United States Department of Transportation
i
Investigation of Stable Atmospheric Stratification Effect on the Dynamics of Descending Vortex Pairs
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1979-02-01
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[PDF-4.32 MB]
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Abstract:The physics of vortex flows in stratified fluids is studied with the objective of determining the influence of stable stratification on the descent of aircraft vortex pairs. Vortex rings descending into linear and discontinuous density stratifications are investigated experimentally and simulated numerically. The computer code used for this is based on a second-order closure turbulence model of the Reynolds stress equations in axisymmetric coordinates. Verification of the code is provided by the agreement found between the measured and calculated results. The two-dimensional version of the code is then used to simulate a measured Boeing-747 vortex descending in stable stratification. The strength and tightness of the measured vortex cores have necessitated developedment of a new method of numerically calculating strong vortex flows. The comparison of measured with calculated descent velocity, descent distance, swirl velocity, and circulation in the vortex is in agreement. It is concluded that turbulence effects must be accounted for in the study of aircraft vortex behavior. It is found that unaleviated vortices remain strong during descent, that the vortices stop descending due to a diffuse region of countersign vorticity outboard and above the cores, and that core separation does not primarily control descent.
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Content Notes:Introduction, Description of the vortex-ring experiment, Vortex-ring numerical calculation technique, Comparison of numerical results with vortex-ring experimental data, Comparison of two-dimensional wake calculations with full-scale flight data, Discussion and conclusions, Appendix
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