• Numerical simulations, laboratory experiments, and visualization were used. • Jet partitions were delineated based on the evolutionary characteristics of the vorticity. • Effect of transverse spacing of vent on vortex structure and flow field parameters. • Synergy angle, cooling effectiveness, and TNC variation rules were obtained. This study investigates the flow structure and heat transfer characteristics of transversely superimposed multi-jet-in-crossflow (JICF) systems at a low velocity ratio ( R = 0.5, defined as the ratio of jet velocity to crossflow velocity) with varying jet-to-jet spacings ( d s /d j = 2–18). The method of combining experiment and simulation was employed to resolve vortex dynamics, thermal fields, and field synergy distributions. A vortex-zone classification framework was developed, dividing the downstream region into strong attachment, weak attachment, fragmentation, and dissipation zones based on normalized vorticity. Results show that positioning the rear-stage jet within the strong attachment zone of the upstream jet enhances convective heat transfer through intensified field synergy, but shortens the downstream cooling persistence due to accelerated thermal diffusion. Conversely, placing it in the fragmentation zone improves cold fluid retention, yielding up to 50% higher cooling effectiveness at 20 d j compared with single-stage configurations. The findings provide a quantitative basis for optimizing vent spacing to balance near-wall heat transfer and far-field thermal insulation, with implications for turbine blade cooling, electronic thermal management, and mine ventilation.
Wang et al. (Tue,) studied this question.