Impedance boundary conditions for time-domain computational aeroacoustics methods

A time-domain impedance condition method has been developed for computational aeroacoustics applications. The basis for this method is the standard impedance condition stated in the frequency domain as the particle displacement continuity equation. The development of the time-domain impedance condition follows the relations among the frequency, z-, and discrete-time domains and a rational function representation of the impedance in the z-domain. The resultant impedance condition is finite, infinite-impulse-response type, digital filter operations in the time-domain, which is suitable to CAA methods. This paper describes the present approach and discusses the time-domain numerical simulations of the NASA Langley flow-impedance tube with a constant depth ceramic tubular liner. Excellent agreement is shown with experimental data at various frequencies and flow conditions.