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A robust stall and stall-precursor detection method for axial fans
Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2026.
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University of Pretoria
2026
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| access_status_str | Open Access |
| author2 | Heyns, P.S. (Philippus Stephanus) |
| author_browse | Heyns, P.S. (Philippus Stephanus) |
| author_facet | Heyns, P.S. (Philippus Stephanus) |
| collection | Thesis |
| dc_rights_str_mv | © 2024 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
| description | Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2026. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/108332 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:37:09.154Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2026 |
| publishDateRange | 2026 |
| publishDateSort | 2026 |
| publisher | University of Pretoria |
| publisherStr | University of Pretoria |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/108332 A robust stall and stall-precursor detection method for axial fans Heyns, P.S. (Philippus Stephanus) Schmidt, Stephan ag.brocco@gmail.com Brocco, Alex UCTD Sustainable Development Goals (SDGs) Axial Fan Stall Detection Stall-Precursor Detection Rotating Instabilities Spike-Type Stall Inception Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2026. Active stall suppression systems possess the ability to prevent the catastrophic failure of main mine fans without the efficiency reductions associated with passive stall suppression systems, such as casing grooves and anti-stall rings. A robust stall detection system is required for the practical implementation of an active stall suppression system in industry. The ability to detect stall precursors would facilitate proactive implementation of the active stall suppression system and prevent the fan from ever entering the mechanically destructive stall condition. To develop a robust stall detection system, an investigation was conducted using experimental data obtained from a 1016 mm-diameter mining ventilation axial fan test-bench, which was developed as a collaborative effort between Air Blow Fans (Pty) Ltd and the Centre for Asset Integrity Management (C-AIM) at the University of Pretoria. The fan test-bench is heavily equipped with a wide variety of sensors, including a zebra-tape shaft encoder and a fast-response pressure probe installed in the rotor casing, in line with 30% of the blade tip chord.Preliminary analysis of the experimental data obtained from the fan test-bench revealed two unique short-length-scale stall precursor types: (i) rotor casing pressure waveform trough magnitude reduction stall precursors and (ii) blade passage pressure dip stall precursors. Both stall precursor types were continuously present during the peak fan pressure operating state. This indicated that they were both linked to rotating instabilities rather than a stall inception mechanism. The trough magnitude reduction stall precursors were only present very close to and at the peak pressure condition, whereas the blade passage pressure dip stall precursors were found at a wide range of operating conditions: from the design point to the peak fan pressure operating state, gradually increasing in strength as the peak fan pressure operating state was approached.The rotor casing pressure waveform trough magnitude reduction stall precursor is postulated to be caused by local blade tip leading-edge flow separation, which results in a reduced pressure differential across the blade tip and a subsequent reduction in the acceleration of the tip leakage flow. The reduced flow acceleration and pressure continuity cause the tip leakage flow pressure to increase (pressure trough magnitude reduction). Experimental evidence suggests that the blade passage pressure dip stall precursors were caused by the low-pressure cores of rotating instability-type radial vortices, which formed in the blade passage just behind the blade tip leading-edge plane and propagated circumferentially to the adjacent blade’s suction-side at part-rotor-speed. These quasi-periodic rotating instability-type radial vortices are postulated to be caused by the interaction between the reversed casing wall flow, the blade tip leakage vortex, and the incoming main passage flow, rather than fluctuating tip leakage vortices. The postulations made relating to the two unique stall precursor types are based on the literature reviewed and the time-averaged, steady-state numerical analysis of the fan test-bench. These stall precursors occurred continuously but stochastically hundreds of revolutions before the onset of rotating stall via spike-type stall inception in the fan test-bench during transient system resistance cases that traversed the fan curve from the stable to the stall operation regions. This provided an opportunity to develop a novel stall and stall-precursor detection method.A novel waveform-difference stall and stall-precursor detection method was developed via the exploitation of advanced signal processing