New advances in aircraft aeroacoustics
Research into acoustic radiation resulting from fluid-structure interactions was previously focused mainly on analysing rigid structures. Furthermore, only the effect of external unsteady flows on the near- and far-field sound propagation has been studied. Scientists initiated the AM10 (The aeroacoustics of elastic structures) project to determine the impact of elasticity on the acoustic field of the system resulting from fluid-structure interactions. Specifically, they developed a theoretical scheme for studying the acoustic radiation resulting from flow unsteadiness and mechanical actuation. Structures studied include flexible airfoil and elastic cylinder configurations. Work mainly focused on analysing the system dynamical near- and far-field responses. The near-field calculation was based on the theory of incompressible potential flows at high Reynolds numbers coupled with a motion equation describing the structure dynamics. The incoming flow unsteadiness was represented through a distribution of upstream fluid vorticity, and mechanical actuation was modelled through leading edge excitations to imitate flapping flight conditions. The system was found to normally amplify actuations containing one of its natural frequencies. This clearly demonstrates the importance of considering the structure elastic degrees of freedom when describing fluid-structure interactions. That resonance mechanism should also have a major effect on far-field sound propagation. Formulation of the aeroacoustic problem was based on a compact body acoustic analogy, thus overcoming the difficulty in obtaining the weak acoustic far field from direct simulations. Results helped researchers shed further light on coupling mechanisms between motion and sound of thin elastic structures, providing the basis for new elasto-acoustic noise control methodologies. These are highly desirable in various applications, including the development of noise control systems for reducing trailing edge noise; monitoring of the acoustic response of flapping wing micro unmanned aerial vehicles; and analysis of natural phenomena such as insect flight sound.
Keywords
Aircraft, aeroacoustics, fluid-structure interactions, elastic structures, noise control
