Flow-Induced Pulsation and Vibration in Hydroelectric Machinery by Peter Dörfler Mirjam Sick & André Coutu

Author:Peter Dörfler, Mirjam Sick & André Coutu
Language: eng
Format: epub
Publisher: Springer London, London

4.1.2 Turbine Components Affected by Vortex Streets

In large hydraulic machines, increased vibration due to vortex streets has occurred quite often. Among the undesired effects are alternating stresses causing mechanical fatigue and sometimes cracking of vital components and, on the other hand, annoying noise centered at the resonant frequency.

Much experience with vibrating stay vanes is documented in the literature. An actual wave of problems occurred in the 1970s when for the first time many large Francis and Kaplan turbines were built, often with fragile profiles not much different from a flat plate with very simple trailing edges. In the meantime, manufacturers are more cautious and this kind of problem has become rare although not exterminated. Figure 4.2 is a graphical summary from Chen’s survey [2] combining results from several sources [3–5]. The relative vibration intensity, expressed as a percentage of the result for the blunt edge, is shown versus the relative length of the tail protruding from the parallel faces, considering also indented shapes (‘negative protrusion’). With his curve, Chen successfully brought some understanding into the large variety of possible shapes. The y-axis in Fig. 4.2 is a relative intensity of the pulsation reaction force, expressed as percent of the blunt rectangular edge serving as reference. Starting from the reference, indented shapes have reduced intensity, see left-hand side of the diagram. Very high amplitudes result in case of protrusions between 50 and 100 % of the blade thickness. If the edge is more acute-angled, then the intensity becomes very low, and the preferable shapes for water turbines belong to this group.

Fig. 4.2Vortex excitation intensity for simple shapes of trailing edge

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