Large Eddy Simulation of the Developing Region of a Rotating Ribbed Internal Turbine Blade Cooling Channel

This study focuses on a Large Eddy Simulation (LES) of the entrance region of a gas turbine blade internal cooling duct. The square channel is fitted with in-line turbulators orthogonal to the flow. The rib height-to-hydraulic diameter ratio (e/D_h) is 0.1, and the rib pitch-to-rib height ratio (P/e) is 10. A constant temperature boundary condition is imposed on the walls and the ribs; the flow Reynolds number is 20,000; and the rotation number is 0.3. Results from these calculations indicate that flow development length is much longer than in a stationary channel because of the large effect of rotational Coriolis forces on mean flow and heat transfer, which only begin to exert a substantial influence after 3 to 4 rib pitches from the entrance to the duct. During the development length, heat transfer augmentation increases on the trailing and smooth walls, while it decreases on the leading wall. At the ninth rib, the mean augmentation ratios are to within −12% and −14% of their fully developed values on the trailing and smooth walls, respectively. At both walls there is a gradual increasing trend which suggests that fully developed conditions have not been achieved by the heat transfer coefficient. On the leading wall, however, all results indicate that the heat transfer coefficient has achieved its fully developed augmentation ratio. The calculation clearly shows that the direct effect of Coriolis forces on turbulent structure and intensity have a much stronger effect on heat transfer augmentation than the effect of secondary flows.