This thesis explores the topic of flow of two immiscible liquids in horizontal pipeline. For this purpose, the experimental apparatus has been set up, that allows to observe the flow of mixture through the transparent pipe. Moderately viscous oil and water (viscosity ratio: 52,81, density ratio: 0.86, interfacial tension: 41,64 mN/m) have been chosen for the experiment. Both fluids were introduced into the pipe through a T-junction. At the end of the apparatus, a mixture of liquids flowed into the separation tank, where both phases were separated. The separated oil was then reused for further measurements. The oil and water flow rates could be individually changed by use control valves, that led to identification of different flow regimes. These varied from stratified flows to fully dispersed ones as the mixture speed increased. All observed flow regimes were plotted in the flow map, that is a function of the inlet velocities of both fluids. For further analysis, a second type of flow map has been created that displays rates as a function of mixture velocity and phase volume fraction. Selected regime was also simulated using software ANSYS FLUENT. The VOF method was used to simulate multiphase flow. This thesis critically evaluates the results of the study and shows the direction for further research in the field of immiscible liquids flow.

The theme of diploma thesis is a design optimization of air distribution in swimming-pool hall with regard to free water surface evaporation. This problem was solved according to determined criterions with the aid of CFD simulation. Experimental measurement part of the thesis deals with evaporation problems where own formula for this physical phenomenon is determined. This formula is compared with already known algorithms. Author suggests that such formula might be integrated in CFD software.

No description available.

Severe accidents in a Light Water Reactor (LWR) have been a subject of the research for the last three decades. The research in this area aims to further understanding of the inherent physical phenomena and reduce the uncertainties surrounding their quantification, with the ultimate goal of developing models that can be applied to safety analysis of nuclear reactors. The research is also focusing on evaluation of the proposed accident management schemes for mitigating the consequences of such accidents. During a hypothetical severe accident, whatever the scenario, there is likelihood that the core material will be relocated and accumulated in the lower plenum in the form of a debris bed or a melt pool. Physical phenomena involved in a severe accident progression are complex. The interactions of core debris or melt with the reactor structures depend very much on the debris bed or melt pool thermal hydraulics. That is why predictions of heat transfer during melt pool formation in the reactor lower head are important for the safety assessment. The main purpose of the present study is to advance a method for describing turbulent natural convection heat transfer of a melt pool, and to develop a computational platform for cost-effective, sufficiently-accurate numerical simulations and analyses of Core Melt-Structure-Water Interactions in the LWR lower head during a postulated severe core-melting accident. Given the insights gained from Computational Fluid Dynamics (CFD) simulations, a physics-based model and computationally-efficient tools are developed for multi-dimensional simulations of transient thermal-hydraulic phenomena in the lower plenum of a Boiling Water Reactor (BWR) during the late phase of an in-vessel core melt progression. A model is developed for the core debris bed heat up and formation of a melt pool in the lower head of the reactor vessel, and implemented in a commercial CFD code. To describe the natural convection heat transfer inside the volumetrically decay-heated melt pool, we advanced the Effective Convectivity Conductivity Model (ECCM), which was previously developed and implemented in the MVITA code. In the present study, natural convection heat transfer is accounted for by only the Effective Convectivity Model (ECM). The heat transport and interactions are represented through an energy-conservation formulation. The ECM then enables simulations of heat transfer of a high Rayleigh melt pool in 3D large dimension geometry. In order to describe the phase-change heat transfer associated with core debris, a temperature-based enthalpy formulation is employed in the ECM (the phase-change ECM or so called the PECM). The PECM is capable to represent possible convection heat transfer in a mushy zone. The simple approach of the PECM method allows implementing different models of the fluid velocity in a mushy zone for a non-eutectic mixture. The developed models are validated by a dual approach, i.e., against the existing experimental data and the CFD simulation results. The ECM and PECM methods are applied to predict thermal loads to the vessel wall and Control Rod Guide Tubes (CRGTs) during core debris heat up and melting in the BWR lower plenum. Applying the ECM and PECM to simulations of reactor-scale melt pool heat transfer, the results of the ECM and PECM calculations show an apparent effectiveness of the developed methods that enables simulations of long term accident transients. It is also found that during severe accident progression, the cooling by water flowing inside the CRGTs plays a very important role in reducing the thermal load on the reactor vessel wall. The results of the CFD, ECM and PECM simulations suggest a potential of the CRGT cooling as an effective mitigative measure during a severe accident progression. / QC 20101119

