Abstract
Rapid changes in the operating point of a hydropower plant cause transients in the hydraulic system. The flow will oscillate between the surge shaft and the reservoir until the oscillations are damped out by the friction. This paper investigates different friction models for oscillating flow, such as a quasi-steady model, Vítkovský’s model, and a one-term model. The governing equations for transient flow were solved by using rigid water column theory. The simulations were compared with experimental results from a small-scale test rig. The test rig consisted of a small reservoir, a horizontal pipe, and a surge shaft. The oscillations were induced by closing a valve downstream of the surge shaft. Measurements were obtained with pressure transducers.
Highlights
1.1 BackgroundWith increased focus on global warming, a shift towards a greener energy system is needed
Simulations of flow oscillations have been performed with different models of friction and different solution schemes
The quasi-steady friction model did not give enough damping of the oscillations compared with the measurements, while the one-term model gave too much damping in the beginning of the oscillations, and not enough damping towards the end
Summary
1.1 BackgroundWith increased focus on global warming, a shift towards a greener energy system is needed. The energy production from renewable sources is expected to increase in the coming years [1]. The increase of unreliable sources in the energy mix will imply that a more dynamic operation of hydropower plants is required. Changes in the operating point of a hydropower plant induce transients in the hydraulic system. Transients are often split into fast transients such as the water hammer and slow transients such as mass oscillations [1]. The friction in such transitional, unsteady flow is different than the friction in steady flow [2]. One example is rapid changes to the operating point of a hydropower plant, where flow oscillations are induced. The test rig is intended for measurement of head loss, but measurements of more detail is of high interest
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