  The conventional approach to the turbulent energy cascade, based on
Richardson-Kolmogorov phenomenology, ignores the topology of emerging vortices,
which is related to the helicity of the turbulent flow. It is generally
believed that helicity can play a significant role in turbulent systems, e.g.,
supporting the generation of large-scale magnetic fields, but its impact on the
energy cascade to small scales has never been observed. We suggest for the
first time a generalized phenomenology for isotropic turbulence with an
arbitrary spectral distribution of the helicity. We discuss various scenarios
of direct turbulent cascades with new helicity effect, which can be interpreted
as a hindering of the spectral energy transfer. Therefore the energy is
accumulated and redistributed so that the efficiency of non-linear interactions
will be sufficient to provide a constant energy flux. We confirm our
phenomenology by high Reynolds number numerical simulations based on a shell
model of helical turbulence. The energy in our model is injected at a certain
large scale only, whereas the source of helicity is distributed over all
scales. In particular, we found that the helical bottleneck effect can appear
in the inertial interval of the energy spectrum.
