Measurements of Local Wall Heat Transfer Coefficient in Sharp 180 Degree Turns in Multipass Rib-roughened Channels

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The heat transfer characteristics of turbulent air flow in the sharp turns in multipass rib-roughened cooling channels in high temperature gas turbine airfoils are to be studied. The cooling channels will be modeled as a series of rectangular channels, with rib-roughened walls, connected with two 180 degree turns. The local heat transfer coefficient distribution in and near the turns will be determined with both the naphthalene sublimation mass transfer technique and conventional foil heaters-thermocouples method. Experimental results will be obtained for various channel aspect ratios, turn clearance gaps, curvatures of the turn corners, rib geometries, and flow Reynolds numbers typical of turbine engine applications. Corresponding flow visualization experiments with the oil-lampblack technique will supplement the forced convection experiments. Effective blade cooling prolongs the life of advanced gas turbines. The results of this research will contribute to the understanding of the heat transfer and flow characteristics of multipass rib-roughened channels, which is important in the design of turbine engines.