Berkeley Fluids Seminar

Monday, March 6, 2017

3110 Etcheverry Hall, 12:00-13:00

Dr. Jongmin Seo (Stanford University)

Drag reduction and mechanism of bubble depletion in turbulent flows over superhydrophobic surfaces

Abstract: Superhydrophobic surfaces can capture gas pockets within their micro-scale structures when submerged in water. A thin layer of gas pockets forms slippery boundaries for the overlying liquid flow leading to reduced skin friction. Therefore, superhydrophobic surfaces present opportunities for improving hydrodynamic performance over a wide range of systems such as those in naval applications. In most realistic applications, the flow regime is turbulent. However, in such regimes the key physical phenomenon controlling drag reduction, and stability of gas pockets are not well understood. In this work direct numerical simulations of turbulent channel flows with superhydrophobic walls are used to analyze the kinematics as well as interfacial robustness of superhydrophobic surfaces. First, we present a phenomenological model for the estimation of drag reduction of flow near a superhydrophobic surface at high Reynolds numbers. In addition, the present work addresses the robustness of superhydrophobic surfaces by studying the pressure load fields obtained from DNS data. Effects of stagnation pressure formed by slip flow at the leading edge of geometric textures are mainly investigated. Furthermore, the current work studies the dynamics associated with the deformability of the air-water interface when superhydrophobic surfaces are exposed to turbulent flows. In addition, this work examines how the randomness of patterns affects the drag reduction effectiveness and interfacial robustness when superhydrophobic surfaces with random textures are in contact with an overlaying turbulent flow. Finally, we show boundary maps that establish stable and unstable zones of drag reduction to provide implications on the design of SHS.

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Acknowledgments

Prof. Graham Fleming (Vice Chancellor for Research, UC Berkeley)

Prof. Eliot Quataert on behalf of The Theoretical Astrophysics Center and the Astronomy Department (UC Berkeley)

Prof. Philip S. Marcus on behalf of the Mechanical Engineering Department (UC Berkeley)

Prof. Michael Manga (Earth and Planetary Science, UC Berkeley)

Prof. Evan Variano (Civil and Environmental Engineering, UC Berkeley)