Modelling multi-viscosity systems with dissipative particle dynamics D.C. Visser * , H.C.J. Hoefsloot, P.D. Iedema Faculty of Science, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV, Amsterdam, The Netherlands Received 23 December 2004; received in revised form 14 September 2005; accepted 28 September 2005 Available online 10 November 2005 Abstract Dissipative particle dynamics (DPD) is a particle-based simulation technique. It is applicable on time and length scales in-between those typical for molecular modelling and continuum mechanics. These features make DPD an interesting tool in the area of multiphase flows. So far, multiphase DPD simulations were restricted to fluids with the same viscosity, because it was unclear how one could model phases with a different viscosity together. Here, we show how to deal with more than one viscosity in the system. The viscosity of a DPD fluid can be controlled with the friction factor, an input parameter in DPD that characterises the strength of the drag force between interacting particles. So, in a multiphase sys- tem each fluid has its own friction factor, yielding the viscosity of that fluid. Now, the problem is to define the friction factor for the interaction between particles of unlike fluids. This factor has a significant effect on flow dynamics, but lacks a related physical property such as interfacial tension or solubility to specify its value. Three methods are presented to cal- culate the friction factor between particles of unlike fluids. One of these methods only involves the friction factors of the individual fluids and is of most practical use in real applications. The methods are validated for steady and unsteady flow of two adjacent immiscible fluids. Results from these two-phase test cases are consistent with theory. This opens the door to more extensive modelling of multi-viscosity systems with DPD. Ó 2005 Elsevier Inc. All rights reserved. Keywords: Dissipative particle dynamics; Multiphase flow; Viscosity; Interface 1. Introduction Microscopic phenomena play a key role in the dynamic behaviour of multiphase systems. The molecular conformation affects, for instance, the miscibility and interface dynamics of species. Breakup and coales- cence of fluid portions involve pressure gradients and flow on a scale equal to the thickness of the interface. The macroscopic description of conventional continuum-based simulation techniques is often insufficient to model such complex microscopic processes. On the other hand, detailed molecular modelling of multiphase 0021-9991/$ - see front matter Ó 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jcp.2005.09.022 * Corresponding author. Tel.: +31 20 525 5265; fax: +31 20 525 5604. E-mail addresses: visser@science.uva.nl (D.C. Visser), piet@science.uva.nl (P.D. Iedema). Journal of Computational Physics 214 (2006) 491–504 www.elsevier.com/locate/jcp