An agitated circular turbulent jet with a coaxial annular synthetic jet actuator is investigated experimentally. The mean and turbulent velocities are measured by a hot-wire anemometer at a jet Reynolds number of 6400. The measured iso-velocity contour maps indicate that the width of the circular jet is increased even when the intensity of the alternating flow is too weak not to generate a synthetic jet. This can be attributed to the periodic disturbances by the actuator, which agitates the instability in the initial shear layer and moves the shear layer growth to upstream. With a strong agitation so as to generate a strong synthetic jet by itself, the agitated jet has the higher velocity and the larger width than those of unagitated jet. With this agitation, the momentum of the agitated jet is increased and its increment is equal to the momentum of the synthetic jet. Smoke visualization shows clearly that the actuator enhances the dispersion of primary jet fluids. These results are compared with those of a jet at a low Reynolds number of 3088 (Koso, 2005) and it is found that the mixing enhancement is qualitatively same for both Reynolds numbers, but the weak agitation is more effective in the low Reynolds number jet.

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