Simulación de una bomba hidráulica

En el següent projecte final de carrera es comprovarà com funciona la mecànica de fluids computacional. Això s’aconseguirà gràcies a un problema resolt sobre una bomba hidràulica de la que es tenen resultats experimentals. Es tractarà de confirmar el perquè de la utilització de problemes de simulació numèrica y de comprovar així la validesa dels resultats obtinguts. Es realitzaran distintes proves i càlculs per a poder trobar quin és el més adequat i així treure conclusions sobre les diferents opcions i paràmetres que ofereixen els programes. S’intentarà solucionar els problemes que vagin sorgint de forma que finalment s’acabin complint les expectatives inicials

Influence of the boundary conditions on the dynamic behavior of large hydraulic machines

Nowadays, hydropower plays an essential role in the energy market. With the massive entrance of new renewable sources such as wind or solar power, hydropower is the only renewable generating source that can provide fast response and regulation capacity to the electric grid. It can even store the surplus of energy when it is necessary using Reversible Pump-Turbine (RPT) power plants. However, this situation makes that hydraulic turbines are increasingly working at off-design conditions with a high number of start and stops in comparison with ten years ago. At these conditions, the forces and stresses over the structure are high, especially in the runner, documenting some failures along the time. Therefore, it is of paramount importance to study the dynamic behavior of the runner under operation in order to avoid resonance conditions and fatigue problems. To study the dynamic behavior of the runner, both excitation and response have to be determined. Excitation forces have been studied for many years and they can be predicted with good accuracy through computational methods. However, the dynamic response of the runner still needs to be studied in detail. To define this dynamic response, natural frequencies, damping ratios and mode-shapes of the runner have to be estimated under operating conditions and for the different boundary conditions found in a hydraulic turbine. In this thesis, the natural frequencies, damping ratios and mode-shapes of submerged structures under different boundary conditions are studied. As a hydraulic turbine runner is a complex structure where the boundary conditions are fixed, simplified models are used to study the influence of those boundary conditions on their dynamic response. Submerged and confined disks have been used to experimentally study the effects of axial and radial gaps to rigid walls, the effects of rotation and the effects of the acoustic modes of the surrounding fluid on their dynamic response. Moreover, experimental measurements in a large Pump-Turbine and a large Francis turbine prototype have been performed to confirm the knowledge acquired in the simplified models. Numerical models have been also developed and validated in the present work to study the dynamic response of hydraulic turbine runners. This is an Article-Based Thesis, so it is based on three Journal Papers that have been published during the thesis duration. These three Journal Papers are based on the simplified models research, and they are attached and commented though the whole document of this thesis. Moreover, a summary of the findings of the research on hydraulic turbine prototypes is also included to extend the application of the knowledge acquired with the simplified models to actual hydraulic turbine prototypes.Avui en dia l'energia hidràulica té un paper molt important en el mercat energètic. Amb l'entrada massiva de l'energia eòlica i solar, l'energia hidràulica és l'única energia renovable que és capaç de proporcionar una ràpida resposta i capacitat de regulació a la xarxa elèctrica. A més, pot inclús emmagatzemar l'energia sobrant quan és necessari utilitzant les centrals hidroelèctriques reversibles basades en bombes-turbines. Tanmateix, això fa que les turbines hidràuliques treballin en condicions fora de disseny, augmentant també el nombre de parades i arrencades en comparació amb deu anys enrere. En aquestes condicions, les forces i estressos que pateix l'estructura, especialment el rodet de la turbina hidràulica, són molt alts, fet que ja ha provocat important avaries al llarg del temps. Això fa que sigui molt important estudiar el comportament dinàmic del rodet en condicions d'operació per tal d'evitar possibles ressonàncies o problemes de fatiga. Per a estudiar el comportament dinàmic del rodet, s'han de conèixer en detall tant les possibles fonts d'excitació com la resposta dinàmica de la màquina. Les forces d'excitació han estat estudiades des de fa molts anys i actualment es poden determinar amb bona exactitud amb mètodes numèrics. En canvi, la resposta dinàmica de rodets necessita encara ser estudiada amb més detall. Per a fer això, les freqüències pròpies, l'amortiment i els modes propis del rodet han d'estimar-se sota les condicions d'operació de la màquina i per a les diferents condicions de contorn que es poden trobar en una turbina hidràulica. En aquesta tesi s'estudien les freqüències pròpies, amortiment i modes propis d'estructures submergides i sota diferents condicions de contorn. Com que els rodets de les turbines hidràuliques són estructures complexes on les condicions de contorn són fixes, en aquest treball s'han utilitzat estructures més simples per tal d'avaluar la influència d'aquestes condicions de contorn en la seva resposta dinàmica. S'han utilitzat discos submergits i confinats en aigua per a demostrar experimentalment els efectes de les distàncies axials i radials a superfícies rígides i flexibles, els efectes de la rotació i els efectes dels modes acústics del medi fluid en el seu comportament dinàmic. També s'han realitzat mesures experimentals en una gran turbina-bomba i en una gran turbina Francis per a confirmar el coneixement adquirit amb els models simples. A més, s'han desenvolupat i validat models numèrics que prediuen la resposta dinàmica dels rodets de turbines hidràuliques. Aquesta tesi es presenta per compendi d'articles. Els articles que formen part de la tesi han estat publicats com a primer autor en revistes indexades al JCR per sobre del segon quartil. Aquests articles estan basats en la investigació sobre els models simplificats i estan adjuntats al final del document i comentats al llarg del mateix. En el document també s'explica la recerca que s'ha dut a terme en els diferents prototipus de turbines hidràuliques

