## 4 Discussion  
In this study, the flow structure, \(\dot{W}\), overall \(\dot{Q}\), and \(PEC\) characteristics of a novel, high-performance CMJICS with passive flow control that can significantly reduce the adverse effects of crossflow on heat transfer and pressure drop were analyzed through 3D CFD simulations. By deflecting the air jets impinging in the normal direction on the top faces of the hexagonally arranged CPs toward their lateral faces via CGVs, interactions of the crossflow with jets are significantly reduced, and \(\dot{Q}\) is considerably enhanced compared with a flat target surface, at the expense of a small increase in \(\dot{W}\). Since the CPs have a larger diameter than the jet orifices, the impingement cooling of the jets is focused on the top faces of the CPs, and the wall jets formed thereafter are directed by CGVs to the lateral faces of the CPs, effectively cooling them and reducing the interactions of crossflow with the impinging jets. Therefore, the overall \(\dot{Q}\) and \(PEC\) of the novel cooling system developed in \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Literature** & **Protrusion Type** & \(\dot{Q}/\dot{Q}_{o}\) & \(\overline{Nu}/\overline{Nu}_{o}\) & \(PEC\) \\ \hline \multirow{2}{*}{Present study} & Cylindrical protrusion & 1.65 & 0.606–0.917 & 1.05–1.519 \\  & with guide vanes & & & \\  & Detached ribs & 1 & 1.04 & - \\  & [48] & Cubic micro pin fins & 1.34–1.42 & 0.89–0.94 & - \\  & [51] & Square pin fins & 1.25–1.35 & 0.784–0.82 & - \\  & [79] & Horseshoe shaped ribs & 1.27 & - & - \\  & [80] & Full-height pin fins & - & 1.323 & - \\  & [80] & Mini pin fins & - & 1.747 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Performance comparison of various CMJICSs. Figure 20: For \(H_{p}/D\) of 4, the \(PEC\) according to \(D_{p}/D\) at various jet \(Re\) numbers. this study are higher than of a system without flow control, in which the jets impinge on both the protrusions and the base plate or the base plate between the protrusions. As a jet becomes shorter, its advection and diffusion in lateral directions and the entrainment of surrounding fluid decrease. Therefore, the overall \(\dot{Q}\) of the novel CMJICS can be improved by heightening the CPs, both due to the increased magnitude and coherency of the core velocities of the jets and the increased steepness of the shear layer velocity gradients of the jets, as well as the enlarged lateral surface area of the CPs. Moreover, reducing the deflections and deformations of the jets by the crossflow with passive flow control improves the HTCs at the stagnation zones of the impinging jets, thus the \(\dot{Q}\) on the top faces of the CPs. The \(PEC\) of the novel CMJICS improves with increasing height of the CPs due to a minor proportional increase in \(\dot{W}\) compared with \(\dot{Q}\). The \(\dot{Q}\) and \(PEC\) can be further enhanced by increasing the diameter of the CPs, thereby the areas of their top and lateral surfaces, without a noticeable effect on the morphology of the impinging jets. A shape optimization study of both the top edge fillet and the CGV is needed to achieve more effective cooling without flow separation on the lateral face of a CP. The novel CMJICS developed in this study can be adopted to a system having any configuration of coaxial J-CP-GV triplets and properly located spent fluid outlet ports, including the maximum crossflow arrangement. Moreover, MJIECSs configured as a coaxial J-CP-GV ternary array with interspersed effusion holes can be designed to enhance heat transfer in high-flux cooling applications. Finally, effective cooling of the lateral face of a cylindrical or truncated cone-shaped protrusion can also be realized without a CGV by means of an optimally shaped Coanda-effect rounding downstream of a step at the upper edge of the protrusion.