The dynamics of aircraft trailing wakes, whose large-scale structure consists mainly of two counter-rotating vortices, have been actively investigated since the early 1970s, when it became clear that the strong vortices behind heavy aircraft represent a potential hazard to others following behind due to the rolling moment and downwash they induce. This is particularly dangerous near the ground, and today wake vortex behavior is the principal factor determining the minimum separation distances for takeoff and landing, thus limiting airport capacities. With the increase of air traffic and the advent of new very large transport aircraft in the near future, the problem of understanding, predicting, and eventually controlling aircraft trailing wakes has received new interest in recent years. The short-wavelength elliptic instability of a pair of closely spaced counter-rotating vortices is analyzed using water tank experiments and direct numerical simulations. Qualitative and quantitative comparison shows excellent agreement and validates each of these complementary approaches. Both sets of results are used to give a detailed description of the instability characteristics. In the initial phase, the vortices are subject to a three-dimensional perturbation of their internal structure, with a wavelength scaling on the vortex core size and a distinct phase relationship between the two vortices. In the nonlinear evolution of the flow, the growth of the perturbations leads to the generation of secondary vortices and the breakdown of the initial pair into small-scale turbulence, accompanied by a rapid decrease of the average circulation. The growth rate of the instability is found to be higher than the one of the well-known Crow instability. The interaction between both mechanisms is also investigated, and an even faster decay of circulation is observed than for the cases where each instability acts alone. The relevance of these results for realistic aircraft trailing wakes is discussed.


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    Title :

    Elliptic instability of counter-rotating vortices: Experiment and direct numerical simulation


    Additional title:

    Elliptische Instabilität gegenläufig rotierender Wirbel: Experiment und direkte numerische Simulation


    Contributors:
    Laporte, F. (author) / Leweke, T. (author)

    Published in:

    AIAA Journal ; 40 , 12 ; 2483-2494


    Publication date :

    2002


    Size :

    12 Seiten, 15 Bilder, 38 Quellen




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English