From the principle of least action the equation of motion for viscous compressible and charged fluid is derived. The viscosity effect is described by the 4-potential of the energy dissipation field, dissipation tensor and dissipation stress-energy tensor. In the weak field limit it is shown that the obtained equation is equivalent to the Navier-Stokes equation. The equation for the power of the kinetic energy loss is provided, the equation of motion is integrated, and the dependence of the velocity magnitude is determined. A complete set of equations is presented, which suffices to solve the problem of motion of viscous compressible and charged fluid in the gravitational and electromagnetic fields.Keywords: Navier-Stokes equation; dissipation field; acceleration field; pressure field; viscosity.
IntroductionSince Navier-Stokes equations appeared in 1827 [1-2], constant attempts have been made to derive these equations by various methods. Stokes [3] and , in derivation of these equations, relied on the fact that the deviatoric stress tensor of normal and tangential stress is linearly related to the three-dimensional deformation rate tensor and the fluid is isotropic.Khmelnik [5] considered that Navier-Stokes equations are the extremum conditions of some functional, and a method of finding a solution of these equations is described, which consists in the gradient motion to the extremum of this functional.One of the variants of the four-dimensional stressenergy tensor of viscous stresses in the special theory of relativity can be found in book [6]. The divergence of this tensor gives the required viscous terms in the Navier-Stokes equation. The phenomenological derivation of this tensor is based on the assumed condition of entropy increment during energy dissipation. As a consequence, in the comoving reference frame the time components of the tensor, i.e. the dissipation energy density and its flux vanish. Therefore, such a tensor is not a universal tensor and cannot serve, for example, as a basis for determining the metric in the presence of viscosity.In this article, our goal is to provide in general form the four-dimensional stress-energy tensor of energy dissipation, which describes in the curved spacetime the energy density and the stress and energy flux, arising due to viscous stresses. This tensor will be derived with the help of the principle of least action on the basis of a covariant 4-potential of the dissipation field. Then we will apply these quantities in the equation of motion of the viscous compressible and charged fluid, and by selecting the scalar potential of the dissipation field we will obtain the NavierStokes equation. The essential element of our calculations will be the use of the wave equation for the field potentials