This study presents the results of the aerothermal analysis of an axial turbine with rim seal cavity using conjugate heat transfer computation (CHT). The CHT computations were performed for a two-stage turbine with stator well cavity at the sealing flow rates between 0–2% of the main annulus flow utilizing the commercial solver ANSYS CFX. The results were compared with that of conventional uncoupled approaches in which a heat transfer coefficient is first derived from CFD solutions and then taken as boundary condition for a thermal conduction analysis of the solid domains. As it turns out, for the thermal load prediction, the global results obtained by CHT and uncoupled computations were similar, while with the increase of sealing flow rate remarkable differences emerged. In addition, the sealing flow significantly affects the thermal loading of the blade and disk as well as the strength of the secondary vortex. A negative incidence at the downstream rotor leading edge was observed along with the changing of blade loading due to the low tangential momentum cavity egress flow.
This paper presents a study analyzing the aerodynamic effect and loss mechanism of hub and shroud leakage flow for an axial turbine stage. A series of computational fluid dynamics computations were performed to investigate the effect of various complexity of leakage configurations on the flow field. It is found that a non-linear relationship between different flow systems emerges in the vicinity of both the shroud and hub leakage flow exhibiting a deviation of flow direction and a radial shift of flow pattern, while the efficiency drop caused by the shroud and hub leakage configurations can be added linearly. By analyzing the expansion process in the cooled turbine and the spatial distribution of viscous dissipation term, the loss sources which can be directly traced back to the flow phenomena were indentified. Based on the aerodynamic feature of the turbine, an analytical approach to separate and quantify loss sources was proposed and applied to analyze the turbine. Four kinds of loss mechanisms, referred to as cavity losses, mixing losses, extra losses, and the leakage work reduction, were observed and their contributions were eventually represented by efficiency penalty.
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