(509c) Continuum/Mesoscale/Molecular Level Hybridization in Complex Fluid Flows

Sesha Hari Vemuri, Yu Liu, Myung S. Jhon, and Lorenz T. Biegler

Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213

Considerable effort is being dedicated to understand the range of time and length scale phenomena that take place in a broad range of systems including colloidal suspensions, polymer solutions, micro- and nano hydrodynamic flows, especially in biological systems. These systems are characterized by multiscale interaction between “large and slow” polymer particles, and “small and fast” solvent particles [1]. A detailed modeling of such systems can be provided by a molecular dynamics (MD) simulation where the motion of all the particles is tracked via Newton’s equations of motion. However, this approach has severe drawbacks due to the limitations on typical length scale covered in the MD simulations and the computational time scaling as O(N²), where N is the number of particles. On the other hand, the continuum based theory breaks down for these systems as the confinement size is comparable to or smaller than the molecular/pseudo-particle mean free path.

Mesoscopic models, and notably those arising from kinetic theory, are natural candidates to fill this gap because they operate precisely at intermediate scales between the atomistic and continuum levels. During the past two decades, lattice Boltzmann method (LBM), which originates from Boltzmann transport equation has proven successful to model characteristic features of nano/microscopic flows, such as the occurrence of slip boundary conditions near solid walls [2]. Furthermore, being a pseudo particle simulation methodology, it has the advantages of easily implementing easily the rotational degrees of freedom of the particles [3], and ability of simulating multi-physical phenomena in complex geometries. In this work, we present a hybrid MD/LBM method for the simulation of hydrodynamic phenomena in polymer solutions and colloidalsystems.

This will be achieved by generating a buffer zone at the component interface (e.g., polymer-solvent interface, fluid-boundary interface etc.)  where both MD and LBM solutions are valid. Here, the particle velocities and forces obtained are exchanged between particles modeled by LBM and those modeled by MD [3]. The constrained dynamics algorithm forces the instantaneous mean particle velocity to equate the continuum solution at the other boundary. The equations of motion in the MD are also modified to match the external force obtained from the LBM via proper scaling.

To validate our hybrid model, we examine our results of the benchmark complex fluid flow systems including including colloidal solution & flow in a confined geometry and will extend our analysis towards the complex multi-physical phenomena various applications.

[1] A. Chatterji and J. Horbach, J. Chem. Phys., 122, 184903 (2005)

[2]  J. Horbach and S. Succi, Phys. Rev. Lett., 96, 224503 (2006)

[3] P. Ahlrichs and B. Dünweg, Int. J. Mod. Phys. C, 09, 1429 (1998)