Coarse Graining in Hydrodynamics and Effects of Fluctuations

We address the physical meaning of hydrodynamic approach related with the coarse graining scale in the frame work of variational formulation. We point out that the local thermal equilibrium does not necessarily play a critical role in the description of the collective flow patterns. We further show that the effect of viscosity is also formulated in the form of the variational method including fluctuations.