Diana Maria Bucur

Water Quality in Hydroelectric Sites

The most widely form of renewable energy is the hydropower, which produces electrical power using the gravitational force of falling or flowing water. Comparing to fossil fuel powered energy plants, hydropower plants are considered „green” energy source, because they do not produce direct waste and have almost no output level of greenhouse gas carbon dioxide. Hydropower is the most important source of renewable electricity generation – 86.3 %, and essential to operate the others sources of renewable energy that are random generation.

Detection of cavitation vortex in hydraulic turbines using acoustic techniques

Cavitation phenomena are known for their destructive capacity in hydraulic machineries and are caused by the pressure decrease followed by an implosion when the cavitation bubbles find an adverse pressure gradient. A helical vortex appears in the turbine diffuser cone at partial flow rate operation and can be cavitating in its core. Cavity volumes and vortex frequencies vary with the under-pressure level. If the vortex frequency comes close to one of the eigen frequencies of the turbine, a resonance phenomenon may occur, the unsteady fluctuations can be amplified and lead to important turbine and hydraulic circuit damage. Conventional cavitation vortex detection techniques are based on passive devices (pressure sensors or accelerometers). Limited sensor bandwidths and low frequency response limit the vortex detection and characterization information provided by the passive techniques. In order to go beyond these techniques and develop a new active one that will remove these drawbacks, previous work in the field has shown that techniques based on acoustic signals using adapted signal content to a particular hydraulic situation, can be more robust and accurate. The cavitation vortex effects in the water flow profile downstream hydraulic turbines runner are responsible for signal content modifications. Basic signal techniques use narrow band signals traveling inside the flow from an emitting transducer to a receiving one (active sensors). Emissions of wide band signals in the flow during the apparition and development of the vortex embeds changes in the received signals. Signal processing methods are used to estimate the cavitation apparition and evolution. Tests done in a reduced scale facility showed that due to the increasing flow rate, the signal -- vortex interaction is seen as modifications on the received signals high order statistics and bandwidth. Wide band acoustic transducers have a higher dynamic range over mechanical elements; the systems reaction time is reduced, resulting in a faster detection of the unwanted effects. The paper will present an example of this new investigation technique on a vortex generator in the test facility that belongs to ICPE- CA.

Water hammer effect characterization using an acoustic signal processing approach

The paper presents an acoustic signal processing approach for the surveillance of a water pipe and the characterization of the water hammer effect. The experiment is based on ultrasonic transceivers and the validation is made with pressure sensors. The major objective is to quantify the pressure variation into the pipe using a non-intrusive method. Therefore, the speed of the transient was determined making use of the time-of-flight (TOF) which was obtained using the Recurrence Plot Analysis (RPA). Several comparisons between the signal processing approach and the classical techniques highlight the advantage of the non-intrusive method.

Aeration solution of water used by hydraulic turbines to respect the environmental policies

Preserving the quality of the water is a major concern from ecological, economical and sustainable development point of view, but also a condition when using water for renewable energy production. The European Water Policy defines a common regulation for sustainable and integrated management of water corps and requires that all impact factors to be considered. The environmental friendly concept represents a necessity for worldwide hydropower development. The dissolved oxygen in water courses represents an essential parameter which allows the preservation and development of aquatic habitat. The objective of the work is identification and study of a new solution which will contribute to improvement of the dissolved oxygen quantity in water used as renewable energy resource, so necessary to the aquatic life. The proposed solution takes in consideration the optimum between aeration parameters and energy consumption, in order to be implemented in hydraulic turbines.

