Complete measurement of helicity and its dynamics in vortex tubes

• Autores: Martin W. Scheeler, Wim M. van Rees, Hridesh Kedia
• Localización: Science, ISSN 0036-8075, Vol. 357, Nº 6250, 2017, págs. 487-491
• Idioma: inglés
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• Resumen

  • Helicity, a topological measure of the intertwining of vortices in a fluid flow, is a conserved quantity in inviscid fluids but can be dissipated by viscosity in real flows. Despite its relevance across a range of flows, helicity in real fluids remains poorly understood because the entire quantity is challenging to measure. We measured the total helicity of thin-core vortex tubes in water. For helical vortices that are stretched or compressed by a second vortex, we found conservation of total helicity. For an isolated helical vortex, we observed evolution toward and maintenance of a constant helicity state after the dissipation of twist helicity by viscosity. Our results show that helicity can remain constant even in a viscous fluid and provide an improved basis for understanding and manipulating helicity in real flows.