First we present high resolution large eddy simulations (LES) for the flow past a circular cylinder at Reynolds number 3900 to prove the quality of the simulations. A thorough grid convergence study is presented, and the agreement in the mean flow statistics between our simulations and the references is excellent. Then we apply a no-slip boundary condition at the spanwise boundaries of the cylinder, with aspect ratios of 6, 12 and 24. This results in large changes in the shear layers and wake topology, even for an aspect ratio of 24. Even though the boundary layers along the side walls are only about 0.4 diameters thick, they nevertheless manage to stabilize the shear layers all the way through the channel, thus effectively delaying the roll-up and transition to a turbulent wake
