Direct Numerical Simulations of the Turbulent Flow over Super-Hydrophobic and Liquid Infused Surfaces: Effect of the Dynamics of the Interface on the Drag




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Superhydrophobic surfaces (SHS) and liquid infused surfaces (LIS) are studied through direct numerical simulations of a turbulent channel flow and a Couette flow. Either SHS or LIS are placed on the lower wall and modeled with the immersed boundary method. The dynamics of the interface between the two fluids is fully coupled to the Navier Stokes equations and solved with a Level Set method. A parametric study has been performed varying the viscosity ratio between the two fluids, substrate geometry, Reynolds number and Weber number. Different flow configurations are considered from ideal cases to more realistic, to assess the interface stability and drag of SHS and LIS. Because the viscosity ratio in LIS is closer to one, the interface is more stable. For SHS, even with very high interfacial tension, large deformations of the interface were observed. It is found that the dynamics of the interface has a detrimental effect on the drag reduction performance. A realistic configuration with random pinnacles as a substrate is studied in order to understand the effect that asperities in SHS and LIS have on drag. The form drag generated by the asperities showed to affect significantly the drag reducing properties of SHS and LIS. A roughness scale has been defined and proposed as a design criteria for drag reduction.



Drag (Aerodynamics), Hydrophobic surfaces, Level set methods, Viscosity