Enhancement of mixing via flow-induced flutter of a flexible membrane is explored for small-scale mixers that operate at low Reynolds numbers. Flow induced flutter and mixing in a duct flow is simulated using fully coupled fluid-structure-scalar interaction simulations including two-way coupling between the fluid and structure. The fluid and structural dynamics are analyzed and their impact on the mixing performance is characterized. The sensitivity of the system to the Reynolds number and to the membrane’s size and shape are also examined. It is shown that these flutter mixers create complex vortex structures even at low Reynolds numbers and these vortex structures lead to complex stretching and folding of fluid interfaces resulting in rapid mixing.

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Heat transfer enhancement due to flapping flags in a heated duct flow is studied using three-dimensional (3D) fully coupled fluid–structure–thermal simulations. Following prior work, which was limited to two-dimensional models, we examine the mechanisms and the heat transfer performance for a more realistic, 3D model of a flag in a rectangular duct heat exchanger. We then examine the role of the flag aspect-ratio and spanwise confinement, which are key design parameters for this device. We find that the narrow flags do not exhibit sufficiently energetic flapping to generate any meaningful heat transfer enhancement. We also find that the wide flags significantly increase heat flux and an increase in the width of the flag can further increase the thermal enhancement factor.

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