This work concerns the interaction between a mean flow and large‐scale coherent structures in a wall jet at low Reynolds numbers in the case of single and multiple modes. The Navier–Stokes equations have been used to study the evolution of the wall jet and, in particular, its kinetic energy. The nonlinear interaction problem has been solved by means of the integral method taking into account the shape assumptions and local linear theory to obtain characteristics of coherent modes in the wall jet. It has been observed that the fundamental wave in case of a single mode, extracts its energy from the mean flow. When considering the fundamental mode superposed to its first subharmonic one with a phase difference &thgr;=0, it can be observed that there are interactions between the mean flow and these waves. Energy is extracted from the mean flow to the fundamental wave and then to its first subharmonic mode. The evolution of the thickness of the jet &dgr; and the maximum velocityUfor each dimensionless downstream coordinate is also shown with a growth of increasing of &dgr; and decreasing ofU. Initial conditions play an important role. In this work, fine‐grained turbulence quantities have been neglected. Some comparisons with experimental results have been performed. ©1996 American Institute of Physics.