ith one controlled extraction and one uncontrolled extraction, calculation of the flow channel at all stage, design and calculation of the regulation valve and create connection diagram of steam turbine and air cooled condenser. At the beginning of this work is an overview of manufacturers of steam turbines and their unified products. Master thesis was developer with G-Team, a.s. as using calculations and the instructions given in the recommended literature with supporting CFD simulations to determine the loss coefficients and FEA simulations to determine the eigenfrequencies blades.

In the flow past bluff bodies for a certain range of velocity a periodical vortex shedding emerges which is known as von Kármán vortex street. This phenomenon causes the periodical alteration of pressure field which affects the body. Should the vortex shedding frequency be similar to the body natural frequency, the amplitude of vibration significantly increases which can lead to fatigue cracking. In the case of water turbines, this phenomenon often affects the stay vanes. Both the vortex shedding frequency and the lift force amplitude can be influenced by the modification of the trailing edge geometry. The aim of this thesis is to use CFD computation in order to find the optimal geometry of the stay vane trailing edge for the specific Francis turbine unit.

This master´s thesis analyzes an effect of wind load on the ventilated facade claddings. The analysis is performed on the various types of facades, from unventilated to ventilated facades with a different geometrical arrangement of facade shell. The theoretical part describes the basic knowledge about the theory of flow, turbulence modeling, determining an optimal domain, verification of the calculation model and user interface in the ANSYS software. The final part compares the value of the wind load reduction depending on the change of the gap widths and the size of ventilated spaces. The resulting values are obtained by CFD simulations. The thesis includes a design and an assessment of the steel hall construction.

Radiale Diffusoren beeinflussen signifikant die Qualität der thermischen Schichtung in Warmwasserspeichern. Um die Effizienz der Energiespeicherung zu verbessern, ist das Verständnis des komplexen Strömungsverhaltens notwendig. Diese Arbeit liefert Grundlagen zur Beschreibung der auftretenden Effekte und stellt ein geeignetes CFD-Simulationsmodell vor. Als Untersuchungsobjekt dient eine neuartige Speicherkonstruktion, wobei der Radialdiffusor direkt an einer schwimmenden Decke montiert ist. Vorteile dieser Anordnung werden aufgezeigt, die auftretenden Strömungseffekte beschrieben sowie der Einfluss verschiedener Beladergeometrien auf die thermische Schichtung untersucht. Für das Entladen bis 98 °C bei Atmosphärendruck wurde ein strömungsoptimierter Freiformdiffusor entwickelt, um Kavitation beim Ansaugen zu vermeiden. Die Untersuchungen zeigen außerdem, dass bei der Beladung über dem Umfang des Radialdiffusors ein stark asymmetrisches und einseitig gerichtetes Ausströmen auftreten kann. Gegenmaßnahmen in Form von Leit- und Lochblechen stellen ein nahezu symmetrisches Ausströmen wieder her und verbessern damit die Schichtungsqualität. Neben umfangreichen numerischen Studien mit RANS und LES fanden zahlreiche Experimente im Labor und an einem 100 m³-Speicher statt. / Radial diffusers have a significant influence on the quality of thermal stratification in hot water storage tanks. In order to improve the efficiency of energy storage, it is necessary to understand the complex flow behaviour. This thesis provides a basis for describing the effects and introduces a CFD simulation model. An innovative storage tank construction is used as the object of investigation, whereby the radial diffuser is mounted directly to a floating ceiling. Advantages of this arrangement are shown, flow effects are described and the influence of different loader geometries on the thermal stratification is investigated. For discharging up to 98 °C at atmospheric pressure, a flow-optimized free-form diffuser was developed to avoid cavitation inside the loading device. The tests also show that a highly asymmetrical and unidirectional flow over the circumference of the radial diffuser can occur during loading. Thanks to countermeasures like baffles and perforated plates, an almost symmetrical outflow can be restored and the stratification quality improved. In addition to numerical studies with RANS and LES, numerous experiments in the laboratory and at a 100m3 store were performed.

