The aim of this paper is to present, discuss and assess transient case studies in refurbished and new hydropower schemes with complex water conveyance systems. Modern hydraulic transient analysis approach, control strategies and modeling are outlined. Hydraulic transients are flow disturbances caused by a change from one steady state to another. Transients can disturb overall operation of the plant and damage the system components. Parameters that define the extent of the analysis, modelling and solution methods are covered. Detailed transient analysis was performed using commercial software package SIMSEN that includes a number of hydraulic and electrical components. The pakage incorporates standard steady state skin friction model. The paper concludes with one case study of refurbished (Doblar 1 HPP) and one case study of a new hydro powerplant (Toro 3 HPP). Computational results agree well with the in-situ measured results. For relatively slow transients the steady state skin friction model is appropriate.
F.17 Transfer of existing technologies, know-how, methods and procedures into practice
COBISS.SI-ID: 13827867A large-scale pipeline apparatus at Deltares, Delft, The Netherlands, has been used for acoustic resonance tests. The apparatus consisted of an upstream end constant-head reservoir, a horizontal 200-mm-diameter 49-m-long steel pipeline and an oscillating valve at its downstream end. In addition to standard instrumentation, two distinctive instruments have been used: hot-film wall-shear-stress sensors and a PIV set-up for measurement of velocity profiles. Pulsating flow tests have been performed with an average flow at Reynolds number 22,000. The frequency of oscillation varied between 1.5 Hz and 100 Hz. When one of the excitation frequencies met the liquid system’s natural frequency, the system went into resonance. Moreover, when one of the frequencies coincided with a structural natural frequency of the pipeline, the liquid-filled pipeline experienced fluid-structural resonance. Results of three distinctive runs (including a hydraulic resonance case with oscillating frequency fex = 5 Hz, a non-resonance case with fex = 10 Hz and a fluid-structural resonance case with fex = 12.5 (13) Hz) indicated that the axial pipe-wall vibrations for the fluid-structural resonance case are significantly higher than in the hydraulic resonance and non-resonance cases. In addition, excessive pipeline vibrations were clearly visible in the PIV images. This fact is very important for evaluation of relative fluid velocity and consequently unsteady wall shear stress (unsteady skin friction). Comprehensive coupled experimental treatment of liquid-filled pipeline in hydraulic and fluid-structural resonance conditions is presented in the literature for the first time.
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 14289179This paper deals with transfer of knowledge gained during the research project into the industry. Hydraulic transient control methods in Slovenian refurbished Francis turbine hydropower schemes are presented. Transient control strategies include alteration of operational manoeuvres, transient control devices, suitable water conveyance system layout and operational limits. Computational model and modern hydraulic transient control approaches are outlined as well. The paper concludes with practical implementation of two case studies: refurbishment of Doblar 1 HPP and Moste HPP. Both hydropower plants are equipped with Francis turbine units and have undergone refurbishment in the years 2010 to 2013. Computational results agree well with the in-situ measured results. It has been shown that for relatively slow transients the steady state skin friction model used in simulations is appropriate.
F.01 Acquisition of new practical knowledge, information and skills
COBISS.SI-ID: 14532379This paper presents a novel water hammer interferometer. In essence, it is an acoustic tube interferometer using the controlled closure of two valves. The device generates two water hammer waves that interfere with each other along the liquid-filled pipeline. The superposition of the two waves can generate pressure head variations of different frequencies and amplitudes. The frequency and shape of pressure histories are controlled via the delayed closure of one of the two valves. The interference phenomena in an ideal pipeline system are described with the aid of basic water hammer theory.
F.06 Development of a new product
COBISS.SI-ID: 1024255580The aim of the research project is to develop a model that would consider unsteady friction of turbulent liquid flow. Such a model could be included in 1D computational code to analyze flow in complex pipelines. A CFD study in an axisymmetric flow domain was conducted to better understand the phenomenon in oscillating flow. Different settings of boundary conditions were used based on experimental investigation. Several variations of settings in Ansys Fluent CFD package are introduced and discussed. The geometry and discretization procedure is shown along with full transcript of command lines in Gambit preprocessing tool. 1D-MOC program coded in Matlab is also included. This program is the base for 1D-MOC – 2D-CFD simulation system. Key results are processed and plotted within OriginPro. Based on the given data, one could replicate all the work that is presented.
F.23 Development of new system-wide, normative and programme solutions, and methods
COBISS.SI-ID: 14541339