Two anechoic wind tunnels have been installed in the Acoustics Centre of the LMFA at École Centrale de Lyon since the early 1980s. They were the result of joining open-section wind tunnels and a large-scale soundproof room.
General presentation
The supersonic anechoic wind tunnel is continuously fed with air (airflow 1 kg/s) by a 350 kW centrifugal compressor chilled by a water and air heater. It is used to study the high-subsonic and supersonic aspects of jet engines whose nozzles have a traditional diameter of 20-60 mm. Flow velocity can reach Mach 1.55 for a convergent nozzle with a diameter of 38 mm.
The subsonic anechoic wind tunnel is continuously fed with air (airflow max. 20 kg/s) by an 800 kW centrifugal ventilator. The maximum length of the test section is 8 m. Flow velocity can reach Mach 0.5 for a 300x400 mm exit section and Ma = 0.8 for a 200 mm circular section.
These two wind tunnels lead to an anechoic test chamber. With the wind tunnels at full power, the residual noise level in the anechoic chamber remains under 25 dBA.
Application examples
Investigations undertaken in the Acoustic Centre’s wind tunnels cover aeronautics (subsonic and supersonic jet engine noise, fan and airframe noise, high-lift device and landing gear noise), components or models of land vehicles or even metrological developments in aeroacoustics (optical methods, innovative cavity pressure sensors, source localisation methods and antennae).
The wind tunnels can be combined to use the supersonic wind tunnel’s flow as the primary airflow for a coaxial jet, while the secondary jet is obtained by the subsonic wind tunnel. This type of assembly facilitates the study of the flight effect on the sound properties of supersonic jet engines.