[ES] Teniendo en cuenta la cantidad de motores de combustión interna que se encuentran en activo actualmente, y sus potenciales emisiones de contaminación si se realizaran de forma incontrolada por el parque automovilístico, las normativas internacionales son cada vez más estrictas en cuanto a la cantidad de gases perjudiciales para el medio ambiente que pueden emitir dichos motores de manera unitaria. Debido a ello, se han ido desarrollando e implantando técnicas de reducción de contaminantes como el downsizing en el cual se reduce el tamaño del motor para reducir el consumo, la implantación de motores híbridos y la Recirculación de Gases de Escape. Esta técnica de recirculación puede abordarse de dos maneras alternativas: la Recirculación de Gases de Escape de Ruta Larga inyecta dichos gases antes del compresor, mientras que la Recirculación de Gases de Escape de Ruta Corta (o alta presión) los reinyecta después del compresor, en el mismo colector de admisión del motor. Dado que en ambas configuraciones se produce una inyección directa del flujo recirculado en la corriente principal, en el presente trabajo se propone un estudio numérico de la mezcla entre las corrientes de aire y gases recirculados usando un software comercial de mecánica de fluidos computacional (STAR-CCM+). En la configuración de Ruta Larga se ha propuesto en primer lugar estudiar el efecto en los parámetros globales del compresor de una entrada heterogénea compuesta por aire y gases de escape. Para ello, se han analizado 9 puntos de funcionamiento distintos, tratando de abarcar el mapa completo del compresor centrífugo con una tasa de inyección constante. Se ha demostrado, por un lado, la necesidad de un esquema transitorio de cálculo para la obtención de resultados confiables en todo el dominio del compresor. Por otro lado, se ha demostrado que, con tasas de penetración de flujo estándar, la inyección de gases recirculados no tiene un impacto reseñable en las prestaciones del compresor, con excepción de la zona de bombeo. En segundo lugar, se ha desarrollado un diseño numérico de experimentos en configuración de Ruta Larga con el objetivo de encontrar correlaciones entre la condensación generada en dichas uniones (la cual puede aparecer bajo ciertas condiciones de operación del motor) y la mezcla entre las corrientes de aire y gases de escape. Se ha demostrado que la penetración de los gases en la corriente principal es un factor clave en la condensación generada, aumentando la cantidad de mezcla entre ambas corrientes. En la configuración de Ruta Corta se han realizado estudios de configuración numérica tratando de estudiar la influencia de factores como malla, tamaño del paso temporal y modelos de turbulencia en la distribución final de los gases de escape entre los diferentes cilindros del motor. Se ha demostrado que los submodelos RANS pueden predecir la mayor parte de puntos de operación tanto en variables medias como instantáneas comparando resultados numéricos con mediciones experimentales. Fijando una configuración numérica, posteriormente se han analizado diferentes mezcladores en colectores de motores de 4 y 6 cilindros, demostrando la aplicabilidad de los índices de mezclado desarrollados y cuantificando la influencia de los diferentes efectos físicos que influyen en la distribución y mezcla de los gases de escape en la corriente principal. / [CA] Tenint en compte la quantitat de motors de combustió interna que es troben en actiu actualment, i les seues potencials emissions de contaminació si es realitzaren de manera incontrolada pel parc automobilístic, les normatives internacionals són cada vegada més estrictes quant a la quantitat de gasos perjudicials per al medi ambient que poden emetre aquests motors de manera unitària. A causa d'això, s'han anat desenvolupant i implantant tècniques de reducció de contaminants com el downsizing en el qual es redueix la grandària del motor per a reduir el consum, la implantació de motors híbrids i la Recirculació de Gasos de Fuita. Aquesta tècnica de recirculació pot abordar-se de dues maneres alternatives: la Recirculació de Gasos de Fuita de Ruta Llarga injecta aquests gasos abans del compressor, mentre que la Recirculació de Gasos de Fuita de Ruta Curta (o alta pressió) els reinjecta després del compressor, en el mateix collector d'admissió del motor. Atés que en totes dues configuracions es produeix una injecció directa del flux recirculat en el corrent principal, en el present treball es proposa un estudi numèric de la mescla entre els corrents d'aire i gasos recirculats usant un programari comercial de mecànica de fluids computacional (STAR-CCM+). En la configuració de Ruta Llarga s'ha proposat en primer lloc estudiar l'efecte en els paràmetres globals del compressor d'una entrada heterogènia composta per aire i gasos de fuita. Per