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This paper numerically investigates both the inline and staggered arrays of circular multiple swirling air jets that impinge perpendicularly onto a smooth flat surface. The simulations were conducted for various flow and geometric parameters, such as Reynolds number (Re = 11,600, 24,600, and 35,000), jet‐to‐surface distance (H/D = 1, 2, 3, and 4), jet‐to‐jet separation distance (Z/D = 1.5, 3.0, and 4.5) and swirl numbers (S = 0, 0.3, and 0.75), where D is the nozzle diameter. For S = 0.75, a strong recirculation develops due to the vortex breakdown, depends on Z/D, around the axis and near the wall. The extent of the recirculation is larger for the staggered array. Intense heat transfer is anticipated at strong swirl and close impingement cases with the expense of uniformity; whereas a relatively even heat transfer is observed for larger impingements. The increase in jet‐to‐jet separation enhances the overall cooling effect and the staggered configuration of nozzles gives better performance. It appears that both the crossflow and turbulence around the periphery of each jet predominantly govern the heat transfer characteristics. The enhancement of heat transfer occurs for increasing Re, and the overall Nusselt number (Nu) prediction is scaled by Ren, with n dependent on S. Finally a correlation is developed for the average Nusselt number to relate different control parameters.

This research investigates the flow aspects and thermal behavior of multiple air jet impingements on a flat plate through two different geometrical arrangements. A variety of flow conditions and geometrical parameters are considered including Reynolds number, swirl number, impingement distance, and jet-to-jet separation. A numerical approach is adopted to conduct the analysis using the shear stress transport (SST) k-ω turbulence model in the commercial computational fluid dynamics (CFD) software package ANSYS Fluent v17. Results reveal that the static pressure is uniformly distributed on the impingement surface for the higher nozzle-to-surface distance at a strong swirl flow, while for noswirl and medium-swirl configurations, the static pressure is accumulated at the stagnation regions. A lower impingement distance improves the cooling performance while a higher impingement distance accelerates the consistency in temperature distribution. Moreover, the staggered nozzle arrangement is found superior in terms of generating integrity in thermal cooling. Overall, the pressure coefficient enhances by up to 126% for medium swirl (S = 0.3) and 67% for high swirl (S = 0.75) cases, and in terms of Reynolds number (Re), the pressure coefficient decreases by 12% and 15% for Re = 24,600 and 35,000, respectively, compared to Re = 11,600. Besides, the average Nusselt number amplifies by 8% and 17% for medium (S = 0.3) and high swirl (S = 0.75) flow, respectively, while compared to Re = 11,600, the average Nusselt number raises by 58% and 98% for Re = 24,600 and 35,000, respectively. The eddy viscosity increases strongly with the growth of swirl intensity, while a monotonous vorticity distribution is achieved at high swirl conditions.

Jet impingement has immense applications in industrial cooling, such as glass tempering, turbine blades, electrical equipment, etc. The interplay in-between several jet arrangements and the effect of swirl intensity require enormous study to achieve steady heat transfer. This paper numerically investigates an inline array of 25 circular confined swirling air jets impinging vertically on a flat surface. In this regard, three-dimensional simulations are executed using the finite volume method for a number of control parameters, such as Reynolds number (Re = 11600, 24600, and 35000), impinging distance (H/D = 0.25, 0.5, 1), swirl number (S = 0.3 and 0.75) and jet-to-jet separation distance (Z/D = 2.5), where, D is the nozzle diameter. Impinging pressure distribution, flow velocity, surface Nusselt number, and Reynolds stresses are investigated for different operating conditions. The results reveal that both the wall pressure and surface Nusselt number are comparatively uniform in the case of high swirl flow. Moreover, distinct heat transfer behavior is observed from the unconfined condition for high swirl flow in which the heat transfer is constant after a certain radial distance. The Reynolds normal stress adjacent to the nozzle exit is more rigorous than the downstream regions while Reynolds shear stress varies unpredictably along the radial direction. In addition, an estimated 102 % enhancement in average Nusselt number is observed for high swirl flow, at a Reynolds number increment from 11600 to 35000. This enhancement is evident by 23 % in terms of thermal performance factor.  Besides, the average Nusselt number and thermal performance factor augmented by 19 % and 8 %, respectively, for an increased swirl intensity at low a Reynolds number (Re =11600).