For gas flows in microfluidic configurations, the Knudsen layer close to the wall can comprise a substantial part of the entire flowfield and has a major effect on quantities such as the mass flow rate through micro devices. The Knudsen layer itself is characterized by a highly nonlinear relationship between the viscous stress and the strain rate of the gas, so even if the Navier-Stokes equatio...

The dynamic resistance of a sphere with a general inhomogeneous slip boundary condition is analyzed in Newtonian unbounded uniform flow at low Reynolds number. The boundary condition is treated as a perturbation to a homogeneous sphere, assuming that the slip length magnitude b is much smaller than the sphere radius a . To first order, the effect of inhomogeneous slip is the same as that of a r...

The boundary layer flow of Cu-water based nanofluid with heat transfer over a stretching sheet is numerically studied. Second order velocity slip flow model is considered instead of no-slip at the boundary. The governing partial differential equations are transformed into ordinary one using similarity transformation, before being solved numerically. Numerical solutions of these equations are ob...

The hydrodynamics of a flagellated microorganism is investigated when swimming close to a planar free-slip surface by means of numerical solutions of the Stokes equations obtained via a Boundary Element Method. Depending on the initial condition, the swimmer can either escape from the free-slip surface or collide with the boundary. Interestingly, the microorganism does not exhibit a stable orbi...

In microfluidic applications involving high-frequency acoustic waves over a solid boundary, the Stokes boundary-layer thickness δ is so small that some non-negligible slip may occur at the fluid-solid interface. The classical problem of steady acoustic streaming over a flat boundary is therefore revisited to include the effect of slip modelled using the Navier boundary condition u|y=0 = Ls∂yu|y...

Rapid advances in microelectromechanical systems have stimulated the development of compact devices, which require effective cooling technologies (e.g., microchannel cooling). However, the inconsistencies between experimental and classical theoretical predictions for the liquid flow in microchannel remain unclarified. Given the larger surface/volume ratio of microchannel, the surface effects in...

Maxwell’s original slip boundary condition is widely misapplied in current rarefied gas flow calculations (e.g. in hypersonics, microfluidics). If its commonly-accepted form is applied in simulations of gas flows over curved or moving surfaces, crucial physics can be lost. We give examples of such cases. We also propose a new higher-order boundary condition which is based on Maxwell’s original ...

In this paper, implementation of an extended form of a no-slip wall boundary condition is presented for the three-dimensional (3-D) lattice Boltzmann method (LBM) for solving the incompressible fluid flows with complex geometries. The boundary condition is based on the off-lattice scheme with a polynomial interpolation which is used to reconstruct the curved or irregular wall boundary on the ne...