EXPERIMENTAL INVESTIGATION OF GAS JETS IN CONFINED SWIRLING AIR FLOW.

Although there have been numerous investigations on the characteristics of confined jets and co-axial jets, little is known of the behavior of jets in a confined swirling flow, especially jets of a lighter fluid issuing into a heavier fluid. The present investigation addresses this latter question directly and reports on the fluid dynamics of gas jets of different densities in confined swirling flows. Results for air and helium/air jets show that jets in confined flow with large area ratio are highly dissipative. As a result, both air and helium/air jet center line velocity decays rapidly. However, the similarity between air and helium/air jets ends here. For air jets, the jet-like behavior in the tube center disappears at about 20 diameters downstream of the jet exit. This phenomenon is independent of the initial jet velocity. The turbulence field at this point also decays to that of the background swirling flow. On the other hand, a jet-like behavior in the tube center is noticed even at 40 diameters for the helium/air jets. The subsequent flow and turbulence field depend highly on the initial jet velocity. Since the jets are fully turbulent, therefore, independent of jet Reynolds number, and the jet momentum fluxes for both air and helium/air jets are the same, the cause of this difference in behavior is attributed to the combined action of swirl and density difference. This observation can have significant impact on the design of turbine combustors and solid fuel ramjets subject to spin.