## 2 Research Object and Case Settings  
Based on the typical internal cooling structure of turbine blades presented by [PERSON] [8], the trapezoidal trailing edge cooling channels with lateral extraction slots are modeled in this paper, shown in Figure 1. The coolant enters the channel from the bottom surface and flows through a 135 mm long inlet extension to achieve a fully developed state. Then the coolant flows into the main channel of trailing edge whose radial length is 206 mm, and the dimples/protrusions are evenly arranged on the wall of both sides. In addition, six lateral slots are set up at the short side, from which the coolant is discharged.  
Figure 1: Typical internal cooling structure of turbine blade (left) [8] and the trailing edge cooling channels studied in this paper (right).  
Figure 2 shows the structures and parameters of five channel outlet configurations, where Figure 2a is the channel without second passage (OC1), and it can be seen that six lateral slots with the width of 20 mm and the pitch of 34 mm, are evenly arranged in the radial direction; Figure 2b is the channel with radially inward flow second passage (OC2); Figure 2c is the channel with radially outward flow second passage (OC3); Figure 2d is the channel with lateral extraction and top region outflow (OC4); (e) is the channel with both sides lateral extractions (OC5). Figure 2f displays the cross section of trailing edge channel with second passage. The main channel has a cross section of isosceles trapezoid with a long side of 21.6 mm, a short side of 6 mm and a height of 59 mm. The thickness and length of lateral slot are 3 and 8 mm, respectively. And the second passage has a rectangular cross section of \(19\times 16\) mm. It should be noted that the different outlet configurations have the same main channel, lateral slots and second passage.  
Figure 3 shows the dimple/protrusion structure and arrangement in the trailing edge channels, where Figure 3a is the arrangement of dimple/protrusion, Figure 3b,c are the cross sections with dimples and protrusions, respectively. It can be seen that the inline arrangement of 4 (spanwise or axial direction) \(\times\) 13 (streamwise or radial direction) is applied for dimples/protrusions, whose diameter and depth-to-diameter ratio are 9 and 0.2 mm, respectively. Four parameters \(P_{1}\), \(P_{2}\), \(P_{x}\), \(P_{z}\), related to the layout, are 13, 9.7, 15, 12 mm, respectively. In this paper, three dimple/protrusion arrangements, i.e., all dimple (named dimple case), all protrusion (named protrusion case), dimple-protrusion staggered arrangement with the first row of dimple (named dimple-protrusion case) are considered.  
Table 1 gives the case settings of this investigation, mainly including two parts. In the Part I, the effect of channel outlet configuration is studied using smooth channels, and the flow and heat transfer characteristics are analyzed for five outlet configurations within the _Re_ range of 10,000-100,000. In the Part II, the effect of dimple/protrusion arrangement is explored based on the OC4 structure, and flow and heat transfer characteristics are discussed for three dimple/protrusion arrangements within the _Re_ range of 10,000-100,000.  
Figure 2: Structures and parameters of different channel outlet configurations.