Influence of swirl and ingress on windage losses in a low-pressure turbine stator-well cavity

Richard Jackson, Loizos Christodoulou, Zhihui Li, Carl M. Sangan, Stephen Ambrose, Richard Jefferson-Loveday, Gary D. Lock, James A. Scobie

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Abstract

As part of the drive towards achieving net-zero flight by 2050, the development of ultra-high bypass ratio engines will place greater importance on the efficiency of the low-pressure turbine. Stator-well cavities can be a significant source of loss within this system, primarily due to the ingestion of annulus air, which can rotate at a speed less than that of the disc. This paper presents the results of a joint experimental/numerical campaign to relate windage torque to the flow physics in a scaled, engine-realistic stator-well geometry with superposed flows. The primary variables were the pressure ratio across the stator row and the swirl ratio at inlet to the cavity. This is the first paper to relate simultaneous torque and swirl measurements in a stator-well cavity. The numerical simulations have also provided insight into the fluid dynamic behaviour. A reduction in cavity windage torque with superposed flow rate was shown, consistent with the increase in swirl measured by experiments and predicted by computations. The pre-swirled superposed flows reduce the ingestion of negatively swirling fluid from the annulus, effectively increasing the swirl ratio of the flow in the cavity towards that of the rotor. This reduces windage losses; at the design condition with superposed flow, the cavity windage torque reduced by 60% of that of the reference case. Sealing effectiveness increased with superposed flow rate. This was demonstrated through gas concentration measurement/simulations, a reduced radial flow velocity into the cavity and a reduced mass flow rate across the interstage seal. The application of a turbulent transport model showed that ingestion could be explained by shear-driven diffusion. Ingestion increased as inlet swirl ratio reduced, while the pressure ratio was found to have a negligible influence on windage moment coefficient, swirl ratio and sealing effectiveness. In addition to providing fluid dynamic insight, the gas concentration results can be used for validating thermomechanical models. The results in this paper will be of practical interest to the engine designer who wishes to scale information to engine-operating conditions.
Original languageEnglish
Article number173
Number of pages17
JournalExperiments in Fluids
Volume64
Issue number11
Early online date24 Oct 2023
DOIs
Publication statusPublished - 30 Nov 2023

Bibliographical note

Funding This project was funded by Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation program (H2020-GAP-886112-ACUHRA).

Availability of data and materials: Supporting data can be made available to bona fide researchers. Details of how to request access are available at the University of Bath data archive (http://dx.doi.org/10.15125/BATH-00116).

Funding Information:
This project was funded by Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation program (H2020-GAP-886112-ACUHRA).

Funding Information:
The authors thank Matt Hawthorne at Added Scientific Ltd for his support in this project. The doublets were printed by Laser Prototypes Europe Ltd with support on design for manufacture by Added Scientific. The calculations were performed using the University of Nottingham HPC Facility and Sulis at HPC Midlands Plus, which was funded by EPSRC grant EP/T022108/1.

Funding Information:
The authors thank Matt Hawthorne at Added Scientific Ltd for his support in this project. The doublets were printed by Laser Prototypes Europe Ltd with support on design for manufacture by Added Scientific. The calculations were performed using the University of Nottingham HPC Facility and Sulis at HPC Midlands Plus, which was funded by EPSRC grant EP/T022108/1.

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