Implementation of a height function method to alleviate spurious currents in CFD modelling of annular flow in microchannels

The use of the continuum surface force (CSF) model in surface tension modelling using the volume of fluid (VOF) method is known to introduce unphysical velocities, called parasitic or spurious currents arising mostly from poor calculation of interface curvature. In this paper, a modified 2-D axisymmetric height function (HF) method is proposed and implemented in parallelised computations. The default CSF method in the commercial software ANSYS Fluent 15.0 is replaced using User-Defined Functions (UDFs) of ANSYS Fluent and the improvements obtained are evaluated in test cases with stationary and moving interfaces. The application of the HF method to annular flow modelling has shown massive improvements in interface modelling and potential for research on annular flow hydrodynamics and heat transfer.