Low order modelling of flow-control techniques for turbulent skin-friction reduction

In the present thesis a linearized formulation of the Navier-Stokes equations is used to study two main subjects: the generation of near-wall streaks in turbulent boundary layers and the response of turbulent wall-bounded flows to streamwise-travelling waves of spanwise oscillations of the bounding walls. For the purposes of the present work, these oscillations of the wall have been considered as a flow control mechanism. A mathematical model, based on a velocity-vorticity formulation linearized around a turbulent mean base flow, is adopted to simulate the fluid flow equations. A hybrid spectral-finite differences solver has been employed to numerically implement the linearized system. A review on turbulent streak generation is presented and the concepts of exponential growth, algebraic growth and viscous dissipation of small-scale perturbations are linked to the concept of transient growth. Mechanisms of generation of near-wall streaks are explored using a large set of sources of excitation for the linearized Navier- Stokes equations (LNSE). Two types of sources, here labelled as Excitation Mechanisms (EM), are employed: a body-force source and an initial condition. The selection of parameters for the excitation mechanisms is performed based on the definition of a multi-step optimization problem. The different EMs studied consist of a restricted number of parameters, and therefore can be considered as a Low Order Model (LOM) for the generation of streaks. It is shown that both types of EM produce satisfactory results for the streak generation process evaluated in terms of experimentally expected optimal spanwise scales. Finally, a large set of numerical experiments are conducted to evaluate the response of the LNSE with optimised EM, to the flow control by a spanwise oscillating wall. By comparing the results between the response of the LNSE considered here to this type of flow control against a drag-reduction map obtained by DNS in other studies, it is possible to assess the correlation between streak evolution and disruption of the skin-friction drag. A good agreement between these two responses is found for the parameter space of the streamwise-travelling spanwise oscillation waves

Herramientas de software con licencia pública general para el modelado por elementos finitos

En el presente artículo se presentan los resultados de una revisión realizada a varios programas con licencias GPL para el modelamiento de problemas con elementos finitos. Este estudio permitió realizar la caracterización de estos programas teniendo en cuenta criterios como el tipo de análisis permitido, la compatibilidad con programas CAD, el tipo de soporte ofrecido, la actualización de las versiones, el tipo de interfaz de usuario implementado y la curva de aprendizaje para nuevos usuarios, entre otros. Posteriormente se estudiaron tres casos diferentes, los cuales fueron modelados con elementos finitos empleando distintos programas GPL. En la parte final del documento se comparan los resultados obtenidos con software libre, los arrojados por un programa comercial (Ansys), y los modelos analíticos derivados de la solución de la ecuación diferencial que rige el fenómeno particular, obteniendo una convergencia aceptable entre todos los resultado

Proyección de costos de un bus articulado con motor dedicado a gas natural para ser utilizado en los sistemas de transporte masivo de colombia

El objetivo del presente trabajo es mostrar los resultados del estudio comparativo de costos entre dos buses articulados que operan con diferentes combustibles, gas natural comprimido y diesel. Los resultados se utilizarán para establecer la viabilidad económica de la implementación de flotas de este tipo de buses en los sistemas de transporte masivo de las grandes ciudades colombianas. La proyección se realizó siguiendo las recomendaciones de operación y mantenimiento dadas por los fabricantes de los buses. Posteriormente se consideran tres costos importantes: motor e indispensables, combustible y mantenimiento preventivo. Para este estudio se supone la vida útil de los buses como de 10 años, y se plantean dos escenarios diferentes para la evolución de los precios del combustible. Los resultados muestran que los costos de operación y mantenimiento tienen un comportamiento similar entre ambas tecnologías, aún cuando los costos asociados al mantenimiento preventivo son menores para el bus alimentado con gas natural, en contraste con el análisis de los costos de motor e indispensables.Sin embargo es importante anotar que la mayor influencia sobre los costos de operación y mantenimiento recae en el comportamiento del precio de los combustibles. El artículo describe la naturaleza y estructura de los diferentes costos implementados en el estudio y la contribución de cada uno en el análisis económico, obteniendo así los costos de operación y mantenimiento para las dos tecnologías

How to Modify LAMMPS: From the Prospective of a Particle Method Researcher

LAMMPS is a powerful simulator originally developed for molecular dynamics that, today, also accounts for other particle-based algorithms such as DEM, SPH, or Peridynamics. The versatility of this software is further enhanced by the fact that it is open-source and modifiable by users. This property suits particularly well Discrete Multiphysics and hybrid models that combine multiple particle methods in the same simulation. Modifying LAMMPS can be challenging for researchers with little coding experience. The available material explaining how to modify LAMMPS is either too basic or too advanced for the average researcher. In this work, we provide several examples, with increasing level of complexity, suitable for researchers and practitioners in physics and engineering, who are familiar with coding without been experts. For each feature, step by step instructions for implementing them in LAMMPS are shown to allow researchers to easily follow the procedure and compile a new version of the code. The aim is to fill a gap in the literature with particular reference to the scientific community that uses particle methods for (discrete) multiphysics

How to modify LAMMPS: from the prospective of a particle method researcher

LAMMPS is a powerful simulator originally developed for molecular dynamics that, today, also accounts for other particle-based algorithms such as DEM, SPH, or Peridynamics. The versatility of this software is further enhanced by the fact that it is open-source and modifiable by users. This property suits particularly well Discrete Multiphysics and hybrid models that combine multiple particle methods in the same simulation. Modifying LAMMPS can be challenging for researchers with little coding experience. The available material explaining how to modify LAMMPS is either too basic or too advanced for the average researcher. In this work, we provide several examples, with increasing level of complexity, suitable for researchers and practitioners in physics and engineering, who are familiar with coding without been experts. For each feature, step by step instructions for implementing them in LAMMPS are shown to allow researchers to easily follow the procedure and compile a new version of the code. The aim is to fill a gap in the literature with particular reference to the scientific community that uses particle methods for (discrete) multiphysics

