Effects of pin-fins with trapezoidal endwall on heat transfer characteristics in gas turbine blade internal cooling channels

All the studies about pin-fins so far focus on investigating the geometry and configurations of pin-fins to perceive the mechanism of the flow and vortices and maximize the heat transfer efficiency index (HTEI) of the channel. However, questions remained about the effect of the endwall, which can be used to develop and conserve the vortices around the pins. These vortices are typically the key factors influencing the heat transfer capacity of the channel but have not been investigated properly. This work numerically investigates the vortices development and preservation of the channel with three types of endwall-turbulation systems, i.e., the flat endwall, the protruding endwall, and the indented endwall, and the structure of the flow therein. The heat transfer characteristics, which include Nusselt number, friction factor, and HTEI, are studied and compared between all cases with Reynolds numbers ranging from 7400 to 36000. It is reported in the results that, with these new endwall configurations, the high heat transfer regions near the pin-fins are remarkably enlarged compared to the flat endwall. Moreover, in the meantime, both the new endwall configurations enhanced the heat transfer capacity of the channel near the pin-fins, represented by the Nusselt number. The HTEI of these two new designs outperform the baseline case by 37.8 % with the indented endwall and 15.9 % with the protruding endwall. It is discovered that the increase in Nu when applying the trapezoidal endwall to the channel is mainly produced by the combination of the indentations and the protrusions. The protrusions are meant to increase the momentum of the gas passing through it so that the flow will interact more productively with the heated wall. The indentations, on the other hand, enlarge the area of the horseshoe vortices (HV) and preserve it when it is on the verge of collapse. By varying the height of the indentation and the protrusion, it is found that with the small height, both configurations produce a much lower friction factor but much higher heat transfer capacity, leading to a relatively higher HTEI, up to 77.7 % and 41.5 % higher than the flat endwall case of the indented and protruding endwall, respectively. The investigations resulted in diminishing the wake behind the pin-fin with a high-height trapezoidal endwall. For the indented endwall, the deep endwall increases the velocity at the entrance of the indentations and induces more turbulence when the flow exits them. These phenomena result in higher heat transfer of the channel. Besides, the highly elevated protruding endwalls increase heat transfer by creating more turbulence around them and the pin-fins but induce more pressure loss penalty. These results indicated the great potential for improving the heat transfer capability of pin-fins by optimizing endwall con-figurations, which could benefit future designs for industries.