Acoustic design evaluation of an anechoic wind tunnel

This paper presents the acoustic design of a new anechoic wind tunnel and its evaluation through simulations and experiments. An experimental method is proposed to estimate, in situ, the individual transmission losses of acoustically treated guide vanes and diffuser, without flow, from measured impulse responses. Results are compared with finite element simulations, showing comparable 1/3-octave transmission losses from 1 to 5 kHz; however, the simulations are highly sensitive to the material properties in the impedance model. The total background noise in the wind tunnel test section is estimated from transmission losses and compared with measurements at 70 m/s flow. Below 200 Hz, agreement is good; at higher frequencies, measured noise is up to 30 dB higher due to turbulent boundary layer and Kevlar roughness noise. An airfoil noise benchmark is also presented, showing a single-microphone signal-to-noise ratio up to 8 dB below 1–2 kHz.