flow.yaml

The file flow.yaml is required to prescribe the characteristics of the fluid, as well as the initial and boundary conditions of the flow.

Here, we provide an example of such a file followed by an explanation of its content.

Note: text is case-sensitive.

Example

The following file could be used to simulate external flows over bodies:

- nu: 0.025
  initialVelocity: [1.0, 0.0]
  initialPerturbation: [0.0, 0.0]
  boundaryConditions:
    - location: xMinus
      u: [DIRICHLET, 1.0]
      v: [DIRICHLET, 0.0]
    - location: xPlus
      u: [CONVECTIVE, 1.0]
      v: [CONVECTIVE, 0.0]
    - location: yMinus
      u: [DIRICHLET, 1.0]
      v: [DIRICHLET, 0.0]
    - location: yPlus
      u: [DIRICHLET, 1.0]
      v: [DIRICHLET, 0.0]

File options

• nu: (mandatory) the kinematic viscosity of the fluid. Can be any positive number.
• initialVelocity: (mandatory) this is the initial velocity of the fluid set throughout the computational domain. For 2d flows, two components are required within square brackets, separated by a comma.
• initialPerturbation: (optional, default: [0.0, 0.0]) initial sinusoidal perturbation in the x- and y- directions.
• boundaryConditions: (mandatory) specifies the velocity boundary condition on each edge of the domain. These are listed in subsections, which need to be indented using two spaces.
  • Each boundary edge is represented by its relative location on the Cartesian axes - xMinus, xPlus, yMinus and yPlus.
  • For each component of velocity (u and v) on the boundary, you can specify the type of boundary condition and an associated value. There are four types currently available: DIRICHLET, NEUMANN, and CONVECTIVE.
  • The number following the type of boundary conditions is interpreted as:
    • for a DIRICHLET type: the value of that component of velocity at the boundary.
    • for a NEUMANN type: the value of the normal derivative of that component at the boundary.
    • for a CONVECTIVE type: the speed at which the fluid is convected out of the boundary. The values for the components normal to the boundary are ignored.
  • Specific types of boundary conditions can be created by using a suitable combination of the above. For example, a slip boundary condition on the yMinus boundary would use homogeneous Neumann for u and zero Dirichlet for v.
• In the above 2d example, the kinematic viscosity of the fluid is set to 0.025. xMinus is the inlet, yMinus and yPlus are the outer boundaries and xPlus represents the outlet. Dirichlet boundary conditions are used on each edge of the computational domain (velocity fixed to (1.0, 0.0)), except at the outlet where a convective condition is used (the flow is convected in the x-direction with speed 1.0). The initial velocity field is set to (1.0, 0.0) everywhere in the domain.