Forced wall jets over a convex wall (Coanda flows) are being investigated using 3D Navier-Stokes simulations. The focus of our numerical investigations is to study the development and interaction of large coherent structures in the turbulent Coanda flow. These coherent structures, namely large spanwise "rollers" and longitudinal Gortler-type vortices, can greatly influence the development of the Coanda wall jet along the surface of a cylinder and its eventual separation from the cylinder surface. In our numerical simulations of the Coanda flow over a cylinder segment, selective forcing is employed to either enhance or suppress both types of coherent structures. The effect of the selective forcing on the spreading and decay rate of the jet is then studied. It is found that both forcing of the spanwise structures and forcing of the streamwise structures increases the streamwise velocity decay of the wall jet, while only the forcing of spanwise structures significantly enhances the spreading rate.