Picturing pervasive but puzzling particle clusters

Sandstorms, cloud formation, asthma inhalers, blood—these all have something in common: they’re particle-laden flows. This widespread type of flow consists of solid particles or liquid droplets suspended in a transporting fluid. Particle-laden flows are observed in both natural and human-made systems, including applications such as drug delivery, bio-weapons, industrial processes and conventional combustion systems.

Particle clustering reduces the performance of some particle-laden flow systems, but researchers don’t know enough about this phenomenon yet to limit its effect. To learn more about particle clustering, Lau et al. employed high-speed imaging to measure the location, velocity and concentration of micrometer-sized particles in a turbulent jet coming from a long pipe.

They generated the first four-dimensional experimental measurements of clustered particle structure. The measurements revealed that the particle clusters are rope shaped and usually positioned obliquely to the bulk flow, and form inside the pipe close to the pipe wall. The particles are also coherent, which means they retain their properties, such as size and shape, for a long time. This suggests that the clusters will continue moving downstream for long distances, a relevant finding for industrial processes in which a cluster could form upstream and then move through the system.

Author Timothy Lau said that this work advances understanding of the complex dynamics of particle clustering, which can potentially lead to a step change in our fundamental understanding of particle-laden systems. However, there’s still more to learn about particle-laden flows. Next, the authors want to conduct a similar experiment but add heating and use different flow geometries to more closely match industrial processes.

Source: “Resolving the three-dimensional structure of particles that are aerodynamically clustered by a turbulent flow,” by Timothy C. W. Lau, Jonathan H. Frank, and Graham J. Nathan, Physics of Fluids (2019). The article can be accessed at https://doi.org/10.1063/1.5110323 .