The pressurePIDControlInletVelocity is a velocity boundary condition that tries to generate an inlet velocity that maintains a specified pressure drop between two face zones downstream. The zones should fully span a duct through which all the inlet flow passes.

An incompressible, lossless analysis of the flow between the inlet and the two face-zones is performed. An ideal inlet velocity is thereby calculated from the user-specified pressure drop. This analysis can include the transient effect of the inlet velocity change. In this case, a shape factor is included to represent non-linearity in the duct cross section.

The average pressure drop between the two face zones is measured. The same incompressible, lossless analysis is performed using this pressure drop. The difference between the two computed velocities is considered as an error. The ideal inlet is modified so as to drive this error to zero. This is accomplished by means of a PID control algorithm, for which non-dimensional gains are specified by the user.

The shape factor takes a value of 0 for a linear change in cross sectional area between the two face zones. A value of 1 represents a step change in area at the mid-point between the zones. A smooth cubic or cosine profile between two zones with zero divergence is typically represented by a factor of between 0.2 and 0.25.


The condition requires entries in both the boundary and field files.

Boundary file

    type            patch;

Field file

    // Mandatory entries
    type                pressurePIDControlInletVelocity;
    upstream            <word>;
    downstream          <word>;
    deltaP              <scalar>;
    P                   <scalar>;
    I                   <scalar>;
    D                   <scalar>;

    // Optional entries
    shapeFactor         <scalar>;
    p                   <word>;
    phi                 <word>;
    rho                 <word>;
    error               <scalar>;
    errorIntegral       <scalar>;

    // Inherited entries


Property Description Type Required Default
type Type name: pressurePIDControlInletVelocity word yes -
upstream Name of the upstream face zone word yes -
downstream Name of the downstream face zone word yes -
deltaP Desired pressure difference between upstream and downstream scalar yes -
P Proportional gain scalar yes -
I Integral gain scalar yes -
D Derivative gain scalar yes -
shapeFactor Nozzle shape factor scalar no 0.0
phi Name of flux field word no phi
rho Name of density field word no rho
error Error scalar no 0.0
errorIntegral Error integral wrt time scalar no 0.0

The inherited entries are elaborated in:

Further information


  • N/A

Source code:



  • Introduced in version v3.0+