Multiphysics#

This subsection defines the multiphysics interface of Lethe and enables the solution of Auxiliary Physics in addition to traditional fluid dynamics simulations.

subsection multiphysics
  set fluid dynamics                  = true

  # Thermal physics
  set heat transfer                   = false
  set viscous dissipation             = false
  set thermal buoyancy force          = false

  # Tracer
  set tracer                          = false

  # Multiphase flow
  # Conservative Level-Set method
  set cls                             = false

  # Cahn-Hilliard equations
  set cahn hilliard                   = false

  # Electromagnetics
  set electromagnetics                = false
  set microwave heating               = false
end

  • fluid dynamics: controls if the fluid dynamics are solved. This is true by default and can be turned to false to enable calculation of an auxiliary physic only. When appropriate, this can decrease drastically the computation time.

Tip

fluid dynamics = false and heat transfer = true enables to solve the heat transfer equations with a large time step, with the fluid velocity being defined from the Initial Conditions.

  • heat transfer: controls if the heat transfer auxiliary physics are solved. This is an advection-diffusion equation.

    When set heat transfer = true, these optional parameters can be used:

    • viscous dissipation: controls if the viscous dissipation is taken into account in the heat transfer equation.

    • thermal buoyancy force: controls if the thermal buoyancy force is taken into account in the Navier-Stokes equations. The thermal buoyancy force is calculated using the Boussinesq approximation.

See also

The heat transfer solver is used in the example Warming up a Viscous Fluid.

  • The tracer parameter adds a passive tracer auxiliary physics. This is an advection-diffusion equation.

See also

The tracer solver is used in the example Tracer in Static Mixer.

See also

The CLS solver is used in the example Dam-Break.

  • The cahn hilliard parameter enables multiphase flow simulations, with two fluids separated by a free surface, using the Cahn-Hilliard equations.

    See Cahn-Hilliard for advanced Cahn-Hilliard parameters, Initial Conditions for the definition of the Cahn-Hilliard conditions and Physical properties - two phase simulations for the definition of the physical properties of both fluids.

  • The electromagnetics parameter enables the solution of the time-harmonic Maxwell equations.

    See Time-Harmonic Maxwell for advanced time-harmonic Maxwell parameters, Boundary Conditions - Multiphysics for the definition of the electromagnetic boundary conditions and Physical Properties for the definition of the physical properties of the medium.

    When set heat transfer = true, in addition to the electromagnetic solver, the optional parameter microwave heating can be used to enable the calculation of the heat source due to the electromagnetic fields. If set microwave heating = true, the following heat source is calculated and added to the right-hand side of the heat transfer equation:

    \[Q_\text{em}=-\nabla \cdot \overline{\mathbf{S}} = \frac{1}{2}\sigma|\mathbf{E}|^2 + \frac{1}{2}\omega\varepsilon_0\varepsilon_\mathrm{im}|\mathbf{E}|^2 + \frac{1}{2}\omega\mu_0\mu_\mathrm{im}|\mathbf{H}|^2,\]

    where \(\overline{\mathbf{S}}\) is the time-averaged Poynting vector, \(\sigma\) is the conductivity, \(\varepsilon_0\) is the vacuum permittivity, \(\varepsilon_\mathrm{im}\) is the imaginary part of the relative permittivity, \(\mu_0\) is the vacuum permeability, \(\mu_\mathrm{im}\) is the imaginary part of the relative permeability, and \(\mathbf{E}\) and \(\mathbf{H}\) are the electric and magnetic fields, respectively.

See also

The electromagnetic solver can be used on its own, an example is available in Waveguide.