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Initial Condition

The InitialCondition block specifies the solver’s starting flow field.

You must provide one expression per primitive variable for the selected physics model.
For example, for the ideal_gas model the required primitives are P, U, V, W, and T.
For other models, refer to the Physics Models page for the complete list of required primitives.

Structure​

InitialCondition
{
    P = "<expression>"
    T = "<expression>"
    U = "<expression>"
    V = "<expression>"
    W = "<expression>"
}

All primitive-variable expressions are mandatory. The solver will fail to start if any are missing or cannot be evaluated.

Expressions​

  • Coordinates: x, y, z give the global Cartesian position of each cell center.
  • Distance field: dist provides a geometric distance field (currently unsigned; its exact definition may change in future versions).
  • Dictionary parameters: Any value defined in the dictionary can be referenced, e.g. Qinf::pinf or M0.
  • Math functions: The full math expression parser is available (basic arithmetic, powers, trigonometric and hyperbolic functions, sqrt, log, exp, etc.).
  • Units: All quantities are in the solver’s global unit system.

Expressions are evaluated at each cell center in the global frame.
If you assign a global velocity such as U=100.0, V=0.0, W=0.0, subdomains that are rotated will see this velocity rotated into their local orientation.

Examples​

1. Boundary-layer–type initial condition​

InitialCondition
{
    P = "Qinf::pinf"
    T = "Qinf::Tinf"
    U = "Qinf::uinf * tanh(dist/0.02)"
    V = "Qinf::vinf * tanh(dist/0.02)"
    W = "Qinf::winf * tanh(dist/0.02)"
}

This configuration initializes a flow that is nearly quiescent close to immersed surfaces and smoothly transitions to freestream values over a thin region (here 0.02 solver units).
It is useful when the initial field should approximately satisfy a no-slip or low-speed condition near walls, such as in external aerodynamics with boundary-layer formation. This approach can be a useful robustness measure in high-speed simulations.

2. Uniform freestream​

InitialCondition
{
    P = "Qinf::pinf"
    T = "Qinf::Tinf"
    U = "Qinf::uinf"
    V = "Qinf::vinf"
    W = "Qinf::winf"
}

This initializes a perfectly uniform freestream everywhere, suitable for flows without immersed surfaces or when no near-wall damping is desired.