City Research Online

Abstract

This thesis presents a numerical investigation into the performance and flow dynamics of Micro Radial Compressors (MRCs), focusing on understanding loss mechanisms and flow behaviours under off-design operating conditions. Two distinct MRC designs were studied: Compressor A featuring a 2D radial shrouded impeller and Compressor B utilizing a mixed flow unshrouded impeller. Using both steady-state RANS with a K-ω turbulence model and LES, both incompressible, the study aimed to investigate the specific sources of losses inherent in MRCs and provide a detailed comparison of the predictive capabilities of these computational approaches.

The performance prediction capabilities of both CFD methods were evaluated against experimental data. Results indicated better agreement for LES, particularly at higher flow rates and at design point. Analysis of the shrouded design revealed an axisymmetric pattern of partial stall within the compressor passages and their stabilization effect on the overall compressor dynamics, believed to be caused by an interaction between the equal number of blades in the impeller and diffuser.

The thesis also explores the introduction of passive flow control features, specifically atmospheric vents designed to reduce shrouded impeller recirculated leakage flow, and their effect on enhancing compressor efficiency. Although unoptimized, these features were effective in reducing drag on the impeller, increasing pressure ratio and efficiency, and exhibited no drawbacks or negative effects across the range of operation explored.

Investigation into the behaviour of the unshrouded impeller design indicates a complex interaction between tip leakage flow, impeller inlet recirculation and surge. Furthermore, the effect of operating conditions on the mechanism of tip leakage reintroduction to the main flow was explored, revealing a variation in observed behaviour between design and off-design conditions.

Overall, the study emphasizes the need for unsteady high-fidelity simulations in understanding and optimizing MRC performance, especially under off-design conditions. It contributes to the field by highlighting the limitations of steady-state RANS in capturing the transient and complex flow features of MRCs, advocating for a more nuanced approach combining RANS for initial design and LES, or more feasibly DES, for detailed flow analysis. The findings from this research not only provide a deeper understanding of the flow mechanisms in MRCs but also propose pathways for future design and operational optimizations.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > T Technology (General) T Technology > T Technology (General) > T201 Patents. Trademarks T Technology > TA Engineering (General). Civil engineering (General) T Technology > TJ Mechanical engineering and machinery
Departments:	School of Science & Technology > Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

Export

Downloads