Multiphase flows: Rich physics, challenging theory, and big simulations

Hydrodynamic interactions in multiphase flows result in rich multiscale physics, such as clustering and pseudoturbulence, with important practical implications. Alternative theoretical formulations that overcome current challenges, and particle-resolved direct numerical simulations to build accurate closure models for unclosed terms that arise in these statistical theories, are outlined as promising future research directions. The study provides a perspective on the importance of integrating theoretical, modeling, computational, and experimental efforts at different scales.