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Paper   IPM / Physic / 7272
School of Physics
  Title:   A Special Class in Vanishing Helicity Ideal Flows
1.  H. Eshraghi
2.  Yousefali Abedini
  Status:   Published
  Journal: J. Math. Phys.
  Vol.:  46
  Year:  2005
  Pages:   043102
  Supported by:  IPM
The derivation of a Lagrangian invariant so called spirality is reviewed through th Lagrangian coordinates. The value of the spirality is fixed up to a gauge transformation. The helicity conservation follows directly from this invariant. Among all ideal flows with zero helicity in a domain of flow frozen into the fluid motion, a special class is introduced. This special topoogical class has the possibility to transform its spirality to be identically zero everywhere in the domain. For those simply connected domains of motion, a necessary and a sufficient condition are presented for these zero apirality flows.

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