Assessing airfoil tonal noise reduction potential using flow-induced vibration of an elastic panel at various angles of attack

In this paper the potential of airfoil tonal noise reduction using flow-induced vibration of an elastic panel mounted on NACA 0012 airfoil at low Reynolds number of 5 X 10^4 and angle of attack of 3 by perturbation evolution method is studied. The panel is designed to resonate in conjunction with airfoil boundary layer instabilities to absorb the flow energy while sustaining its vibrational displacement. Initially, direct aeroacoustic simulation is carried out to analyze the flow characteristics of rigid airfoil. The location and structural parameters of elastic panel are carefully evaluated to achieve the desired resonance condition. Subsequently, perturbation evolution method is utilized to study the aeroacoustic-structural interaction between the flow field and elastic panel and analyze the effectiveness of designed panel in airfoil tonal noise reduction. For the selected flow condition, numerical results reveal an average tonal noise reduction of 3.5 dB as compared to 2.1 dB for elastic panel designed for angle of attack of 5°. The enhancement in panel effectiveness at lower angle of attack is attributed to the presence of longer separation bubble which enables the panel to absorb much more energy from boundary layer instabilities within the region of separated flow on the suction surface of airfoil.