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, for example, model a porous lining or specifying an outlet impedance. The condition is based on 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.

Enter the value of the Normal impedance Zn (SI unit: Pa·s/m). Click to select the Wall impedance at solid boundary check box if the impedance is at a wall with no normal velocity component (slip condition) for the background flow. This simplifies the equations that are solved for this boundary condition.

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