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You are here : eLibrary : IAHR World Congress Proceedings : 32nd Congress - Venice (2007) : THEME C: Fluid Mechanics and Hydraulics : Experimental investigation of vortex ropes in a straight cone draft tube
Experimental investigation of vortex ropes in a straight cone draft tube
Author : Kirschner Oliver, Ruprecht Albert
In the last few years, hydropower plants are increasingly operating at off-design conditions in order to follow the demand in the electrical grid. In this context, the ability of hydropower plants handling the operation in a wide range of off-design conditions has become more important. But one of the major difficulties in hydraulic turbines is the vortex rope in the draft tube, especially for Francis turbines running in part load. The numerical prediction of unsteady flow structures and flow phenomena like a vortex rope by using CFD becomes possible with the fast development of computer performance. Previous simulations show that complex models are necessary, in order to describe the phenomena correctly, see Ruprecht (2002). For validating these models, measurements on a model pump-turbine with a simplified straight draft tube, instead of the usual used elbow draft tube, are accomplished. The first part of the measurements selects operating points for further investigation in the second part. Therefore in a first step the hill chart for turbine operation was measured. Afterwards special measurements for pre-selected points were made. The focus was on unsteady pressure measurements at the draft tube wall and unsteady measurements of forces, torques and tilting moments on the runner of the turbine. For a few of these pre-selected operating points the vortex rope in the diffuser was visualized by cavitation in the core of the rope. With this visualisation the different structures of the vortex rope could be identified for detailed investigation. At one of these visualized operation points a trigger signal for periodically phase locked velocity measurements with a constant movement of the vortex rope is available. Only in this operating point phase-locked measurements with PIV were done. In other operating points time averaged velocities were measured
File Size : 4,134,851 bytes
File Type : Adobe Acrobat Document
Chapter : IAHR World Congress Proceedings
Category : 32nd Congress - Venice (2007)
Article : THEME C: Fluid Mechanics and Hydraulics
Date Published : 01/07/2007
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