The computational fluid dynamics （CFD） method is used to numerically simulate a propeller wake flow field in open water. A sub-domain hybrid mesh method was adopted in this paper. The computation domain was separate...The computational fluid dynamics （CFD） method is used to numerically simulate a propeller wake flow field in open water. A sub-domain hybrid mesh method was adopted in this paper. The computation domain was separated into two sub-domains, in which tetrahedral elements were used in the inner domain to match the complicated geometry of the propeller, while hexahedral elements were used in the outer domain. The mesh was locally refined on the propeller surface and near the wake flow field, and a size function was used to control the growth rate of the grid. Sections at different axial location were used to study the spatial evolution of the propeller wake in the region ranging from the disc to one propeller diameter （D） downstream. The numerical results show that the axial velocity fluctuates along the wake flow; radial velocity, which is closely related to vortices, attenuates strongly. The trailing vortices interact with the tip vortex at the blades＇ trailing edge and then separate. The strength of the vortex shrinks rapidly, and the radius decreases 20% at one diameter downstream.展开更多
The density, viscosity and conductivity of ionic liquids （ILs）, 1-octyl-3-methylimidazolium tetrafluoroborate （[omim][BF4]）, 1-octyl-3-methylimidazolium chloride （[omim][C1]）, 1-hexyl-3-methylimidazolium tetrafl...The density, viscosity and conductivity of ionic liquids （ILs）, 1-octyl-3-methylimidazolium tetrafluoroborate （[omim][BF4]）, 1-octyl-3-methylimidazolium chloride （[omim][C1]）, 1-hexyl-3-methylimidazolium tetrafluoroborate （[hmim] BF4]）, 1-hexyl- 3-methylimidazolium chloride （[hmim][C1]）, 1-hexyl-3-methylimidazolium hexafluorophosphate （[hmim][PF6]）, and the [omim][BF4] ＋ [omim][Cl], [hmim][BF4] ＋ [hmim][C1], and [hmim][PF6] ＋ [hmim][C1] binary mixtures were studied at dif- ferent temperatures. It was demonstrated that the densities of both the neat ILs and their mixtures varied linearly with temper- ature. The density sensitivity of a binary mixture is between those of the two components. The excess molar volumes （l/e） of [hmim][BF4] ＋ [hmim][C1] and [hmim][PF6] ＋ [hmim][C1] mixtures are positive in the whole composition range. For [omim][BF4] ＋ [omim][C1], the VE is also positive in the [omirn][C1]-rich region, but is negative in the [omim][BF4]-rich re- gion. The viscosity or conductivity of a mixture is in the intermediate of those of the two neat ILs. For all the neat ILs and the binary mixtures studied, the order of conductivity is opposite to that of the viscosity. The Vogel-Tammann-Fulcher （VTF） equations can be used to fit the viscosity and conductivity of all the neat ILs and the binary mixtures. The neat ILs and their mixtures obey the Fractional Walden Rule very well, and the values of the Walden slopes are all smaller than unit, indicating obvious ion associations in the neat ILs and the binary mixtures.展开更多
基金Supported by Fundamental Research Funds for the Central Universities(Grant No.HEUCFT1001)Ph.D Programs Foundation of Ministry of Education of China(Grant No.10702016)
文摘The computational fluid dynamics （CFD） method is used to numerically simulate a propeller wake flow field in open water. A sub-domain hybrid mesh method was adopted in this paper. The computation domain was separated into two sub-domains, in which tetrahedral elements were used in the inner domain to match the complicated geometry of the propeller, while hexahedral elements were used in the outer domain. The mesh was locally refined on the propeller surface and near the wake flow field, and a size function was used to control the growth rate of the grid. Sections at different axial location were used to study the spatial evolution of the propeller wake in the region ranging from the disc to one propeller diameter （D） downstream. The numerical results show that the axial velocity fluctuates along the wake flow; radial velocity, which is closely related to vortices, attenuates strongly. The trailing vortices interact with the tip vortex at the blades＇ trailing edge and then separate. The strength of the vortex shrinks rapidly, and the radius decreases 20% at one diameter downstream.
基金supported by the National Natural Science Foundation of China (21133009, 21073207, 20903109)
文摘The density, viscosity and conductivity of ionic liquids （ILs）, 1-octyl-3-methylimidazolium tetrafluoroborate （[omim][BF4]）, 1-octyl-3-methylimidazolium chloride （[omim][C1]）, 1-hexyl-3-methylimidazolium tetrafluoroborate （[hmim] BF4]）, 1-hexyl- 3-methylimidazolium chloride （[hmim][C1]）, 1-hexyl-3-methylimidazolium hexafluorophosphate （[hmim][PF6]）, and the [omim][BF4] ＋ [omim][Cl], [hmim][BF4] ＋ [hmim][C1], and [hmim][PF6] ＋ [hmim][C1] binary mixtures were studied at dif- ferent temperatures. It was demonstrated that the densities of both the neat ILs and their mixtures varied linearly with temper- ature. The density sensitivity of a binary mixture is between those of the two components. The excess molar volumes （l/e） of [hmim][BF4] ＋ [hmim][C1] and [hmim][PF6] ＋ [hmim][C1] mixtures are positive in the whole composition range. For [omim][BF4] ＋ [omim][C1], the VE is also positive in the [omirn][C1]-rich region, but is negative in the [omim][BF4]-rich re- gion. The viscosity or conductivity of a mixture is in the intermediate of those of the two neat ILs. For all the neat ILs and the binary mixtures studied, the order of conductivity is opposite to that of the viscosity. The Vogel-Tammann-Fulcher （VTF） equations can be used to fit the viscosity and conductivity of all the neat ILs and the binary mixtures. The neat ILs and their mixtures obey the Fractional Walden Rule very well, and the values of the Walden slopes are all smaller than unit, indicating obvious ion associations in the neat ILs and the binary mixtures.
