Effects of superhydrophobicity on transition in a spatially developing boundary layer

Superhydrophobic surfaces have exhibited achieving significant skin-friction drag reduction in wall-bounded turbulent flows. In fully-developed turbulent channel flow, it has been reported that drag reduction can be characterized by the slip length over a range of Reynolds numbers and surface geometrical properties. The effects of superhydrophobic surfaces on flow transition to turbulence are also of great interest for engineering applications. This study investigates the effects of superhydrophobic surface on transition to turbulence in a spatially developing boundary layer. In our direct numerical simulations, small disturbances containing unstable frequencies are introduced to an incoming Blasius boundary layer to trigger transition, with and without a superhydrophobic wall downstreams. The computational domain covers the laminar, transition and fully-developed turbulent regions. The superhydrophobic surface consists of alternating air pockets, supported by surface tension between the gas the liquid, and the no-slip wall. A number of superhydrophobic surface geometries are considered and their effects on transition to turbulence are compared. Flow statistics are examined, and the effects of grid resolution on the superhydrophobic transition simulations are discussed.