Abstract
dc:description.abstractCompressor bleed refers to the removal of flow from part way through the compressor for use in turbine cooling and other operational applications. Typical bleed systems in Industrial Gas Turbines comprise of an annular slot in the compressor casing, leading to external cavities. Aspiration refers to a form of flow control that utilises small holes for targeted suction within the compressor flow path. This thesis investigates the performance of aspirated compressor stators as part of the compressor bleed system. Two key research questions are addressed. First, what is the impact of aspiration on the compressor flow field? Second, how should aspiration be integrated into the compressor bleed system? To answer these questions, computational simulations of aspirated stators are performed, and experimental measurements from a two-stage research compressor with aspiration in the first stage stator are used, within this thesis. In response to the first research question, in simulations, aspiration bleed is shown to have two key effects on the compressor passage flow. First, the suction reduces the boundary layer thickness on the blade surface, resulting in a smaller midspan wake and up to a 40% reduction in passage stagnation pressure coefficient compared to a non-aspirated blade. Second, the suction towards the endwall alters the secondary flows, affecting the onset of open corner separation formation. When the aspiration hole array is centred at 50% blade chord, the separation formation is suppressed to 6° higher stator incidence. Furthermore, doubling the suction on lower 50% of blade span, through altering the design of the aspiration hole array, is shown to suppress the separation formation to 12° higher incidence than the non-aspirated blade. In experimental measurements, a 3D printed annulus of aspirated stators fail to suppress the formation of an open corner separations on the blade hub at high incidence. This is found to be caused by blockage within the internal bleed cavity which reduces suction towards the stator hub. The 3D printed aspirated stators are altered to block the aspiration holes over the upper 50% of blade span, successfully suppressing the formation of the corner separations to 1.8° higher incidence than only extracting bleed through an annular slot. In addressing the second research question of this thesis, simulations show that aspiration bleed produces over 5 times the stagnation pressure drop between the compressor passage upstream of the stator and the external bleed cavity, when compared to extracting bleed through an annular slot at the same bleed design condition. This results in aspiration bleed causing double the thermodynamic loss though the integrated stator bleed system. However, extracting 25% of the total bleed through aspiration and 75% through an annular bleed slot, reduces the system thermodynamic loss by over 5% across all simulated incidences, when compared to using only annular bleed. Results from simulations are used in a Gas Turbine cycle model, showing that splitting the rear stage bleed equally between an aspirated stator and an annular bleed slot within the 12th compressor stage increases the cycle efficiency by over 0.1 percentage points whilst satisfying the operation requirements of the bleed and turbine cooling system.
Degree
thesis:*- Name dc:type.qualificationname
- Doctor of Philosophy (PhD)
- Level dc:type.qualificationlevel
- Doctoral
- Grantor dc:publisher.institution
- University of Cambridge
- Year dc:date.issued
- 2024
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Waldren, Jonathan
- Advisor dc:contributor.advisor
-
- Pullan, Graham
Subjects
dc:subject × 4Rights
dc:rightsIdentifiers
dc:identifier.*- DOI dc:identifier.doi
- https://doi.org/10.17863/CAM.115529
- OAI identifier oai:identifier
- oai:www.repository.cam.ac.uk:1810/379436