Wall Curvature Effect on Overall Thermal Performances of Film Cooling Covered by Thermal Barrier Coatings With Various Geometries

Film cooling coupling with surface thermal barrier coating (TBC) has been widely adopted, bringing to an intensive need of comprehensive overall thermal characteristics. In present work, combined effects of hole-geometry, wall curvature, and cooling air flowrate on the metal overall effectiveness and wall heat flux were discussed. Typical local regions of turbine vanes were simplified as convex, concave, and flat walls. Spraying TBC generated four hole-configurations, including Standard Cylindrical-hole (SC), transverse Trenched-hole (TT-hole), and two modified trenched-holes with Semicircle-shaped Trench (ST) and Sine Wave-shaped Trench (SWT). The ST reduces the exposed area and the SWT improves the fluid-diversion effect of TT. Based on the engine-matched hot-side Biot-numbers, overall cooling effectiveness measurements were carried out under typical blowing ratios (BRs) from 0.5 to 2.0, through capturing wall temperatures by an infrared thermal sensor and thermocouples. Conjugate heat transfer simulations were also conducted, showing good agreement with the experimental data and hence providing additional insights into the heat transfer features and film cooling jet behaviors. The results indicated that the wall curvature effects on overall thermal parameters are relatively weaker, in comparison with the hole-geometry and BR. The trenches can further weaken the wall curvature effect. Comparisons of trench-designs reveals that achievement of strong fluid-diversion in trench is an important principle of trench-modification, which can acquire not only superior overall cooling characteristics, but also a relatively large ability to prevent the hot gas ingestion and the hole-blockages by harmful contaminant-depositions.