Patent ID: 8714003

Claim:
A wind tunnel comprising: a closed section for aeroacoustic measurements, wherein inner walls of the closed section comprise a sound-absorbing coating which, from the inner walls, comprises: a first cavity defined between the inner walls and a first microperforated panel, the first cavity having a thickness D 1 in a range of 20≦D 1 ≦50 mm filled with a fibrous material with a flow resistance R in a range of 10≦R≦50 kRayl/m; the first microperforated panel having a thickness t 1 in a range of 0.25≦t 1 ≦0.75 mm and with a perforation percentage p 1 in a range of 15≦p 1 ≦30%; a second cavity defined between the first microperforated panel and a second microperforated panel, the second cavity having a thickness D 2 in a range of 10≦D 2 ≦30 mm; the second microperforated panel having a thickness t 2 in a range of 0.25≦t 2 ≦0.75 mm and with a perforation percentage p 2 in a range of 15%≦p 2 ≦30%.