Nowadays, unsteady calculation of Navier-Stokes equations thanks to Large Eddy Simulation (LES) and all the more Direct Numerical Simulation (DNS) are still beyond the scope of current supercomputers for industrial interests. On the other hand, statistical methods (RANS) less numerically expensive, don't allow to describe broad band phenomena (for instance acoustic sources). Locally coupled methods make it possible to draw benefit of this two kind of approach (RANS and LES). An original method of this type, which can be seen as an extension of the Non-Linear Disturbance Equation (NLDE), is developped in this work. It consists in a decomposition into three parts of the exact solution of the Navier-Stokes equations : mean flow, resolved fluctuations and unresolved (subgrid) fluctuations. The mean flow is computed using a classical RANS method, while resolved fluctuations are derived from a LES method, only on the critical spots of the flow. The code was implemented on the NEC SX5 supercomputer of ONERA and assesed on several incompressible (plane chanel flow) and compressible (turbine blade, high lift system) application cases. The potentialities of the method are demonstrated and an original boundary condition is developped. The method succeds to predict the correct flow behaviour for all these configurations and can be applied locally, what provide a large reduction of the computational cost.