An experimental study of the flow structure in arrays of cold bidirectional swirling jets

Abstract

Jets arrays have become a promising technology for industrial applications, including heat transfer and combustion processes. This paper presents the first experimental results of arrays of bidirectional swirling jets, including their flow structures and specific turbulent interactions. Particle image velocimetry of non-reacting linear arrays showed the formation of recirculation zones within each jet of the array. These regions are the most stable, with fluctuations less than 0.002 of the bulk inlet velocity Vin. In addition, jets merging locations also show a significant decrease in velocity fluctuations, with values V′/Vin < 0.005, which is most clearly seen at a smaller pitch distance. However, the highest turbulent fluctuations occur in shear layers, reaching values of V'/Vin ≈ 0.02 for linear arrays and V'/Vin ≈ 0.03 for planar configurations. The flow structure of planar arrays is more complex, leading to the formation of secondary vortex structures at locations of jet interaction. This results in a significant decrease in the flow swirl number, from an initial value of Sin = 2.1 in the vortex chamber, to S1 = 0.36–0.49 at z/dout2 = 1 and S2 = 0.19–0.27 at z/dout2 = 2 beyond the outlet nozzle. Strong cross-sectional motions are observed in planar arrangements, leading to the development of additional regions of negative axial velocity between the outlet nozzles. The boundaries of these regions have nearly zero axial velocity values and can provide reliable ignition and flame stabilization in the case of reactive bidirectional jets. Therefore, the flow structure in planar arrays forms a large stabilization zone, and the obtained results can be used to develop a new multipoint combustion technique.