1) Kelvin-Helmholtz instability leading to vortex rolling up,(2) first time vortex agglomeration.(3) jet colunn self-excited oscillation,(4) shear layer self-excited oscillation,(5)“ordered tearing“,(6) turbulence in the case of U1<4m/s (the “ordered tearing“ does not exist when U1>4m/s),correspondingly,the spatial evolution of the temporal asymptotic behavior of a dynamical system can be described as follows:(1) Hopt bifurcation,(5) chaos(“weak turbulence“)in the case of U1<4m/s(superharmonic bifurcation does not exist when U1>4m/s).The proposed new terms,superharmonic and reversed superbarmonic bifurcations,are characterized of the frequency doubling rather than the period doubling.A kind of unfamiliar vortices referred to as the helical structure was discovered experimentally when the forward velocity around 2m/s and the velocity range from 1.1 to 2.3,There are two base frequencies contained in the flow system and they could coexist as indicated by the Wigner-Ville-Distribution and the temporal asymptotic behavior of the dynamical system corresponding to the helical vortex could be described as 2-torus as indicted by the 3D reconstructed phase trajectory and correlation dimension.The scenario of the spatial evolution of helical structures could be described as follows:the jet column is separated into two parts at a certain spatial location and they entangle each other to form the helical vortex until the occurrence of those separated jet columns to reconnect further downstream with the result that the flow system evolves into turbulence in a catastrophic form.Correspondingly,the dynamical system evolves directly into 2-tiorus through the supercritical Hopf bifurcation followed by a transition from a quasi-periodic attractor to a strange attractor.In the case of U1=2m/s,the parametric evolution of the temporal asymptotic behavior of the dynamical system as the velocity ratio increases from 1 to 3 could be described as follows:(1)2-torus(Hopf bifurcation),(2) limit cycle(reversed Hopf bifurcation),(3) strange attractor (subbarmonic bifurcation).     

以二羧酸二苯甲醚和吡啶基三唑为配体构筑的钴(Ⅱ)配合物的合成、结构、热稳定性及DFT计算(英文)

基于V型配体4,4′-二羧酸二苯甲醚(H2oba)和刚性配体3-(3吡啶基)-5-(4′吡啶基)-1-H-1,2,4三唑(3,4′-Hbpt),在水热条件下与醋酸钴制备了一种新的配位聚合物[Co(oba)(3,4′-Hbpt)]·H2O,并对其进行X-射线单晶衍射、热重分析、元素分析和红外光谱表征。配合物为单斜晶系,P21/c空间群,完全脱质子的oba2-配体的2个羧基连接Co髤离子形成八元环,3,4′-Hbpt配体和H2oba桥连2个Co髤形成二十五元环。相邻的八元环和二十五元环进一步通过oba2-作支柱连接,形成了二维的层-孔结构。采用密度泛函理论(DFT)方法,在B3LYP/6-31*G(d)和6-31**G(d,p)水平上对配体H2oba结构进行优化计算,探讨了其稳定性,前线轨道以及最优构型,计算结果与化合物1中H2oba的构象一致。