FORMATION IN CYLINDER WAKES AT LOW REYNOLDS-NUMBERS

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