Active control ofa rectangular jet has been attempted to rnanipulate the vortex shedding interval in the major shear IayeL The aspect ratio ofthe nozzle cross − section is 15, and the Reynolds number based on the shorter side length ofthe nozzle is 6700 . It is considered essential that the vortex distribution along the each major shear layer plays an important role to characterize a rectangular jet behavioL In the present investigation , it was remarkably observed that the jet spreads more

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... ly in the minor directlon and contracts more greatly in major direction by the asymmetric excitation than that of the non −excited jet . Hot wire measurement was conducted , and could provide the mean , coherent and random velocity components from the instantaneous velocity signal . The measurement results showed that t わe coherent vortices are generated in synchronization with the excitation frequency and the rnode . In addition , it was revealed that the inclined vortex rings are formed and interacted with each other only when the jet was excited by asymmetric mode . Thejet spreading is attributed to the tilting alignment ofthe vortex ring , and thejet contracting in minor direction is due to the selfLinduced defbrmation ofthe rectangular vortex ring .