Reference / Input deck / model / boundary conditions / outflow

outflow

type: outflow

Pressure-based outflow boundary condition.

zonesrequired reference kind mass flow rate reference radiusrequiredstatic pressure ratioadvanced mass flow ratioadvanced

zonesrequired

list of zone ids·required

Mesh zone ids this boundary condition applies to.

Used in3DBump

Guidance: Choosing boundary conditions →

reference

str·not set by default

Reference condition the outflow ratios are taken relative to.

Used in3DBump

kind

not set by default

How the outflow state is set.

Options

Value	What it does
pressure	The exit pressure is set from a static pressure ratio relative to 'reference'.
massflow	Scales the local velocity so the integrated mass flow across all zones matches the requested value.
radial pressure gradient	As 'pressure', but the static pressure ratio holds at 'reference radius' rather than uniformly.

Demonstration: what reference/model/boundary-conditions/outflow#kind does From the pipe case

Outlet mass flow against cycle in a turbulent pipe, for a mass-flow outlet and a static-pressure outlet, with the imposed mass flow marked

Both runs use the same mesh, Menter SST with wall functions and a total-pressure inlet; only the outlet changes. The pressure ratio is not tuned to the 10 kg/s target: a pressure outlet sets the pressure, and the flow follows.

setting reference/model/boundary-conditions/outflow#kindvalues massflow, pressurecase pipe

Used in3DBump

Guidance: Choosing boundary conditions →

static pressure ratioadvancedpressure / radial pressure gradient only

float·default 1

Exit static pressure as a ratio of the reference static pressure.

Used in3DBump

mass flow ratemassflow only

float·not set by default·> 0 kg/s·'mass flow rate' is required when solver.solver settings.type is 'compressible' and mass flow ratio is unset; give either 'mass flow rate' or 'mass flow ratio', not both

Mass flow rate through the outlet zones, as a magnitude: the inflow or outflow type sets the direction. The mesh must be in metres.

mass flow ratioadvancedmassflow only

float·not set by default·> 0·'mass flow ratio' only applies when reference is set

Outlet mass flow divided by the reference mass flux, rho_out U_out A_out / (rho_ref U_ref), with A_out in mesh units; a magnitude, since the inflow or outflow type sets the direction.

reference radiusrequiredradial pressure gradient only

float·required·in m

Radius at which the static pressure ratio is defined