Interaction of flows with slender structures and liquid-infused surfaces
Tid: Fr 2022-05-20 kl 10.15
Plats: Kollegiesalen (Room nr: 4301), Brinellvägen 8
Ämnesområde: Teknisk mekanik
Respondent: Johan Sundin , Linné Flow Center, FLOW, Teknisk mekanik
Opponent: Associate Professor Daniel Chung, University of Melbourne
Handledare: Shervin Bagheri, Linné Flow Center, FLOW, SeRC - Swedish e-Science Research Centre, Teknisk mekanik
Surface textures and protrusions can be used to control or gain information about a flow. We investigate the solid-flow interaction of filamentous structures and liquid-infused surfaces (LIS). Both filamentous structures and LIS are used by organisms and can be exploited in technical applications.
Numerical simulations show that the filament resonance frequency is central to the interaction of a filament bed with turbulent flows. This frequency can be changed by varying filament mass or elasticity. Heavy filaments are only affected by slow turbulence structures and can be used to obtain information about those. Light filaments can create regions of high permeability, increasing drag. The thesis explores a sensor concept consisting of a doubly supported filament made of a soft material. The soft material makes the filament durable as it can sustain large strains.
LIS consist of a solid texture infused with a lubricant. The lubricant can decrease drag, increase heat transfer or be a protective coating. LIS with longitudinal grooves subjected to turbulent flow are investigated by numerical simulations using a volume-of-fluid (VOF) method. The capillary waves on the interfaces are more prominent for lower surface tension or wider grooves. For an inappropriately designed LIS, capillary waves can increase drag. Design criteria are constructed to avoid such waves. The VOF method is also compared to molecular dynamics simulations to assess its accuracy.
Drag degradation might occur because of surfactant traces in the flow. The surfactants adsorb onto the interfaces and produce Marangoni stresses. Surfactant-contaminated laminar flow over LIS with transverse grooves are investigated numerically and described using an analytical model. The external flow also induces recirculation of the LIS lubricant. The lubricant flow can be used to increase the surface heat flux. This mode of heat transfer can be relevant if the solid and liquid conductivities are similar, both for laminar and turbulent external flows.