Flow disturbances were introduced upstream of a rectangular nozzle and spreading jet confined by top and bottom plates to determine the effect on the velocity profiles. The mean velocity and turbulence distributions in the symmetrical mixing regions near a given nozzle are presented for several upstream disturbance intensity levels and several jet nozzle exit velocities. For the essentially two-dimensional jet flow from a high aspect ratio nozzle the results at several upstream disturbance intensity levels revealed the mean velocity distribution to be self-preserving near the nozzle. Over a large range of upstream disturbance intensity inputs the location of the virtual origin for each mixing region changed significantly while the mixing regions exhibited a constant maximum dimensionless spread rate. Other results for the essentially three-dimensional jet flow from a low aspect ratio nozzle did not show self-preservation in the mixing regions and furthermore revealed extraordinary changes in the velocity profiles.

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