Effect of Turning Vane Configurations on Heat Transfer and Pressure Drop in a Ribbed Internal Cooling System

The ribbed serpentine blade cooling system is a typical configuration in the modern gas turbine airfoil. In this study, experimental and the numerical efforts were carried out to investigate the local heat transfer and pressure drop distribution of a ribbed blade cooling system with different configurations in the turn region. A test rig containing a ribbed rectangular U-duct with a 180 deg round turn was built in Tsinghua University for this study. The transient liquid crystal method was applied to get the heat transfer distribution. Nine test cases with three turn configurations under three Reynolds numbers were carried out in the experiment. Pressure was measured along the duct in order to determine the influence of turning vane configurations on pressure drop. The test cases were also analyzed numerically based on Reynolds-averaged Navier-Stokes (RANS) with three different turbulence models: the $k-ε$ model, the SST reattachment model, and the Omega Reynolds stress (ORS) turbulence model. Both the experimental and numerical results showed a significant influence of the turning vane configuration on the heat transfer and pressure drop in the convective cooling channel. Among the three configurations, the loss coefficient of turn in configuration 2 was lowest due to the introduction of turning vane. Even the ribs were added in the turn region of configuration 3, the loss coefficient and friction factor are reduced by 23% and 17.5%, respectively. Meanwhile, the heat transfer in baseline configuration is still the highest. As the introduction of turning vane, the heat transfer in the region after turn was reduced by 35%. In configuration 3, the heat transfer in the turn region was enhanced by 15% as the ribs installed in the turn region. In the before turn region, the pressure drop and heat transfer was not influenced by the turn configuration. All the turbulence models captured the trend of heat transfer and pressure drop distribution of three test sections correctly, but all provide overpredicted heat transfer results. Among the models, the ORS turbulence model provided the best prediction. While aiming at high heat transfer level and low pressure drop, it is suggested that a suitable turn configuration, especially with the turning vane and/or the ribs, is a promising way to meet the conflicted requirements of the heat transfer and pressure drop in the convective cooling system.