국내 최대 기계 및 로봇 연구정보

기술보고서

기술보고서 게시판 내용
타이틀	Numerical Studies of Swirling Turbulent Flows in Conventional and DS Burners
저자	Yan LIU; Shigeru HAYASHI
Keyword	swirling flow; turbulent models; numerical calculation; burner; fuel-air mixing
URL	http://send.nal.go.jp/send/jpn/dlpdf.php3/naltr1318t.pdf?id=NALTR0001318T
보고서번호	NAL TR-1318T
발행년도	1997.1
출처	NAL (National Aerospace Laboratory of Japan)
ABSTRACT	In this paper,the effects of swirler configurations on the turbulent flows and fuel-air mixing process in a swirl burner are investigated by numerical simulations.The configurations studied are a unique double swirler(DS)which is designed for low-NOx emissions,and two conventional single swirlers with different hub diameters and the same opening area.The double-swirler has a pair of co-rotational swirls and a convergent duct.One of them is attached to the inlet of the duct and the other is externally and concentrically attached to the duct at the exit.Combustion air flows into a flame tube through both duct and the annular passage of the outer swirler.In the conventional swirlers,combustion air flows through the annular with swirl vanes.The study is performed using a finite volume formulation.A body-fitted non-orthogonal grid system is specially generated for predicting flows in the double swirler.In the study,three different turbulent models,e.g.,the standard κ-ε model,RNG κ-ε model,and Reynolds StrModel(RSM),are used to calculate turbulent properties in the flow,and their predictive abilities are assesed and compared to each other.The flow characteristics in the burners and their variations with the inlet flow conditions are then analyzed numerically.The results in this study indicate that these three different turbulent models all give general flow characteristics of the swirling flows considered in this work,but show different predictions of the size of central toroidal recirculation zone(CTRZ),mainly in the downstream of the flow.The experimental evaluation conducted for the flow in the DS burner indicates that the predicted CTRZ sizes given by the standard κ-ε model show comparatively good agreement with the experiment data,while the RNG κ-ε model predicts the rigid vortex motion in the strongly swirling flow more accurately.It is found from the predictions conducted for the conventional burners that the RSM model is also able to improve the prediction of the rigid vortex motion.The study of thfects of inlet conditions on flow patterns reveals that the double swirler possesses unique advantage over conventional swirlers,e.g.,the flow pattern as well as the fuel concentration distribution in the burner could actually be controlled by changing the ratio of the air flow rate in the inner and outer swirlers or the fuel flow rate through the fuel nozzle.A high-velocity jet is produced near the exit of the double swirler,and it may enhance the mixing process of the air and fuel due to opposing effect of the jet and the reverse flow in the burner.The flow patterns in the burners with conventional swirlers of different hub diameters,on the other hand,are similar,and they do not change significantly with variation of the inlet conditions when the swirler vane angle remains the same.The difference in the swirler hub diameters,however,changes the size of CTRZ.The smaller hub may decrease the width of CTRZ in the burner.