Generalized Navier-Stokes equations with nonlinear anisotropic viscosity

The purpose of this work is to study the generalized Navier-Stokes equations with nonlinear viscosity that, in addition, can be fully anisotropic. Existence of very weak solutions is proved for the associated initial and boundary-value problem, supplemented with no-slip boundary conditions. We show that our existence result is optimal in some directions provided there is some compensation in the remaining directions. A particular simplification of the problem studied here, reduces to the Navier-Stokes equations with (linear) anisotropic viscosity used to model either the turbulence or the Ekman layer in atmospheric and oceanic fluid flows.Portuguese Foundation for Science and Technology, PortugalPortuguese Foundation for Science and Technology [UID/MAT/04561/2019][SFRH/BSAB/135242/2017