a això, s'han analitzat 9 punts de funcionament diferents, tractant d'abastar el mapa complet del compressor centrífug amb una taxa d'injecció constant. S'ha demostrat, d'una banda, la necessitat d'un esquema transitori de càlcul per a l'obtenció de resultats de confiança en tot el domini del compressor. D'altra banda, s'ha demostrat que, amb taxes de penetració de flux estàndard, la injecció de gasos recirculats no té un impacte ressenyable en les prestacions del compressor, amb excepció de la zona de bombament. En segon lloc, s'ha desenvolupat un disseny numèric d'experiments en configuració de Ruta Llarga amb l'objectiu de trobar correlacions entre la condensació generada en aquestes unions (la qual pot aparéixer sota unes certes condicions d'operació del motor) i la mescla entre els corrents d'aire i gasos de fuita. S'ha demostrat que la penetració dels gasos en el corrent principal és un factor clau en la condensació generada, augmentant la quantitat de mescla entre tots dos corrents. En la configuració de Ruta Curta s'han realitzat estudis de configuració numèrica tractant d'estudiar la influència de factors com a malla, grandària del pas temporal i models de turbulència en la distribució final dels gasos de fuita entre els diferents cilindres del motor. S'ha demostrat que els submodelos RANS poden predir la major part de punts d'operació tant en variables mitjanes com instantànies comparant resultats numèrics amb mesuraments experimentals. Fixant una configuració numèrica, posteriorment s'han analitzat diferents mescladors en col·lectors de motors de 4 i 6 cilindres, demostrant l'aplicabilitat dels índexs de barrejat desenvolupats i quantificant la influència dels diferents efectes físics que influeixen en la distribució i mescla dels gasos de fuita en el corrent principal. / [EN] Considering the amount of internal combustion engines (ICEs) existing nowadays, and the pollutants that they could potentially emit, it is no surprise that international standards are getting increasingly severe regarding the allowed limits of pollutants that can be released by such engines. For this reason, different techniques have been developed in order to diminish pollutants, as downsizing in which the engine size is reduced to decrease the consumption, the hybridation of engines and the exhaust gases recirculation (EGR). This recirculation technique can be addressed by 2 different paths: Low Pressure EGR (LP-EGR) which reintroduce the exhaust gases before the compressor, while High Pressure EGR (HP-EGR) injects exhaust gases after the compressor in the intake manifold. Since both configurations deal with a direct injection of the recirculated flow in the main stream, in the present work a numerical study of the mixing between air and EGR flows is proposed, using a commercial code of computational fluid dynamics (STAR-CCM+). In LP-EGR configuration has been proposed the study of the influence of a heterogeneous inlet (composed by air and exhaust gases) on the main performance of a centrifugal compressor. To do that, 9 different operating points have been analyzed, trying to cover the whole map of the compressor with a constant injection rate. It has been demonstrated the necessity of a transient scheme for obtaining reliable results in the complete domain of the compressor. On the other hand, it has been proved that, with standard penetration rates of the flow, EGR do not have a remarkable impact in the performance of the compressor, besides the surge zone. In LP-EGR scheme, a numerical design of experiments has been developed with the aim to find correlations between the generated volume condensation (which can appear under some operating points of the engine) and the mixing between air and exhaust gases. It has been proved that the penetration of the EGR in the main stream is a key factor in volume condensation, increasing the amount of mixing between the streams. In HP-EGR configuration, different studies of numerical configuration have been conducted trying to find the influence of factors like mesh, time-step size, and turbulence models in the final distribution of exhaust gases between the cylinders of the engine. RANS submodels have demonstrated that can predict most of the operating points both average and instantaneous variables in comparison with experimental measurements. After that, fixing a numerical setup, different mixers in 4 and 6 cylinder manifolds have been calculated, showing the applicability of the developed mixing indexes, and quantifying the influence of the different physical effects that can influence in the mixing and distribution between air and exhaust gases streams. / García Olivas, G. (2021). Numerical study of EGR mixing and distribution in a piston engine intake line [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/179406 / TESIS

