Near-wall scaling of the Navier-Stokes constitutive relations for accurate micro gas flow simulations

A new model is described for micro gas flows that combines a second-order slip boundary condition with a near-wall scaling of the Navier-Stokes constitutive relations. This scheme, which is easily implemented within a conventional CFD framework, is shown to be far more accurate than the conventional second-order slip model at predicting high Knudsen number micro Couette and Poiseuille flows. It is also of equivalent computational cost, and as such, represents a more attractive alternative to the conventional slip approach. It is also shown that the current model is capable of accurately predicting combined Couette/Poiseulle flows at a much higher Knudsen number than second-order slip conditions, which bodes well for the applicability of the scheme to more general configurations.