Film cooling performance and aerodynamic characteristics of mid-passage gap in turbine guide vane doublets

Abstract

In engineering practice, high-pressure turbine guide vanes are generally manufactured as single- or double-airfoil sections, inevitably introducing mid-passage gaps (MPGs) between adjacent sections. Although doublet vanes can reduce leakage losses, there is little research analyzing their flow and cooling characteristics. This study numerically focuses on the differences in cooling and aerodynamic characteristics among gapless structures, singlets, and doublets. The results show that MPGs complicate the vortex system near the endwall of the passage, and doublets alter the characteristics of vortex interactions downstream of the trailing edge (TE). Gas ingress and radial leakage jets are the primary flow features introduced by MPGs. The gas ingress leads to an increase in the leakage rate and narrows the outflow area, resulting in an enhancement of the leakage. Leakage jets roll up into leakage vortex (LV) under cross-flow and also enhances upper passage vortex (UPV). Entrained into these vortices, the coolant effectively cools the endwall downstream of MPGs. The UPV adheres closely to the suction side of the passage, whereas the LV adheres to the pressure side. Consequently, in the region downstream of the TE, the LV interacts with the UPV from the adjacent passage rather than from the same passage. Therefore, the flow field downstream of the TE in doublets is not a simple alternating superposition of that from gapless structures and singlets. Instead, it develops distinct loss and cooling characteristics in doublets. Additionally, MPGs significantly enhance the wake, while doublets introduce new periodic characteristics to the outlet flow field.