Development of fully 3-D numerical model for cross-field swirling flow simulation

Abstract

Swirling flow plays an important role in many engineering applications. Its function not only can increase the fuel/air mixing effect, but also can create a recirculation region in the downstream to stabilize the flame. Since the geometry of the boiler is irregular and with several wall-burners, a fully 3-D numerical modelfor flow field simulation is required. For validation, the axi-symmetric swirling flow field is first calculated and used to compare with Lilley's measured date. Next, the confinement geometry is changed from round to rectangle and the injection area ratio is varied to study the recirculation flow behavior. In the following,the effect of four swirling flow injection interactions on the whole flow field structure will be discussed. The results show that the case with single entry the rectangular boundary creates a secondary flow and squeezing the recirculation zone to force it stretches. The degree of squeezing depends upon the expansion area ratio. However, the results with four entries show that the shape of recirculation zone of each burner is strongly dependent on the whole cross-field structure. In addition, the interactions of four swirl jets result in the formation of a central recirculation zone. The degree of the effect is strongly related to the inlet swirl strength.