In a computational study on a high aspect ratio air jet array impingement cooling channel in a maximum crossflow scheme, compared with a uniform jet array and elongated pin fins arrangement, both the efficiency and effectiveness of the system having circular pin fins and more jets on the upstream are higher [53]. In MJISCs where fluid is discharged in either the transverse or opposite direction of the jets, the interaction of wall jets formed by impingement of neighboring immersed jets on the target plate generates fountains. Vortices formed in the shear layers between the immersed jets and fountains deteriorate convective heat transfer by reducing the normal momentum of impinging jets. The cooling performance of MJISCs with fluid discharging in the transverse direction of the jets degrades more since not only normal components of momentum of jets decrease further due to deflection, deformation, and spread of immersed jets by the crossflow, but also boundary-layer thickness increases toward the exit ports. While the cooling performance of a moderate crossflow scheme deteriorates gradually toward both side discharge ports due to increasing deflection, deformation, and spread of jets, that of a maximum crossflow system having a single side discharge port degrades significantly due to excessive crossflow accumulation near the port [34; 40; 54; 55; 56; 57; 58]. According to the literature cited above, the effects of the geometric parameters of protrusions and passive flow control structures having various shapes placed on a target surface on the thermal-fluid performance of CMJICS have not been extensively studied so far. Therefore, the objective of this study is to evaluate the effects of jet _Re_ number and geometric parameters of a novel CMJICS with hexagonally arranged coaxial jet-cylindrical protrusion-guide vane (J-CP-GV) triplets on cooling performance and fluid pumping power requirement through 3D CFD simulations. In this study, first, a novel compound multi-jet impingement cooling system (CMJICS) involving multiple cylindrical protrusion-coaxial guide vane (CP-CGV) pairs placed in a hexagonal configuration on a flat target plate has been developed. In the proposed design, in a confined space, each immersed air jet emanating from a coaxial circular orifice in a flat perforated plate above the target plate impinges in the normal direction on the top face of the corresponding cylindrical protrusion (CP) equipped with a suitably shaped coaxial guide vane (CGV). Due to the smaller diameter of the orifices than that of the CPs, the stagnation zone of an impinging jet and a wall jet formed after impingement enable concentrated highly effective cooling as it spreads on the circular top face of the corresponding CP. A suitably shaped and positioned CGV around a CP directs the wall jet from its top face to its lateral face and then onto the flat target plate, both augmenting cooling with minimal flow separation and significantly mitigating crossflow and fountains' interaction with impinging jets. Increasing the height of the CPs shortens the lengths of the impinging jets, reduces their deflection and deformation due to crossflow, and improves the flatness of their core velocity profile and steepness of their shear layer velocity gradients and, therefore, their cooling performance. As the height of a CP increases, heat transfer is further enhanced due to the enlarging lateral face area. Therefore, as the height of the CPs increases, the adverse effects of the interaction of impinging jets with crossflow and fountains on system cooling performance and pressure drop are significantly reduced, while the \(\dot{Q}\) increases significantly at the expense of slightly increased \(W\) due to the CGVs. The \(\dot{Q}\) can be further enhanced by increasing the diameter of the CPs due to further enlargement of their lateral face area with a minor increase in \(\dot{W}\). Therefore, the system \(PEC\) can achieve exceptionally high values.