Comparison of Heat Transfer Measurements With Computations for Turbulent Flow Around a 180 deg Bend

Results of detailed heat transfer measurements are presented for all four walls of a 180 deg 1:1 aspect ratio duct. Experiments using a transient heat transfer technique with liquid crystal thermography were conducted for turbulent flow over a Reynolds numbers range of 12,500–50,000. Computational results using a Navier–Stokes code are also presented to complement the experiments. Two near-wall shear-stress treatments (wall functions and the two layer wall integration method) were evaluated in conjunction with k–ε formulation of turbulence to assess their ability to predict high local gradients in heat transfer. Results showed that heat transfer on the convex and concave walls is a manifestation of the complex flow field created by the 180 deg bend. For the flat walls, the streamwise average Nusselt number increases to approximately two times the fully developed turbulent flow value. Ninety degrees into the bend, the importance of the cross-stream gradients is evident with the Nusselt number varying from approximately one to three times the fully developed turbulent flow value. The numerical predictions with two-layer wall integration k–ε turbulence model show very good agreement with the experimental data. These results reinforce the need to predict local heat transfer rates accurately in cooling passages of advanced turbine airfoils to enhance the durability of these components.