techniques, the fan laws, and the newly obtained understanding of the rotating instability-type stall precursors. The novel waveform-difference method can detect both rotating instability-type and spike-type stall precursors. Additionally, it can detect the presence of rotating stall and surge, regardless of the inception mechanism.The novel waveform-difference method is robust to different steady-state speeds, speed transients, varying levels of noise, and small geometric changes associated with maintenance events and general wear. Additionally, based on its development and the theoretical understanding of how air density changes result in direct magnitude-scaling of the rotor casing pressure waveform’s deterministic component, the method would be robust to changes in ambient air temperature and pressure.The robustness of the novel waveform-difference method theoretically allows it to be calibrated on a single test fan and, thereafter, be applied to all fans in industry that have the same design as the test fan without further calibration, regardless of differences in the operating condition and small geometrical variations. This significantly improves the method’s practicality for industrial implementation. However, additional experiments are required to explicitly prove this one-shot calibration claim. The novel waveform-difference method detected stall 1.582 seconds (39.0 revolutions) and stall precursors 11.564 seconds (285.2 revolutions) before an industry-standard modified Petermann probe detected stall during a transient system resistance case, which traversed the fan curve from the stable to the stall operation regions. An additional benefit of the novel waveform-difference method is its partial robustness to minor fouling since the rotor casing pressure probe utilised has a large diaphragm rather than small pressure taps that get easily blocked by fouling. A limitation of the novel waveform-difference method is its high complexity, subsequent high computational resource demand for real-time implementation, and its case-specific minimum allowable shaft speed limitation (30% of the maximum shaft speed for the fan test-bench utilised). The speed limitation is necessary due to the increase in the relative magnitude of the underlying low-amplitude stochastic pressure fluctuations and low-frequency noise components, compared to the speed-dependent magnitudes of the blade-traversal-induced rotor casing pressure waveform features at low speeds. Lastly, the novel waveform-difference method is tailored specifically for mining ventilation axial fans with thick blades. Therefore, it will be unsuited for other axial turbomachinery types. Additionally, it is best suited for fans that exhibit rotating instabilities and experience spike-type stall inception to facilitate the detection of the associated stall precursors.The algorithm used to implement the novel waveform-difference stall and stall-precursor detection method currently exists in an offline format. Future work will involve developing the waveform-difference method algorithm for real-time implementation. This will involve the implementation of parallel processing and efficient data-handling strategies, as well as tools to facilitate visualisation for remote monitoring. Additionally, future work will include unsteady large-eddy numerical simulations of the fan test-bench to provide more accurate numerical evidence for the postulations made in this work that relate to the two unique rotating instability-type stall precursors. Air Blow Fans (Pty) Ltd Mechanical and Aeronautical Engineering MEng (Mechanical Engineering) Unrestricted Faculty of Engineering, Built Environment and Information Technology SDG-09: Industry, innovation and infrastructure 2026-02-17T12:49:46Z 2026-02-17T12:49:46Z 2026-05-18 2026-01-01 Dissertation * A2026 http://hdl.handle.net/2263/108332 https://doi.org/10.25403/UPresearchdata.31350571; https://doi.org/10.25403/UPresearchdata.31350490 en © 2024 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. application/pdf University of Pretoria |
| spellingShingle | UCTD Sustainable Development Goals (SDGs) Axial Fan Stall Detection Stall-Precursor Detection Rotating Instabilities Spike-Type Stall Inception A robust stall and stall-precursor detection method for axial fans |
| title | A robust stall and stall-precursor detection method for axial fans |
| title_full | A robust stall and stall-precursor detection method for axial fans |
| title_fullStr | A robust stall and stall-precursor detection method for axial fans |
| title_full_unstemmed | A robust stall and stall-precursor detection method for axial fans |
| title_short | A robust stall and stall-precursor detection method for axial fans |
| title_sort | robust stall and stall precursor detection method for axial fans |
| topic | UCTD Sustainable Development Goals (SDGs) Axial Fan Stall Detection Stall-Precursor Detection Rotating Instabilities Spike-Type Stall Inception |
| url | http://hdl.handle.net/2263/108332 https://doi.org/10.25403/UPresearchdata.31350571; https://doi.org/10.25403/UPresearchdata.31350490 |