title: Time evolution of the eddy viscosity in two-dimensional navier-stokes flow
abstract: The time evolution of the eddy viscosity associated with an unforced two-dimensional incompressible Navier-Stokes flow is analyzed by direct numerical simulation. The initial condition is such that the eddy viscosity is isotropic and negative. It is shown by concrete examples that the Navier-Stokes dynamics stabilizes negative eddy viscosity effects. In other words, this dynamics moves monotonically the initial negative eddy viscosity to positive values before relaxation due to viscous term occurs.
authors.affiliation: Departamento de Matematica Aplicada, CMAUP, Universidade do Porto, Rua das Taipas 135, 4050 Porto, Portugal.
authors.initials: M
authors.lastname: Chaves
authors.initials: S
authors.lastname: Gama