Stavros Kassinos

Molecular Simulation of Water in Carbon Nanotubes

7.1. Water Structure in Carbon Nanotubes 5020 7.2. Radial, Axial, and Total Water Density 5023 7.3. Hydrogen Bonds 5024 7.4. Filling Carbon Nanotubes with Water 5025 7.5. Dipole Moment 5026 7.6. Proton Transport in Water 5027 7.7. Transport Properties 5027 8. Driven Flow 5029 9. Charged Carbon Nanotubes 5029 10. Polarizable Carbon Nanotubes 5030 11. Selective Partitioning 5030 12. Functionalized Carbon Nanotubes 5031 13. Conclusions 5031 14. Acknowledgments 5031 15. References 5031

One-point turbulence structure tensors

The dynamics of the evolution of turbulence statistics depend on the structure of the turbulence. For example, wavenumber anisotropy in homogeneous turbulence is known to affect both the interaction between large and small scales (Kida & Hunt 1989), and the non-local effects of the pressure–strain-rate correlation in the one-point Reynolds stress equations (Reynolds 1989; Cambon et al . 1992). Good quantitative measures of turbulence structure are easy to construct using two-point or spectral data, but one-point measures are needed for the Reynolds-averaged modelling of engineering flows. Here we introduce a systematic framework for exploring the role of turbulence structure in the evolution of one-point turbulence statistics. Five one-point statistical measures of the energy-containing turbulence structure are introduced and used with direct numerical simulations to analyse the role of turbulence structure in several cases of homogeneous and inhomogeneous turbulence undergoing diverse modes of mean deformation. The one-point structure tensors are found to be useful descriptors of turbulence structure, and lead to a deeper understanding of some rather surprising observations from DNS and experiments.

Thermal Conduction in Magnetized Turbulent Gas

Using numerical methods, we systematically study in the framework of ideal MHD the effect of magnetic fields on heat transfer within a turbulent gas. We measure the rates of passive scalar diffusion within magnetized fluids and make the comparisons (1) between MHD and hydrodynamic simulations, (2) between different MHD runs with different values of the external magnetic field (up to the energy equipartition value), and (3) between thermal conductivities parallel and perpendicular to the magnetic field. We do not find apparent suppression of diffusion rates by the presence of magnetic fields, which implies that magnetic fields do not suppress heat diffusion by turbulent motions.

One-point modelling of rapidly deformed homogeneous turbulence

One-point turbulence models are important tools for engineering analysis. A good model should have a viscoelastic character, predicting turbulent stresses proportional to the mean strain rate for slow deformations and stresses determined by the amount of strain for rapid distortions. Our goal is to build a one-point turbulence model with this character, and this requires a one-point model for rapid distortions. Here it is shown that the turbulent stresses introduced by Osborne Reynolds do not, by themselves, provide an adequate tensorial base for one-point modelling of rapidly distorted turbulence because they do not carry critical information about the turbulence structure. The deficiency is shown to be most pronounced in flows subjected to strong mean rotation. Additional one-point tensors that do carry the missing information are introduced, and the complexities of a model that would have an adequate tensorial base are assessed. A new type of one-point structure-based turbulence model that overcomes the basic deficiency of Reynolds-stress transport models, but without the excessive complexity of multiple tensor variables, is then described. The ideas behind the rapid distortion version of this new model are presented, along with results for some special cases.

Magnetohydrodynamic turbulence at moderate magnetic Reynolds number

We consider the case of homogeneous turbulence in a conducting fluid that is exposed to a uniform external magnetic field at low to moderate magnetic Reynolds numbers (by moderate we mean here values as high as 20). When the magnetic Reynolds number is vanishingly small (

Three dimensional flow around a circular cylinder confined in a plane channel

R_m \ll 1

Self-diffusivity, hydrogen bonding and density of different water models in carbon nanotubes

), it is customary to simplify the governing magnetohydrodynamic (MHD) equations using what is known as the quasi-static (QS) approximation. As the magnetic Reynolds number is increased, a progressive transition between the physics described by the QS approximation and the MHD equations occurs. We show here that this intermediate regime can be described by another approximation which we call the quasi-linear (QL) approximation. For the numerical simulations performed, the predictions of the QL approximation are in good agreement with those of MHD for magnetic Reynolds number up to

The transport of a passive scalar in magnetohydrodynamic turbulence subjected to mean shear and frame rotation

R_m \sim 20

Structure-based turbulence modeling for wall-bounded flows

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Large-eddy simulations of the turbulent Hartmann flow close to the transitional regime

This paper presents two- and three-dimensional direct numerical simulations of the flow around a circular cylinder placed symmetrically in a plane channel. Results are presented in the Reynolds number range (based on the cylinder diameter and centerline velocity) of 10 to 390 for a blockage ratio (ratio of the cylinder diameter to the channel height) of 0.2. The aim of this work was to investigate in detail the confinement effect due to the channel’s stationary walls on the force coefficients and the associated Strouhal numbers, as well as on the generated flow regimes. Present results suggest a transition from a 2-D to a 3-D shedding flow regime between Re = 180 and Re = 210. This transition was found to be dominated by mode A and mode B three dimensional instabilities, similar to those observed in the case of an unconfined circular cylinder. This is the first time that the existence of the two modes, and of naturally occurring vortex dislocations, has been confirmed via full 3-D simulations for the case...