Complex turbulent flows in engineering applications or in the environment are becoming more complex with the effects of several external factors (pressure gradients, roughness …). The transposition of our knowledge acquired through the study of canonical flows to more complex ones is not straightforward and raises several questions. An important category of complex turbulent wall flows is adverse pressure gradient turbulent boundary layer (APG TBL) flows. In this study, the APG TBL flows and the mechanism and interaction of turbulence structures occurring in these flows will be investigated by direct numerical simulations.