Capturing the Knudsen layer in continuum-fluid models of nonequilibrium gas flows

A wall function to scale the constitutive relations so that both the velocity slip and Knudsen-layer structure can be captured within a continuum-fluid formulation for locally nonequilibrium gas flows is proposed. This wall function is based on a simple Knudsen-layer solution of the Boltzmann equation and improves the predictive capabilities of the Navier-Stokes equations for a variety of flow configurations. This method could be used as a simple and practical technique for incorporating the Knudsen-layer structure within conventional fluid dynamic simulations. The technique could be used in conjunction with higher-order constitutive relations evaluated outside the Knudsen layer.