A detailed experimental program was carried out specifically to generate data to improve flow modeling of relaminarization on swept leading edges under high-lift conditions. This is, to the authors' knowledge, the first time some key features of relaminarization and subsequent retransition on swept wings have been documented under controlled wind-tunnel conditions. Virtually all flow conditions with R > 250 (R = Reynolds number characterizing the attachment-line contamination) (about eight test cases) showed strong evidence of relaminarization at the wind-tunnel chord Reynolds number of 1.3x106. Relaminarization is accompanied by a certain reduction in shear-stress fluctuation levels depending on the acceleration history and maximum values of the local streamwise acceleration parameter Ks attained. The results on wing A (7301 airfoil-flap geometry, swept at 45 deg) have shown a spectacular decrease in the intermittency to values less than 0.2, which is caused by the large acceleration leading to maximum values of Ks of about 9x106. On wing B (NLR 7301 airfoil-flap geometry, modified near the leading edge with a larger nose radius, swept at 60 deg), the decrease in levels was relatively less (0.70), consistent with lower maximum values of Ks. In all the relaminarized flows, retransition of the (relaminarized) boundary layer was triggered by the presence of a laminar-separation bubble, which occurred just downstream of the peak suction location on the wing. The present data set (at a chord Reynolds number of 1.3x106) suggests that relaminarization at a swept leading edge can occur for maximum values of Ks greater than about 3x106. Flight Reynolds numbers are often associated with appreciably larger maximum values of Ks (8-10x106 and therefore may often be expected to result in relaminarization. The present results and those obtained in flight on a Boeing 737- 100 aircraft indicate that Ks is a useful parameter for correlating the occurrence of relaminarization on swept leading edges; but Ks would have to be in excess of about 6x106 to result in relatively low intermittency in the relaminarized boundary layer. For these flows, separation bubbles following the relaminarization are well correlated with separation bubbles in more pristine laminar boundary layers; the bubble length can be estimated based on the transition Reynolds number. Based on the present work, the following guidelines emerge from the point of view of flow modeling: For given wing and flow conditions, if the value of Ks exceeds, say 3x106, then relaminarization of the mean flow with moderate values of intermittency is likely. In such cases, it is meaningful to run laminar boundary-layer calculations from the attachment line (although the attachment line is turbulent) for the wing upper surface and trigger transition in the calculation across the laminar separation bubble or at the beginning of the adverse pressure gradient following the suction peak. The preceding suggestion presumes that retransition is not caused by crossflow instabilities, which should of course be verified.


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    Title :

    Relaminarization on swept leading edges under high-lift conditions


    Additional title:

    Relaminarisierung der Grenzschicht an der Vorderkante von Pfeilflügeln mit hohem Auftrieb


    Contributors:
    Viswanath, P.R. (author) / Mukund, R. (author) / Narasimha, R. (author) / Crouch, J.D. (author)

    Published in:

    AIAA Journal (online) ; 44 , 11 ; 2621-2629


    Publication date :

    2006


    Size :

    9 Seiten, 14 Bilder, 1 Tabelle, 25 Quellen




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English




    RELAMINARIZATION ON SWEPT LEADING EDGES UNDER HIGH-LIFT CONDITIONS

    Viswanath, P. R. / Mukund, R. / Narasimha, R. et al. | British Library Conference Proceedings | 2004


    Relaminarization on Swept Leading Edges Under High-Lift Conditions

    Viswanath, Peruvemba / Mukund, R / Narasimha, Roddam et al. | AIAA | 2004


    Relaminarization on Swept Leading Edges Under High-Lift Conditions

    P Viswanath / R Mukund / R Narasimha et al. | AIAA | 2006



    Leading-edge transition and relaminarization phenomena on a subsonic high-lift system

    Van Dam, C. P. / Vijgen, P. M. H. W. / Yip, L. P. et al. | NTRS | 1993