Study on the flow field and concentration characteristics of the multiple tandem jets in crossflow

The characteristics of single and multiple tandem jets (n=2, 3, 4) in crossflow have been investigated using the realizable k-ɛ model. The results of this model agree well with experimental measurements using PIV (Particle Image Velocimetry) or LIF (Laser Induced Fluorescence). We analyzed the calculated results and obtained detailed properties of velocity and concentration of the multiple jets in the pre-merging and post-merging regions. When the velocity ratio is identical, the bending degree of the leading jet is greater than that of the rear jets. The last jet penetrates deeper as the jet number increases, and the shielding effect of the front jet declines with jet spacing increase. Interaction of the jet and crossflow induces formation and development of a counter-rotating vortex pair (CVP). CVP makes the distribution of concentration appear kidney-shaped (except in the merging region), and maximum concentration is at the center of the counter-rotating vortex. Concentration at the CVP center is 1.03–1.4 times that of the local jet trajectory. Post-merging velocity and concentration characteristics differ from those of the single jet because of the shielding effect and mixing of all jets. This paper presents a unified formula of trajectory, concentration half-width and trajectory dilution, by introducing a reduction factor.

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