Multiphase flow is a term which refers to the flow and interaction of several phases within the same system where distinct interfaces exist between the phases. Multiphase flows can be dispersed flows (such as bubbly, droplet, and particle flows) or stratified flows (such as free surface flows, or annular film flow in pipes)
STAR-CCM+ provides five distinct models to meet the requirements of these two categories of flow:
The Lagrangian Multiphase model: this model solves the equation of motion for representative parcels of the dispersed phase as they pass through the system. It is intended for systems that consist mainly of a single continuous phase carrying a relatively small volume of discrete particles, droplets, or bubbles. It is suited where the interaction of the discrete phase with physical boundaries is important.
The Multiphase Segregated Flow model: this model is more generally known as the Eulerian Multiphase model in the literature, but that term has been given a wider significance in STAR-CCM+. The Multiphase Segregated Fluid model solves conservation equations for mass, momentum, and energy for each phase. Phase interaction models are provided to define the influence exerted by one phase upon another across the interfacial area between them.
The Volume of Fluid (VOF) model: this model is provided for systems containing two or more immiscible fluid phases, where each phase constitutes a large structure within the system (such as typical free surface flows). This approach captures the movement of the interface between the fluid phases, and is often used for marine applications.
The Discrete Element Model (DEM): this model is an extension of the Lagrangian Multiphase model, but where individual particles are modeled rather than representative parcels, and where inter-particle contact forces are explicitly accounted for.
The Fluid Film model: this model predicts the dynamic characteristics of wall films using boundary layer approximations and assumed velocity and temperature profiles across the depth of the film. Film transport is predicted using thin shells that lie across the surface of solid walls on which the film is formed.