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    • Henry Weller's avatar
      Solvers: Added support for extrapolated pressure boundary conditions · fc2ce737
      Henry Weller authored
      The boundary conditions of HbyA are now constrained by the new "constrainHbyA"
      function which applies the velocity boundary values for patches for which the
      velocity cannot be modified by assignment and pressure extrapolation is
      not specified via the new
      "fixedFluxExtrapolatedPressureFvPatchScalarField".
      
      The new function "constrainPressure" sets the pressure gradient
      appropriately for "fixedFluxPressureFvPatchScalarField" and
      "fixedFluxExtrapolatedPressureFvPatchScalarField" boundary conditions to
      ensure the evaluated flux corresponds to the known velocity values at
      the boundary.
      
      The "fixedFluxPressureFvPatchScalarField" boundary condition operates
      exactly as before, ensuring the correct flux at fixed-flux boundaries by
      compensating for the body forces (gravity in particular) with the
      pressure gradient.
      
      The new "fixedFluxExtrapolatedPressureFvPatchScalarField" boundary
      condition may be used for cases with or without body-forces to set the
      pressure gradient to compensate not only for the body-force but also the
      extrapolated "HbyA" which provides a second-order boundary condition for
      pressure.  This is useful for a range a problems including impinging
      flow, extrapolated inlet conditions with body-forces or for highly
      viscous flows, pressure-induced separation etc.  To test this boundary
      condition at walls in the motorBike tutorial case set
      
          lowerWall
          {
              type            fixedFluxExtrapolatedPressure;
          }
      
          motorBikeGroup
          {
              type            fixedFluxExtrapolatedPressure;
          }
      
      Currently the new extrapolated pressure boundary condition is supported
      for all incompressible and sub-sonic compressible solvers except those
      providing implicit and tensorial porosity support.  The approach will be
      extended to cover these solvers and options in the future.
      
      Note: the extrapolated pressure boundary condition is experimental and
      requires further testing to assess the range of applicability,
      stability, accuracy etc.
      
      Henry G. Weller
      CFD Direct Ltd.
      fc2ce737
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