## 1 Introduction
[7] enhanced heat transfer performance using the double swirl chambers (DSC) cooling technology with multiple in-line nozzles in the leading edge of gas turbine blades to, as the special configuration can, produce two anti-rotation swirls. Compared with traditional impingement cooling, the new cooling method can provide more uniform heat transfer distribution and a higher heat transfer rate in the axial chamber. A better globally averaged thermal performance coefficient can be obtained with the new cooling technology when inlet slots and Re are the same. [PERSON] et al. [8] investigated the effect of channel shape on the cooling performance of DSC technology using five double swirl channels formed by two overlapping elliptic cylinders with different length ratios between the vertical and the horizontal semi-axis. The results showed that the largest length ratio between the vertical and the horizontal semi-axis of the target channel produced the lowest flow loss, largest averaged \(Nu\) and best heat transfer performance. Heat transfer distribution on the target surface becomes more uniform with the length ratio decreasing. The enhancements of the maximum overall averaged \(Nu\) and heat transfer performance with DSC are about 30% and 33%, respectively. The studies mentioned above indicate that swirling flow in the cooling chamber in the leading edge can improve the cooling effect, which sets a clear direction for future research. Compared with the complex swirling flow chamber, a special jet nozzle is relatively simple to generate swirling flow. The application of swirl, i.e., superimposition of a circumferential or tangential velocity component to the axial jet flow, can markedly affect the flow and turbulence characteristics of a jet. Compared with the conventional non-swirling case, the swirling jet spreads more rapidly and widely, and entrains the surrounding fluid at a greater rate. Thus, the growth rate of turbulence intensity is higher, and the mean velocity decays more rapidly. Under the comprehensive effect of turbulence intensity and velocity decay, the heat transfer coefficient on the target surface may be enhanced or weakened according to the swirl element. In recent years, different inserts have been introduced to generate swirling jets and generally include a screw rod, twisted tapes/strips, or a guide vane inside a nozzle which can form a swirl element. [PERSON] et al. [9] employed a screw rod with eight narrow channels with an angle of \(\theta\) = 0\({}^{\circ}\) or 21\({}^{\circ}\). They observed that the presence of an insert modified the flow and increased the \(Nu\) values in comparison with classical round jet flow only for a small nozzle-to-plate distance. Using a twisted belt as a flow guiding element, [PERSON] et al. [10; 11] compared the heat transfer characteristics between the swirling impinging jet and the round hole jet with the twisted rate \(y/w\) = 3-6, \(H/D\) = 2-8, and \(Re\) = 4000-16,000. Under the condition of a small \(H/D\) with large \(y/w\) and \(Re\), the \(Nu\) of the target surface reached the maximum, and the coefficient of heat transfer of the rotating jet was higher than that of the round hole jet; however, when \(H/D\) was large, the result reversed. With a twisted strip used to generate the swirling flow, [PERSON] et al. [12] investigated the flow and heat transfer enhancement mechanism of a swirling impinging jet array with \(H/D\) = 4, \(Re\) = 20,000, and \(S\) = 0-0.94. They found that as the swirling number increased, the jet dispersion became larger. Compared with the traditional round hole jet, the heat transfer of the swirling jet was enhanced at \(S\) = 0.4; the intensity of heat transfer was weakened at a large swirling number, i.e., \(S\) = 0.78 and \(S\) = 0.94. Our research group [13; 14] recently reported a threaded nozzle, which generated swirling flow and enhanced heat transfer performance of impinging jets under the vertical and inclined conditions compared with the conventional round hole.