A TIME-DOMAIN IMPLEMENTATION OF SURFACE ACOUSTIC-IMPEDANCE CONDITION WITH AND WITHOUT FLOW

The impedance condition in computational aeroacoustic applications is required in order to model acoustically treated walls. The application of this condition in time-domain methods, however, is extremely diffi cult because of the convolutions involved. In this paper, a time-domai n method is developed which overcomes the computational difficulties a ssociated with these convolutions. This method builds on the z-transfo rm from control and signal processing theory and the z-domain model of the impedance. The idea of using the z-domain operations originates f rom the computational electromagnetics community. When the impedance i s expressed in the z-domain with a rational function, the inverse z-tr ansform of the impedance condition results in only infinite impulse re sponse type, digital, recursive filter operations. These operations, u nlike convolutions, require only limited past-time knowledge of the ac oustic pressures and velocities on the surface. Examples of one-and tw o-dimensional problems with and without how indicate that the method p romises success in aeroacoustic applications.