Research of wall roughness effects based on Q criterion

The wall roughness shows a great impact on flow field in a micro-channel. This paper investigates wall roughness effects based on Q criterion. The direct simulation Monte Carlo method is employed to simulate the flow field. It reveals the physical mechanism behind the phenomenon that the Poiseuille number (fRe) increases more significantly for smaller roughness element spacing. Besides, it demonstrates the phenomenon of flow fluctuation and the physical mechanism behind it. Furthermore, it indicates that the Poiseuille number of roughness element combination is determined by large roughness elements. It also provides suggestions on the simplification of real wall roughness profile.