Article
Time-Domain Simulation of an Anechoic Duct Termination with Mean Flow (de)
* Presenting author
Abstract:
Low-reflecting or anechoic duct terminations are essential utilities in aeroacoustic test rigs, e.g., for assessing the in-duct sound radiation of centrifugal or axial fans. These terminations usually provide a steadily widening geometry to ensure a smooth transition of the wave impedance toward the end of the finite duct. The scientific literature and the DIN 5136:2003 suggest various layouts for anechoic terminations. However, most of today's available research on anechoic duct terminations is based on experimental assessments. Considering numerical simulations on this topic could reveal further insights into the underlying physics, but comprises several challenges, e.g., modeling of the damping material and the background flow. This contribution presents a finite-element-simulation workflow for an anechoic duct termination constructed concordant to the DIN 5136:2003 norm. We employ a recently developed time-domain formulation of the Johnson-Champoux-Allard-Lafarge (JCAL) equivalent fluid model that exploits auxiliary variables to emulate the transient absorption properties of the damping material. Further, we consider a uniform background flow at various flow speeds by applying Pierce's operator to the acoustic wave equation. The time-domain simulations are verified by comparison of the computed power transmission loss and the absorption coefficient to frequency-domain simulations and acoustic reference measurements.