The aerodynamic characteristics of strongly swirled coaxial jets issuing from a divergent nozzle into stagnant-air surroundings have been studied. Maps of the central reverse-flow zone and detailed measurements of mean velocity have been obtained in the region close to the exit of the nozzles and the effects of varying the level of swirl and the ratio of the momenta in the central and annular jets have been examined. The level of swirl and the momentum flux ratio are found to influence significantly the flow type and stability. The measurements are compared with calculations obtained by numerical solution of the time-averaged equations governing conservation of mass and momentum. The calculation procedure is also used to examine the effects of burner geometry and heat release on flow type.

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