Convected field analysis of flat panels response to turbulent boundary layer induced excitation

Abstract

Abstract The main objective of the work was the development of a procedure allowing the study of the effect of fluid loading over the vibration response of a plate driven by a TBL excitation field. The reasons for such analysis are concerned with the limitations of the main numerical codes available on the market when dealing with the subject, and the need for the extension of the existing predictive capabilities of deterministic methodologies, when facing with the stochastic pressure distribution over a flat plate. The availability of such specific tools is judged as mandatory for the improvement and/or better classification of the design criteria for the enhancement of modern aircraft acoustic comfort. After recalling and rearranging the theoretical concepts applicable to the aeroelastic behaviour of flat plates, to be used as a reference for the validation process, two different numerical approaches are herein presented. A first procedure was elaborated by using a vibro-acoustic coupling formulation, in which an appropriate convected field Green function was employed, and by relying on the modal information provided by FEM based numerical tools. An alternative numerical procedure was developed by employing the aeroelastic module of NASTRAN commercial code, in which the baffle condition was sought and obtained throughout proper adaptation and tuning of the input parameters. Both procedures were built up to be applicable to any baffled flat plate, including sandwich and composite panels. A two-ways validation process, based on the assumption of point forces loading conditions, was carried out by introducing the fluid back reaction contribution associated to the convected field in the frequency response solution of the first procedure. The evidence of the convected field effect on the panel response was highlighted, mainly associated to a reduction of the investigated panel stiffness properties due to aeroelastic interactions. A preliminary study on stochastic loading conditions response was performed by considering a “rain on the roof” excitation, while the final investigation, focused on the TBL induced excitation field, confirmed the potentiality of the proposed procedures in dealing with the subject. The relevance of a correct estimation of the convected field contribution on the plate response in terms of both qualitative and quantitative aspects is pointed out, specially for what concerns the attenuation of a plate vibration energy.