Direct numerical simulations of bubble—particle collisions in homogeneous isotropic turbulence*

Bubble--particle collisions in turbulence are key to engineering processes. However, the behaviour of suspended species in turbulent flow fields are intricate and sometimes counter-intuitive, making it difficult to predict the collision rate. For example, bubbles and particles segregate as they preferentially concentrate in different flow regions. While this effect is expected to reduce the effective inter-species collision rate, enhanced relative velocities due to opposite responses to fluid accelerations may counteract this phenomenon. This study aims to unravel how these potentially competing effects influence the collision rate of bubbles and particles in turbulence. We perform simulations using the point-particle approach to cover a range of the relevant parameters, such as the Stokes number and the Taylor Reynolds number. Our results suggest existing models in the literature do not capture the collision rate in the tested parameter range accurately. This highlights the need for models that more truthfully capture the underlying physics.