Indiana University-Purdue University Indianapolis (IUPUI) / Atherosclerotic lesions of human beings are common diagnosed in regions of arte- rial branching and curvature. The prevalence of atherosclerosis is usually associated with hardening and ballooning of aortic wall surfaces because of narrowing of flow path by the deposition of fatty materials, platelets and influx of plasma through in- timal wall of Aorta. High Wall Shear Stress (WSS) is proved to be the main cause behind all these aortic diseases by physicians and researchers. Due to the fact that the atherosclerotic regions are associated with complex blood flow patterns, it has believed that hemodynamics and fluid-structure interaction play important roles in regulating atherogenesis. As one of the most complex flow situations found in cardio- vascular system due to the strong curvature effects, irregular geometry, tapering and branching, and twisting, theoretical prediction and in vivo quantitative experimental data regarding to the complex blood flow dynamics are substantial paucity. In recent years, computational fluid dynamics (CFD) has emerged as a popular research tool to study the characteristics of aortic flow and aim to enhance the understanding of the underlying physics behind arteriosclerosis. In this research, we study the hemo- dynamics and flow-vessel interaction in patient specific normal (healthy) and dilated (diseased) aortas using Ansys-Fluent and Ansys-Workbench. The computation con- sists of three parts: segmentation of arterial geometry for the CFD simulation from computed tomography (CT) scanning data using MIMICS; finite volume simulation of hemodynamics of steady and pulsatile flow using Ansys-Fluent; an attempt to perform the Fluid Structure Simulation of the normal aorta using Ansys-Workbench. Instead of neglecting the branching or smoothing out the wall for simplification as a lot of similar computation in literature, we use the exact aortic geometry. Segmen- tation from real time CT images from two patients, one young and another old to represent healthy and diseased aorta respectively, is on MIMICS. The MIMICS seg- mentation operation includes: first cropping the required part of aorta from CT dicom data of the whole chest, masking of the aorta from coronal, axial and saggital views of the same to extract the exact 3D geometry of the aorta. Next step was to perform surface improvement using MIMICS 3-matic module to repair for holes, noise shells and overlapping triangles to create a good quality surface of the geometry. A hexahe- dral volume mesh was created in T-Grid. Since T-grid cannot recognize the geometry format created by MIMICS 3-matic; the required step geometry file was created in Pro-Engineer. After the meshing operation is performed, the mesh is exported to Ansys Fluent to perform the required fluid simulation imposing adequate boundary conditions accordingly. Two types of study are performed for hemodynamics. First is a steady flow driven by specified parabolic velocity at inlet. We captured the flow feature such as skewness of velocity around the aortic arch regions and vortices pairs, which are in good agreement with open data in literature. Second is a pulsatile flow. Two pulsatile velocity profiles are imposed at the inlet of healthy and diseased aorta respectively. The pulsatile analysis was accomplished for peak systolic, mid systolic and diastolic phase of the entire cardiac cycle. During peak systole and mid-systole, high WSS was found at the aortic branch roots and arch regions and diastole resulted in flow reversals and low WSS values due to small aortic inflow. In brief, areas of sudden geometry change, i.e. the branch roots and irregular surfaces of the geom- etry experience more WSS. Also it was found that dilated aorta has more sporadic nature of WSS in different regions than normal aorta which displays a more uniform WSS distribution all over the aorta surface. Fluid-Structure Interaction simulation is performed on Ansys-WorkBench through the coupling of fluid dynamics and solid mechanics. Focus is on the maximum displacement and equivalent stress to find out the future failure regions for the peak velocity of the cardiac cycle.