Experimental investigation of the effect of using sound absorbing walls in reducing wind tunnel background noise

In the present study the aeroacoustic characteristics of an aerodynamic open circuit wind tunnel is experimentally investigated by furnishing its test section by noise absorbing panels. The objective is to evaluate the effectiveness of sound absorbing walls in reducing the wind tunnel background noise and to investigate the effect of its various parameters such as the thickness of sound absorbing materials on the background noise levels. The results showed that the presence of standing waves across the test section considerably increases the background noise levels for the frequencies higher than about 750 Hz. Using sound absorbing panels at the upstream of the test section improves the acoustic performance of the wind tunnel at mid to high-frequencies while increases the background noise at low-frequencies. The acoustic performance of the wind tunnel is improved at middle frequency range of 150-400 Hz by increasing the sound absorbing materials thickness. The existence of the air gap behind the sound absorbing materials results in a slight improvement in the wind tunnel's aeroacoustic performance at frequencies lower than 300 Hz. Finally, the results showed that using sound transmitting stretched fabric instead of sound absorbing materials results in a significant reduction of the background noise at all frequency range