EXPERIMENTAL STUDY OF LARGE STRUCTURE IN THE FAR WAKES OF TWO-DIMENSIONAL BLUFF BODIES.

Smoke-wire flow visualization and hot-wire anemometry have been used to study near and far wakes of two-dimensional bluff bodies. For the case of a circular cylinder at 70 less than Re less than 2000, a very rapid (exponential) decay of velocity fluctuations at the Karman vortex street frequency is observed. Measured prominent frequencies in the far cylinder wake are in good agreement with those estimated by two-dimensional locally-parallel inviscid linear stability theory, when streamwise growth of wake width is taken into account. Finally, three-dimensionality in the far wake of a circular cylinder is briefly discussed and a mechanism for its development is suggested based on a secondary parametric instability of the subharmonic type.