| Further improving the efficiency of the gas turbine requires a deeper understanding of the unsteady flow mechanisms inside the turbine.Wake vortex is an important origin of unsteadiness and losses in high-pressure turbines and has a significant influence on turbine pressure ratio,efficiency and noise.High-pressure turbine wake vortices have higher characteristic frequencies than other secondary flows,and therefore require high-speed response experimental measurement instruments or high-fidelity unsteady flow solvers.In the experimental research,the main difficulty lies in the transport process of the wake vortex in the high-speed rotating rotor and its interaction with the secondary vortex system of the rotor.In terms of numerical simulation,the flow in a high-pressure turbine is a complex three-dimensional unsteady flow with multi-scales and multi-frequencies.The RANS/URANS method cannot accurately capture the flow with separation,strong shear and mixing,including the wake vortex length characteristics.The DNS,LES methods can well solve this kind of flow,but for the high-Reynolds-flow in high-pressure turbine,the computational cost is too expensive and it is not affordable for the industry.Therefore,the development of high-efficiency,high-fidelity numerical flow solver is important for deepening the understanding of the flow mechanism,partially replacing experiments,shortening the R&D design cycle in the industry,and reducing costs.In terms of numerical tools,this paper implements a delayed detached eddy simulation method with an adaptive low-dissipation numerical scheme,which enables finegrained capture of coherent structures in the flow field and is validated with the VKI LS89 case.In this paper,based on the second law of thermodynamics and the tripledecomposition of unsteady physical quantities,the evaluation method for losses caused by unsteady effects is developed.The investigation reveals that the contribution of the unsteady effect in the high pressure turbine flow to the loss is the main part,and provides the direction and theoretical basis for the unsteady optimization design of the high pressure turbine blade.In the aspect of mechanism study,the development,length characteristics and unsteady effect losses of the high pressure turbine vane wake vortex are studied with the delayed detached eddy simulation and proper orthogonal decomposition methods.By the“asymmetric plugging effect”and the “dual eddy model”,the mechanism of the wake vortex's scale characteristics was first explained,which laid the foundation for further understanding and modelling of the wake.At the same time,the wake vortex-shock wave interaction and wake vortex-pressure waves interaction are investigated.On this basis,the quasi-three-dimensional high-pressure turbine stage and three-dimensional high-pressure turbine stage were numerically simulated using the delayed detached eddy simulation method.The basic stator-rotor interaction effects are studied with special attention paid to the wake vortex transportation.Two modes of the wake vortex transportation and overtaking phenomena are discovered.The influence of the annular flow passage and the end wall on the flow in the three-dimensional high-pressure turbine is revealed,the flow field topology in the high-pressure turbine stage is delineated,and the influence of the upstream wake vortex on the secondary vortex system in the rotor passages is revealed.In summary,this paper develops a delayed detached eddy simulation method with an adaptive low-dissipation numerical scheme,proposes an loss assessment method for unsteady effects based on the second law of thermodynamics,and explores the development and transport of wake vortices in high-pressure turbines.The interaction between wake vortices and the secondary vortex system are also revealed.The work in this paper lays a good foundation for further exploration of the multi-scales unsteady flow and heat transfer mechanism of high-pressure turbines. |
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