Interfacial flow over slip boundary on underwater hierarchical surface structures

Interfacial flow is involved in varieties of natural phenomena and plays important roles in industrial applications. Boundary slippage, usually realized by underwater superhydrophobicity, provides a promising method to regulate interfacial flow and even complex bulk fluid transport by controlling the development of boundary layers and changing the near-wall flow structures. In this talk, a systematic study is presented on the stability and flow control of slip boundary with hierarchical surface structures. Basic physical laws underlying the dynamic evolution of the metastable states are revealed, enabling the prediction of plastron longevity and the realization of ultimate stable state both in closed and open systems. Upon the realization of slip boundary, in a confined microfluidics, three-dimensional backflow over liquid-gas interface is discovered, which is demonstrated to be caused by the interfacial tension gradient along the liquid-gas interface. In a turbulent boundary layer flow, slip boundary is implemented to substantially reduce drag. In a separation flow, hierarchical surface structures are demonstrated to be able to effectively control the flow separation. The current work paves the way for practical applications of Navier-slip boundary in flow control.