The interaction between two canonical flows, a wake mixing layer interaction, has recieved recent interest (Heitz, 1999, Lamballais and Silvestrini 2002, Braud 2003) due to a food industry problem. The aim of this study is to extend the low dimensional analysis of this particular flow configurations. For this purpose PIV data acquired by Braud et al (2004) and calculations performed by Lamballais and Silvestrini (2002) are used. This work allow us to make a link between the thre-dimensional organization and the secondary unsteady movement from the low velocity side to the high velocity side of the mixing layer, appearing in this highly 3D flow configuration.