Simultaneous transient operation of a high head hydro power plant and a storage pumping station in the same hydraulic scheme

This paper presents an on-site experimental analysis of a high head hydro power plant and a storage pumping station, in an interconnected complex hydraulic scheme during simultaneous transient operation. The investigated hydropower site has a unique structure as the pumping station discharges the water into the hydropower plant penstock. The operation regimes were chosen for critical scenarios such as sudden load rejections of the turbines as well as start-ups and stops with different combinations of the hydraulic turbines and pumps operation. Several parameters were simultaneously measured such as the pumped water discharge, the pressure at the inlet pump section, at the outlet of the pumps and at the vane house of the hydraulic power plant surge tank. The results showed the dependence of the turbines and the pumps operation. Simultaneous operation of the turbines and the pumps is possible in safe conditions, without endangering the machines or the structures. Furthermore, simultaneous operation of the pumping station together with the hydropower plant increases the overall hydraulic efficiency of the site since shortening the discharge circuit of the pumps.

On the vortex parameter estimation using wide band signals in active acoustic system

This paper proposes a new method for detection of the vortex presence in fluid flow based on an active acoustic system. The experiment that validates the theory was done on a reduced scale facility using ultrasonic transceivers. The main objective was to highlight the effect of a cavitation vortex on an applied wide band signal. In order to accomplish that, the Recurrence Plot Analysis (RPA) was investigated which emhasizes similar states of a dynamic process. The Tests were done from no vortex cavitation flow to vortex cavitation flow and backward.

EPANET Modelling of a High Head Pumped-Storage Hydropower Facility

A complex hydraulic facility is modelled in EPANET. The system consists in an underground high head Hydro Power Plant (HPP) and a Pumping Station (PS), operating in a pumped-storage hydropower scheme with three reservoirs. The complexity of the system is due to its unusual configuration, where the PS discharges the water directly into the HPP penstock. The PS is equipped with 2 × 10 MW pumps. The HPP is equipped with 2 × 75 MW Francis turbines. The simulations allow assessing the energy production and/or consumption in various scenarios, offering a tool to decision makers, to wittingly choose the operation mode of the facility.

Sensitivity analysis on flow rate estimation using design of experiments: Application to the pressure-time method

The present work investigates the flow parameters influence over the accuracy of flow rate determination by means of Design of Experiments -a statistical procedure widely used for experiments. The method used for the estimation of the flow rate derives from the standard pressure-time method, modified and improved - the solution is obtained by solving the water hammer equations considering an unsteady friction factor. The influence of the following parameters over the final moment of the flow rate variation regime is determined: the time of valve closure, the Reynolds number of the flow and the type of the closure law. A 23 factorial design is chosen to test the manner the three parameters influence, separately and together, the time value that should be chosen for the end of the flow rate variation regime. The results will help understand the influence of these parameters and the way in which they should be modeled within the flow rate determination method.

Implementation of the standard wall function in numerical computation software

The paper presents the validation of the implementation made by the user of the standard wall function for the standard k-ε turbulence model against the built-in standard wall function for the standard k-ε turbulence mode, in numerical computation software (ANSYS Fluent). A comparison was made between the results of two flow simulations: the first case consisted in using the built-in standard wall function and in the second case the implemented standard wall function was considered. The numerical simulations were made for the water flow inside a 3D diffuser. The results showed that both the wall functions used had a similar influence on the simulated flow.

Material constraints on high-speed design

Current high-speed circuit designs with signal rates up to 100Gbps and above are implying constraints for dielectric and conductive materials and their dependence of frequency, for component elements and for production processes. The purpose of this paper is to highlight through various simulation results the frequency dependence of specific parameters like insertion and return loss, eye diagrams, group delay that are part of signal integrity analyses type. In low-power environment designs become more complex as the operation frequency increases. The need for new materials with spatial uniformity for dielectric constant is a need for higher data rates circuits. The fiber weave effect (FWE) will be analyzed through the eye diagram results for various dielectric materials in a differential signaling scheme given the fact that the FWE is a phenomenon that affects randomly the performance of the circuit on balanced/differential transmission lines which are typically characterized through the above mentioned approaches. Crosstalk between traces is also of concern due to propagated signals that have tight rise and fall times or due to high density of the boards. Criteria should be considered to achieve maximum performance of the designed system requiring critical electronic properties.