Numerical studies on the hydraulic and mixing performances of fluid flow around a cylinder in microchannel with vertical flexible flag

Oscillating flexible flag due to the force exerted by periodic flow behind a cylinder is a significant technique to enhance mixing. To analyze its hydraulic and mixing performances, this paper numerically studies the pressure drop and mixing efficiency of fluid flow in a microchannel mounted with a cylinder and vertical flexible flag (CCFF) with different height and deformability in a wide range of Reynolds number Red based on the cylinder diameter. The simple channel without cylinder and flag (SC) and the channel with cylinder and rigid flag (CCRF) are also studied as comparisons. It is found that the mixing within CCFF occurs mainly due to the molecular diffusion at small and moderate Re-d, and its pressure drop and mixing efficiency increase with the increasing flag height. At large Re-d, the mixing in CCFF is highly enhanced by the vortices detached from the vibrating flag, and its pressure drop and mixing efficiency first increase and then reach a slight decrease or quasi-steady value with the increasing flag height. Compared with SC, the pressure drop of CCFF is always larger than that of SC, however, the mixing efficiency of CCFF is larger than that of SC only when Re-d or the flexible flag height is large enough. Comparing with CCRF, the pressure drop and mixing efficiency of CCFF are close to or smaller than those of CCRF at small and moderate Re-d, however, at large Red, CCFF has smaller pressure drop and larger mixing efficiency, and the maximum decrease of pressure drop could be up to 61.09% and the maximum increase of mixing efficiency could be up to 11.46% compared with CCRF.