Manifold interpretation of Navier-Stokes equations

Solution 1:

For the Navier Stokes equation, I am rather doubtful, because the presence of the viscosity term makes the equation not time-symmetric. And the geodesic flow is necessarily time-symmetric.

If you remove the viscosity term, you are down to the Euler equation, for which there is a well-known characterisation due to V I Arnold.

Solution 2:

Maybe Lagrangian coordinates is what you are after.