向心透平级叶轮内三维复杂流动的数值研究

对向心透平叶轮内部复杂流动在级环境下进行了全三维黏性数值模拟,结合拓扑学原理分析了设计工况和非设计工况下其内流动分离及各种涡系发展的演变过程,初步建立了向心透平叶轮内的旋涡模型,阐述了流动损失的形成机理。研究表明:向心透平叶轮内部涡系与轴流式透平存在较大差别,且流动分离及涡系主要集中在吸力面侧;设计工况下向心透平叶轮内的主要旋涡包括马蹄涡、通道涡及泄漏涡,其主要表现为通道涡与泄漏涡相互影响和掺混,是主要损失的形成原因;非设计工况下,主流在叶轮叶片前缘处发生大范围的分离及回流,造成了较大的能量损失,但二次流损失所占比例较小。     

分子链长对烷烃硫醇分子电输运性质的影响

在杂化密度泛函理论的基础上,利用弹性散射格林函数方法研究了烷烃硫醇系列分子的电输运性质,并同实验结果进行了比较。研究结果表明,在低的外加偏压下,烷烃硫醇分子电流值随着分子链长度的增加而指数减小,其衰减常数约为1.41/CH2,且衰减常数基本上与外加偏压值的大小无关。分子末端原子与探针的距离具有较大地自由度,不同的接触距离导致了分子的电流值有较大地差别。     

Hydration effect on the electronic transport properties of oligomeric phenylene ethynylene molecular junctions

A first-principles computational method based on the hybrid density functional theory is developed to simulate the electronic transport properties of oligomeric phenylene ethynylene molecular junctions with H₂O molecules accumulated in the vicinity as recently reported by Na {\it et al.} [\wx{Nanotechnology}{18} 424001 (2007)]. The numerical results show that the hydrogen bonds between the oxygen atoms of the oligomeric phenylene ethynylene molecule and H₂O molecules result in the localisation of the molecular orbitals and lead to the lower transition peaks. The H₂O molecular chains accumulated in the vicinity of the molecular junction can not only change the electronic structure of the molecular junctions, but also open additional electronic transport pathways. The obvious influence of H₂O molecules on the electronic structure of the molecular junction and its electronic transport properties is thus demonstrated.