Design and characterization of a multifunctional low-speed anechoic wind tunnel at HKUST

The Hong Kong University of Science and Technology (HKUST) has installed and commissioned an Ultra-quiet Noise Injection Test and Evaluation Device (UNITED). This facility is the first closed-circuit anechoic wind tunnel in Hong Kong. Calibrations and improvements have been made to improve the aerodynamic and aeroacoustic performance since its commissioning in 2016, and various experiments have been conducted in it. The test section is enclosed within a 3.2 m × 3.1 m × 2 m anechoic chamber, and it can be configured as either open-jet or closed test section. The exit plane of the contraction section has a dimension of 0.4 m × 0.4 m, and the flow speed of the test section can be varied from 10 m/s up to 70 m/s. In this paper, the major design constraints and design principles of key wind tunnel sections are described. To achieve low background noise, a silencer network is carefully designed, and a low-noise axial fan is specially designed and manufactured for the wind tunnel circuit. It is shown that the metrics of aerodynamic and aeroacoustic performances are comparable to similar facilities across the world. Representative research activities are also briefly summarized in this paper. Particularly, the measurement of trailing edge noise of a flat plate is demonstrated. The measured trailing edge noise collapses well under the classical fifth power-law scaling, suggesting the good performance of the entire measurement system.