Mixing enhancement mechanism and flow characteristics of a micromixer with lune-shaped spoiler

Efficient mixing remains a fundamental challenge in microfluidic systems due to the dominance of laminar flow at low Reynolds numbers. In this work, we propose a novel micromixer integrated with lune-shaped spoiler array units. Combining experimental flow visualization and numerical simulation, we systematically investigate the influence of concave–concave, concave–convex, convex–convex, and convex–concave lune-shaped spoiler micromixer (VC-LSM) arrangements on internal flow patterns and mixing performance over the Reynolds number range of 1–100. The results show that lune-shaped spoilers effectively enhance mixing by inducing secondary flows and complex vortex structures that disrupt the stratified fluid interface. Among all designs, the VC-LSM configuration exhibits the optimal comprehensive performance. It achieves a maximum mixing index of 0.9996, while maintaining a pressure drop of 46.40 kPa at Re = 100. From the perspective of vortex topology evolution, the potential mechanism of the VC-LSM mixing enhancement was revealed. It is found that horseshoe vortices, hairpin vortices, and ivory vortices were generated in mixing channel of VC-LSM, and their combined effect enhanced the fluid shear and disturbance. Particularly, the newly formed ivory vortex induces the generation of additional shear layers, which continuously act on the fluid interface. The mutual entrainment of the fluids is enhanced, resulting in an increase in the contact area, which is a key factor for the excellent mixing performance of VC-LSM. These findings provide a practical structural design strategy for high-performance passive micromixers, with promising applications in lab-on-a-chip systems, biochemical analysis, and microreactors.