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The A2 (AeroAcoustic) wind tunnel is one of the main test facilities of the Engineering Fluid Dynamics (EFD) Group of the UT. It is also known as the 'silent' wind-tunnel because it walls has a special treatment meant to absorb practically all the noise produced by the air flow, which can reach up to 240 km/h. Thanks to that, the tunnel is suited for measuring simultaneously the aerodynamic and the noise of applications related to aviation, drones, green energy production and home appliances.
Description of the Wind Tunnel facility
A schematic layout of the silent Wind Tunnel at the University of Twente is shown above. The system is powered by a 130 kW electrical motor connected to two large radial turbines (1). Due to heat created by friction at high velocities, the air is cooled by a water-cooled heat exchanger (2). To avoid propagation of the noise generated by the turbines and tubes of the heat exchanger to the anechoic chamber, acoustic dampening panels are installed (3). Upstream of the test section, the flow is made laminar when it passes through the settling chamber (5) and a number of anti-turbulence grids (6). Subsequently, the air flows through a contraction (7) to eventually reach a closed test section (8) and exit the nozzle into the anechoic chamber (9). The jet stream is recollected at (10) and a closed system is formed. Additional acoustic damping is applied to the collector (11) in order to reduce reflections and noise generated by the corner vanes (4).
The test section dimensions are 0.7 m x 0.9 m. Measurements can both be performed in the closed test section as well as in the open jet.
Anechoic chamber
The open jet test section of the wind tunnel is located inside of a large anechoic chamber which has dimensions 6 × 6 × 4 m. The current walls of the chamber have acoustic foam insulation which is being held in place by metal perforated plates as shown in Figure 2. This provides an acoustic environment for broadband noise of approximately 160 Hz and higher. The floor of the anechoic chamber is treated with acoustic foam and has a support of metal grids enabling people to walk inside the chamber and providing sufficient support for experimental setups. Two different types of nozzles can be currently deployed inside the anechoic chamber. One with dimensions 700 × 900 mm (height × width) and another with opening dimensions of 351 × 450 mm. The latter can be used to obtain higher flow velocities and is designed for aeroacoustic purposes.
Left is the anechoic chamber before renovation whereas the right shows the renovated anechoic chamber.