Reducing wake flow with paper-cutting control surfaces

Control surfaces are essential for maximizing efficiency when a fluid flows across an object. Failure to control the flow can result in vortex shedding, which leads to unsteady loads, wake-induced vibration, and acoustic noise. These impact performance and can even cause damage to structures. Designing proper control surfaces becomes challenging when the flow is dynamic, as existing passive surfaces are unable to compensate for changing conditions.

Wen et al. designed a passive flow control surface for a bluff body using the principles of kirigami. In experimental tests, their design reduced turbulence and shear stress significantly when compared to uncontrolled surfaces.

Kirigami, the art of paper cutting, offers a simple solution to changing flow conditions. Kirigami structures predictably deform out-of-plane when a force is applied. Choosing the right materials and cuts allows researchers to ‘program’ a control surface that will stay flat in standard conditions and deform when needed.

“By stretching and relaxing kirigami sheets, an array of tilted surface elements can be easily activated and deactivated on the surface of a bluff body, significantly improving the control performance compared to traditional methods,” said author Xin Wen.

The authors constructed several kirigami shapes such as triangular and circular cuts, and evaluated their performance using a wind tunnel. Their results indicate that kirigami shapes perform at least as well as traditional passive control surfaces, and in some configurations are more effective at suppressing unsteady shedding vortices.

The team plans to study additional designs to achieve even better results. They hope to broaden the possible applications for their kirigami structures to additional environments, such as on airfoils.

Source: “Dynamic kirigami structures for wake flow control behind a circular cylinder,” by Xin Wen, Dong Wang, Ziyu Chen, Fan Yang, Chengru Jiang, and Yingzheng Liu, Physics of Fluids (2023). The article can be accessed at https://doi.org/10.1063/5.0130369 .