The flow in three-dimensional (3-D) microscale backward-facing step is investigated using the direct simulation Monte Carlo method. To ensure the rationality of two-dimensional (2-D) simplification for a 3-D structure, the flow characteristics of the 3-D microscale backward-facing step flows with various cross-section aspect ratios are compared with those of 2-D simplification. When the cross-section aspect ratio of 3-D flow cases is greater than 5, the approaching level of 3-D flows to 2-D simplification is over 98% for the nitrogen flow with inlet Knudsen number (Kn) of 0.04. Moreover, it is found that the approaching level decreases as Kn increases. The dependence between the vortex stability and the cross-section aspect ratio is studied. It is found that the flow separation, recirculation, and reattachment will disappear as the cross-section aspect ratio is less than 1 for flows with inlet Kn of 0.04.
Numerical Heat Transfer, Part A: Applications 57(5), pp.331-345