The vortex wake hazard has been of concern to the aerospace and air transport industries for more than 30 years and particularly since large aircrafts such as the Boeing 747 came into service. The spacing between aircrafts under instrument flight rules on final approach, as imposed by the International Civil Aviation Organisation, is the limiting factor on airport capacity. It has been suggested that in the absence of such restrictions, an increase in capacity of as much as 10-20% could be achieved. Naturally occurring instabilities such as the long wave Crow instability are one of the mechanisms that can bring about the break-up of aircraft wake vortex pairs. Encouraging the early onset of such instabilities by active or passive means offers the possibility of accelerating wake break-up and dissipation with favourable consequences in terms of safe aircraft separation and airport capacity. This paper describes an experimental investigation of the evolution of the Crow instability in a counter rotating vortex pair perturbed by a pulsed air sheet. Flow measurements were made using two-dimensional particle image velocimetry and two methods devised to detect wake break-up from the two-dimensional data. Pulsed excitation at a wavelength within the range amplified by the Crow instability resulted in wake break-up and the formation of vortex rings at a downstream distance reduced by up to 37% compared to the baseline case. For excitation at a wavelength outside the excited range early break-up was also observed but the extent of the accelerated break-up was reduced as the amplitude of the excitation was increased.


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    Title :

    Natural and forced evolution of a counter rotating vortex pair


    Additional title:

    Natürlicher und erzwungener Verlauf eines gegenläufig rotierenden Wirbelpaares


    Contributors:
    Bearman, P. (author) / Heyes, A. (author) / Lear, C. (author) / Smith, D. (author)

    Published in:

    Experiments in Fluids ; 40 , 1 ; 98-105


    Publication date :

    2006


    Size :

    8 Seiten, 6 Bilder, 2 Tabellen, 19 Quellen




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English




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