Numerical Investigation of Heat Transfer Characteristics of Pin-Fins with Roughed Endwalls in Gas Turbine Blade Internal Cooling Channels

Abstract

In modern jet engines, the effective cooling structure design is essential to both increase turbine efficiency and, in the meantime, maintain structural integrality. Pin-fin arrays play a crucial role in the cooling mechanism of the turbine blade internal cooling system. In the context of investigating the efficiency of cooling techniques using pin-fins, while the other studies focus on the pin-fin configurations, the current study is a step towards optimizing cooling cascade endwalls for better maneuver and reservation of vortices which lead to higher heat transfer near the endwalls. This study presents the results from the investigations of the flow-field and heat transfer characteristics of the pin-fin arrays with roughed endwalls, i.e., recessed endwalls and extruded endwalls types. The heat transfer and pressure drop characteristics of the channel are numerically examined to compare with those of the flat endwalls case within a range of inlet Reynolds number, which varies from 7400 to 36000. Both the leading and trailing sides of the channel are divided into five regions in the streamwise direction to understand further the heat transfer capacity of the pin-fins and the endwalls. The results show that, with these new endwall configurations, the high heat transfer regions near the pin-fins are remarkably enlarged compared to the flat endwalls. And in the meantime, both the new endwall arrangements enhance the heat transfer capacity of the channel near the pin-fins. The two new designs outperform the baseline case, with the heat transfer efficiency index (HTEI) improved by 37.8% for the recessed endwalls and 15.9% for the extruded endwalls. By varying the height of the indentation and the protrusion, it is found that, with smaller heights, both configurations produce a much lower friction factor. However, with much higher heat transfer capacity, leading to relatively higher values of heat transfer efficiency index (HTEI), up to 77.7% and 41.5% of the recessed and extruded endwalls are higher than HTEI of the channel with flat endwalls. These results indicate the great potential for improving the heat transfer capability of pin-fins by optimizing endwall configurations.