  In this work the exact and approximate analytical solution of the GHE for
turbulent flow in channel are presented. It was discovered first by numerical
simulations, Fedoseyev and Alexeev (2010), and now the explicit formula are
obtained. The solution is a superposition of the laminar (parabolic) and
turbulent (superexponential) solutions. The analytical solution compares well
with the experimental data by Van Doorne (2007) for axial velocity and data by
Nikuradse (1933) for axial velocity, for flows in pipes.
  It is proposed to explain the nature of turbulence as oscillations between
the laminar (parabolic) and turbulent (superexponential) solutions. Good
comparison of the analytical formula, a difference of the parabolic and
superexponential solutions, for turbulent velocity fluctuations with the
experiment by Van Doorne (2007) confirmed this suggestion. The Navier-Stokes
equations do not have the superexponential solution.
  The obtained analytical solution provides a complete structure of the
turbulent boundary layer that compares well with the experiments by Wei and
Willmarth (1989). It also presents an explicit verifiable proof that Alexeev's
generalized hydrodynamic theory (GHE) is in close agreement with experiments
for turbulent flows.
