An Experimental Investigation of the Influence of Superhydrophobic Surfaces on Turbulent Boundary Layer Separation

We investigate the separation of a turbulent boundary layer (TBL) in an adverse pressure gradient over a convex backward facing ramp coated with a superhydrophobic surface (SHS). Past research has shown that the location of TBL separation can be modified by the increased skin friction over a rough surface. SHSs in specific cases have been shown to also be effective in modifying the skin friction in a TBL. In our experiment, we investigate the influence of an air infused SHS-induced reduction in skin friction on the location of TBL separation. A TBL develops over a flat plate in a water tunnel, reaching a Reynolds number based on fetch distance on the order of Re_x ≈ 10⁶. The developed boundary layer then separates in an adverse pressure gradient as it flows over a diverging ramp with a constant radius of 127mm. The location of separation on the ramp is compared for the cases with and without an SHS coating, and the flow is characterized by particle image velocimetry (PIV).