Automation of a turbine tip clearance preliminary calculation process

Abstract

An aeronautical gas turbine engine design is a multidisciplinary iterative process requiring an efficient interaction between each discipline tool and process in order to find the best compromise satisfying all the conflicting domains involved. The gas turbine engine design traditionally has two main stages: the pre-detailed design and the detailed design phases. During the first phase of the design, time is the main concern and the fidelity of the results may be impacted. This may compromise the engineers’ ability to thoroughly explore the envelope of potential designs and thus lead to the selection of a sub-optimal system concept. Considering the time-consuming analysis and resources-intensive tools used during the detailed design phase, it is extremely difficult to correct an unsatisfactory concept at that stage of an engine’s design. The use of Multidisciplinary Design Optimization techniques at a preliminary design phase (Preliminary MDO or PMDO) allows correcting this by investing more effort at the pre-detailed phase in order to prevent the selection of an unsatisfactory concept early in the design process. PMDO system implementation requires bringing as much knowledge as possible in the early phases of the design where the freedom to make modification is at a maximum. This imposes the use of higher fidelity tools that communicate effectively with each other. Considering the impact of the turbine tip clearance on an engine’s efficiency, an accurate tool to predict the tip gap is a mandatory step towards the implementation of a full PMDO system for the turbine design. Moreover, tip clearance calculation is a good candidate for PMDO technique implementation considering that it implicates various analyses conducted on both the rotor and stator. This thesis presents the results obtained by developing an automated process to execute thermal and stress analyses on a turbine rotor and housing, and leading to the computation of the turbine stage’s closure during a given mission along with its cold build clearance. For the analyses automation of the rotor and housing, the proposed conceptual system integrates a thermal boundary conditions automated calculator and interacts with a simplified air system generator and with several design tools based on parameterized CAD models. Compared to a regular preliminary tip clearance calculation process, the proposed conceptual system offers a considerable increase in the accuracy of the results as they revealed to be close to the one generated by the detailed design tools used as target. Moreover, this design process revealed to be faster than a common preliminary design phase while leading to a reduction of time spent at the detailed design phase. The system being automated and faster than the one of a regular pre-detailed design phase, it was possible to run iteration loops in order to determine the worst mission in terms of tip clearance closure. The proposed system also allowed running a targeted sensitivity analysis of the tip clearance leading to the identification of parameters that should be focused on when optimizing a turbine’s tip clearance. Finally, by requiring fewer user inputs this system decreases the risk of human errors while entirely leaving the important decisions to the designer.

Date	8 Jun 2018
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Saïd Hany Moustapha (Supervisor) & François Garnier (Co-supervisor)