combined numerical and experimental study of heat transfer of a turbine airfoil cooling channel with angled ribs and a 180-degree u-bend turn

Abstract

Turbine airfoils cooling technology has been developing for more than 60 years to protect turbine airfoils from high temperature airflow. Rib-roughened cooling channel inside turbine airfoil is one of the most efficient way. This study investigates thermal behavior of a turbine airfoil cooling channel around a rib-roughened 180-degree turn for two different rib arrangements. Numerical and experimental methods are used to obtain heat transfer coefficients for different Reynolds numbers. The test rig is made up of two rectangular channels of aspect ratio 1/6 connected together with a U-bent. This two-legged channel is roughened with 45° ribs in two arrangements. In the Baseline arrangement, the ribs are pointing away from the flow direction, while in the second arrangement, the ribs point towards flow direction. The numerical model is identical to the test rig in geometry and in boundary conditions. A total of 15 million hexahedral structured meshes are used in both numerical models. For turbulence, the realizable − model is selected with enhanced wall treatment. Experimental tests are done using steady state liquid crystal thermography for a range of Reynolds number from 5000 to 40000. The results of numerical models and experimental data are compared and discussed. Numerical simulations and experimental data show good agreement for flow field parameters such as friction factor and turn losses. The heat transfer results, however, show a 20 to 30 percent difference with the numerical results being higher than the test data. One major conclusion of this study is that the rib geometry and U turn have strong influence on the heat transfer coefficient distribution.