Describe different approaches for modeling multiphase flows in CFD.

Multiphase flow modeling depends on phase fractions and interface resolution needs: (1) Euler-Euler: treats both phases as interpenetrating continua with separate conservation equations; includes Volume of Fluid (VOF) for immiscible fluids with sharp interface tracking, Mixture model for homogeneous flows, and Eulerian model for dispersed phases. (2) Euler-Lagrange: continuous phase solved on Eulerian grid while dispersed phase (particles, droplets, bubbles) tracked as Lagrangian particles; suitable for dilute dispersions (<10% volume fraction). (3) Interface tracking: Level-Set and VOF for accurate surface tension and interface dynamics. Model selection depends on coupling strength, phase fraction, size distribution, and computational resources. Applications: fluidized beds, sprays, boiling, sedimentation.