Abstract

In various settings in nature and industry, certain types of substrates promote increased fluid flow through sliding. Large-scale examples include the flow of ice sheets, such as that of Greenland and Antarctica, over bedrock lubricated by a layer of subglacial till. Small-scale examples include the lotus leaf and fabricated hydrophobic surfaces, which are of use for various industrial applications, from microfluidics and flow delivery in the pharmaceutical and biotechnology industries, to drag reduction applications in the aeronautics and maritime industries, for example. What makes these types of surfaces slippery is their microstructure, which cushions the flow from below, promoting slip. However, it remains a challenge to design substrates that are slippery enough for appreciable sliding to be seen for certain types of flows – particularly large-scale viscous flows. This talk goes through the development of a theoretical and experimental framework for generating slip underneath viscous fluids on the large scale while minimising the effects of unwanted fluid-mechanical instabilities. We build into this framework the freedom to adjust slip, as desired, and capture it by a macroscopic sliding law. We also demonstrate examples of environmental and industrial phenomena, and related experiments, where such basal sliding is important.