The Karman Vortex Street is a type of phenomenon which is generally illustrated by examples in which a long, solid, smooth circular cylinder moves at constant velocity through a fluid. The long axis of the cylinder is perpendicular to the relative velocity vector. Eddies form on the downstream side of the cylinder and detach at a regular temporal rate. The eddies form alternately in two places either side of the "flow axis". The downstream wake behind the cylinder can be described as a series of alternating, counter-rotating vortices. Karman vortex streets can also be generated by cylinders with other cross-sections, even by flat plates.
Is it possible to generate a "vortex street" which consists of a single series of co-rotating vortices?
Consider an infinitely wide river with a flat bottom and water flowing steadily from west to east and a solid, smooth cylinder with semi-circular x-section attached (curved surface upwards) to the riverbed with its long axis running north-south. Now is it possible, under certain combinations of fluid viscosity, fluid velocity and cylinder geometry, that, on the downstream side of the cylinder, tubular vortices parallel to the cylinder will periodically form, grow and detach and be carried downstream at regular time intervals?