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Title: Investigation of turbocharger compressor map width enhancement
Author: Sivagnanasundaram, Subenuka
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2012
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Abstract:
This thesis presents an investigation of a shroud bleed slot system of a compressor stage from a turbocharger unit used in heavy duty diesel engines of approximately 300 kW. The first part of the work presented in this thesis deals with a detailed analysis of a compressor stage with and without a shroud bleed slot, and various slot geometries which include three different widths and three different positions of the slot. The second stage of this study is an investigation of an addition of a set of vanes in the annular cavity of the shroud bleed slot system. This investigation was performed using both CFD modelling and experimental measurements. The CFD model used a full stage steady state approach. Very good agreement was achieved between the experimental measurements of efficiency, pressure ratio and mass flow rate and those values predicted by the CFD model over the entire performance map, providing confidence in the CFD model as a tool to help understand the flow features of the bleed slot, its various geometries and an addition of annular cavity vanes. The first stage of the study emphasises the significance of the inclusion of a shroud bleed slot into the conventional turbocharger compressor stage and the appropriate choice of the slot geometry in order to achieve as the widest map possible. In comparison with the non-bleed slot compressor stage, the bleed slot significantly extended the map width at the higher speeds, by reducing the surge mass flow rate. However, no or very little improvement was found at lower speeds. The analysis of changes to design parameters revealed that it is vital to obtain an optimised geometry of the bleed slot system for a compressor stage to achieve a wider map without compromising other performance characteristics of the compressor. This study also discloses the importance of an optimised shape of the shroud bleed slot system to increase the compressor performance by avoiding the recirculation losses within the slot and cavity passages at both choke and surge flow conditions. In the second stage of the work presented in this thesis, three different types of the annular cavity vane (straight, positive curved and negative curved vanes) have been designed and investigated. The purpose of the annular cavity vane technique is to remove some of the positive swirl that can be carried through the bleed slot system, which would influence the pressure ratio. In addition to this, the series of cavity vanes provides better guidance to the slot recirculating flow before it mixes with the impeller main inlet flow. Better guidance of the flow improves the mixing at the inducer inlet in the circumferential direction. As a consequence, the stability of the compressor is improved at lower flow rates and a wider map can be achieved. The impact of these three cavity vane designs on the map width and performance of the compressor has been highlighted through a detailed analysis of the impeller and cavity vane bleed slot flow field. Interestingly, all three types of cavity vane showed an improvement in map width by moving the surge point to a lower mass flow rate with no significant efficiency penalty over the entire operating range. This improvement was most evident at the highest running speed. In particular, the negative curved vane showed a significant increase in map width which represents an extra 67% improvement in map width that was achieved between the baseline bleed slot and non-bleed slot configurations.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.580087  DOI: Not available
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