Isothermal slip flow over curved surfaces

Abstract

It has long been recognised that the no-slip-boundary condition employed in the Navier–Stokes equations can only be applied when the Knudsen number, Kn⩽10 −3. If the Knudsen number is increased beyond this value, rarefaction effects start to influence the flow and the molecular collision frequency per unit area becomes too small to maintain the no-slip-boundary condition. Unfortunately, Maxwell's famous slip equation describing the velocity discontinuity at the wall is often misapplied when analysing flows over curved or rotating boundaries. In the present study, a generalised version of Maxwell's slip equation is used to investigate low Knudsen number isothermal flow over walls with substantial curvature. The generalised slip equation is written in terms of the tangential shear stress to overcome the limitations of the conventional slip-boundary treatment. The study considers a number of fundamental, but challenging, rarefied flow problems and demonstrates that Maxwell's conventional slip equation is unable to capture important flow phenomena over curved or rotating surfaces.