Computational fluid dynamics wall boundary conditions

From this, the velocities of particles flowing near the wall can be characterized. However, the absorption parameter a must be determined empirically. Sokhan et al. [48, 63] used this model in nonequilibrium molecular dynamics simulations to describe boundary conditions for fluid flow in carbon nanopores and nanotubes under Poiseuille flow. The authors found slip length of 3nm for the nanopores [48] and 4-8 nm for the nanotubes [63]. However, in the first case, a single factor [4] was used to model fluid-solid interactions, whereas in the second, a many-body potential was used, which, while it may be more accurate, is significantly more computationally intensive. 

The density fluctuations arising near the boundary from the implementation of the conservative force at the waU is a cause of concern when implementing the no-sUp boundary condition. To address this, a no-sUp scheme based on the equivalent force between the waU and fluid particles may he introduced. In this method, layers of frozen particles are chosen as in the frozen-layer scheme, but a key difference is that the coefficient for the conservative force is adjusted in a manner so as to incorporate wall and fluid particle interactions. This leads to a correct no-slip implementation without fluctuations in density. Another proposal to reduce density fluctuations near the walls represents the boundary with two layers of frozen particles. The particles that penetrate the boundary are made to bounce back into the computational domain. No-sUp at the wall is produced by using a twin image of the system being simulated. The second image has the same configurations and dynamics as the first, but operates with a different... 

Nagayama et al. [57] carried out nonequilibrium molecular dynamic simulations to study the effect of interface wettability on the pressure driven flow of a Lennard-Jones fluid in a nanochannel. The velocity profile changed significantly depending on the wettability of the wall. The no-slip boundary condition breaks down for a hydrophobic wall. Siegel et al. [58] developed a two-dimensional computational model for fuel cells. 

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