Key words: jet, vortex, instability, excitation, frequency, mode.

Abstract: A numerical study of the instabilities is realized for 2D incompressible, isothermal and plane jet. The eulerian numerical finite volume method is used. Numerical parameters and boundary conditions are optimized for the studied configuration. This study was operated for moderate Reynolds numbers. The flow is perturbated at the entry of the nozzle. The excitation frequency is a harmonic or sub-harmonic of the natural instability. The instability amplification depends on the excitation frequency. A response mode inherent to the shear flows was detected. The vortex energy is amplified allowing to know their sinuous or varicose behavior. The vortex dissociation and pairing phenomena are highlighted.