  Energy flux plays a key role in the analyses of energy-cascading turbulence.
In isotropic turbulence, the flux is given by a scalar as a function of the
magnitude of the wavenumber. On the other hand, the flux in anisotropic
turbulence should be a geometric vector that has a direction as well as the
magnitude, and depends not only on the magnitude of the wavenumber but also on
its direction. The energy-flux vector in the anisotropic turbulence cannot be
uniquely determined in a way used for the isotropic flux. In this work,
introducing two ansatzes, net locality and efficiency of the nonlinear energy
transfer, we propose a way to determine the energy-flux vector in anisotropic
turbulence by using the Moore--Penrose inverse. The energy-flux vector in
strongly rotating turbulence is demonstrated based on the energy transfer rate
obtained by direct numerical simulations. It is found that the direction of the
energy-flux vector is consistent with the prediction of the weak turbulence
theory in the wavenumber range dominated by the inertial waves. However, the
energy flux along the critical wavenumbers predicted by the critical balance in
the buffer range between in the weak turbulence range and the isotropic
Kolmogorov turbulence range is not observed in the present simulations. This
discrepancy between the critical balance and the present numerical results is
discussed and the dissipation is found to play an important role in the energy
flux in the buffer range.
