Direct Numerical Simulation and Wall-Resolved Large Eddy Simulation in Nuclear Thermal Hydraulics

International audienceThe critical review discusses the most accurate methods for description of turbulent flows: the computationally very expensive direct numerical simulation (DNS) and slightly less accurate and slightly less expensive large eddy simulation (LES) methods. Both methods have found their way into nuclear thermal hydraulics as tools for studies of the fundamental mechanisms of turbulence and turbulent heat transfer. In the first section of this critical review, both methods are briefly introduced in parallel with the basic properties of the turbulent flows. The focus is on the DNS method, the so-called quasi-DNS approach, and the coarsest turbulence modeling approach discussed in this work, which is still on the very small-scale, wall-resolved LES. Other, coarser turbulence modeling approaches (such as wall-modeled LES, Reynolds Averaged Navier-Stokes (RANS)/LES hybrids, or RANS) are beyond the scope of the present work. Section II answers the question: "How do the DNS and LES methods work?" A short discussion of the computational requirements, numerical approaches, and computational tools is included. Section III is about the interpretation of the DNS and LES results and statistical uncertainties. Sections IV and V give some examples of the DNS and wall-resolved LES results relevant for nuclear thermal hydraulics. The last section lists the conclusions and some of the challenges that might be tackled with the most accurate techniques like DNS and LES

Homogeneous bubble nucleation limit of mercury under the normal working conditions of the planned European Spallation Source

In spallation neutron sources, liquid mercury is the subject of big thermal and pressure shocks, upon adsorbing the proton beam. These changes can cause unstable bubbles in the liquid, which can damage the structural material. While there are methods to deal with the pressure shock, the local temperature shock cannot be avoided. In our paper we calculated the work of the critical cluster formation (i.e. for mercury micro-bubbles) together with the rate of their formation (nucleation rate). It is shown that the homogeneous nucleation rates are very low even after adsorbing several proton pulses, therefore the probability of temperature induced homogeneous bubble nucleation is negligible.Comment: 22 Pages, 11 figures, one of them is colour, we plan to publish it in Eur. Phys. J.

Estudio de prefactibilidad técnico-económico para construcción de residencial para el adulto mayor en la ciudad de Santiago

Tesis (Ingeniero Civil Industrial)El objetivo de este estudio es contribuir al mejoramiento de la calidad de vida del adulto mayor en la Región Metropolitana a través de la construcción de una comunidad residencial. Para la elaboración de este estudio, se toma como base un completo estudio de segmento de personas mayores a 60 años, a través de fuentes de información de tipo estadístico, principalmente del Instituto Nacional de Estadísticas (INE), del Ministerio de Desarrollo Social y del Servicio Nacional de Adultos Mayores (SENAMA). Éstos proporcionarán importantes datos y conclusiones que serán relevantes para la confección de la propuesta planteada. A pesar de tener un formato tipo, cabe destacar que será un trabajo desde lo general a lo particular. Las empresas de servicios de hoy en día buscan y necesitan diferenciarse de sus competidores, de esa forma pueden lograr una mayor sustentabilidad económica en el tiempo. En esta línea, un gran número de ellas se encuentran continuamente investigando y desarrollando nuevos proyectos, previo análisis y realización de estudios de perfil, prefactibilidad y factibilidad, otorgando información relevante sobre invertir en el proyecto a ejecutar. Para ello, se llevará a cabo un estudio de pre factibilidad de proyecto en el cual se requiere realizar ciertas delimitaciones, para así segmentar el tipo de personas que eventualmente harán uso de las instalaciones que se propondrán más adelante avanzado el proyecto, definiendo aspectos relevantes, el proceso, las características del servicio, oportunidades y grado de diferenciación asociados al proyecto, entre otros

Computational Fluid Dynamics for Gas-Liquid Flows

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Direct numerical simulation of the passive heat transfer in a turbulent flow with particle

Turbulent non-isothermal fully developed channel flow with solid particles was investigated through Direct Numerical Simulation combined with the point-particle approach. The focus was on the interactions between discrete and continuous phase and their effect on the velocity and the temperature of the particles. It has been found that low momentum inertia particles have a mean temperature similar to the fluid temperature and this effect is almost independent of particle thermal inertia. For particles with larger momentum, the inertia thermal effect is more complex, particle temperature in the near-wall and buffer region is significantly lower than the fluid temperature. The difference between the fluid mean temperature and particle mean temperature increases along with the momentum response time. This may have important consequences on the chemical reactions, technological processes and on the accuracy of temperature measurement techniques based on seeding particle

Direct Numerical Simulation of Turbulent Heat Transfer Modulation in Micro-Dispersed Channel Flow

The object of this paper is to study the influence of dispersed micrometer size particles on turbulent heat transfer mechanisms in wall-bounded flows. The strategic target of the current research is to set up a methodology to size and design new-concept heat transfer fluids with properties given by those of the base fluid modulated by the presence of dynamically-interacting, suitably-chosen, discrete micro- and nano- particles. We run Direct Numerical Simulation (DNS) for hydrodynamically fully-developed, thermally-developing turbulent channel flow at shear Reynolds number Re=150 and Prandtl number Pr=3, and we tracked two large swarms of particles, characterized by different inertia and thermal inertia. Preliminary results on velocity and temperature statistics for both phases show that, with respect to single-phase flow, heat transfer fluxes at the walls increase by roughly 2% when the flow is laden with the smaller particles, which exhibit a rather persistent stability against non-homogeneous distribution and near-wall concentration. An opposite trend (slight heat transfer flux decrease) is observed when the larger particles are dispersed into the flow. These results are consistent with previous experimental findings and are discussed in the frame of the current research activities in the field. Future developments are also outlined.Comment: Pages: 305-32