Effects of Confinement and Reynolds Number Variation on the Flow Field of Swirling Jets

Swirling jets are commonly used in the burners of gas turbines to enhance mixing or to stabilize the flames. In this manuscript, a stereo (3C2D) particle image velocimetry (SPIV) was applied to examine the near exit region of an isothermal swirling jet inside an octagonal-shaped combustion chamber with a focus on the effects of confinement and Reynolds number (Re) variation on the swirling flow field. Measurements were performed on an axial plus tangential entry swirl burner with a geometric swirl number (Sg) of 1.8 and two different Re, corresponding to 10,900 and 21,800. The results observed in our experimental work are scaled appropriately with the swirl number based on the flux of the axial momentum. The contours of the mean axial velocity field reveal the occurrence of vortex breakdown (VB) for the confined jets compared to the unconfined jets for both Reynolds numbers. Upon confinement, the flow field is dominated by the existence of VB with a wider central recirculation zone (CRZ) and with enhanced axial velocity fluctuations. The enhancement in the Re further increased the CRZ and enhanced the magnitudes of the mean axial velocity and its fluctuations. The outcome obtained from these results includes a better knowledge of the swirl jet in the swirl burner's near region. In addition, the experimental data can be useful for validating computational fluid dynamics (CFD) modeling.