Superhydrophobic surfaces to reduce form drag in turbulent separated flows

TL;DR

This study demonstrates that superhydrophobic surfaces can effectively reduce flow separation and form drag in turbulent water flows over bluff bodies, expanding their application beyond friction drag reduction.

Contribution

The paper introduces the novel application of superhydrophobic surfaces for reducing form drag in turbulent separated flows through numerical simulations.

Findings

Superhydrophobic surfaces reduce flow separation in turbulent water flows.

Numerical simulations show decreased form drag with superhydrophobic modifications.

Superhydrophobic surfaces offer a new technique for drag reduction on bluff bodies.

Abstract

The drag force acting on a body moving in a fluid has two components, friction drag due to fluid viscosity and form drag due to flow separation behind the body. When present, form drag is usually the most significant between the two and in many applications, streamlining efficiently reduces or prevents flow separation. As studied here, when the operating fluid is water, a promising technique for form drag reduction is to modify the walls of the body with superhydrophobic surfaces. These surfaces entrap gas bubbles in their asperities, avoiding the direct contact of the liquid with the wall. Superhydrophobic surfaces have been vastly studied for reducing friction drag. We show they are also effective in reducing flow separation in turbulent flow and therefore in reducing the form drag. Their conceptual effectiveness is demonstrated by studying numerical simulations of turbulent flow over a bluff body, represented by a bump inside a channel, which is modified with different superhydrophobic surfaces. The approach shown here contributes to new and powerful techniques for drag reduction on bluff bodies.