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.
Some experimental results on spiral vortex breakdown
Einige Versuchsergebnisse zum wendelförmigen Wirbelaufplatzen
Zeitschrift für Flugwissenschaften und Weltraumforschung ; 19 , 6 ; 359-365
1995
7 Seiten, 13 Bilder, 18 Quellen
Aufsatz (Zeitschrift)
Englisch
Wirbelströmung , geometrische Form , Strömungsvorgang , Druckerhöhung , Vergleichsmessung , Wasserkanal , Gasblase , Wasserstoff , sichtbare Strömung , Tragflügel , Laser-Doppler-Anemometer , Übergangsbereich , Simulationsmodell , Position , Wirbelkern , Integralgleichung , Rückströmung , Staupunkt , Strömungsgeschwindigkeitsmessung , Geschwindigkeitsverteilung , Druckgradient
Some experimental results on spiral vortex breakdown.
Online Contents | 1995
|Experimental and Numerical Results on Spiral Vortex Breakdown
British Library Conference Proceedings | 1996
|An experimental investigation of spiral vortex breakdown
AIAA | 1994
|Onset of the spiral mode of vortex breakdown
AIAA | 1997
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