# Boundary Conditions

# Freestream

External freestream condition. The velocity components, both at the boundaries and inside domain, are initialized according to the following equations, based on the angle of attack, and the side slip angle, :

Where Mach is specified in the freestream section of case config. Note that the velocity components on the left hand side are non-dimensional as used in Flow360 solver. Also, for flow simulations with a freestream boundary condition, flow fields will be initialized according to this boundary condition.

Optionally, an expression for each of the non-dimensional velocity components can be specified.

# parameters:

  • optional Velocity: an expression for each of non-dimensional velocity components as a function of x, y and z.

    • example: ["2 * cos(y)", "-2 * sin(x)", "0"]

# NoSlipWall

No-slip wall condition for a viscous impermeable boundary. Optionally, a tangential velocity can be representative of a moving or rotating wall.

# parameters:

  • optional Velocity: an expression for each of non-dimensional velocity components as a function of x, y and z.

    • example: ["2 * cos(y)", "-2 * sin(x)", "0"] specifies a wall rotating around the z axis at an angular velocity of 2
    • default: [0, 0, 0]

# SlipWall

Slip wall condition for an inviscid impermeable boundary. Also used for symmetry condition.

# IsothermalWall

Isothermal wall boundary condition. A static “Temperature” is specified in Kelvin. Optionally a tangential velocity can be representative of a moving or rotating wall.

# parameters:

  • Temperature: wall (static) temperature in Kelvin (K),

    • it can be expressed as a function of x, y, z.
    • example: "cos(y) * sin(x)"

  • optional Velocity: an expression for each of non-dimensional velocity components as a function of x, y and z.

    • example: ["2 * cos(y)", "-2 * sin(x)", "0"] specifies a wall rotating around the z axis at an angular velocity of 2
    • default: [0, 0, 0]

# SubsonicOutflowPressure

Subsonic outflow boundary condition, enforced through static pressure ratio. This is the target ratio of boundary static pressure to freestream static pressure.

# parameters:

  • staticPressureRatio: target ratio of boundary static pressure to freestream static pressure.

# SubsonicOutflowMach

Equivalent static pressure outflow boundary condition set via a specified subsonic Mach number. The flow is assumed to be adiabatic and isentropic. The static pressure, , is updated according to:

where is total pressure for boundary point calculated by using actual local Mach number for this point.

# parameters:

  • MachNumber: target outflow Mach number at the boundary. Must be less than 1.

# SubsonicInflow

Subsonic inflow boundary condition, enforced via total pressure ratio and total temperature ratio, for nozzle or tunnel plenum. These are the target ratios of boundary total pressure and total temperature to freestream static values. The input values can be calculated using isentropic flow relations (opens new window).

# parameters:

  • totalPressureRatio: target ratio of boundary total pressure to freestream static pressure.
  • totalTemperatureRatio: target ratio of boundary total temperature to freestream static temperature.
  • rampSteps: ramp steps for pressure and temperature ratios.
    • this is the number of pseudo-time steps during which the total pressure and the total temperature ratios are ramped up initially from 1 to the target ratios.

# MassOutflow

Outflow boundary condition via mass-flow-rate out of the simulation domain through this boundary.

# parameters:

  • massFlowRate: Mass Flow Rate

    • This is the integrated mass flow rate out of the simulation domain through this boundary, calculated as density * normal velocity * area, .
    • nondimensionalization used: the freestream density, the freestream speed of sound, and the mesh length unit:

# MassInflow

Inflow boundary condition via mass-flow-rate into the simulation domain through this boundary.

# parameters:

  • massFlowRate: Mass Flow Rate

    • This is the integrated mass flow rate into the simulation domain through this boundary, calculated as density * normal velocity * area, .
    • nondimensionalization used: the freestream density, the freestream speed of sound, and the mesh length unit:

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