Comparison of heat transfer enhancement of an internal blade tip with metal or insulating pins

Cooling methods are needed for the turbine blade tips to ensure a long durability and safe operation. A common way to cool the tip is to use serpentine passages with 180-deg turn under the blade tipcap taking advantage of the three-dimensional turning effect and impingement like flow. Improving internal convective cooling is therefore required to increase the blade tip life. In the present study, the augmented heat transfer of an internal blade tip with pin-fin arrays has been investigated numerically using a conjugated heat transfer approach. The computational models consist of a twopass channel with 180-deg turn and an array of pin-fins mounted on the tip-cap, and a smooth-tip two-pass channel. The computational domain includes the fluid region and the solid pins as well as the tip regions. Turbulent convective heat transfer between the fluid and pins, and heat conduction within pins and tip are simultaneously computed. The main objective of the present study is to observe the effect of the pin material on heat transfer enhancement of pin-finned tips. It is found that due to the combination of turning impingement and pin-fin crossflow, the heat transfer coefficient of the pin-finned tip is a factor of 2.4 higher than that of a smooth tip at the cost of an increased pressure drop by about 10%. Disregarding the factor of the increased active heat transfer area, the tip with metal Aluminium pins provides around 15% and 7% higher heat transfer enhancement than the tips with insulting Wood pins and Renshape pins, respectively.