An experimental investigation was carried out on an isolated rectilinear airfoil in order to survey the acoustic and aerodynamic effects of an acoustically soft coating consisting of filaments (velvet), covering the entire airfoil surface, at incidences of 0 deg, of maximum lift-to-drag ratio and of maximum lift of the uncoated airfoil. The results are summarized as follows: 1) The coating was found to reduce the A-weighted sound pressure level of noise generated by the airfoil at each incidence. The coating reduced the sound pressure level in the frequency range critical from the viewpoint of human audition, and increased it at lower and higher frequencies less significant from the aspect of A-weighting. 2) The coating increased the wall friction. This resulted in unfavorable aerodynamic effects, manifesting themselves for the most part on the suction side. The acceleration and the related depression have been moderated on the suction surface. The suction side boundary layer and consequently, the wake, have been thickened. The turbulence has been intensified in the boundary layer and in the wake. Such phenomena were more pronounced at high incidence, at which the coating caused even the separation of the suction side boundary layer, remaining still attached without coating. These effects led to unacceptably strong reduction in lift and increase in drag, being very drastic at high incidence. 3) To retain the beneficial acoustic effects but to avoid the unfavorable aerodynamic impact, further studies are necessary. This should involve coating combined with acoustically transparent plastic foil layer, various coating materials and configurations restricted to only a part of the airfoil surface, and various inlet turbulence levels. Air foils of porous or/and visco-elastic materials are also to be tested. 4) For a better understanding of noise reduction mechanisms due to coating, the former experiments shall be supplemented with turbulence spectra measurements over the blade surface and in the wake.


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    Title :

    Study of the aero-acoustic and aerodynamic effects of soft coating upon airfoil


    Contributors:


    Publication date :

    2006


    Size :

    9 Seiten, 12 Bilder, 3 Tabellen, 17 Quellen




    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




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