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Appl. Sci. 2017, 7(8), 862; doi:10.3390/app7080862

Axial Fan Blade Vibration Assessment under Inlet Cross-Flow Conditions Using Laser Scanning Vibrometry

Institute of Process Machinery and Systems Engineering, University of Erlangen-Nuremberg, Cauerstr. 4, 91058 Erlangen, Germany
This paper is an extended version of our paper published in 17th International Symposium on Applications of Laser Techniques to Fluid Mechanics, Lisbon, Portugal, 6–10 July 2014.
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Received: 4 July 2017 / Revised: 13 August 2017 / Accepted: 14 August 2017 / Published: 22 August 2017
(This article belongs to the Special Issue Laser Scanning)
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Abstract

In thermal power plants equipped with air-cooled condensers (ACCs), axial cooling fans operate under the influence of ambient flow fields. Under inlet cross-flow conditions, the resultant asymmetric flow field is known to introduce additional harmonic forces to the fan blades. This effect has previously only been studied numerically or by using blade-mounted strain gauges. For this study, laser scanning vibrometry (LSV) was used to assess fan blade vibration under inlet cross-flow conditions in an adapted fan test rig inside a wind tunnel test section. Two co-rotating laser beams scanned a low-pressure axial fan, resulting in spectral, phase-resolved surface vibration patterns of the fan blades. Two distinct operating points with flow coefficients of 0.17 and 0.28 were examined, with and without inlet cross-flow influence. While almost identical fan vibration patterns were found for both reference operating points, the overall blade vibration increased by 100% at the low fan flow rate as a result of cross-flow, and by 20% at the high fan flow rate. While numerically predicted natural frequency modes could be confirmed from experimental data as minor peaks in the vibration amplitude spectrum, they were not excited significantly by cross-flow. Instead, primarily higher rotation-rate harmonics were amplified; that is, a synchronous blade-tip flapping was strongly excited at the blade-pass frequency. View Full-Text
Keywords: axial fan; inlet cross-flow; blade vibration; laser scanning vibrometry; tracking laser Doppler vibrometry; wind tunnel axial fan; inlet cross-flow; blade vibration; laser scanning vibrometry; tracking laser Doppler vibrometry; wind tunnel
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Heinemann, T.; Becker, S. Axial Fan Blade Vibration Assessment under Inlet Cross-Flow Conditions Using Laser Scanning Vibrometry. Appl. Sci. 2017, 7, 862.

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