Drag reduction by plastron in featureless turbulent Taylor-Couette flow: torque and 2D PIV measurements

In underwater environments, superhydrophobic surfaces can form a plastron between the water and the surface, depending on the surface characteristics. This plastron induces slip at the wall, subsequently reducing friction drag. The drag reduction in laminar flow has been extensively demonstrated based on the geometric characteristics of superhydrophobic surfaces. However, in turbulent flow, it is challenging to experimentally study drag reduction due to the difficulty of maintaining the plastron and precisely measuring friction drag. We developed a Taylor-Couette flow device capable of producing featureless turbulence through exact counter-rotation, enabling precise torque measurement and near-wall velocity field analysis over a wide range of Reynolds numbers using water as the working fluid. The formation and maintenance of the plastron in the turbulent regime are achieved using superhydrophobic surfaces with a hierarchical porous structure and Teflon coating. The presentation will include the drag reduction performance by the plastron for shear Reynolds numbers up to 16,000, comparisons of mean and turbulent quantities with and without the plastron, and validation results of the Taylor-Couette flow measurements.