Clustering of a particle-laden Faraday wave in microgravity

Particle-laden flows are prevalent in nature, from volcanic ash deposition over the ocean to algae blooms in lakes to microplastic debris at the surface of any body of water. Particles at the surface of these fluid flows are driven by capillary flotation and capillary immersion forces, and are entangled by the presence of gravity. A lot of work has been done to characterize the movement of these particles, either as single particles or a few at a time, over still or moving surfaces. However, isolating the capillary immersion forces can be difficult to do in a terrestrial environment. The work presented here discusses the use of the Portland State University Dryden Drop Tower to isolate immersion forces on a particle-laden parametrically excited surface wave. An open cylindrical container is externally vibrated by a mechanical wave driver, imposing parametrically excited surface waves where microparticles are dispersed. Particle tracking is performed on cases of varying wave frequencies and particle concentrations for terrestrial and microgravity conditions. Results presented are from drop tower experiments and the Portland State University Dryden drop tower, with a discussion about future work aboard the International Space Station.