Biomedical subjects

P Stansell

Publications and source records attributed to P Stansell.

6 recordsLinked to original sources

PubMed2006

Scaling of circulation in buoyancy generated vortices.

The temporal evolution of the fluid circulation generated by a buoyancy force when two-dimensional (2D) arrays of 2D thermals are released into a quiescent incompressible fluid is studied through the results of numerous lattice Boltzmann simulations. It is observed that the circulation magnitude grows to a maximum value in a finite time. When both the maximum circulation and the time at which it occurs are nondimensionalised by appropriately defined characteristic scales, it is shown that two simple Prandtl number (Pr) dependent scaling relations can be devised that fit these data very well over nine decades of Pr spanning the viscous and diffusive regimes and six decades of Rayleigh number (Ra) in the low Ra regime. Also, obtained analytically is the exact result that circulation magnitude continues to grow in time for a 2D laminar or turbulent single buoyant (3D) vortex ring in an infinite unbounded fluid.

Journal Article↗

PubMed2006

Nonequilibrium steady states in sheared binary fluids.

We simulate by lattice Boltzmann the steady shearing of a binary fluid mixture undergoing phase separation with full hydrodynamics in two dimensions. Contrary to some theoretical scenarios, a dynamical steady state is attained with finite domain lengths L(x,y) in the directions (x,y) of velocity and velocity gradient. Apparent scaling exponents are estimated as Lx approximately gamma (-2/3) and Ly approximately gamma(-3/4). We discuss the relative roles of diffusivity and hydrodynamics in attaining steady state.

Journal Article↗

PubMed2005

Application of the lattice Boltzmann model to simulated stenosis growth in a two-dimensional carotid artery.

The lattice Boltzmann model is used to observe changes in the velocity flow and shear stress in a carotid artery model during a simulated stenosis growth. Near wall shear stress in the unstenosed artery is found to agree with literature values. The model also shows regions of low velocity, rotational flow and low near wall shear stress along parts of the walls of the carotid artery that have been identified as being prone to atherosclerosis. These regions persist during the simulated stenosis growth, suggesting that atherosclerotic plaque build-up creates regions of flow with properties that favour atherosclerotic progression.

Animals↗

PubMed2005

Physical and computational scaling issues in lattice Boltzmann simulations of binary fluid mixtures.

We describe some scaling issues that arise when using lattice Boltzmann (LB) methods to simulate binary fluid mixtures--both in the presence and absence of colloidal particles. Two types of scaling problem arise: physical and computational. Physical scaling concerns how to relate simulation parameters to those of the real world. To do this effectively requires careful physics, because (in common with other methods) LB cannot fully resolve the hierarchy of length, energy and time-scales that arise in typical flows of complex fluids. Care is needed in deciding what physics to resolve and what to leave unresolved, particularly when colloidal particles are present in one or both of two fluid phases. This influences steering of simulation parameters such as fluid viscosity and interfacial tension. When the physics is anisotropic (for example, in systems under shear) careful adaptation of the geometry of the simulation box may be needed; an example of this, relating to our study of the effect of colloidal particles on the Rayleigh-Plateau instability of a fluid cylinder, is described. The second and closely related set of scaling issues are computational in nature: how do you scale-up simulations to very large lattice sizes? The problem is acute for systems undergoing shear flow. Here one requires a set of blockwise co-moving frames to the fluid, each connected to the next by a Lees-Edwards like boundary condition. These matching planes lead to small numerical errors whose cumulative effects can become severe; strategies for minimizing such effects are discussed.

Complex Mixtures↗

PubMed2004

Dispersed phase of particles in rotating turbulent fluid flows.

Certain effects, caused by rotating turbulent fluid flows in the presence of gravitational force, for transport of particles dispersed in fluid are suggested and quantified through kinetic or probability density function approach based macroscopic equations. These results are exact when turbulent fluctuations in fluid velocity along the particle path have Gaussian distribution.

Journal Article↗

PubMed2004

Application of the lattice Boltzmann method to arterial flow simulation: investigation of boundary conditions for complex arterial geometries.

The application of the lattice Boltzmann method (LBM) to carotid artery blood flow is investigated, in particular, the importance of the boundary conditions is considered. Simulations are presented using two different boundary conditions: the traditional half-way bounce-back and an extrapolation scheme. The two methods are described and compared with respect to arterial flow simulation. The results indicate that the extrapolation scheme is preferable in narrow arteries, or when a stenosis is present in a larger artery.

Algorithms↗