Flexible structures enhance fluid mixing in a channel flow.

Fluid mixing plays a pivotal role in many industrial operations. Within the realms of biomedical diagnostics and chemical applications related to drug development, compact systems known as microfluidic devices are prevalent. Within these systems, a thorough mixing of samples and reagents is paramount. Traditional mixing techniques like active stirrers or additional pumping, suitable for larger devices, aren't feasible for these micro-sized tools due to factors such as limited channel length and flows dominated by viscosity. As a result, passive mixing, which relies on molecular diffusion, flow transitions, and chaotic advection, becomes the preferred method. To promote mixing in these tiny devices, researchers have proposed specific geometric designs that amplify the contact surface area while minimizing the diffusion pathway. Examples include baffled designs, separation-re-lamination mixers, and serpentine-shaped mixers.In our study, we ventured into using flexible structures instead of the typical rigid obstructions within the channel. Our findings indicate that these flexible structures create periodic vortex patterns, functioning as passive stirrers, thereby enhancing the mixing efficiency compared to rigid counterparts. We delved into the impact of factors like structure flexibility and inlet flow rate on mixing efficiency and pressure head loss. Introducing these flexible structures can turn a consistent inlet flow into a periodic flow within the channel. This internal 'pumping' effect caused by our passive stirrer design prompts flow transitions, and fosters improved fluid mixing. Devices that can mix more efficiently can indeed propel advancements in microfluidic technology. Furthermore, these innovative methods could be adapted for broader industrial mixing applications.