Fluid Flow Characteristics of Swirl Jet Near Nozzle Exit under Strong Swirl

Abstract

Experimental studies of fluid flow near field of double tube swirler and under strong swirl condition were conducted by use of LDV and high-speed video recorder. The swirl jet out of the annular part is expanded drastically as soon as it is exhausted from the nozzle. With this motion, straight flow out of the inside tube is induced to change its direction into radial flow and then recirculating flow on the center line is induced. The spreading rate of swirl radius decreases where swirl flow and straight flow, which has been turned to radial flow, merge with each other. Then the expansion of swirl radius increases again and the flow characteristics of the outer region of the swirl jet shift to the self-preserving type, independent of the inner flow. The scale of the recirculating flow and the degree of jet spread are experimentally correlated with swirl number.
The flow profile near the nozzle exit fluctuates dynamically with time. The fluctuation of flow can be recognized as involving three types of coherent profiles : axisymmetric, axi-unsymmetric and one-way types.
The fluid flow fluctuation causes the first and second peaks of intensity distribution, which correspond to the places where straight flow changes its direction rapidly and where they are merge into the annular swirl jet, respectively.