“…The main concern in this research is to analyze numerically problem (P) and problem (F) using the nonconforming finite element method where the velocity is approximated by lowest order Crouzeix-Raviart element and the pressure with piecewise constant functions [10]. The a priori error analysis of problem (P) has been proposed with discontinuous Galerkin method in [11], while numerous studies using conforming approximation of the velocity have been contributed by researchers, see among others [12,13,14,15,16,17,18]. The finite element method is now well adapted for approximating the solution of partial differential equations written in weak form (including variational inequalities, see [19,20,21,22,23,24]), and the search for efficient and simple non conforming finite element methods for Stokes, Navier-Stokes equations driven by nonlinear slip boundary conditions has not yet been well explored by researchers (except the early work of the author in [11]).…”