Columnar vortices which are embedded in a flow field with increasing pressure in axial direction tend to vortex breakdown. Moderate adverse pressure gradients induce breakdown in form of a 'spiral' type at free vortices, without neighbouring surfaces. To study this phenomenon in detail, experiments were conducted in a water tunnel with a tip vortex stimulated to spiral-type breakdown. For varying pressure gradients continuously and smoothly, a special test setup was developed. The vortex center was visualized by small hydrogen bubbles. By means of flow visualization and LDV (Laser Doppler Velocimetry) measurements, the transition of the slender vortex into a spiral breakdown domain was studied . To analyze the experimental results, a simulation model was developed which permitted to reconstruct vortex structure and center position. It is shown that this type of vortex breakdown is not an abrupt structural change as the 'classical' definition proposes, but more a smooth transformation from one state to another. It is characterized by turning the vortex center into a spiral path, without an essential modification of the vortex structure, before the ordered structure is destroyed by selfinduction. Moreover can be shown that the appearance of stagnation or reversal of the axial flow, which are stated generally as secondary effects of vortex breakdown, is not an essential feature of spiral breakdown.


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    Title :

    Some experimental results on spiral vortex breakdown


    Additional title:

    Einige Versuchsergebnisse zum wendelförmigen Wirbelaufplatzen


    Contributors:


    Publication date :

    1995


    Size :

    7 Seiten, 13 Bilder, 18 Quellen



    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English




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    Cheung, K. / Jumper, E. / Nelson, R. | AIAA | 1994



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