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Journal of Flow Visualization and Image Processing
SJR: 0.161 SNIP: 0.312 CiteScore™: 0.1

ISSN Druckformat: 1065-3090
ISSN Online: 1940-4336

Journal of Flow Visualization and Image Processing

DOI: 10.1615/JFlowVisImageProc.v14.i1.20
pages 17-34


A. Munjiza
School of Engineering and Materials science, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom
E. Rougier
Queen Mary, University of London, Mile End Road E1 4NS, UK
N. W. M. John
Queen Mary, University of London, Mile End Road E1 4NS, UK


According to the Knudsen number four different types of flow regimes can be identified: continuum, slip, transition, and free-molecular flow. The continuum flow regime is well described by the Navier−Stokes equations. The slip flow can also be described by the Navier−Stokes equations, provided that some special boundary conditions are prescribed. In the transition and the free-molecular flow regimes, the flow is described by the Boltzmann equation, which is a molecular-based model. By using this model, it is possible to solve the high Knudsen number flow problems through molecular-based direct simulation techniques.
However, independent of micro-flow research the particulate-solids research community has developed the so-called Discrete Element Method. In recent years, QMUL and MIT research groups (Munjiza, Williams) have revolutionarized these methods by inventing a set of linear packing-density-independent search algorithms, which have enabled systems comprising billions of particles to be considered on a desktop machine. Recently the QMUL group has applied the method to micro-flows. The most important aspect of this new method is accurate integration of motion of individual molecules including interaction between molecules.
As temporal and spatial constraints make the visualization of micro-flows in experimental research difficult, the new method is an ideal tool for visualization of micro-flows. The power of these new visualization tools is best demonstrated through the so-called "virtual movies" obtained from simulations. Through these movies the observer is given an opportunity to see the motion of individual atoms of a fluid and their interaction with each other and with the boundary.