Leading edge cooling cavities in modern gas turbine airfoils play an important role in maintaining the leading edge temperature at levels consistent with airfoil design life. These cavities often have a complex cross-sectional shape to be compatible with the external contour of the airfoil at the leading edge. In some current designs, to enhance the heat transfer coefficient along the leading edge of an airfoil, the cooling flow enters the leading edge cavity from the adjacent cavity through a series of cross-over holes, cast on the partition wall between the two cavities. The cross-over jets impinge on the leading-edge wall then form a cross- flow that moves towards the airfoil tip. In this experimental setup, there were nine cross-over holes with race-track-shaped cross-sections on the partition wall. To investigate the effects of cross-flow created by the upstream jets (spent air) on the flow through each hole and on the impingement heat transfer coefficients, five cross-over flow arrangements were studied. These flow arrangements were for 0, 1, 2, 3 and 4 jets upstream of the cross-over hole number 5 for which the impingement heat transfer coefficients were measured. Tests were run for a jet to target wall distance ratio, Z/Dh, of 2.81 and a range of local jet Reynolds numbers (where measurement were performed) from 7,000 to 32,000. For the numerical analyses, all tested geometries were meshed with all-hexa structured mesh of high near-wall concentration. Boundary conditions identical to those of experiments were applied and several turbulence model results were compared. The numerical analyses also provided the share of each cross-over hole from the total flow for different geometries. Comparisons between the experimental and numerical results are also made. The major conclusions of this study were: a) cross-flow produced by the upstream jets caused a slight reduction in impingement heat transfer coefficients, b) depending on the location of the cross-over holes with respect to the incoming jet into the supply channel and the number of cross-over holes, there could be a significant variation in mass flow rate through the cross-over holes, and c) the numerical predictions of impingement heat transfer coefficients, using the standard high Reynolds number k - ε turbulence model in conjunction with the generalized wall function, were in good agreement with the measured values for most cases thus CFD could be considered a viable tool in airfoil cooling circuit designs.
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