Annu. Rev. Fluid Mech. 24, 281-312 (1992).
Summary: A general theoretical review of helicity in flows that are laminar or turbulent is presented with references to corresponding experimental investigations. The topological nature of the helicity invariant is examined, and the turbulent dynamo mechanism is discussed in relation to the phenomenon of helicity. Helicity is also discussed in terms of being a topological constraint in relaxation to equilibrium, and attention is given to the structure of turbulence and the suppression of nonlinearity. Observational and experimental data related to helical structures are reviewed including the generation of helicity in helicity-free flows, quantitative measurements of helicity, and the application of of helicity density as a pseudoscalar quantity for characterizing complex 3D flows. Other topics of significance are addressed including skew diffusion, the AKA effect, and relaxation under modified Euler equation evolution.
For the entire collection see Zbl 0742.00036.