Shape reconfiguration through origami folding boosts drag reduction

Being flexible is an effective self-protection strategy for objects exposed to strong winds; it reduces their drag through shape streamlining and reduction of their frontal area. Slender objects like sheets deform primarily through bending, but introducing a network of folds expands the accessible deformation modes. Such origami folding notably allows for large shape changes, which would drastically alter fluid loading on the system when placed in a flow. Here, we study how articulated kinematics impact reconfiguration processes in an airflow and subsequent drag reduction, starting with a single waterbomb origami unit. We show that its ability to fold into a very compact object exacerbates drag reduction, to the point that fluid loading saturates in strong flows and no longer depends on flow speed. We investigate the underlying fluid/structure mechanisms through a combination of experiments and theoretical modeling, to evaluate in particular the influence of the crease pattern and the origami mechanical properties. Results pave the way to understand the impact of creases on fluid-elastic processes. Such creases are ubiquitous in nature (as in leaves and insect wings) and synthetic thin-walled structures, which are systems brought to interact with a fluid environment.