Impedance and Interior Impedance
Use the Impedance or Interior Impedance condition to specify an acoustic impedance on an exterior boundary or as a transfer impedance on an interior boundary. The impedance can be any expression and can, for example, be a function of the frequency (freq). The condition can be used to model a porous lining in a duct or specifying an outlet impedance. The condition is based on the Ingard-Myers condition, see Ref. 1 and About the Impedance Boundary Condition located in the Theory Background for the Aeroacoustics Branch section. The condition is a so-called low frequency approximation; the viscous boundary layer of the background flow is assumed infinitely thin at the impedance wall.
Impedance (Ingard-Myers)/Interior Impedance (Ingard-Myers)
Enter the value of the Normal impedance Zn (SI unit: Pa·s/m). This can be an analytical expression or data provided through an interpolation function. Click to select the Grazing flow conditions check box, if the impedance is at a boundary with no normal velocity component for the background flow, u0·n = 0. This simplifies the equations that are solved for in the boundary condition.
Constraint Settings
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box.
Excluded Edges/Points
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box. See Suppressing Constraints on Lower Dimensions for details.
For systems with a trailing edge on an airfoil or with an edge singularity between a liner and a rigid wall, the exclude edges and points functionality can be used to set up an appropriate Kutta condition. See Suppressing Constraints on Lower Dimensions.