http://hdl.handle.net/2117/3254 2013-05-22T14:39:57Z http://hdl.handle.net/2117/18852 Title: Analysis of the dynamic response of pump-turbine runners. Part I: Experiment Authors: Presas Batlló, Alexandre; Valero Ferrando, M.del Carmen; Huang, Xingxing; Egusquiza Estévez, Eduard; Farhat, Mohamed; Avellan, François Abstract: When in operation, pump-turbine runners have to withstand large pressure pulsations generated by the rotor-stator interaction. The analysis of the dynamic behavior of these structures is necessary to avoid damage. For this analysis a realistic model of the runner is necessary. When the runner is submerged in water and inside the casing, its dynamic response is greatly affected. The added mass effects of the surrounding fluid and the proximity of the head-cover and bottom-cover may reduce the natural frequencies. The frequency reduction produced by the added mass effects and the influence of the boundary conditions has to be known for a safe design of the runner. In this paper an experimental investigation on the dynamic response of a model runner is presented. A reduced scale model of a pump-turbine was tested outside and inside the casing with different boundary conditions. For the excitation of the runner at different frequencies piezoelectric patches were used. The response was measured with miniature accelerometers located in several positions inside the runner. From the measurements the natural frequencies and mode-shapes of the runner were calculated using EMA. The influence of the added mass and of the boundary conditions is presented and discussed. 2013-04-17T12:02:49Z http://hdl.handle.net/2117/17894 Title: Analysis if the dynamic response of pump-turbine runners- Part I: Experiment Authors: Presas Batlló, Alexandre; Valero Ferrando, M.del Carmen; Egusquiza Estévez, Eduard; Huang, Xingxing; Farhat, Mohamed; Avellan, François Abstract: When in operation, pump-turbine runners have to withstand large pressure pulsations generated by the rotor-stator interaction. The analysis of the dynamic behavior of these structures is necessary to avoid damage. For this analysis a realistic model of the runner is necessary. When the runner is submerged in water and inside the casing, its dynamic response is greatly affected. The added mass effects of the surrounding fluid and the proximity of the head-cover and bottom-cover may reduce the natural frequencies. The frequency reduction produced by the added mass effects and the influence of the boundary conditions has to be known for a safe design of the runner. In this paper an experimental investigation on the dynamic response of a model runner is presented. A reduced scale model of a pump-turbine was tested outside and inside the casing with different boundary conditions. For the excitation of the runner at different frequencies piezoelectric patches were used. The response was measured with miniature accelerometers located in several positions inside the runner. From the measurements the natural frequencies and mode-shapes of the runner were calculated using EMA. The influence of the added mass and of the boundary conditions is presented and discussed. 2013-02-20T11:36:21Z http://hdl.handle.net/2117/17748 Title: The effect of cavitation on the natural frequencies of a hydrofoil Authors: Torre Rodríguez, Óscar de la; Escaler Puigoriol, Francesc Xavier; Egusquiza Estévez, Eduard; Dreyer, Matthieu; Farhat, Mohamed 2013-02-14T09:23:34Z http://hdl.handle.net/2117/17739 Title: Cavitation intensity measured on a Naca 0015 hydrofoil with various gas contents Authors: Ekanger, Jarle V.; Kjeldsen, Morten; Escaler Puigoriol, Francesc Xavier; Kawakami, Ellison; Arndt, Roger E. A. 2013-02-13T17:52:20Z http://hdl.handle.net/2117/17724 Title: Desarrollo de conocimiento para la mejora del mantenimiento predictivo en el sector eólico Authors: Escaler Puigoriol, Francesc Xavier 2013-02-13T14:35:16Z http://hdl.handle.net/2117/15553 Title: Caracterización del tipo de cavitación mediante dinámica computacional de fluidos para posteriores aplicaciones al estudio experimental del daño por cavitación Authors: Moll, Flavio; Manuele, Diego; Coussirat Núñez, Miguel Gustavo; Guardo Zabaleta, Alfredo de Jesús; Fontanals García, Alfred Abstract: La cavitación se corresponde a una estructura bifásica (líquido-vapor) cuando la presión del líquido disminuye hasta su presión de vapor, pv. Esta disminución de pv puede deberse a diversos factores relacionados con la hidrodinámica del flujo y las propiedades físicas del fluido, pudiendo presentar diferentes características. En la cavitación hidrodinámica, pueden distinguirse efectos que pueden producir un acoplamiento fluido-estructura (lock-in) que puede favorecen la falla del material, sólido que confina al fluido, lo que conduce a la pérdida de rendimiento y daño mecánico en turbomáquinas. Los ensayos experimentales muestran que el estado de cavitación desarrollada puede tener diferentes estructuras, (e.g. de burbujas, de lámina, supercavitación, etc.), siendo algunas de ellas de tipo periódica. Estas estructuras dependen del estado fluidodinámico del flujo, siendo algunas de ellas más agresivas desde el punto de vista del daño por cavitación. Debido al costo de los experimentos, es de interés evaluar si mediante dinámica computacional de fluidos (CFD) se puede caracterizar el tipo de estructura que posee la zona de vaporización/colapso