New guidelines for ISO 9053 based on CFD simulations of the static airflow resistivity of a perforated solid

The acoustic absorption coefficient of the acoustic absorbers is directly impacted by the airflow resistivity. The ISO 9053 explains the measurement procedure and specify the size and mounting of specimens, and the flow velocities. The main constraint of the standard is to maintain a stable linear flow so that the resistance is independent of the velocity. Additionally, it suggests a straight cylindrical pores specimen whose airflow resistivity value can be calculated theoretically. Any other specifications about the calibration specimen design are given. As the flow dynamics inside the perforated low porosity solid behave nonlinearly, it is important to integrate further guidelines in the design of the calibration specimens and measurements. This work presents CFD calculations results using OpenFoam, on the flow resistivity of a cylindrical solid containing a single perforation. The airflow velocity was determined based on the Reynolds number at the pore, which was varied between 0.33 to 2000. Different calibration specimens were tested by varying the length and the perforation diameter. An excellent agreement was observed between CFD and experimental data with an error of 5 %. The results show that the second-order extrapolation of specific resistance should be limited to Reynolds numbers equal to 500.