Energy analysis and discretization of nonlinear impedance boundary conditions for the time-domain linearized Euler equations

Highlights: • Admissibility of impedance boundary conditions is rigorously defined. • TDIBCs are shown to be best enforced through the scattering operator. • Validation of the analysis in a nonlinear impedance tube. • TDIBCs are deduced from the oscillatory-diffusive representation of physical models. • Application to two linear flow ducts. Time-domain impedance boundary conditions (TDIBCs) can be enforced using the impedance, the admittance, or the scattering operator. This article demonstrates the computational advantage of the last, even for nonlinear TDIBCs, with the linearized Euler equations. This is achieved by a systematic semi-discrete energy analysis of the weak enforcement of a generic nonlinear TDIBC in a discontinuous Galerkin finite element method. In particular, the analysis highlights that the sole definition of a discrete model is not enough to fully define a TDIBC. To support the analysis, an elementary physical nonlinear scattering operator is derived and its computational properties are investigated in an impedance tube. Then, the derivation of time-delayed broadband TDIBCs from physical reflection coefficient models is carried out for single degree of freedom acoustical liners. A high-order discretization of the derived time-local formulation, which consists in composing a set of ordinary differential equations with a transport equation, is applied to two flow ducts.