Downstream Decay of a Two-Dimensional Jet-Wake in a Co-flowing Stream
T. Ly, P. Jan, J.C. Larue

Similarity solutions for the flow downstream of a two-dimensional jet in a co-flowing stream show that near the exit plane, the downstream variation of the flow properties should be consistent with "jet-like" behavior. Further downstream, when the difference between the centerline and freestream velocity is small, the similarity solutions show that the flow properties should become consistent with "wake-like" behavior. Past results have not exhibited this expected change in behavior. The purpose of this experiment is to verify whether the similarity predicitons are correct. The experiment was performed in a 60x90 cm cross-section, wind tunnel with a plane two-dimensional jet exhausting from a 3.17 mm gap at the trailing edge of a NACA 0012 airfoil. Time resolved measurements of two velocity components were recorded at various downstream positions. The downstream variation of the half-width was determined for jet to freestream velocity ratios of 5, 8, 10 and was found to be proportional to downstream distance near the jet exit, and to the square root of the downstream distance further downstream which corresponds to the values predicted from similarity theory.

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