Effects of Flow Rate Ratio and Swirl Number on Heat Transfer and Flow Field in Combined Swirl Impinging Jets

Combined impingement jets are a promising cooling technique for enhancing heat transfer and uniformity. This study focuses on understanding the heat transfer and flow field of a combined impinging jet. It presents a novelty by addressing the compound effects of two important characteristics of a combined impingement jet: the swirl number and the flow rate ratio. To achieve this objective, combined impinging jets with axial and tangential velocities are produced using a combined nozzle that has circular and quadruple helical flow sections. The flow rate ratio is defined to examine the effects of the separate flow rates of the circular and quadruple helical sections of the combined nozzle, keeping the total flow rate constant at 75 L/min. The study is carried out for two different flow rate ratios (0.2 and 0.5) and a dimensionless nozzle-plate distance of 1. On the other hand, depending on the geometry of the combined nozzle, the swirl number is 0.0, 0.3, 0.6, 0.8, and 1.7. All parameters studied are investigated separately for confined and unconfined jet cases. The results demonstrate that the numerical model agrees with the experimental findings. It is observed that increasing the flow rate ratio from 0.2 to 0.5 results in a decrease in the Nusselt number of 28.4%–29.5% in the unconfined jet case and 28.7%–30.4% in the confined jet case, depending on the change in swirl number. Increasing the flow rate ratio improves heat transfer uniformity better than enhancing the swirl number. The swirl number becomes more effective on heat transfer and pressure with an increasing flow rate ratio. The confinement plate used to create the confined case reduces the drag ratio compared to the confined case. Finally, one advantage of the combined nozzle geometry is that the saddle-shaped formation, which negatively affects heat transfer uniformity, is not observed in the local Nusselt number distribution. © 2026 Taylor & Francis Group, LLC.