AM10

The Aeroacoustics of Elastic Structures

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 Obiettivo del progetto (Objective)

'The proposed research combines knowledge in two major disciplines in aeronautical sciences: aeroacoustics and aeroelasticity. While each of the disciplines has been the subject of extensive studies for more than half a century, the combination of the two, particularly in the context of thin-structure aeromechanics, supplies a new set of challenging problems that need to be addressed. The project will develop a theoretical scheme for studying the combined effects of flow unsteadiness (incident gust or localized turbulence) and external forcing (boundary actuation) on the aeroelastic and aeroacoustic behaviors of elastic structures. At first, the dynamical problem will be formulated and studied. Then, the dynamical description will serve as an effective 'source term' for the evaluation of the acoustic field. The formulation of the aeroacoustic problem will be based on a compact-body acoustic analogy, thus avoiding the traditional difficulty in obtaining the weak acoustic far field from direct simulations. The results are expected to shed light on the mechanisms coupling between the motion and sound of thin elastic structures, and to lead to the development of novel elasto-acoustic noise-control methodologies. These are highly desirable in various applications, including the development of 'green' noise-control systems for the reduction of trailing edge noise, the monitoring of the acoustic signature of flapping-wing micro-unmanned-aerial-vehicles (MUAVs), and the analysis of natural phenomena such as insect-flight sound. The objectives of the project are in line with ongoing efforts in the European Community to develop new techniques for the design of noise reduction systems in both civil and military applications.'

Introduzione (Teaser)

EU-funded scientists are aiming to shed new light into the aeroacoustic and aeroelastic behaviour of elastic structures in the aeronautics sector.

Descrizione progetto (Article)

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 EU-funded project 'The aeroacoustics of elastic structures' (AM10) to determine the impact of elasticity on the acoustic field of the system resulting from fluid-structure interactions. To be more specific, they are developing a theoretical scheme for studying the acoustic radiation resulting from flow unsteadiness and mechanical actuation. Structures studied include flexible-airfoil and elastic-cylinder configurations.

To begin with, researchers analysed the dynamical near-field sound response of the fluid-structure interaction system using suitable flow and mechanical actuation models. The system was found to normally amplify actuations containing one of its natural frequencies. This clearly demonstrates the importance of considering the structure's elastic degrees of freedom when describing fluid-structure interactions. This resonance mechanism should also have a major effect on far-field sound propagation.

To calculate the far-field sound propagation component, the project is using a novel acoustic analogy with sound sources that include fluid vorticity and structure motion. Analyses have shown that fluid vorticity is the main acoustic radiation component. Nevertheless, structure motion in the form of leading-edge pitching and heaving, is the indirect cause of acoustic radiation. This is because vorticity is generated by the body trailing edge motion.

Project findings are expected to shed light on the coupling mechanisms between motion and sound of elastic structures. The resulting novel elasto-acoustic noise-control methodologies could find applications in civil and military aviation systems.