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The Influence of a Vortex-Flow Throttle on Transmission and Reflection of Pressure Wave

Author(s): Boris Huber; Reinhard Prenner

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Abstract: In order to reduce watermass oscillations, special vortex-flow throttles have been installed in some Austrian high-head power plants. They are situated at the end of the lower surge chamber, at the beginning of the rising shaft of the surge tank. The asymmetrical shape of this throttle element-similar to a Francis-turbine with its spiral case and straight axial suction diffusor-causes significantly different head-losses between up-and downsurging water levels for reasons of varied streamflow. Pressure waves induced by valves, turbines, pumps and regulation processes may damage the concrete tunnel lining under certain circumstances. This paper attempts to investigate the behavior of this special vortex throttle under transmission of single pressure waves combined with various steady-flow conditions. To ascertain quickly the influence of this throttle element on the pressure wave transmission, the measurement results are depicted as transmission coefficients depending on the gradient of the pressure wave. Furthermore, the experimental results were compared with a mathematical model based on a standard method of characteristics (MOC), in order to obtain the unsteady differences from the assumptions of the quasi-steady calculation.


Year: 1999

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