Investigation of flow in microchannels with superhydrophobic surfaces using hybrid DSMC-NS method accompanied with IP approach

In the recent years, superhydrophobic surfaces have received significant attention due to properties such as drag reduction and self-cleaning. Specially in microchannels where the surface forces are dominant, superhydrophobic surfaces are widely applicable. A superhydrophobic surface can be made by grooving the surface. In this case, flow of gas caught in grooves may represent rarefied flow depending on the gas pressure and the length scale of the microcavity. Therefore, the gas flow should be treated with particle based approaches such as direct simulation of Monte Carlo, DSMC. In this paper laminar flow in superhydrophobic microchannels with ribs and cavities aligned perpendicular to the channel axis is investigated using a hybrid DSMC-NS (Navier-Stokes) method. In addition, Information preservation technique (IP) is employed to reduce statistical fluctuations of the DSMC method due to low speed flow in gaseous phase. The effects of the length of the cavity on the flow parameters such as effective slip length, velocity slip and velocity profile are investigated and the results are compared with the simplified method of using NS equations with shear free (SF) boundary condition on the gas-liquid interface. It is shown that the differences between the hybrid DSMC-NS method and SF solution increase as the shear free fraction increases. However, the difference is less than 6% for cases studied in this work. Therefore, it is acceptable to use the SF approach to reduce computational costs. Specially for Fc < 0.2 where the difference is less than 3%.