Heat transfer and pressure drop measurements on rotating matrix cooling geometries for airfoil trailing edges

In the present paper the combined effects of rotation and channel orientation on heat transfer and pressure drop along two scaled up matrix geometries suitable for trailing edge cooling of gas turbine airfoils are investigated. Experimental tests were carried out under static and rotating conditions. Rotating tests were performed for two different ori- entations of the matrix channel with respect to the rotating plane: 0deg and 30deg. This latter configuration is representative of the exit angle of a real gas turbine blade. Test models are designed in order to replicate an internal geometry suitable for blade trail- ing edge cooling, with a 90deg turning flow before entering the matrix array which has an axial development. Both the investigated geometries have a cross angle of 45deg be- tween ribs and different values of sub-channels and rib thick- ness: one has four sub-channels and lower rib thickness (open area 84.5%), one has six sub-channels and higher rib thickness (open area 53.5%). Both geometries have a converging angle of 11.4deg. Matrix models have been axially divided in 5 aluminum elements per side in order to evaluate the heat transfer coefficient in 5 different locations in the main flow direction. Metal tempera- ture was measured with embedded thermocouples and thin-foil heaters were used to provide a constant heat flux during each test. Heat transfer coefficients were measured applying a steady state technique based on a regional average method and varying the sub-channel Reynolds number Res from 2000 to 10000 and the sub-channel Rotation number Ros from 0 to 0.250 in order to have both Reynolds and Rotation number similitude with the real conditions. A post-processing procedure, which takes into account the tem- perature gradients within the model, was developed to correctly compute average heat transfer coefficients starting from discrete temperature measurements.