Conjugate Heat Transfer Enhancement of an Internal Blade Pin-Finned Tip-Wall

Abstract

To improve gas turbine performance, the operating temperature has been increased continuously. However, the heat transferred to the turbine blade is substantially increased as the turbine inlet temperature is increased. Cooling methods are therefore needed for the turbine blades to ensure a long durability and safe operation. The blade tip region is exposed to the hot gas flow and is difficult to cool. A common way to cool the tip is to use serpentine passages with 180-deg turn under the blade tip-cap taking advantage of the three-dimensional turning effect and impingement. Increasing internal convective cooling is therefore required to increase the blade tip life. In this paper, augmented heat transfer of a blade tip with internal pin-fins has been investigated numerically using a conjugate heat transfer approach. The computational model consists of a two-pass channel with 180-deg turn and an array of pin-fins mounted on the tip-cap. The computational domain includes the fluid region and the solid pins as well as the solid tip regions. Turbulent convective heat transfer between the fluid and pins, and heat conduction within pins and tip are simultaneously computed. The inlet Reynolds numbers are ranging from 100,000 to 600,000. Details of the 3D fluid flow and heat transfer over the tip surface are presented. A comparison of the overall performance of the two models is presented. It is found that due to the combination of turning impingement and pin-fin cross flow, the heat transfer coefficient of the pin-finned tip is a factor of about 3.0 higher than that of a smooth tip. This augmentation is achieved at the cost of a pressure drop penalty of about 7%. With the conjugate heat transfer method, not only the simulated model is close to the experimental model, but also the distribution of the external tip heat transfer can be relevant for thermal design of turbine blade tips.