Experimental study of noise reduction design for a fully acoustically lined, low-turbulence, low-noise engineering wind tunnel

To improve the measurement accuracy and reduce background noise in aerodynamic acoustic wind tunnels, this study focuses on the noise reduction design of the 4 m × 3 m fully acoustically lined, low-turbulence, low-noise large-scale aeroacoustic wind tunnel (BHAW) at Beihang University. It investigated noise reduction measures for the fan section, tunnel body, acoustic guide vanes, and collector section, with experimental validation conducted in the D5 aeroacoustic wind tunnel at Beihang University. Drawing on the DNW-LLF wind tunnel and findings from the D5 experiments, an acoustic treatment was developed for BHAW, ensuring minimal impact on turbulence intensity in the test section. The outer wall of the fan section was treated with micro-perforated panels and sound-absorbing foam (stainless steel micro-perforated panels with a 2% perforation rate and 600 mm thick sound-absorbing foam) to reduce fan rotational noise, particularly in the low-to-mid frequency range. Inside the tunnel, perforated panels combined with 200 mm thick sound-absorbing foam were used to attenuate mid-to-high frequency noise. To further reduce friction-induced noise in the first diffuser channel, a 3 mm thick acoustically transparent felt was applied over the perforated panels. The four corner guide vanes adopt a dual-arc configuration with double-sided acoustic treatment. In the collector section, a perforated panel with sound-absorbing foam was installed at an 8° contraction angle. Additionally, the exterior of the collector was wrapped with acoustically transparent felt to mitigate airflow impact noise. Wind tunnel measurements indicated that the turbulence intensity in the model region of the open test section ranged from 0.07% to 0.095% under various flow velocities, while in the closed test section it ranged from 0.041% to 0.046% (less than 0.05% for the design specification), meaning the turbulence intensity in the open section was approximately 1.7 to 2.1 times that of the closed section. At the design speed of 80 m/s, the far-field noise level of the open test section was measured to be between 74.0 and 74.4 dB(A) (less than 75 dB(A) for the design specification). Compared with the RTRI wind tunnel, the BHAW tunnel achieved approximately 7 dB noise reduction in the low-frequency range, exhibited comparable noise levels in the high-frequency range, and had an overall sound pressure level that was 0.6～1.0 dB lower than that of RTRI.