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  1. Apr 23, 2016
    • Henry Weller's avatar
      plenumPressureFvPatchScalarField: New plenum pressure boundary condition · 88561eea
      Henry Weller authored
      This condition creates a zero-dimensional model of an enclosed volume of
      gas upstream of the inlet. The pressure that the boundary condition
      exerts on the inlet boundary is dependent on the thermodynamic state of
      the upstream volume.  The upstream plenum density and temperature are
      time-stepped along with the rest of the simulation, and momentum is
      neglected. The plenum is supplied with a user specified mass flow and
      temperature.
      
      The result is a boundary condition which blends between a pressure inlet
      condition condition and a fixed mass flow. The smaller the plenum
      volume, the quicker the pressure responds to a deviation from the supply
      mass flow, and the closer the model approximates a fixed mass flow. As
      the plenum size increases, the model becomes more similar to a specified
      pressure.
      
      The expansion from the plenum to the inlet boundary is controlled by an
      area ratio and a discharge coefficient. The area ratio can be used to
      represent further acceleration between a sub-grid blockage such as fins.
      The discharge coefficient represents a fractional deviation from an
      ideal expansion process.
      
      This condition is useful for simulating unsteady internal flow problems
      for which both a mass flow boundary is unrealistic, and a pressure
      boundary is susceptible to flow reversal. It was developed for use in
      simulating confined combustion.
      
      tutorials/compressible/rhoPimpleFoam/laminar/helmholtzResonance:
          helmholtz resonance tutorial case for plenum pressure boundary
      
      This development was contributed by Will Bainbridge
      88561eea
    • Henry Weller's avatar
      fireFoam: Added optional hydrostatic initialization of the pressure and density · 673e0d17
      Henry Weller authored
      Also added the new prghTotalHydrostaticPressure p_rgh BC which uses the
      hydrostatic pressure field as the reference state for the far-field
      which provides much more accurate entrainment is large open domains
      typical of many fire simulations.
      
      The hydrostatic field solution is controlled by the optional entries in
      the fvSolution.PIMPLE dictionary, e.g.
      
          hydrostaticInitialization yes;
          nHydrostaticCorrectors 5;
      
      and the solver must also be specified for the hydrostatic p_rgh field
      ph_rgh e.g.
      
          ph_rgh
          {
              $p_rgh;
          }
      
      Suitable boundary conditions for ph_rgh cannot always be derived from
      those for p_rgh and so the ph_rgh is read to provide them.
      
      To avoid accuracy issues with IO, restart and post-processing the p_rgh
      and ph_rgh the option to specify a suitable reference pressure is
      provided via the optional pRef file in the constant directory, e.g.
      
          dimensions      [1 -1 -2 0 0 0 0];
          value           101325;
      
      which is used in the relationship between p_rgh and p:
      
          p = p_rgh + rho*gh + pRef;
      
      Note that if pRef is specified all pressure BC specifications in the
      p_rgh and ph_rgh files are relative to the reference to avoid round-off
      errors.
      
      For examples of suitable BCs for p_rgh and ph_rgh for a range of
      fireFoam cases please study the tutorials in
      tutorials/combustion/fireFoam/les which have all been updated.
      
      Henry G. Weller
      CFD Direct Ltd.
      673e0d17
    • Henry Weller's avatar
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