On the Lamb vector and the hydrodynamic charge
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This work is an attempt to test the concept of the hydrodynamic charge (analogous to the electric charge in electromagnetism) in the simple case of a coherent structure such as the Burgers vortex. We provide experimental measurements of both the so-called Lamb vector and its divergence (the charge) by two-dimensional particles images velocimetry. In addition, we perform a Helmholtz–Hodge decomposition of the Lamb vector in order to explore its topological features. We compare the charge with the well-known Q-criterion in order to assess its interest in detecting and characterizing coherent structure. Usefulness of this concept in studies of vortex dynamics is demonstrated.
KeywordsVortex Vorticity Particle Image Velocimetry Coherent Structure Vortex Core
Two of us (Sh. S. and V. S.) are grateful to E. Segre for providing us a multi-pass correlation algorithm and for his help in software support. This work is partially supported by grants from Israel Science Foundation, Binational US–Israel Foundation, and by the Minerva Centre for Nonlinear Physics of Complex Systems. G.R. was financially supported by a grant “post-doc CNRS” (S.P.M. section 02) during his post-doctoral stay in Nice. A.W. was supported by DFG grant SCHE 663/3-7.
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