Simulación de una bomba hidráulica

En el següent projecte final de carrera es comprovarà com funciona la mecànica de fluids computacional. Això s’aconseguirà gràcies a un problema resolt sobre una bomba hidràulica de la que es tenen resultats experimentals. Es tractarà de confirmar el perquè de la utilització de problemes de simulació numèrica y de comprovar així la validesa dels resultats obtinguts. Es realitzaran distintes proves i càlculs per a poder trobar quin és el més adequat i així treure conclusions sobre les diferents opcions i paràmetres que ofereixen els programes. S’intentarà solucionar els problemes que vagin sorgint de forma que finalment s’acabin complint les expectatives inicials

Overview of the experimental tests in prototype

Experimental tests in prototype are necessary to understand the dynamic behaviour of the machine during different operating points. Hydraulic phenomena as well as its effect on the structure need to be studied in o rder to avoid instabilities during operation and to extend the life - time of the different components. For this purpose, a complete experimental study of a large Francis turbine prototype has been performed installing several sensors along the machine. Pres sure sensors were installed in the penstock, spiral case, runner and draft tube, strain gauges were installed in the runner, vibration sensors were used in the stationary parts and different electrical and operational parameters were also measured. All the se signals were acquired simultaneously for different operating points of the turbine.Postprint (published version

Influence of the boundary conditions on the natural frequencies of a Francis turbine

Natural frequencies estimation of Francis turbines is of paramount importance in the stage of design in order to avoid vibration and resonance problems especially during transient events. Francis turbine runners are submerged in water and confined with small axial and radial gaps which considerably decrease their natural frequencies in comparison to the same structure in the air. Acoustic-structural FSI simulations have been used to evaluate the influence of these gaps. This model considers an entire prototype of a Francis turbine, including generator, shaft, runner and surrounding water. The radial gap between the runner and the static parts has been changed from the real configuration (about 0.04% the runner diameter) to 1% of the runner diameter to evaluate its influence on the machine natural frequencies. Mode-shapes and natural frequencies of the whole machine are discussed for all the boundary conditions testedPostprint (published version

Detection of hydraulic phenomena in francis turbines with different sensors

Nowadays, hydropower is demanded to provide flexibility and fast response into the electrical grid in order to compensate the non-constant electricity generation of other renewable sources. Hydraulic turbines are therefore demanded to work under o -design conditions more frequently, where di erent complex hydraulic phenomena appear, a ecting the machine stability as well as reducing the useful life of its components. Hence, it is desirable to detect in real-time these hydraulic phenomena to assess the operation of the machine. In this paper, a large medium-head Francis turbine was selected for this purpose. This prototype is instrumented with several sensors such as accelerometers, proximity probes, strain gauges, pressure sensors and a microphone. Results presented in this paper permit knowing which hydraulic phenomenon is detected with every sensor and which signal analysis technique is necessary to use. With this information, monitoring systems can be optimized with the most convenient sensors, locations and signal analysis techniquesPostprint (published version

