We propose a mechanism for the previously unexplained formation of spanwise cells observed in the vortex street wake of finite-length cylindrical bluff bodies at low Reynolds numbers. It involves the spatial growth of the secondary Eckhaus instability of oblique vortex shedding, controlled by end effects, and leads to a new interpretation of observed wake frequency relations. Predictions of cell size variations and wake patterns are obtained from the phenomenological Ginzburg-Landau model, and good agreement is found with experimental observations.

• Received 4 June 1996

DOI:https://doi.org/10.1103/PhysRevLett.78.1259