Visualization and quantitation of unsteadiness of film cooling near stagnation line of a double-wall cooled vane leading edge

Advanced double-wall cooling configuration has a large potential to reduce the highest heat load level in turbine vane leading-edge region both internally and externally. However, to date, the related knowledge of flow and thermal performances is still relatively scarce. In present work, the fluid-interaction-induced unsteady film cooling in leading-edge region of a double-wall cooled vane was of main concern, since that the cooling unsteadiness level is a crucial influencing factor of component durability. A time-resolved planar quantitative light sheet (QLS) system was designed to visualize the transient jet-behaviors and acquire the concentration-variations due to the unsteady film cooling jets. The atomizing dry-ice was validated as the suitable tracer particles, effectively avoiding the particle-blockages in the internal small-scale cooling-cavities of double-wall configuration. The effects of the amount and location of jet-ejections on the jet-trajectory, time-averaged film effectiveness and cooling unsteadiness levels in the stagnation zone of a double-wall cooling configuration with an actual vane geometry were deeply discussed. The relatively uniform time-averaged film coverage along the vane span can be found; however, the jets near the hub end-wall can produce the higher wall coverage fluctuation and the more unsteady jet-penetration. Increasing ejection-amount can change the jet-trajectory, as well as improve the time-averaged film effectiveness over the entire surface and the cooling unsteadiness level in some regions. The statistics of transient QLS data indicated that the unsteady film coverage and jet-penetration have the random feature. In general, besides the time-averaged cooling performances widely concerned in previous literature, the detailed knowledge of cooling unsteadiness level is also needed intensively, to design the more efficient double-wall cooling scheme in vane's stagnation region, which has the improved component-durability as well.