  Most existing theoretical studies of momentum transport focus on calculating
the Reynolds stress based on quasilinear theory, without considering the
\emph{nonlinear} momentum flux-$<\tilde{v}_r \tilde{n} \tilde{u}_{\|} >$.
However, a recent experiment on TORPEX found that the nonlinear toroidal
momentum flux induced by blobs makes a significant contribution as compared to
the Reynolds stress [Labit et al., Phys. Plasmas {\bf 18}, 032308 (2011)]. In
this work, the nonlinear parallel momentum flux in strong turbulence is
calculated by using three dimensional Hasegawa-Mima equation. It is shown that
nonlinear diffusivity is smaller than quasilinear diffusivity from Reynolds
stress. However, the leading order nonlinear residual stress can be comparable
to the quasilinear residual stress, and so could be important to intrinsic
rotation in tokamak edge plasmas. A key difference from the quasilinear
residual stress is that parallel fluctuation spectrum asymmetry is not required
for nonlinear residual stress.
