A new study from the University of Alabama, which will be presented at the 2019 American Physical Society Meeting in Boston later this month, found that specialized scales on the mako shark’s fins and along its flank help the predator reach speeds of nearly 80 miles per hour.
They found tiny — approximately 0.2-millimeter in width — flexible scales that can bend at angles in excess of 40 degrees from the body—opposite of the flow of water. This reduces pressure drag forces on the shark as it moves through the water.
“The dimples on a golf ball are an example of separation control that reduces pressure drag by maintaining attached flow around the ball and reducing the size of the wake. You can hit a golf ball with dimples 30 percent farther than if the same ball were smooth,” aeronautical engineer and researcher Amy Lang said.
Using skin samples from a mako shark that were tested in a water tunnel a technique called digital particle image velocimetry to produce detailed measurements of the water flow velocity over and around the skin, Lang and her associates found that that flow separation was indeed being controlled by a “passive bristling” capability of the microscopic surface geometry of the shark’s scales.
These findings could lead to new designs to reduce drag on aircraft and helicopters, increasing their agility.