Wake of tandem cylinders near a wall

If the wall gap is decreased to 0.3 diameters, an extended low speed region appears close downstream of the cylinders. A POD mode similar to a vortex shedding is still present; however it cannot be associated to an alternate Von Kármán street. The shed structures show a shorter wavelength than the Von Kármán shedding in far-from-the ground cases and are accompanied by a flapping jet-like structure ejected from the wall gap between the cylinder and the wall. The jet strongly changes the features of the wake on the side opposite to that of the wall, thus suggesting a possible coexistence between jet oscillations and shedding.