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Karadzic U.,University of Montenegro | Bulatovic V.,University of Montenegro | Bergant A.,Litostroj Power
Strojniski Vestnik/Journal of Mechanical Engineering

A flexible experimental apparatus for investigating water hammer and column separation in an unsteady friction-dominated pipelines has been developed and designed. The apparatus has been tested for steady and unsteady flow conditions. Transient cavitation and column separation phenomena have been observed in a number of experimental runs. Water hammer has been triggered by both the closing and opening of electro-pneumatic (EV) and hand-operated (HV) valves. The experimental data have been compared with results given from in-house numerical code written in Visual Fortran based on the method of the characteristics (MOC) with a convolution-based unsteady friction model (CBM) included. The column separation and transient cavitation phenomena are modelled via a discrete gas cavity model (DGCM). There is good agreement between the experimental and numerical results; the model is robust and, therefore, it is recommended for engineering practice. In addition, the influence of variations of the pressure wave speed and the uncertainty in flow rate measured by the electromagnetic flow meter are also investigated. © 2014 Journal of Mechanical Engineering. All rights reserved. Source

Hofler E.,Litostroj Power | Gale J.,Litostroj Power | Bergant A.,Litostroj Power
Transactions of the Canadian Society for Mechanical Engineering

The paper presents a procedure for hydraulic design and analysis of the blade geometry of a high specific speed runner of the Saxo-type double-regulated vertical axial turbine. The meridional through-flow in the passage from the conical guide vane apparatus to the draft-tube elbow is designed by a streamline curvature method (SCM). To validate the design method and predictions and to investigate the design duty point and a number of off-design operating regimes, an extensive CFD simulation inside the entire turbine water-passage is performed. The flow patterns downstream the guide vane apparatus and the runner exit flow are analyzed. The focus of the analysis is on distribution of the angular momentum alongside the turbine, as well as on its impact on the flow around the runner blades. The SCM design procedure presented in the paper proves to be a robust and accurate tool for the runner blade row design. Source

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