L. D. Landau noted [2, p. 296] that these equations are true for the local turbulence structure, but in a turbulent flow, the presence of a velocity rotor is limited to a finite space and the equations should show exactly this distribution of turbulent vortices.
Landau calls Henri Navier's representations model [2, p. 73] (in a footnote).
We show a model of the physical flow pattern on which the Navier equations are based:
What is described by this model, a solution of the Navier-Stokes equations can be found for this. This model can perfectly describe special cases.
Let's compare the motion model from the work of A. Navier with the turbulence model proposed by A. N. Kolmogorov.
Model Of Kolmogorov:
Some authors point out that the Navier-Stokes equations contain turbulence. Apparently, this is not the case. The Navier-Stokes equations can be applied at the lowest level of the Kolmogorov model. In General, the Henri Navier model is physically incorrect compared to the correct Ko
Let's compare the motion model from the work of A. Navier with the turbulence model proposed by A. N. Kolmogorov.
The volume for which the Navier-Stokes equations are compiled is chosen with minimal dimensions that ensure the continuity of the medium. However, this is not essential. Obviously, the cube is incomparably smaller than the space R3.
For a cube, the description of the physical process consists of describing the flow of liquid into and out of it, as well as the effect of viscosity.
For a space R3 with a complex structure of turbulent flow, the physical process is much more complex and the descriptions used for the cube in the derivation of the Navier-Stokes equations are not enough to describe it!
In existing attempts to solve the Navier-Stokes equations, the space R3 is conditionally divided (discretized) by a grid with cubic elements.
Attempts at analytical solutions, for example, in [4], are reduced to assigning boundary conditions for equations and searching for solutions.
The boundary conditions for a cube with sides x, y, x and step Q are written as:
It is obvious that the movement of a liquid in the space R3 and in any space, the Navier model and its representations are not described. The area around the point does not exceed the Kolmogorov scale.
The Navier-Stokes equations are compounded for a physical model of a small Kolmogorov scale and do not correspond to the physical processes of turbulent movement of large volumes of liquid.
In the case of analytically accurate solutions of the Navier-Stokes Equations for the case of the Poiseuille flow, the solution is performed for the physical process described by the process for the cube.
There are methods for direct numerical solution of Navier-Stokes equations[5], [6], [7].
In these (finite-difference) methods, the space is discretized by a grid. The derivative is replaced by an algebraic relation.
It is obvious that numerical methods for the space R3 solve Navier-Stokes equations that do not describe a physical process on the space R3. However, the results of solutions for each grid cube are carried over for an integral solution for the entire grid, i.e. for the space R3.
For the Kolmogorov turbulence model, this approach would mean calculating the scattered energy at all small scales and summing the values obtained for the upper scale. Kolmogorov's model describes the real picture of the fluid flow.
The error in numerical methods of solution is found in their very theoretical basis. We solve a model with a physical process that does not describe the flow on the space R3 for each grid cell and then obtain the calculation result for the entire grid, and therefore for the space R3. In other words, the numerical method applies an incorrect physical model to the solution on the space R3, which does not describe the processes on the space R3.
Proof of the absence of a solution to the Navier-Stokes equations on the space R3 based on the application of Kurt Goedel's incompleteness theorem
To solve the problem, we use Kurt Goedel's incompleteness theorem. Goedel's theorem is given in [7].
The system of equations, including the Navier-Stokes system of equations, is a formal system. As you know, there are questions within the formal system that cannot be answered within these systems.