Low acoustic noise and turbulence (LANT) wind-tunnel at USP-EESC

Abstract

© 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This paper introduces the new low-turbulence, low-background-acoustic-noise, closed-circuit wind-tunnel of the University of Sao Paulo, Sao Carlos School of Engineering (USP-EESC), containing an overview of design criteria and facility specifications. The designed wind-tunnel includes features to improve the flow quality through the reduction of turbulent and acoustic disturbances. Such features suit the wind-tunnel for pure aerodynamic characterization as well as for aeroacoustic experiments. A long settling chamber, a hexagonal honeycomb and five nylon screens were included to minimize flow disturbances in the test-section. Turning vanes are filled with insulation, aiming at reduction and absorption of background acoustic noise, whereas dense acoustic foam was installed on the corners walls, floor and ceiling to provide secondary means of background acoustic noise suppression. The facility has a closed test-section of 1×1 m2cross-sectional area and 3 m length. A purposely designed short contraction with a ratio of 7:1 was used. A variable-speed motor of 110 kW powers a 16-bladed axial fan containing 13 stators and the expected top freestream speed in the test-section is 60 m/s. Preliminary results include the test-section flow characterization, regarding turbulence level and background acoustic noise measurements. An approximately 0.108% turbulence level was obtained for 20 m/s freestream speed, with the measurements conducted with constant temperature hot-wire anemometer circuit and the signal bandpass filtered between 5 and 10,000 Hz. The acoustic characterization was performed with a 112-microphone phased array and data were post-processed with in-house beamforming codes.

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