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What is Energy Helicity Index mean? This page is about helicity in fluid dynamics. For helicity of magnetic fields, see magnetic helicity. For helicity in particle physics, see helicity (particle physics).
In fluid dynamics, helicity is, under appropriate conditions, an invariant of the Euler equations of fluid flow, having a topological interpretation as a measure of linkage and/or knottedness of vortex lines in the flow. This was first proved by Jean-Jacques Moreau in 1961 and Moffatt derived it in 1969 without the knowledge of Moreau's paper. This helicity invariant is an extension of Woltjer's theorem for magnetic helicity.
Let u ( x , t ) {\displaystyle \mathbf {u} (x,t)} be the velocity field and ∇ × u {\displaystyle \nabla \times \mathbf {u} } the corresponding vorticity field. Under the following three conditions, the vortex lines are transported with (or 'frozen in') the flow: (i) the fluid is inviscid; (ii) either the flow is incompressible ( ∇ ⋅ u = 0 {\displaystyle \nabla \cdot \mathbf {u} =0} ), or it is compressible with a barotropic relation p = p ( ρ ) {\displaystyle p=p(\rho )} between pressure p {\displaystyle p} and density ρ {\displaystyle \rho } ; and (iii) any body forces acting on the fluid are conservative. Under these conditions, any closed surface S {\displaystyle S} on which n ⋅ ( ∇ × u ) = 0 {\displaystyle n\cdot (\nabla \times \mathbf {u} )=0} reference
Posted on 21 Dec 2024, this text provides information on Miscellaneous in Governmental related to Governmental. Please note that while accuracy is prioritized, the data presented might not be entirely correct or up-to-date. This information is offered for general knowledge and informational purposes only, and should not be considered as a substitute for professional advice.
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