Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.632708
Title: Numerical model of the flow phenomena preceding surge in the centrifugal blower and assessment of its applicability in designing anti-surge devices
Author: Liskiewicz, Grzegorz
ISNI:       0000 0004 3289 4686
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2014
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Abstract:
The dissertation is devoted to analysis of unstable phenomena in the centrifugal blower. These phenomena are known to be a source of serious threat to safety of the machine and the piping system connected to it. The complexity of centrifugal impellers causes that instabilities therein can have various forms and locations and have been subject of interest for over 60 years. The dissertation consists of two main parts: one of them being a result of the experimental investigations, the other one describing an outcome of the numerical simulations. In the experimental part, three methods of data analysis were applied: static, dynamic and a novel approach referred to as the quasi-dynamic one. The blower was examined in two configurations of the outlet pipe corresponding to different outlet plenum volumes. The results were presented in a form of a performance curve, amplitude plots, scalograms, phase trajectories and spectral maps. The machine was found to operate in four different regimes , namely: the stable regime, the inlet recirculation, the transient phase and the deep surge. The inlet recirculation was identifed as the earliest instability present in the inlet zone. It was characterized by strong pressure jumps and a spectral structure of broadband noise. In the transient phase, the pressure oscillation amplitude grew by one order of magnitude and appeared in all points analyzed. In the deep surge, strong pressure oscillations appeared, with one frequency component close to the Helmholtz frequency. A new factor that can be used for real-time monitoring and early detection of unstable flow phenomena was developed as a result of signal phase trajectory analysis. The second part presents results of the transient numerical simulations conducted with FLUENT and then compared to the experimental data. The full impeller geometry was simulated together with the diffuser, the volute and large volumes of the inlet and outlet pipes. Computations were run at different combinations of the boundary conditions corresponding to different operational points. Simulations with a reduced plenum volume were also conducted analogously to the experimental study. The machine was found to operate in four working regimes: stable regime, pre-surge (impeller instability), presurge (inlet recirculation) and the deep surge. An overview on the machine performance was provided together with a detailed description of particular flow structures. The results were compared to the experimental data by means of, a performance curve, phase trajectories and frequency spectra and were found to be in reasonable agreement. The numerical study introduced a possibility of a detailed analysis of unstable flow structures such as the inlet recirculation, the impeller instability, a the deep surge cycle. The study confirmed that computational methods introduce an opportunity to understand the unstable flow structures in detail and provide a missing link between real flow phenomena and mathematical surge and stall models, which is essential for effective anti-surge protection.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.632708  DOI: Not available
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