Abstract
The combination of designing film cooling and spraying thermal barrier coatings (TBC) is widely used to protect turbine components and improve their durability in extremely terrible operation conditions. Nevertheless, one obstacle to the synergy of both is that partial blockage of film coolant delivery holes (referred to as film holes in this article) is commonly observed in realistic turbine cascades when the TBC material is applied to the components, leading to a significant reduction in the coolant flow area. In the double-row discrete film hole layouts, endwall profiles may lead to variations between upstream film hole blockage (row 1) and downstream film hole blockage (row 2). Therefore, various blocked film hole configurations of this double-row discrete film hole layout are considered in this article, specifically common holes (CH), upstream blocked holes (UBH + DCH), downstream blocked holes (UCH + DBH), and fully blocked holes (FBH). In addition, the aerothermal performance with different endwall profiles (simplified flat endwall and convergent contoured endwall) was comparatively analyzed, aiming to present a relatively comprehensive evaluation of aerothermal performance discrepancy between simplified flat endwall and convergent contoured endwall and provide more insightful references for industrial designers. Based on the double-coolant temperature model, the film hole discharge coefficient (Cd), endwall film cooling effectiveness , secondary film cooling (phantom cooling) effectiveness of vane pressure side (PS), and vane cascade total pressure loss coefficient (TPLC) were experimentally and numerically studied at the design coolant supply pressure condition. Results indicated that partial film hole blockage is pernicious to coolant flowrate, endwall film cooling, and vane PS phantom cooling performances, and thus, the geometric defects of film holes due to TBC application should be adequately considered as part of the film cooling layout designs. Compared to the simplified flat endwall, the deterioration of aerothermal performance is marginal for the convergent contoured endwall. In addition, a remarkable decay of endwall film cooling effectiveness (10.9% in magnitude against CH configuration, approximately twice that of the UBH + DCH configuration), was observed at the UCH + DBH configuration for the convergent contoured endwall, which presented an opposite trend for the simplified flat endwall. This indicates that the downstream film hole blockage should be paid more attention in this double-row discrete film hole layout. The corresponding study findings obtained from studies on simplified flat endwall should be further evaluated for their applicability to those on realistic turbine cascades. Due to the weakened overall interaction intensity between the coolant and the mainstream, the TPLC was found to decrease by 1.2–2.3% for the simplified flat endwall and less than 0.7% for the convergent contoured endwall. Overall, endwall contouring can play a positive role in mitigating the adverse impacts of partial film hole blockage caused by TBC materials deposition and increase the robustness of the vane cascade aerodynamic performance against the geometric defects of film holes.
