Computational results are presented for transient vortex breakdown above a delta wing subject to a pitch-and-hold maneuver to high angle of attack. The flows are simulated by solving the full three-dimensional Navier-Stokes equations on a moving grid using the implicit Beam-Warming algorithm. An assessment of the effects of numerical resolution and favorable comparison with experimental data suggest the computational approach captures the basic dynamics of the onset and initial stages of transient breakdown. The pressure gradient along the vortex axis is found to play a dominant role in the initiation of breakdown. A description of the three-dimensional instantaneous structure of the flowfield is provided for the first time using critical-point theory. The reversed-flow region in the vortex core is associated with pairs of opposite spiral/saddle critical points. At its onset, the vortex breakdown is fairly axisymmetric; however, as it proceeds upstream and a stronger jump takes place along the axis, asymmetric effects become important and culminate in the formation of a bubble-type breakdown. This bubble structure is open and contains within itself a pair of stagnation points that are diametrically opposed and that rotate in the same sense as the upstream swirling flow. These critical points suggest the existence of azimuthal disturbances in the breakdown region. The bubble sectional topology is also found in agreement with recent experimental measurements.
Onset of vortex breakdown above a pitching delta wing
Beginn des Wirbelzusammenbruchs über einem Deltaflügel bei Vergrößerung des Anstellwinkels
AIAA Journal ; 32 , 8 ; 1568-1575
1994
8 Seiten, 14 Bilder, 46 Quellen
Article (Journal)
English
Onset of vortex breakdown above a pitching delta wing
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