Abstract
The evolution of an initially-turbulent wake behind a bluff-body is a useful model for a broad range of flows involving the decay of a local turbulent patch in a stable background density gradient. Such flows encompass many atmospheric and oceanic applications, the latter including also the evolution of wakes of submerged bodies.
In the case of the towed-sphere wake, the initially-turbulent motions evolve into a chain of alternate-signed vortices that remain close to the centreline. The characteristic, well-ordered wake is generated regardless of the relative magnitude of the background density gradient (provided it is nonzero), because eventually, buoyancy forces dominate the decaying flow. The wake geometry appears to be very stable, and the basic pattern has a very long persistence time.
When the large scale structures are generated in the presence of weaker background turbulence, then a vortex pattern detection problem inevitably arises as a requirement for identifying the foreground motions and their possible interactions with the ambient. The space of independent parameter combinations is now large, but experiments can help to identify relevant dimensionless groups.
Although the horizontal motions are most well-known, and are the easiest to visualize, the structure in the vertical direction is also important in determining the dynamics, stability and longevity of the wake in both quiet and noisy environments.
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Spedding, G.R. (1999). Vortex Wakes in Stably-Stratified Fluids. In: Sørensen, J.N., Hopfinger, E.J., Aubry, N. (eds) IUTAM Symposium on Simulation and Identification of Organized Structures in Flows. Fluid Mechanics and Its Applications, vol 52. Springer, Dordrecht. https://doi.org/10.1007/978-94-011-4601-2_15
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DOI: https://doi.org/10.1007/978-94-011-4601-2_15
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