document: Numerical simulation of the gas flow through such non-trivial internal geometries is, however, extremely challenging. This is because conventional continuum fluid dynamics, which assumes that locally a gas is close to a state of thermodynamic equilibrium, becomes invalid or inaccurate as the smallest characteristic scale of the geometry (e.g. the channel height) approaches the mean distance between molecular collisions, λ [1]. An accurate and flexible modelling alternative for these cases is the direct simulation Monte Carlo method (DSMC) [2]. However, DSMC can be prohibitively expensive for internal-flow applications, which typically have a geometry of high-aspect ratio (i.e. are extremely long, relative to their cross-section). The high-aspect ratio creates a formidable multiscale problem: processes need to be resolved occurring over the smallest characteristic scale of the geometry (e.g. a channelʼs height), as well as over the largest characteristic scale of the geometry (e.g. the length of a long channel network), simultaneously.
extractive_keyphrases: accurate and flexible modelling alternative channel height conventional continuum fluid dynamics direct simulation monte carlo method dsmc gas flow long channel network molecular collisions multiscale problem numerical simulation thermodynamic equilibrium
abstractive_keyphrases: high-aspect ratio internal-flow applications