Particlefluid

Particlefluid refers to systems in which discrete solid particles interact with a fluid medium. In such systems, particles may be suspended in an incompressible flow, settle under gravity, or be accelerated by the fluid’s motion. The term encompasses both physical phenomena and computational approaches used to model coupled particle–fluid dynamics, including dilute suspensions and dense mixtures.

Modeling approaches for particlefluid interactions commonly employ Eulerian-Lagrangian methods, where the fluid is solved on a fixed grid and individual particles are tracked with their own equations of motion. The fluid exerts drag, buoyancy, and lift on each particle, while particles can transfer momentum back to the fluid in two-way coupling. One-way coupling neglects the feedback from particles to the fluid. Eulerian-Eulerian two-phase models treat both phases as interpenetrating continua with averaged properties, suitable for dense suspensions. Hybrid approaches, such as combining SPH (smoothed particle hydrodynamics) for fluids with discrete elements for solids, are also used.

Governing equations for particlefluid systems typically include the Navier–Stokes equations for the fluid and Newton’s second law for each particle. For a particle i, the equation of motion is m_i dv_i/dt = F_drag,i + F_buoy,i + F_gravity,i + F_other,i, where drag depends on relative velocity and Reynolds number, and buoyancy accounts for the displaced fluid. The fluid equations incorporate momentum exchange terms from particles in two-way coupling and may include turbulence models and particle dispersion terms.

Applications span sediment transport, spray and atomization, inkjet printing, aerosol dynamics, pharmaceutical aerosols, and combustion with particulate matter. Challenges include accurate drag laws across regimes, near-wall and collision effects, polydispersity, and computational cost in large systems.