OpenFOAM® v1806: New boundary conditions

OpenFOAM® v1806: New boundary conditions

29/06/2018

New outlet Mach number condition

This pressure boundary condition maintains a (subsonic) Mach number at an outlet patch by dynamically adjusting the static outlet pressure. It makes it possible, for example, to simulate the flow in a pre-turbine engine exhaust manifold without resolving details of the flow inside the turbine.

Choked flow

The formulation is derived from a simple model of the gas flow through a nozzle with fixed geometry. The nozzle flow is assumed to be quasi-steady, 1D, isentropic and compressible.

The accompanying boundary conditions for velocity should be pressureInletOutletVelocity

Source code
$FOAM_SRC/TurbulenceModels/compressible/turbulentFluidThermoModels/derivedFvPatchFields/outletMachNumberPressure
Examples
$FOAM_TUTORIALS/combustion/reactingFoam/RAS/chokedNozzle

New swirl fan velocity condition

This condition can be used in combination with a cyclic pressure jump condition to simulate a fan. The existing fan pressure jump condition implements the fan-normal momentum gain. This new velocity jump condition adds a swirl component.

The velocity jump can be specified in two ways:

  • constant velocity
  • constant swirl

In the first mode the velocity is calculated as follows:

pict\relax \special {t4ht=

Where Δp  \relax \special {t4ht= represents the current pressure drop across the cyclic, reff   \relax \special {t4ht= is the effective radius, fan
   eff   \relax \special {t4ht= is the fan efficiency coefficient and rpm  \relax \special {t4ht= the speed of the fan (in revolutions-per-minute).

In the second mode the inner (ri  \relax \special {t4ht=) and outer (ro  \relax \special {t4ht=) radii are provided instead of reff   \relax \special {t4ht=, where for r > ri  \relax \special {t4ht= and r < ro  \relax \special {t4ht= the velocity is given as:

pict\relax \special {t4ht=

where r  \relax \special {t4ht= is the distance from a patch face to the fan axis. Outside ri  \relax \special {t4ht= and ro  \relax \special {t4ht=, U  = 0
  t  \relax \special {t4ht=. The input for this mode is:

useRealRadius   true;
rInner          0.005;
rOuter          0.01;
origin          (0.0453 0.06 0);

If the origin  \relax \special {t4ht= is not provided the centroid of the patch is taken.

Source code
$FOAM_SRC/finiteVolume/fields/fvPatchFields/derived/swirlFanVelocity

New wave modelling: irregular waves

A new irregular wave model based on the frequency-direction spectrum has been added to the suite of available wave models.

The wave height is set according to the equation:

pict\relax \special {t4ht=

[Picture]

[Picture]

Source code
$FOAM_SRC/waveModels/waveGenerationModels/derived/irregularMultiDirectional
Examples
$FOAM_TUTORIALS/multiphase/interFoam/laminar/waveExampleIrregularMultiDirection
Attribution
These boundary conditions were supplied by the Environmental Hydraulics Institute IHCantabria
Integration
The code has been updated by OpenCFD and added to the $FOAM_SRC/waveModels library available to the interFoam family of solvers