LMP Seminar: Small Non-Spherical Particles Falling in Air: an Uncharted Territory

Almost all solid particles in the atmosphere—including ice crystals, pollen, volcanic ash, dust, aerosols, and microplastics—are non-spherical. Only when particles are extremely small (less than about 10 µm) and have specific shapes, such as spheroids or slender bodies, can their behavior in the air be accurately described. However, a large fraction of atmospheric particles are larger, and their behavior remains poorly understood. We have conducted experimental measurements and three-dimensional particle-resolved simulations of variously shaped ellipsoidal particles falling in air. These particles had a particle-fluid density ratio near 1000 and a particle Reynolds number of about 5 in quiescent air. We discovered that, due to their high inertia, these particles exhibit a complex falling trajectory and oscillatory behavior, which were previously unknown. These new findings have significant implications for their transport, collision frequency, and interaction with solar radiation.