Oscillatory flow in stacks of parallel plates is essential for the working of "standing wave" thermo-acoustic devices. In this paper, the flow in the transition from stack to open tube is studied experimentally using particle image velocimetry. When the flow is directed outwards of the stack, vortices originate behind the stack plates. The Strouhal to Reynolds ratio determines the vortex pattern behind the stack plates, varying from a single vortex pair to a complete vortex street. The influence of different plate-end shapes and porosities are also studied. The streaming velocity is measured using two different methods.