Experiencias en el aula: segundo encuentro de prácticas pedagógicas innovadoras

Experiencias de profesores en su quehacer en los distintos ambientes de aprendizaje presenciales y a distancia.La segunda entrega de Experiencias en el aula es una publicación anual que recoge las ponencias ganadoras presentadas en el Segundo Encuentro de Prácticas Pedagógicas Innovadoras, organizado por el Centro de Excelencia Docente aeiou, de la Vicerrectoría General Académica de la Corporación Universitaria Minuto de Dios – UNIMINUTO Todas las ponencias publicadas en la segunda entrega de Experiencias en el aula fueron seleccionadas por evaluadores externos durante la convocatoria al Segundo Encuentro de Prácticas Pedagógicas Innovadoras en el que fueron presentadas; este evento, organizado por el Centro de Excelencia Docente aeiou, y la Vicerrectoría General Académica de la Corporación Universitaria Minuto de Dios- UNIMINUTO, tuvo lugar los días 9 y 10 de octubre de 2017

Influence of Particle Mass Fraction over the Turbulent Behaviour of an Incompressible Particle-Laden Flow

The presence of spherical solid particles immersed in an incompressible turbulent flow was numerically investigated from the perspective of the particle mass fraction (PMF or ϕm), a measure of the particle-to-fluid mass ratio. Although a number of different changes have been reported to be obtained by the presence of solid particles in incompressible turbulent flows, the present study reports the findings of varying ϕm in the the turbulent behaviour of the flow, including aspects such as: turbulent statistics, skin-friction coefficient, and the general dynamics of a particle-laden flow. For this purpose, a particle-laden turbulent channel flow transporting solid particles at three different friction Reynolds numbers, namely Reτ=180, 365, and 950, with a fixed particle volume fraction of ϕv=10−3, was employed as conceptual flow model and simulated using large eddy simulations. The value adopted for ϕv allowed the use of a two-way coupling approach between the particles and the flow or carrier phase. Three different values of ϕm were explored in this work ϕm≈1,2.96, and 12.4. Assessment of the effect of ϕm was performed by examining changes of mean velocity profiles, velocity fluctuation profiles, and a number of other relevant turbulence statistics. Our results show that attenuation of turbulence activity of the carrier phase is attained, and that such attenuation increases with ϕm at fixed Reynolds numbers and ϕv. For the smallest Reynolds number case considered, flows carrying particles with higher ϕm exhibited lower energy requirements to sustain constant fluid mass flow rate conditions. By examining the flow velocity field, as well as instantaneous velocity components contours, it is shown that the attenuation acts even on the largest scales of the flow dynamics, and not only at the smaller levels. These findings reinforce the concept of a selective stabilising effect induced by the solid particles, particularly enhanced by high values of ϕm, which could eventually be exploited for improvement of energetic efficiency of piping or equivalent particles transport systems

Modelo y caracterización del patrón de flujo en un sistema propulsivo - (pequeño motor-cohete)

Magíster en Ingeniería MecánicaMaestrí

Efecto del radio de redondeo de la carina en el desarrollo del flujo a través de un modelo sintético de vías respiratorias

The effect of the rounding radius of the Carina, during inhalation stage for the respiration process, was explored numerically through computational simulations based on a synthetic model of human airways. The geometries were parameterized in terms of the dimensionless curvature of carina. In the present study two Reynolds numbers were explored in laminar flow regime. The results show that the variation of this physiological parameter affects the magnitude and distribution of the wall shear stresses, as well as the behaviour of vortical structures observed in the secondary flow. This parameter also affects, although to a lesser extent, the pressure drops across the branches. The effects produced by the variation of this curvature on physiological aspects of the breathing process are analyzed. Finally, a brief discussion about the advantages of the use of CFD simulation techniques for the study of phenomena associated to biofluids is presented.El efecto del radio de redondeo de la carina durante el proceso de inhalación es explorado numéricamente mediante simulaciones computacionales basadas en un modelo sintético de vías respiratorias. Las geometrías son parametrizadas en términos de la curvatura adimensional de carina. En el presente estudio se exploraron dos números de Reynolds en régimen laminar. Los resultados obtenidos muestran que la variación de este parámetro fisiológico afecta la magnitud y distribución de los esfuerzos cortantes de pared, así como el comportamiento de las estructuras vorticales observadas en el flujo secundario. Este parámetro afecta también, aunque en menor medida, las caídas de presión a través de las ramificaciones. Igualmente se discuten algunos efectos producidos por la variación de dicha curvatura sobre aspectos fisiológicos del proceso de respiración. Finalmente, se hace una breve reflexión acerca de las ventajas del uso de técnicas de simulación computacional CFD para el estudio de fenómenos asociados a biofluidos

Preliminary design and economical study of a biogas production-plant using cow manure

This article presents considerations and results from designing a large- scale biogas production-plant using cow manure. The so designed plant capacity allowed processing the dung from 1,300 cows, producing 500 kW of electrical energy from operating a generator which works on a mixture of diesel and biogas fuel. The design included sizing the cowsheds, the manure-collecting systems, transporting the dung, the digester, the effluent tank and the biogas treatment system. An economic study was also done, concluding that project was viable and the importance of the cost of diesel evolving for determining return on investment time