Soft Matter and Complex Systems Seminar

1) Air boundary layer on rotating disk may support controlled droplet levitation resulting in their high mobility. We show it is possible to levitate a droplet in both laminar and turbulent regimes, provided one properly sets initial condition, i.e. initial distance between moving surface that generates boundary layer and the droplet. We explore the influence of cross-flow instability and associated spiral vortices on the levitation phenomenon. We characterize the role of disk velocity on the droplet shape and levitation distance from the moving surface.

2) We consider the propagation of water waves in a waveguide with a surface-piercing circular cylinder. A plane wave interacting with the cylinder leads to a Fano resonance resulting in strong scattering with a large reflection coefficient. Using a smoothly varying bathymetry whose shape is optimized, we show both numerically and experimentally that broadband and robust backscattering reduction can be obtained below the first cutoff frequency.