Abstract
In order to increase the installed capacity, the refurbishment of Gondo high-head power plant required a modification of the existing surge tank by installing a throttle at its entrance. In a previous study, the geometry of this throttle was optimized by physical modeling to achieve the target loss coefficients as identified by a transient 1D numerical analysis. This study complements previous analyses by means of 3D numerical modeling using the commercial software ANSYS-CFX 19 R1. Results show that: (i) a 3D computational fluid dynamics (CFD) model predicts sufficiently accurate local head loss coefficients that agree closely with the findings of the physical model; (ii) in contrast to a standard surge tank, the presence of an internal gallery in the surge tank proved to be of insignificant effect on a surge tank equipped with a throttle, as the variations in the section of the tank cause negligible local losses compared to the ones induced by the throttle; (iii) CFD investigations of transient flow regimes revealed that the head loss coefficient of the throttle only varies for flow ratios below 20% of the total flow in the system, without significantly affecting the conclusions of the 1D transient analysis with respect to minimum and maximum water level in the surge tank as well as pressure peaks below the surge tank. This study highlights the importance of examining the characteristics of a hydraulic system from a holistic approach involving hybrid modeling (1D, 3D numerical and physical) backed by calibration as well as validation with in-situ measurements. This results in a more rapid and economic design of throttled surge tanks that makes full use of the advantages associated with each modeling strategy.
Highlights
Hydropower represents around 60% of the annual electricity production in Switzerland and is fundamental to the electricity supply sector [1]
This study focuses on Gondo high-head power plant (HPP) in Switzerland, which has been subjected to a moderate increase of installed capacity in 2017
The corresponding head loss coefficients associated with each flow direction are obtained by linear regression according to Equation (2)
Summary
Hydropower represents around 60% of the annual electricity production in Switzerland and is fundamental to the electricity supply sector [1]. The Swiss energy strategy 2050 aims to abandon nuclear energy and develop renewable energy production. The intermittent energy production of the new renewables raised the need for an increase in hydropower production in order to sustain the grid balance. The hydropower production is planned to rise from 35.35 TWh Among the available options to increase the hydroelectric generation capacity is the refurbishment and rehabilitation of existing plants, such as high head power plants (hydraulic head > 200 m). Refurbishment of such plants often requires a modification of the existing surge tanks to handle the increase in generation capacity
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