Chamorro team’s advances on passive flow control published in PNAS
MechSE assistant professor Leonardo Chamorro’s group and collaborators from Purdue and TTU have demonstrated an effective way to control separated flows under adverse pressure gradient (APG) using a bio-inspired coating. It successfully reduces the size of, and moves downstream, the large-scale recirculation region induced in APG. These findings were recently published in the Proceedings of the National Academy of Sciences of the United States of America.
The coating is composed of uniformly distributed pillars with a cylindrical base and diverging tips; essentially, the elements may be seen as a coarse representation of shark denticles.
Supported with laboratory experiments and theoretical arguments based on the averaged Navier-Stokes equations, the researchers suggested that the underlying mechanism responsible for the bubble modulation is related to unsteady suction and blowing controlled by the increasing cross-section of the tips. They also stressed that the ability of the coating to manipulate large-scale recirculation bubbles occurs despite that the so-called roughness parameter of the pillars falls within the hydrodynamically smooth regime.
The distinctive mechanism by which the coating works does not rely on (super) hydrophobicity. Instead, it relies on the generation of distributed wall-normal flow perturbations, giving it the versatility to work under wet or dry conditions. This makes it very useful in a broad range of applications, including flow control, power conversion, energy-efficient transport vehicles, and many others.
“The enhanced wall-normal flow fluctuations induced by the coating also open a number of exiting, concrete possibilities in engineering.”