Kinetics and hydrodynamics of long-wave fluctuations under external random force

A universal phenomenological approach to study evolution of long-wave fluctuations caused by the external random force is developed. The Furutzu–Novikov theorem is generalized for non-Gaussian processes. General kinetic and hydrodynamic equations that include the effect of long-wave fluctuations are derived for the Gaussian distribution of the random force. The nonequilibrium entropy is determined in the presence of fluctuations in the system and the H-theorem is proved. It is shown that the Obukhov–Kolmogorov turbulence spectra can be found from the hydrodynamic equations of long-wave fluctuations obtained in this paper.