Overall thermal performances of backward film cooling with simulated surface thermal barrier coatings at various walls

Abstract

Backward film cooling can protect more efficiently some regions of turbine hot components, in comparison with the forward jet. The rapid increase of operational temperature requires the developments of the coupling of active cooling and thermal barrier coating (TBC). A study on the overall thermal performances of the system of TBC and backward film cooling was conducted through both the overall effectiveness experiments and predictions in a lab environment. The models feature the engine-matched hot-side Biot numbers to acquire the actual overall effectiveness. The concerned factors include the jet-orientation, TBC-thickness, spraying-induced hole-geometry, blowing ratio, and wall curvature. The present TBC-spraying can induce the standard cylindrical (SC) and transverse trenched (TT) holes. In general, the backward film cooling can reduce the potential of TBC insulation, due to the favorable cooling air coverage. The hole-geometry-induced difference in metal overall effectiveness can be significantly weakened by the backward jet. However, the TT design is more proposed, due to the lower TBC temperature. Moreover, relative to the forward jet, the backward one features the larger potential to prevent the thermal damage of exposed metal inside trench from the ingestion of hot gas. Additionally, the wall curvature effect on the TT cooling is insignificant.

Keywords

• Backward jet
• Overall effectiveness
• Thermal barrier coating
• Transverse trench
• Wall curvature
• Biot number similarity