The present paper reveals the design concept as well as results of experimental investigations, which were conducted in the early design stage of the planned AUDI Aero-Acoustic Wind Tunnel. This low-noise open-jet facility, featuring a nozzle exit area of 11 m2 and a top speed of approximately 60 m/s, enables aerodynamic as well as acoustic testing of both, full-scale and model-scale ground vehicles. Ground simulation is provided by means of a moving-belt rig. The surrounding plenum is designed as a semi-anechoic chamber to simulate acoustic free-field conditions around the vehicle. Fan noise will be attenuated below the noise level of the open jet.
The work reported herein, comprises 1/8-scale pilot-tunnel experiments of aerodynamic and acoustic configurations which were carried out at the University of Darmstadt. One of the primary goals was minimisation of collector induced broad-band noise and avoidance of discrete frequency open-jet excitations due to shear layer impingement on the collector. Furthermore, the pressure distribution along the empty test section and its pressure-loss had to be optimized. To match these requirements, a relatively long test section and a large collector appeared to be especially advantageous. Extensive experimental investigations were conducted to optimize the collector's aerodynamic as well as acoustic performance. The results suggested a test-section length of 10 m (=3.1 hydraulic nozzle diameters) and a funnel-type collector featuring a collector-to-nozzle area of about 3.7. Tests with models in the test section showed that even with a blockage ratio of 18 %, reliable aerodynamic data can be obtained. It was found that pressure distributions along comparison models, taken in a large tunnel at low blockage (1.9 %), could be reproduced satisfactorily, if the model was positioned at about 40 % of the test-section length.