• Energy Research

Understanding and simulating the dynamic characteristics of the hydro-turbine governor system is essential to guarantee the safety of the hydro-power systems. This study proposes a modification method of the water head at the draft tube inlet, which is to discretize the draft tube and introduce the excitation term of the vortex rope. The proposed approach is applied for the modeling of the hydro-turbine governor system. The proposed model (Model I) is verified by means of a comparison with a second model (Model II) of the hydro-turbine governor system model without considering the vortex rope and verified against the experimental data during the load reduction. The model developed is accurate providing errors of the water head, inlet water head and flow of the hydro-turbine for Model ¿ are within ±3.3%, ±2% and ±5%, respectively. The proposed model overcomes the limitations of Model ¿ in the time-domain and frequency-domain since that only provides the average pressure at the draft tube, which do not reflect the pressure fluctuation and energy fluctuation. Instead the proposed model allows to capture and model the energy fluctuation during the load reduction as shown in the experimental results. The proposed model promotes the development of the hydro-turbine governor system model. Peer Reviewed

Francis turbines operate in many cases out of its best effici ency point, in order to regulate their output power according to the instantaneous ener gy demand of the grid. Therefore, it is of paramount importance to analyse and determine the unst able operating points for these kind of units. In the framework of the HYPERBOLE project (FP7-E NERGY-2013-1; Project number 608532) a large Francis unit was investigated numericall y, experimentally in a reduced scale model and also experimen tally and numerically in the real prototype. This paper shows the unstable operating points identified during the experimental te sts on the real Francis unit and the analysis of the main characteristics of these instabilities. Fi nally, it is shown that similar phenomena have been identified on previous research in the LMH (Laboratory for Hydraulic Machines, Lausanne) with t he reduced scale model.

Surge tank is an essential device to control hydraulic transient of a Hydroelectric Gnerating Systems (HGS)s. However, various types of surge tanks differently reflect in reducing water hammer and improve performance of HGS. This study aims to analyze the different performance of Air Chamber Tank (ACT) and Orifice Surge Tank (OST) during the successive load rejection process (SULRP). In this study, the mathematical model of the ACT is established and use to analysing the replacement the existing OST in Shitouxia Hydropower station consisting in three parallel unit system. A modified NSGA-II algorithm is used to perform multiple objective optimization ACT properties and to minimize pressure head in ACT and water head at the inlet of units. The optimization result indicates that the proper selection of initial indoor air height and delay time lead to the decrease maximum water head and fluctuation period in surge tank and falls in overspeed and pressure head at inlet of unit. The results show that, the diameter of ACT can be 2 m smaller than the existing OST and it can decrease the fluctuation period from 130 s to 110.7 s while slightly increasing the overspeed in the last unit. The increasing delay time of the closing guide vane of last unit decreases the water fluctuation in ACT and OST and the maximum water fluctuation in OST and ACT reduce with slope -6.2% and -15% when ¿Td is in range of [14], [25] seconds. Finally, the optimized dimension of ACT and OST provides essential guidance for decision-makers to deal with hydraulic transient in SULRP. Peer Reviewed

Venetian blinds (VB) are shading devices of widespread use in residential and corporate buildings. They can reflect or transmit light into buildings and at the same time allow daylighting and exterior views. They can also efficiently block radiative heat from entering the building, and if combined with a heat dissipation system such as forced ventilation, they can improve the thermal performance of double skin façades (DSF). Computational Fluid Dynamics (CFD) has proven to be a useful tool for modeling flow and heat transfer in DSF, including conduction, convection and radiation heat transfer phenomena. The aim of this work is to evaluate, by means of CFD, the influence of several optical, construction and operation parameters of a DSF (such as optical properties of the materials, geometrical relations of the VB or flow stream conditions) in terms of energy savings, measured as a reduction of the solar load entering the building. Results obtained show that parameters such as the proximity of the VB to the exterior skin of the façade or a differentiated surface treatment for the exterior and interior faces of the VB louvers can notably affect the thermal performance of the DSF and hence the heat gains experienced by the building.

The fast change in new renewable energy is affecting directly the required operating range of hydropower plants. According to the present demand of electricity, it is necessary to generate different levels of power. Because of its ease to regulate and its huge storage capacity of energy, hydropower is the unique energy source that can adapt to the demand. Today, the required operating range of turbine units is expected to extend from part load to overload. These extreme operations points can cause several pressure pulsations, cavitation and vibrations in different parts of the machine. To determine the effects on the machine, vibration measurements are necessary in actual machines. Vibrations can be used for machinery protection and to identify problems in the machine (diagnosis). In this paper, some results obtained in a hydropower plant are presented. The variation of global levels and vibratory signatures has been analysed as function as gross head, transducer location and operating points.