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Influence of cavity flow on turbine aerodynamics

Abstract : Turbomachinery is widely used for electrical power generation mechanical drive and aviation industries. Any efficiency improvement can have a significant impact on overall fuel consumption and global emission. The continuous effort to improve efficiency by higher pressure ratio, temperature and aerodynamic improvement in the main annulus passage of the gas turbine made possible to reach a high degree of efficiency. Since the current benefit for increased pressure, temperature and main annulus aerodynamic improvement have become more and more difficult to achieve, a further insight has been given to the flow in mixing and cooling areas. These topics are inherent in gas turbines due to hot gas flows in the main annulus downstream of the combustion chamber. Some relatively cold air is collected at the compressor to achieve various tasks through the secondary air system as bearing pressurization or turbine disc cooling in order to ensure a safe operation. However, the cooling comes as a cost since it is compressed at an appropriate pressure but does not contribute to the cycle output and the net contribution is negative. In addition, the cooling that blows in the cavities of the turbine reduces the output power due to losses associated with the main annulus mixing processes. This thesis aims at understanding the loss generation processes that occur in the main annulus due to the additional purge flow blowing. This phenomenon is tackled using numerical simulation of two configurations with experimental data available and the use of a method to track loss generation based on an exergy formulation (energy balance in the purpose to generate work). This formulation enables a local and directional evaluation of losses. RANS, LES and LES-LBM simulation have been performed with the different solvers available during this thesis: elsA, AVBP and Pro-LB. First, the simulations were led on a low speed linear five nozzle guide vane cascade with an upstream cavity to primarily study the interaction process between the cavity and the mainstream flow over different rim seal geometries and purge flow rates. This configuration made possible to highlight the influence of the purge flow on secondary flows developing in the passage as well as the influence of the mixing layer at the rim-seal interface on pressure fluctuations and passage vortex unsteadiness. The second configuration is a two-stage low-speed low pressure turbine more realistic and closer to an industrial configuration. Different purge flow rates could be supplied in the cavity. The additional rotating effect induced by the rotor disc as well as rotor/stator interaction provided additional phenomena compared to the linear cascade configuration: a complex blowing of the cavity flow in the mainstream due to the cavity entrainment effect, wakes and potential effect, an interaction of upstream wakes and secondary vortices on downstream rows while the feeding process of secondary structures by the cavity flow showed similar behavior than the linear cascade.
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Contributor : Maxime Fiore <>
Submitted on : Saturday, May 11, 2019 - 9:15:12 AM
Last modification on : Wednesday, May 22, 2019 - 1:14:50 AM
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  • HAL Id : tel-02126215, version 1



Maxime Fiore. Influence of cavity flow on turbine aerodynamics. Engineering Sciences [physics]. ISAE - Institut Supérieur de l'Aéronautique et de l'Espace, 2019. English. ⟨tel-02126215⟩