The Experts below are selected from a list of 258 Experts worldwide ranked by ideXlab platform
John Christos Vassilicos - One of the best experts on this subject based on the ideXlab platform.
-
Mixing in vortical, chaotic and turbulent flows
Philosophical transactions. Series A Mathematical physical and engineering sciences, 2002Co-Authors: John Christos VassilicosAbstract:Mixing is discussed in relation to stirring as reflected in the geometry of advected interfaces, the behaviour of Fluid-Element pairs and their separation rates. Stirring is different in vortical, chaotic and turbulent flows because of qualitative differences in spatio-temporal flow structure, thus giving rise to different mixing laws. Important applications of the mixing and stirring properties discussed in this review are chlorine deactivation and ozone depletion in stratospheric mid-latitudes.
-
Kinematic Simulation for Stratified Flows
Fluid Mechanics and Its Applications, 1998Co-Authors: Franck C. G. A. Nicolleau, John Christos VassilicosAbstract:Kinematic Simulations (KS) are Lagrangian models of turbulent dispersion that are based on the integration of Fluid Element (or synonymously, particle) trajectories in realisations of a prescribed turbulent-like Eulerian velocity field. Small-scale turbulent-like flow structures exist in every realisation of these fields and provide enough accuracy to predict correct Lagrangian properties. Each trajectory is smooth and comparable in character to particle trajectories seen in nature and the laboratory.
J.-m. Martinez - One of the best experts on this subject based on the ideXlab platform.
-
On bubble forces in turbulent channel flows from direct numerical simulations
Journal of Fluid Mechanics, 2020Co-Authors: A. Du Cluzeau, G. Bois, A. Toutant, J.-m. MartinezAbstract:The prediction of void fraction, which relies on interfacial force models, is a major issue in the context of boiling. The two-Fluid model requires the modelling of the momentum transfer between phases. When bubbles are small (particle hypothesis), the momentum transfer is related to interfacial forces acting on bubbles. However, the splitting of these forces into drag, lift, added mass, etc., is not straightforward from the local point of view, where only the total interfacial force is defined as an integral of the constraint over the interface. For large-size bubbles, the particle hypothesis can be questioned. The momentum transfer can then be connected to the forces acting on a Fluid Element of the vapour phase. Based on the local and averaged formulations of the Navier-Stokes equations, a new balance equation for forces enables us to define lift, drag, added-mass and dispersion forces acting on a Fluid Element of the vapour phase. This equation gives a local definition for all the forces responsible for spatial distribution of bubbles and reflects the meaning usually assigned to the interfacial forces in the particle approach. Through this means, the link between the local formulation and physical phenomena is established and a new way of modelling the lift force is proposed. Furthermore, a new laminar dispersion force which relies on surface tension and pressure effects is introduced. The analysis of the budget equation on our direct numerical simulation database brings into light the large influence of this laminar dispersion force in the migration process. Different well-known physical behaviours can be modelled via this new force: the horizontal clustering of spherical bubbles in laminar flows and the oscillating trajectories of deformable bubbles.
Philip J. Morrison - One of the best experts on this subject based on the ideXlab platform.
-
Local thermodynamics of a magnetized, anisotropic plasma
Physics of Plasmas, 2013Co-Authors: Richard D Hazeltine, Swadesh M Mahajan, Philip J. MorrisonAbstract:An expression for the internal energy of a Fluid Element in a weakly coupled, magnetized, anisotropic plasma is derived from first principles. The result is a function of entropy, particle density and magnetic field, and as such plays the role of a thermodynamic potential: it determines in principle all thermodynamic properties of the Fluid Element. In particular it provides equations of state for the magnetized plasma. The derivation uses familiar Fluid equations, a few Elements of kinetic theory, the MHD version of Faraday's law, and certain familiar stability and regularity conditions.
-
Fluid Element relabeling symmetry
Physics Letters A, 1996Co-Authors: Nikhil S. Padhye, Philip J. MorrisonAbstract:Abstract Lagrangian symmetries are found for hydrodynamics and magnetohydrodynamics, which result in conservation of potential vorticity and of cross helicity, respectively. These symmetries, which persist in the reduction from Lagrangian to Eulerian variables, directly give rise to Casimir invariants of the Hamiltonian formalism. The mechanism of spontaneous symmetry breaking in a Fluid is also presented.
A. Du Cluzeau - One of the best experts on this subject based on the ideXlab platform.
-
On bubble forces in turbulent channel flows from direct numerical simulations
Journal of Fluid Mechanics, 2020Co-Authors: A. Du Cluzeau, G. Bois, A. Toutant, J.-m. MartinezAbstract:The prediction of void fraction, which relies on interfacial force models, is a major issue in the context of boiling. The two-Fluid model requires the modelling of the momentum transfer between phases. When bubbles are small (particle hypothesis), the momentum transfer is related to interfacial forces acting on bubbles. However, the splitting of these forces into drag, lift, added mass, etc., is not straightforward from the local point of view, where only the total interfacial force is defined as an integral of the constraint over the interface. For large-size bubbles, the particle hypothesis can be questioned. The momentum transfer can then be connected to the forces acting on a Fluid Element of the vapour phase. Based on the local and averaged formulations of the Navier-Stokes equations, a new balance equation for forces enables us to define lift, drag, added-mass and dispersion forces acting on a Fluid Element of the vapour phase. This equation gives a local definition for all the forces responsible for spatial distribution of bubbles and reflects the meaning usually assigned to the interfacial forces in the particle approach. Through this means, the link between the local formulation and physical phenomena is established and a new way of modelling the lift force is proposed. Furthermore, a new laminar dispersion force which relies on surface tension and pressure effects is introduced. The analysis of the budget equation on our direct numerical simulation database brings into light the large influence of this laminar dispersion force in the migration process. Different well-known physical behaviours can be modelled via this new force: the horizontal clustering of spherical bubbles in laminar flows and the oscillating trajectories of deformable bubbles.
J. Legrand - One of the best experts on this subject based on the ideXlab platform.
-
Numerical tracking and circulation time distribution in an infinite Taylor system
Chemical Engineering Science, 2000Co-Authors: K Khellaf, Guy Lauriat, J. LegrandAbstract:A numerical investigation was conducted to compute circulation time of Elementary Fluid Elements in a Taylor vortex reactor. Finite volume method using the SIMPLER algorithm is adopted to solve the conservative equations. The numerical code was first validated. The convective displacements were determined by the three velocity components associated with the current location of the particles. For a given initial Fluid Element, the numerical tracking gives the circulation time which corresponds to a complete rotation (2π).