Publication Date:
1973-11-06
Description:
We have made computational experiments to study the stability and long-time evolution of two-dimensional wakes. We have used the VORTEX code, a finite-difference realization of two-dimensional motions in incompressible inviscid fluids. In the first experiment an initial shear-unstable triangular velocity profile evolves into a non-homogeneous, finite-area, asymmetric vortex array and like-signed regions attract and fuse (or coalesce). Enhanced transport across the profile is due to ‘capture’ and convection of small-scale vortex regions by larger opposite-signed vortex regions. In the following experiments we study the stability of an asymmetric four-vortex finite-area system corresponding to a von Kármán street of point vortices. Here the critical parameter is b/a, the initial transverse-to-longitudinal separation ratio of vortex centres. At [formula omitted] the four-vortex system is stable and we observe that large-area vortex regions develop elliptical (m = 2), triangular (m = 3), etc. surface modes owing to mutual interactions. At b/a = 0 the measured growth rate is smaller than that for the corresponding von Kármán system and at b/a = 0·6 the measured growth rate is larger. At b/a = 0 one vortex undergoes fission in the high-shear field produced by two nearest-neighbour opposite-signed vortex regions. Heuristic comparisons are made with the two-dimensional tunnel experiments of Taneda and others. © 1973, Cambridge University Press. All rights reserved.
Print ISSN:
0022-1120
Electronic ISSN:
1469-7645
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
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