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Helicity, as one of only two inviscid invariants in three-dimensionalturbulence, plays an important role in the generation and evolution ofturbulence. From the traditional viewpoint, there exists only one channel ofhelicity cascade similar to that of kinetic energy cascade. Through theoreticalanalysis, we find that there are two channels in helicity cascade process. Thefirst channel mainly originates from vortex twisting process, and the secondchannel mainly originates from vortex stretching process. By analysing the dataof direct numerical simulations of typical turbulent flows, we find that thesetwo channels behave differently. The ensemble averages of helicity flux indifferent channels are equal in homogeneous and isotropic turbulence, whilethey are different in other type of turbulent flows. The second channel is moreintermittent and acts more like a scalar, especially on small scales. Besides,we find a novel mechanism of hindered even inverse energy cascade, which couldbe attributed to the second-channel helicity flux with large amplitude.

Dual channels of helicity cascade in turbulent flows