A tube with a diffuser is partially submerged in a water tank. A piston, inside the tube, creates an oscillating flow. The curvature of the diffuser is such that no vortices are formed inside. A vortex is formed when the flow gets out of the diffuser and another when it goes in. The path of these vortices when they go out of the diffuser strongly depends on the amplitude and frequency of oscillation forming a large variety of flow patterns. We thank the support of UNAM through project PAPIME PE104907