This paper deals with a numerical method based on the simulation of a 2D tank, for unsteady and laminar two - dimensional incompressible viscous flow. Navier-Stokes and Continuity equations are solved in a fluid domain. These equations are discretized by Finite Differences Method. The pressure is obtained by solving a Poisson equation dealing with a fictitious velocity field. The Poisson equation is solved by a Finite Volume Method. The grid is refined by a new method “Adaptive Selective Mesh Refinement” called “ASMR”.