In this paper, the phenomenological “wall function” method of Lockerby, Reese and Gallis [1] is used to capture important non-equilibrium aspects of gas microflows. The approach is a constitutive scaling method that captures slip at solid walls and the Knudsen layer, a near-wall region where non-linear constitutive behaviour is observed. In this paper the wall function approach is applied to model gas flow through microscale orifice plates, an industrially relevant application. Two key test geometries are investigated, flow through a constriction in a microchannel and flow through a microscale venturi in a microchannel. A range of incompressible, isothermal flows are analysed with the OpenFOAM computational fluid dynamics (CFD) code [10], and numerical results are validated against available experimental data [12]. Following successful verification of the model, the increasing impact of non-equilibrium effects on flow through the test geometries at higher Knudsen numbers is shown. The integration of the constitutive scaling approach with mainstream CFD is shown to be a flexible technique, well-suited to engineering design applications.

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