Heidi Ruiz

Double-Layer Microperforated Panel/Porous Absorber as Liner for Anechoic Closing of the Test Section in Wind Tunnels

This work investigates the use of hybrid double-layer microperforated panel/porous systems as wideband absorbers for applications in the closing of the test area of wind tunnels. For such an application, the absorber should fulfil a twofold requirement: provide absorption in a frequency band ranging from 500 up to 14000 Hz, and the face in contact with the air vein must be free of porous material. The equations for calculating the absorption coefficient at normal incidence allows to predict the performance of such a system as a function of its constitutive parameters. A prototype providing average absorption of 94% in the frequency band (500, 14000) Hz is finally built and validated experimentally in both an impedance tube and a wind tunnel.

Sound absorption of single‐ and double‐layer microperforated insertion units.

Sound absorption by microperforated panels (MPPs) has received increasing attention recently as an alternative in applications with special cleanliness and health requirements. Since the hole diameter‐to‐panel thickness ratio must be close to unity, MPPs result limp, and therefore difficult to handle for practical applications. Microperforated insertion units (MIUs) were proposed recently to solve this trouble. They combine a millimetric panel with a micrometric mesh to provide an absorption curve similar to that of an MPP. The disadvantage of an MIU, as compared with an MPP, is that its performance depends on the tuning of seven parameters. Furthermore, when a double‐layer absorber is required to increase the absorption frequency band, the number of constitutive parameters to be tuned becomes the design rather arduous. Therefore, it could be attractive to know the combination of constitutive parameters, within given variation ranges, which provides the maximum mean absorption for a prescribed frequency b...