Verification and Application of Time-domain Impedance Boundary Conditions in Combined CFD and CAA Simulations
In computational fluid dynamic (CFD) and computational aeroacoustics (CAA) simulations, the wall surface is normally treated as a purely reflective wall. However, some surface treatments are usually applied in experiments. Thus, the results obtained by the simulation and experiment are sometimes not comparable. In the aeroacoustics community, impedance is a quantity to characterize the properties of an acoustically treated surface. i.e. reflectivity and absorption. One of the major numerical challenges in CAA simulations is to define acoustically well-posed boundary conditions. Basically, the impedance boundary condition is a frequency-domain boundary condition. However, CFD and CAA simulations are time-domain computations, which means the frequency-domain impedance boundary condition cannot be applied in simulations. Therefore, several methods, including the three-parameter model, the z-transform method, and the reflection coefficient model, were developed.