Harvard researchers create dimpled fabric to cut drag by 20%

The research is a collaboration between the labs of Katia Bertoldi, the William and Ami Kuan Danoff professor of Applied Mechanics, and Conor J Walsh, the Paul A Maeder professor of Engineering and Applied Sciences. 

Farrell, whose research interests lies at the intersection of fluid dynamics and artificially engineered materials, or metamaterials, led the creation of a unique textile that forms dimples on its surface when stretched, even when tightly fitted around a person’s body. The fabrics utilise the same aerodynamic principles as a golf ball, whose dimpled surface causes a ball to fly further by using turbulence to reduce drag. Because the fabric is soft and elastic, it can move and stretch to change the size and shape of the dimples on demand. 

Adjusting dimple sizes can make the fabric perform better in certain wind speeds by reducing drag by up to 20 per cent, according to the researchers’ experiments using a wind tunnel.

“By performing 3,000 simulations, we were able to explore thousands of dimpling patterns,” Farrell said. “We were able to tune how big the dimple is, as well as its form. When we put these patterns back in the wind tunnel, we find that certain patterns and dimples are optimised for specific wind-speed regions.”

Farrell and team used a laser cutter and heat press to create a dual-toned fabric made of a stiffer black woven material, similar to a backpack strap, and a gray softer knit that’s flexible and comfortable. Using a two-step manufacturing process, they cut patterns into the woven fabric and sealed it together with the knit layer to form a textile composite. Experimenting with multiple flat samples patterned in lattices like squares and hexagons, they systematically explored how different tessellations affect the mechanical response of each textile material.

The textile composite’s on-demand dimpling is the result of a lattice pattern that Bertoldi and others have previously explored for its unusual properties. Stretch a traditional textile onto the body, and it will smooth out and tighten. “Our textile composite breaks that rule,” Farrell explained. “The unique lattice pattern allows the textile to expand around the arm rather than clamp down.

“We’re using this unique property that Bertoldi and others have explored for the last 10 years in metamaterials, and we’re putting it into wearables in a way that no one’s really seen before,” Farrell said.

The paper was co-authored by Connor M McCann and Antonio Elia Forte.

ALCHEMPro News Desk (RR)