Phase-resolved LDV measurements (Laser Doppler Velocimetry) were made of the three-dimensional velocity field and tip vortex structure in the wake of a hovering rotor. A one-bladed rotor was used to generate a single nominally helical vortex, and the structure of this vortex was analyzed at various ages after formation. The present measurements have quantified the tangential velocity profile, axial velocity deficit in the vortex, along with the viscous core size and its growth with age. The following conclusions have been drawn from the study: 1) The tip vortex was found to obtain its maximum strength downstream of the blade, that is within 90-degrees of rotation. The average circulation decreased after this point. 2) The peak tangential velocity in the tip vortex was determined to be about 1/3 of the rotor tip speed. The corresponding viscous core size was estimated to be 3 % chord at formation, growing to 15 % of blade chord after two rotor revolutions. 3) The tangential velocity distribution in the tip vortex was found to agree with the n=2 case of the general series of desingularized profiles proposed by Vatistas, with the Lamb-Oseen model and, at older wake ages, with the n=1 case (Kaufmann or Scully). 4) The tip vortex core was found to grow with wake age, the growth rate increasing with the square-root of age until the first blade passage. An analysis of the growth rate during this period resulted in an eddy viscosity coefficient that was ten-times the laminar value. 5) The axial velocity deficiency in the vortex core was found to exhibit a bell-shaped distribution, but diminished rapidly in magnitude with wake age becoming negligibly small within one rotor revolution. 6) The first blade passage event was found to cause changes to the growth/diffusion of the tip vortex. Thereafter, the core size diminished, but then began to grow again during the later part of the second rotor revolution. This observation should be investigated in more detail since it may have implications for modeling the aeroacoustic effects of BVI (blade vortex interaction) in the rotor environment.


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    Titel :

    Measurements of rotor tip vortices using three-component laser Doppler velocimetry


    Weitere Titelangaben:

    Messung der Rotorspitzenwirbel mit einem Dreikomponenten-Laser-Doppler-Geschwindigkeitsmeßverfahren


    Beteiligte:
    Leishman, J.G. (Autor:in) / Baker, A. (Autor:in) / Coyne, A. (Autor:in)

    Erschienen in:

    Erscheinungsdatum :

    1996


    Format / Umfang :

    12 Seiten, 15 Bilder, 2 Tabellen, 60 Quellen




    Medientyp :

    Aufsatz (Zeitschrift)


    Format :

    Print


    Sprache :

    Englisch





    Measurements of Rotor Tip Vortices Using Three-Component Laser Doppler Velocimetry

    Leishman, J. G. / Baker, A. / Coyne, A. et al. | British Library Conference Proceedings | 1995