Experimental measurements of the natural frequencies and mode shapes of rotating disk-blades-disk assemblies from the stationary frame

Determining the natural frequencies and mode shapes of rotating turbomachinery components from both rotating and stationary reference frames is of paramount importance to avoid resonance problems that could affect the normal operation of the machine, or even cause critical damages in these components. Due to their similarity to real engineering cases, this topic has been experimentally analyzed in the past for disk-shaft assemblies and rotor disk-blades assemblies (bladed-disk or blisk). The same topic is less analyzed for disk-blades-disk assemblies, although such configurations are widely used in centrifugal closed impellers of compressors, hydraulic pumps, pump-turbines, and runners of high head Francis turbines. In this paper, experimental measurements, varying the rotating speed of a disk-blade-disk assembly and exciting the first natural frequencies of the rotating frame, have been performed. The rotating structure is excited and measured by means of PZT patches from the rotating frame and with a Laser Doppler Vibrometer (LDV). In order to interpret the experimental results obtained from the stationary frame, a method to decompose the diametrical mode shapes of the structure in simple diametrical components (which define the diametrical mode shapes of a simple disk) has been proposed. It is concluded that the resonant frequencies detected with a stationary sensor correspond to the ones predicted with the decomposition method. Finally, a means to obtain equivalent results with numerical simulation methods is shown.Postprint (published version

Sensor-based optimized control of the full load instability in large hydraulic turbines

Hydropower plants are of paramount importance for the integration of intermittent renewable energy sources in the power grid. In order to match the energy generated and consumed, Large hydraulic turbines have to work under off-design conditions, which may lead to dangerous unstable operating points involving the hydraulic, mechanical and electrical system. Under these conditions, the stability of the grid and the safety of the power plant itself can be compromised. For many Francis Turbines one of these critical points, that usually limits the maximum output power, is the full load instability. Therefore, these machines usually work far away from this unstable point, reducing the effective operating range of the unit. In order to extend the operating range of the machine, working closer to this point with a reasonable safety margin, it is of paramount importance to monitor and to control relevant parameters of the unit, which have to be obtained with an accurate sensor acquisition strategy. Within the framework of a large EU project, field tests in a large Francis Turbine located in Canada (rated power of 444 MW) have been performed. Many different sensors were used to monitor several working parameters of the unit for all its operating range. Particularly for these tests, more than 80 signals, including ten type of different sensors and several operating signals that define the operating point of the unit, were simultaneously acquired. The present study, focuses on the optimization of the acquisition strategy, which includes type, number, location, acquisition frequency of the sensors and corresponding signal analysis to detect the full load instability and to prevent the unit from reaching this point. A systematic approach to determine this strategy has been followed. It has been found that some indicators obtained with different types of sensors are linearly correlated with the oscillating power. The optimized strategy has been determined based on the correlation characteristics (linearity, sensitivity and reactivity), the simplicity of the installation and the acquisition frequency necessary. Finally, an economic and easy implementable protection system based on the resulting optimized acquisition strategy is proposed. This system, which can be used in a generic Francis turbine with a similar full load instability, permits one to extend the operating range of the unit by working close to the instability with a reasonable safety margin.Postprint (published version

A sound and complete proof system for probabilistic processes

n this paper we present a process algebra model of probabilistic communicating processes based on classical CSP. To define our model we have replaced internal non-determinism by generative probabilistic choices, and external non-determinism by reactive probabilistic choices, with the purpose of maintaining the meaning of the classical CSP operators, once generalized in a probabilistic way. Thus we try to keep valid, as far as possible, the laws of CSP. This combination of both internal and external choice makes strongly difficult the definition of a probabilistic version of CSP. In fact, we can find in the current literature quite a number of papers on probabilistic processes, but only in a few of them internal and external choices are combined, trying to preserve their original meaning. Starting with a denotational semantics where the corresponding domain is a set of probabilistic trees with two kinds of nodes, representing the internal and external choices, we define a sound and complete proof system, with very similar laws to those of the corresponding CSP

Condition monitoring of a prototype turbine. Description of the system and main results

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.Postprint (published version