de las burbujas en diferentes dispositivos hidrodinámicos. Este tipo de flujo muestra una gran complejidad ya que deben tenerse en cuenta el estado bifásico y turbulento del flujo. El objetivo de este trabajo es demostrar si es posible caracterizar mediante CFD el tipo de estructura que se presenta cuando hay cavitación desarrollada, utilizando datos experimentales para una configuración de flujo sobre un escalón, probándose primero las aproximaciones que se obtienen mediante CFD. Se estudia la validación y la sensibilidad a parámetros de modelado con el objetivo de aplicar el conocimiento adquirido a la optimización del diseño de probetas que se insertarán en un banco de ensayos hidrodinámico para la comprobación de la resistencia al daño por cavitación de distintos materiales. Se identifican parámetros que permitan reproducir las condiciones de cavitación más agresiva con el objeto de reducir los tiempos de ensayo. 2012-03-13T10:39:32Z http://hdl.handle.net/2117/13974 Title: Simulation of hot stamping processes Authors: Riera Colom, María Dolores; Coussirat Núñez, Miguel Gustavo; Guardo Zabaleta, Alfredo de Jesús; Valls, I; Casellas Padró, Daniel Abstract: Hot stamping is a thermo-mechanical technique that enables to give to a metallic blank the desired geometry and properties in a single step, where deformation at high temperature, phase transformations and heat transfer are occurring simultaneously and affect mutually. They are several variables controlling the quality of the final component and their relationships are, in some cases, complex. Therefore, a methodology able to take into account all the phenomena involved is necessary in order to understand the influence of the parameters characterising the deformation system. In this work, numerical simulation techniques are implemented as a tool to evaluate the effect of different process parameters in the hot stamping of a Boron steel, with special emphasis on the thermal conductivity of the material of the dies, the cooling system of the tooling and the main features of the contact between metallic blank and tools. A very simple experimental test has been very useful to validate the simulation and to adjust the thermal contact conductance, responsible up to a point for the cooling velocity of the sheet. As a result, the importance of the quality of the thermal contact between the workpiece and tools has to be pointed out. The high thermal conductivity of the material dies allows reducing the duration of the forming cycle. An efficient cooling system limits the maximum temperature in the dies and assures a stable thermal state and consequently, the manufacturing of pieces with a uniform quality in long series is favoured 2011-11-18T19:23:15Z http://hdl.handle.net/2117/13881 Title: Numerical study of the fluid-structure interaction in the diffuser passage of a centrifugal pump Authors: Fontanals García, Alfred; Guardo Zabaleta, Alfredo de Jesús; Coussirat Núñez, Miguel Gustavo; Egusquiza Estévez, Eduard Abstract: Reliable design of turbomachinery is a complex task. In order to gain overall efficiency in the machine performance, designers may have to reduce the gap between the impeller and the diffuser, forcing them to be as closely spaced as possible. In these situations, there may be a strong interaction between them that influences both the aerodynamics and the structural performance of blades and vanes. This phenomenon is called rotor-stator interaction (RSI), and it has a strong influence on the machine behavior. These interactions can have a significant impact on the vibrational and acoustical characteristics of the machine. Sometimes, this interaction has led to blade or vane failure. Unsteadiness and turbulence play a fundamental role in RSI, and the use of computational fluid dynamics (CFD) is becoming a usual requirement in turbomachinery design due to the difficulties and elevated cost of the experimentation required to identify RSI phenomena. Nowadays, a CFD analysis based on Reynolds–averaged Navier–Stokes equations (RANS) and a coupled eddy viscosity turbulence model (EVM) is commonly applied in turbomachinery design. Therefore, the choice of an appropriate turbulence model and the boundary layer treatment is far from trivial, and a suitable turbulence modeling plays an important role for successful CFD results.In this work, an entire stage of a diffuser pump was modeled by means of a commercial CFD code in order to study the pressure fluctuations due to the interaction between the impeller and the diffuser of the pump. The obtained numerical results were compared against the experimental results of Tsukamoto et al.,. Full RANS equations coupled with several EVM were solved for a diffuser pump stage in order to establish the most accurate modeling strategy for a diffuser pump. Boundary layer sensitivity tests were performed, and numerical discretization influence on results was also tested and established. Frequencies of the pressure fluctuations in the diffuser passage are also obtained with several EVM and compared against experimental results. 