Endwall aerothermal and vane phantom cooling performances of turbine nozzle guide vane with trenched holes from applying TBCs

To mitigate the adverse impacts triggered by partial blockage of film holes, the transverse trenches were introduced during thermal barriers coatings (TBCs) application, and various trenched hole schemes of double-row discrete film hole layouts were designed in this paper, particularly upstream trenched holes (UTH), fully trenched holes (FTH) and downstream trenched holes (DTH-1, DTH-2 and DTH-3). In addition, the fully common hole (FCH) and fully blocked hole (FBH) configurations were also provided for comparative analysis of endwall aerothermal performance in realistic turbine cascades. Based on the double-coolant temperature model, endwall aerothermal, vane pressure side (PS) phantom cooling and cascade aerodynamic performances, were analyzed and discussed at design coolant delivery pressure. Results indicated that the transverse trenches contribute to recovering the coolant delivery capacity of film holes, increasing the mass flow ratio from 1.32 % to 1.88 %. Endwall film cooling performance decay triggered by partial film hole blockage can be mitigated by introducing transverse trenches at the downstream film holes (row 2), and even a significant enhancement (more than 40 % in magnitude) is obtained in the region upstream endwall (−0.2 Cx < x < 0). Even though the single-row narrow trenches have a negative impact on vane PS phantom cooling performance, leading to a slight decrease (less than 10 % in levels) compared to the FBH configuration, the root of vane PS is still protected by the separated upstream purge flow at DTH-1 and DTH-3 configurations. Due to enhanced vortex systems near endwall and coolant momentum dissipation, and induced additional vortex system, the thermodynamic energy loss coefficient increases by 0.09 %–0.57 % at trenched hole configurations. In addition, the position of the downstream trenched lip plays a key role in the endwall aerothermal, phantom cooling and cascade aerodynamic performances, and thus, trenched hole schemes should be carefully considered and designed. In general, based on the combined consideration of coolant flow depletion, metal substrate exposure risks and film cooling benefits, the downstream narrow transverse trenches are suggested to be introduced in this film hole layout during TBCs application.