A Numerical Study into the Effect of Optimised Profiled End-Wall Design on High Pressure Turbine Performance

A Numerical Study into the Effect of Optimised Profiled End-Wall Design on High Pressure Turbine Performance

De Prieelle, L.S.B.

Langelaar, M. (mentor)
Van Keulen, A. (mentor)

Mechanical, Maritime and Materials Engineering

Precision and Microsystems Engineering

2014-04-24

In order to provide further improvements in thermal efficiency, engine designers are trying to optimise one of the components of the engine that has to endure the most severe conditions: the High Pressure Turbine. Furthermore, from a cost perspective, turbine designers are constantly trying to reduce the number of blades in the turbine which leads to stronger secondary flow features. Since secondary flow features are one of the main contributors to losses in the turbine, there is a potential for improvements when the development of secondary flow in the stage can be controlled and reduced. The non-axisymmetric profiling of end-walls has shown to be a powerful method to reduce loss and secondary flows. However, the development of consistent measures for the assessment of profiled end-wall designs is still in progress and the loss mechanisms of secondary flows are not yet fully understood. Therefore, the achievement of optimal end-wall design is still challenging. The main obstacle remains the complexity of the three-dimensional flows involved and the difficulty to visualise and accurately evaluate their flow structures. The aim of this thesis is to show that applying profiled end-walls and making use of optimisation algorithms can lead to a reduction of losses in the High Pressure Turbine. A parametric optimisation study has been performed to determine the regions of the hub profiled end-wall in the High Pressure rotor that are having the largest impact on performance. The objective has set to increase component efficiency while constraints have been set in terms of the reaction and inlet capacity of the High Pressure stage. A high efficiency improvement is obtained by the profiled end-wall created near the leading edge, while the profiled end-wall close to the trailing edge of the blade loses most of its efficiency improvement due to its strong violation of the constraints. Analysis of the flow field has revealed that the profiled end-wall near the leading edge is affecting the interaction of inlet boundary layer flow and purge flow emerging from the rim seal. By creating an effective flow passage, the profiled end-wall forces the purge flow to emerge from the rim seal closer to the suction surface of the blade. In this way, the profiled end-wall is influencing the development of the hub passage vortex. A new post-processing method has been developed based on the generation of entropy in order to gain a deeper understanding of the flow mechanisms taking place. The specific entropy generation has shown to be a powerful tool to identify loss sources and compare designs. It has been determined that the reduction in work losses due to shear stresses between adjacent cells in the numerical domain has the largest contribution to the reported efficiency improvements. Two loss reduction mechanisms have been identified. By forcing the purge flow to stay close to the suction surface, shear stress work losses that were first being generated by flow that was entrained between the hub passage vortex and suction side of the blade have been eliminated. The second loss reduction mechanism has been identified to be the weakening of the vortical character of the hub passage vortex. The flow of the hub passage vortex has shown to be aligned with the main flow direction and shear stress work losses initially generated by interaction with main and hub end-wall boundary layer flow are absent in the profiled end-wall design.

Numerical Study
Optimised Profiled End-Wall Design
High Pressure Turbine

http://resolver.tudelft.nl/uuid:4ef5f1a7-ebd9-4a05-96e1-cabc71d42d63

2018-04-24

Student theses

master thesis

(c) 2014 De Prieelle, L.S.B.