On condition that the engineering cost remains the same, optimization of wicket-gate closing law has always been the most economical and efficient way to reduce the incident risk and guarantee the security of hydro-turbine and the whole hydraulic network. In this paper, improved approaches for optimization of wicket-gate closing law are proposed. A new nonlinear evaluating function is developed and a wicket-gate closing law optimization method dealing with different hydro-transient cases (different water levels, operation conditions, combination cases etc) is introduced. Based on these improvements and genetic algorithm, a series of practical engineering scheme studies are preformed and the results are illustrated. The numerical calculation results show that the new non-linear evaluating function is of great advantages compared to traditional evaluating function in distribution of safety margin of each optimization goal. Optimized WG closing law by multi-mode optimum method is proved to be accurate and universal to different hydro-transient cases.

"Valsan" is a small Hydro Power Plant, 5 MW, situated at about 160 km north of Bucharest, Romania, on the small "Valsan" river in a remote mountainous area. It is equipped with a single Francis turbine. The penstock is located in the access shaft of the HPP. "Hidroelectrica", the Romanian company that operates the HPP, was trying to implement a remote penstock failure detection system. Starting from a classic hydraulic problem, the authors of the paper derived a method for failure detection and localization on the pipe. The method assumes the existence of 2 flow meters and 2 pressure transducers at the inlet and outlet of the pressurized pipe. Calculations have to be based on experimental values measured in a permanent regime for different values of the flow rate. The method was at first tested on a pipe, in the Hydraulic Laboratory of the Technical University of Civil Engineering Bucharest. Pipe failure was modelled by opening of a valve on a tee branch of the analyzed pipe. Experimental results were found to be in good agreement with theoretical ones. The penstock of the "Valsan" HPP, was modelled in EPANET, in order to: i) test the method at a larger scale; ii) get the right flow and pressure transducers that are needed to implement it. At the request of "Hidroelectrica" a routine that computes the efficiency of the turbine was added to the monitoring software. After the system was implemented, another series of measurements were performed at the site in order to validate it. Failure was modelled by opening an existing valve on a branch of the penstock. Detection of the failure was correct and almost instantaneous, while failure location was accurate within 5% of the total penstock length.

In the present work new criteria of optimal design method for turbine runner [1] are proposed. Firstly, based on the efficient method which couples direct simulation of 3D turbulent flow and engineering semi empirical formulas, the combined method is built for hydraulic energy losses estimation in the whole turbine water passage and the efficiency criterion is formulated. Secondly, the criterion of dynamic loads minimization is developed for those caused by vortex rope precession downstream of the runner. This criterion is based on the finding that the monotonic increase of meridional velocity component in the direction to runner hub, downstream of its blades, provides for decreasing the intensity of vortex rope and thereafter, minimization of pressure pulsation amplitude. The developed algorithm was applied to optimal design of 640 MW Francis turbine runner. It can ensure high efficiency at best efficiency operating point as well as diminished pressure pulsations at full load regime.

Numerical simulations of turbulent flow in a simplified draft tube are carried out. The main emphasis of these simulations is on the investigation of different turbulence closure models in predicting the flow behavior. Both steady and unsteady simulations are performed for axisymmetric as well as three-dimensional grid in an axisymmetric geometry, and results are compared with available experimental data. It is seen that steady simulations, performed with FLUENT and OpenFOAM, using Reynolds-Averaged Navier-Stokes (RANS) models for the axisymmetric and three-dimensional flow geometries give the same symmetric results. These steady, symmetric results underpredict the levels of turbulent kinetic energy (by at least 40%) and axial velocity (by at least 14%) near the centerline of the draft tube. No significant improvement is achieved applying various turbulence RANS models such as realizable k-ε, RNG k-ε, SST k-ω and v 2 −f model. Unsteady simulations are also performed using both URANS and hybrid URANS/LES (DES) turbulence closure approaches. It is seen that URANS models cannot capture the self-induced nature of the vortex rope and result in steady solutions due to steady boundary conditions while hybrid URANS/LES model can capture unsteady features of the flow. Importance of time-dependent inlet boundary conditions is discussed and it is shown that predictions are improved (at least 10%) by applying time-dependent boundary conditions which include turbulence fluctuations at inlet. Finally, results of two methods of vortex rope identification (iso-pressure surface and Δ-criterion) are compared.

Mixed flow pump is wildly used in many field, the performance of the whole pump is affected by the flow in the impeller to a great extend. To make clear the flow phenomena in the mixed flow impeller at design and off-design flow rate condition, a mixed flow unshrouded impeller was manufactured and the flow in the impeller at design and off-design flow rate was experimental measured by Particle Image Velocimetry (PIV) in this paper. In the experiment test device, the volute was specially design and manufactured by transparent material. According to the experimental result, the distribution of time-average relatively velocity showed the velocity near blade pressure surface at design flow rate decreases and then increases from inlet to outlet of the impeller, and that near blade suction surface increase and then decreases. The velocity near the suction surface decrease from hub to casing, and the minimal velocity appears near the casing and suction surface. Near the impeller outlet, the relative velocity near blade pressure surface varies a little alone the span direction; Back-flow phenomena were found at passages outlet near casing and mid-span sections at partial flow rate. To clarify the effect of volute geometry on the velocity distribution, the flow in different impeller passages relatively to the volute tongue was test and the result showed that the velocity distribution in different passages was similar.

The pumped storage plant undertakes the task for peak regulation, frequency modulation, phase modulation and accident standby in the electric grid system. Since the design consideration of a pumped storage plant is different from the conventional hydropower plant, the "S" shaped characteristic of pump-turbine will appear in four quadrants characteristic curves, and this characteristic will lead to a series of instabilities while the pump-turbine start at low water head. This paper presents the CFD simulation results of a pump-turbine model with the full flow passage which are compared with model test results. Based on the comparison, the hydraulic reason of the "S" shaped characteristic is discussed and a new concept of partial reverse pump is put forward, i.e. the reverse flow at inlet of runner is the real hydraulic cause of "S" shaped characteristic of a pump-turbine when the unit discharge descends to a certain degree. With the decrease of unit discharge, the effect of partial reverse pump becomes more and more obvious, which leads to an increase of head and finally results the "S" shaped characteristic of a pump-turbine.