Wahl, Tony Lee. 1990. "Thesis - Draft Tube Surging Hydraulic Model Study, Submitted in partial fulfillment of the requirements for the degree of Master of Science, Colorado State University, Fort Collins, Colorado, Summer 1990". Bureau of Reclamation, Report Number PAP-660.
Abstract: The phenomenon of draft tube surging has been investigated using a model hydraulic turbine. Pressure fluctuations at the throat of the draft tube were measured using piezoresistive pressure transducers, and the signals were analyzed using a dynamic signal analyzer and a digitizing oscilloscope. Dimensionless pressure and frequency parameters were calculated for the dominant pressure pulsation at each test point. The dimensionless parameters have been related to the dimensionless swirl parameter of the flow in the draft tube, and maps have been constructed showing the variation of these parameters on the turbine hill curve. In some operating regions the pressure and frequency parameters do not correlate well with the swirl parameter; the pressure and frequency parameter maps constructed on the same axes as the hill curve are preferred for presentation of the test results in these regions. A twin vortex surging mode has been identified in the model, and the region of its occurrence has been defined on the turbine hill curve. The twin vortex produces pressure pulsations at more than twice the frequency typically associated with draft tube surging. In addition, the relationship of the pressure parameter to the draft tube swirl parameter appears to be affected by the twin vortex. Evidence from the literature suggests that this surging mode also occurs in other nearly homologous units. A qualitative investigation of the occurrence of synchronous and asynchronous pressure pulsations has been performed. Evidence of synchronous pulsations was obtained at several test points. Recommendations are given for more detailed research in this area.
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