fluid Fluid

Fluids are represented as continuous fields with local properties governed by the Navier-Stokes equation. Each point along the field, defined here as a lattice, is characterized by a set of kinematic properties (pressure, velocity, etc.) and physical properties (density, rheology, etc.). Fluid motion follows a Eulerian specification, unlike particle motion which uses the Lagrangian concept of individual particle dynamics. As such, fluid properties are only defined at distinct lattice positions across the simulation domain. The resolution of the lattice is governed by the simulation resolution.

Fluids in M-Star CFD are characterized by two key specifications: the configuration and the rheology. The fluid configuration describes the number of fluid phases considered in the model. The fluid rheology is a constitutive relationship that defines the local fluid viscosity.

Fluid Configurations

  • Single Phase: A single fluid with no interface. This is the most common fluid configuration. Appropriate for modeling filled pipes/vessels with no sloshing or interfacial mixing.

  • Free Surface: A single fluid with a dynamic interface. Appropriate for modeling sloshing, filling, and driving simulations.

  • Immiscible Two Fluid: Two fluids and the dynamic interface between the fluids, which is modeled explicitly. Appropriate for two-fluid mixing, dispersion processes, and bubble break-up simulations.

  • Background Fluid: A set of background fluid properties with no fluid dynamics. Appropriate for particle laden systems with one-way coupling.

  • No Fluid: No fluid is considered and no fluid properties are specified. Appropriate for conduction heat transfer systems where fluid mechanics are not pertinent.

Fluid Rheology

  • Newtonian Fluid: A fluid with a constant and uniform viscosity.

  • Power-law Fluid: Local fluid viscosity is calculated from the local shear rate using a user-defined flow consistency index, flow behavior index, and yield stress.

  • Carreau Fluid: Local fluid viscosity is calculated from the local shear rate using a user-defined characteristic time, power index, and infinite/zero share rate viscosities.

  • Cross Fluid: Local fluid viscosity is calculated from the local shear rate using a user-defined rate constant, time constant, and infinite/zero share rate viscosities.

  • Bingham Plastic Fluid: A viscoelastic fluid with a user-defined yield-stress and viscosity.

  • Custom Fluid: A user-defined expression for the local fluid viscosity.