2011-11-14T16:03:43Z http://hdl.handle.net/2117/12961 Title: PM21 Creping & Cleaning Vibrations February 2011 Authors: Escaler Puigoriol, Francesc Xavier 2011-07-13T12:30:28Z http://hdl.handle.net/2117/12954 Title: PM21 Creping & Cleaning Vibrations March 2011 Authors: Escaler Puigoriol, Francesc Xavier 2011-07-13T09:49:40Z http://hdl.handle.net/2117/9899 Title: Detailed study of the rotor-stator interaction phenomenon in a moving cascade of airfoils Authors: Fontanals García, Alfred; Coussirat Núñez, Miguel Gustavo; Guardo Zabaleta, Alfredo de Jesús; Egusquiza Estévez, Eduard Abstract: In turbomachinery the Rotor-Stator Interaction (RSI) is an important phenomenon that has a strong influence on the machine behavior. These interactions can have a significant impact on the vibrational and acoustical characteristics of the machine. Unsteadiness and turbulence play a fundamental role in complex flow structure and the use of Computational Fluid Dynamics (CFD) is becoming a usual requirement in design in turbomachinery due to the difficulties and high cost of the necessary experiments needed to identify RSI phenomena. The flow inside a turbomachinery working under design condition is complex but apparently, when working under off-design conditions, it becomes more complex due to the boundary layer separation phenomena. Therefore, the choice of an appropriate turbulence model is far from trivial and a suitable turbulence modeling plays a very important role for successful CFD results. In this work the RSI generated between a moving cascade of blades and fixed flat plate located downstream were studied by means of CFD modeling and compared against experimental results. Design and off-design conditions were modeled and a detailed comparison between them has been made. To analyze in detail the flow pattern, mean velocities in the boundary layer were obtained and compared against experimental results. Furthermore, results concerning to turbulence intensity were compared against an experimental database. It was observed that for each operating condition, the flow in the cascade show special features. For flow inside the turbomachine under design conditions there is no separation, the wake is thin and the characteristic length of the eddies is small. For off-design conditions, there is a large separation and the wake is thick with large eddies. The results obtained can be used to obtain a deeper insight into the RSI phenomena. 2010-10-21T11:11:17Z http://hdl.handle.net/2117/9718 Title: Modal behavior of a reduced scale pump-turbine impeller. Part II. Numerical Simulation Authors: Valero Ferrando, M.del Carmen; Huang, Xingxing; Egusquiza Estévez, Eduard; Farhat, Mohamed; Avellan, François Abstract: A numerical simulation has been carried out to analyze the modal behavior of a reduced scale pump-turbine impeller. The simulation has been done using FEM method, in air and in water. The same boundary conditions than in the experiment were considered: free body in air and free body submerged in a reservoir of water. A sensitivity analysis to determine the influence of the number of elements was done. The influence of the input parameters was also taken into account. Finally, a mesh with 165000 elements for the impeller in air and of 508676 for the impeller in water was used. The results obtained with the simulation have been compared with the experimental ones (paper 1). Both the natural frequency values and the mode-shapes were compared. The numerical results showed small deviation from experiment in the first modes in modes with low modal density. In some coupled modes been found. With the updated model the mode-shapes have been analyzed. Some modes with high modal density have been found. As indicated in the experiment, the effect of the added mass reduces the natural frequencies and also changes the characteristics of the coupled modes 2010-10-15T09:58:07Z http://hdl.handle.net/2117/9717 Title: Modal behavior of a reduced scale pump-turbine impeller. Part I. Experiments Authors: Escaler Puigoriol, Francesc Xavier; Hutter, J.K.; Egusquiza Estévez, Eduard; Farhat, Mohamed; Avellan, F. Abstract: An experimental investigation has been carried out to quantify the effects of surrounding fluid on the modal behavior of a reduced scale pump-turbine impeller. The modal properties of the fluid-structure system have been obtained by Experimental Modal Analysis (EMA) with the impeller suspended in air and inside a water reservoir. The impeller has been excited with an instrumented hammer and the response has been measured by means of miniature accelerometers. The Frequency Response Functions (FRF’s) have been obtained from a large number of impacting positions in order to ensure the identification of the main mode shapes. As a result, the main modes of vibration have been well characterized both in air and in water in terms of natural frequency, damping ratio and mode shape. The first mode is the 2 Nodal Diameter (ND), the second one is the 0ND and the following ones are the 3ND coupled with the 1ND. The visual observation of the animated mode shapes and the level of the Modal Assurance Criterion (MAC) have permitted to correlate the homologous modes of vibration of the fluid-structure system in air and in water. From this comparison the added mass effect on the natural frequencies and the fluid effect on the damping ratios have been quantified for the most significant modes. With the surrounding water, the natural frequencies decrease in average by 10%. On the other hand, the damping ratios increase in average by 0.5%. In any case, the damping ratio appears to decrease with the frequency value of the mode 2010-10-15T09:53:22Z