Turbulent Flow and Heat Transfer in Variable Geometry U-Bend Blade Cooling Passage

Resumo

It has been a common practice that serpentine cooling passages are used in gas turbine blade to enhance the cooling performance. Insufficient cooled blades are subject to oxidation, creep rupture, and even melting of the material. To control and improve temperature of blade; it requires better understanding of a flow behavior and heat transfer inside the curved U-bends. The interactions between secondary flows and separation lead to very complex flow patterns. To accurately simulate these flows and heat transfer, and to improve the cooling performance, both refined turbulence models and higher-order numerical schemes are indispensable tools for turbine designers. Previous studies have shown that the flow and heat transfer characteristics through curved bends, even with a moderate curvature, cannot be accurately simulated. It is the conventional belief and practice that the usage of a proper turbulence model and a reliable numerical scheme achieves accurate computations. The three-dimensional turbulent flows and heat transfer in a square U-bend duct are numerically studied by using a nonlinear low-Reynolds number (low-Re) k-ω, k-ε and RSM models and the cubic terms are included to represent the effects of extra strain-rates such as streamline curvature and three-dimensionality on both turbulence normal and shear stresses. The finite volume method incorporated with a higher-order bounded interpolation scheme has been employed in the present study. The objective of this study is to validate the simulations using RSM, k-ω, and k-ε models with the experimental results. Three different Reynolds numbers, 36,000, 60,000 and 100,000, were used.