CFD and experimental study on the effect of progressive heating on fluid flow inside a thermal wind tunnel

A detailed Computational Fluid Dynamics (CFD) and experimental investigation into characterizing the fluid flow and thermal profiles in a wind tunnel was carried out, highlighting the effect of progressive heating on the non-uniformity flow profile of air. Using controllable electrical heating elements, the operating temperatures in the test-section were gradually increased in order to determine its influence on the subsequent velocity and thermal profiles found inside the test-section. The numerical study was carried out using CFD FLUENT code, alongside validating the experimental results. Good correlation was observed as the comparison yielded a mean error of 6.4% for the air velocity parameter and 2.3% for the air temperature parameter between the two techniques. The good correlation established between the numerically predicted and experimentally tested results identified broad scope for using the advanced computational capabilities of CFD applicable to the thermal modeling of wind tunnels. For a constant temperature process, the non-uniformity and turbulence intensity in the test section was 0.9% and 0.5%, which is under the recommended guidelines for wind tunnels. The findings revealed that the increase in temperature from 20 °C to 50 °C reduced the velocity by 15.2% inside the test section

CFD and experimental data of closed-loop wind tunnel flow

The data presented in this article were the basis for the study reported in the research articles entitled ‘A validated design methodology for a closed loop subsonic wind tunnel’ [1], which presented a systematic investigation into the design, simulation and analysis of flow parameters in a wind tunnel using Computational Fluid Dynamics (CFD). The authors evaluated the accuracy of replicating the flow characteristics for which the wind tunnel was designed using numerical simulation. Here, we detail the numerical and experimental set-up for the analysis of the closed-loop subsonic wind tunnel with an empty test section

Experimental and Numerical Modeling of Fluid Flow

This Special Issue provides an overview of the applied experimental and numerical flow, models, which are used to investigate fluid flow in complex situations. The investigated problems are related to fundamental processes or new applications. As demonstrated, the field of the application of experimental and numerical flow models is constantly expanding

Computational fluid dynamics (CFD) applied to buildings sustainable design: natural ventilation. Case study

Tesis por compendioThrough the last decades, building designers should deal with reliable design strategies to take advantage of natural resources in order to increase energy efficiency in buildings, as well as to promote sustainable development and add value to the society. This thesis proposes a reliable building design strategy to improve buildings energy efficiency by means of natural ventilation (NV) use. The strategy consists in evaluating the most suitable architectural solution in a particular case study taking into account environmental conditions and building surroundings in order to maximize NV use since the early building design stage. Computational fluid dynamics (CFD) techniques are used to conduct the research. This is a powerful design tool that permits buildings NV behaviour simulation prior to building construction. Therefore, the aim of the thesis is to provide a real case study building in which the NV design strategy is applied to show a reliable example and support building design decisions since the design stage. The design strategy is based on the use of a commercial numerical code that solves the fluid mechanic equations. The CFD software simulates the features that influence NV and predicts its behaviour in the different building configurations prior to building construction. This numerical technique allows, on the one hand, the visualization of air flow paths in buildings. On the other hand, many quantifiable parameters are calculated by the software. Through the analysis and comparison of those parameters, the best architectural solutions are chosen. With regards to all possible architectural decisions, the research is focused on the façade configuration selection and the building location. First of all, the NV design strategy feasibility is analysed in a particular region: the Mediterranean Valencian Coastal area (Spain). The region is characterized by the uniform conditions of the prevailing wind during the warm season. Then, a validated CFD simulation is used to analyse qualitatively and quantitatively the building surrounding influence on wind paths through and around buildings. The objective is to compare different façade opening positions and select the alternative that takes more profit of the NV resources available. Additionally, a general quantification of the ventilated façade contribution to buildings energy efficiency is presented under the frame of the façade configuration selection. Secondly, two simulations are conducted to analyse two different building locations. The assessment of surrounding buildings influence on building NV behaviour is done through validated CFD models. Some parameters and visualizations are proposed to be used in the quantitative and qualitative assessment of each solution respectively. Then, the best location alternative with regards to NV performance is selected. Finally, the research is concluded with the case study building full-scale construction. The indoor CFD simulation used from the beginning is then successfully validated. The NV building behaviour is also successfully verified. Additionally, contrasted performance indexes are used to evaluate indoor comfort conditions: draught risk (DR), predicted mean vote (PMV) and predicted percentage of dissatisfied people (PPD). The results show that comfort conditions can be reached more energy efficiently by means of NV use. Afterwards, it is verified how the comfortable indoor environment conditions are ensured and optimized by the NV use. Although the design strategy is applied to a particular building design, the design strategy potential is that it could be applied to all buildings. Consequently, major potential energy savings could be achieved.Durante las últimas décadas los agentes involucrados en el diseño de edificios deben de utilizar estrategias fiables de diseño que les permitan aprovechar los recursos naturales del entorno con el objetivo de aumentar la eficiencia energética de los edificios así como promover el desarrollo sostenible y generar valor añadido para la sociedad. Esta tesis propone una estrategia de diseño fiable de edificios para mejorar su eficiencia energética mediante el uso de la ventilación natural (NV por sus siglas en inglés "natural ventilation"). La estrategia consiste en evaluar la solución arquitectónica más adecuada teniendo en cuenta las condiciones ambientales y el entorno de los edificios con el objetivo de maximizar el uso de la ventilación natural desde la fase inicial de su diseño. En esta tesis se aplica la estrategia de diseño a un caso de estudio real y particular. La estrategia de diseño se basa en el uso de un código numérico comercial que resuelve las ecuaciones de la mecánica de fluidos (CFD por sus siglas en inglés "computational fluid dynamics"). El software CFD simula las características que influyen en la ventilación natural y predice su comportamiento en los edificios antes de su construcción. Esta técnica numérica permite la visualización del flujo de aire en los edificios. Además, el software permite calcular parámetros que son analizados y comparados posteriormente para elegir la solución arquitectónica que suponga un mejor comportamiento de la ventilación natural. Con respecto a todas las decisiones arquitectónicas posibles, la investigación se centra en la selección de la ubicación del edificio y de la configuración de los huecos de su fachada. En primer lugar, se analiza la viabilidad de la estrategia de diseño en una región determinada: la zona costera Mediterránea de la Comunidad Valenciana. La región se caracteriza por las condiciones uniformes del viento predominante durante la estación cálida. A continuación, se utiliza una simulación de CFD validada para analizar cualitativamente y cuantitativamente la influencia de los edificios circundantes en los flujos del viento a través y alrededor de los edificios circundantes. El objetivo es comparar distintas posiciones de los huecos de la fachada para seleccionar la alternativa que mejor aproveche los recursos de ventilación natural disponibles. Además, se presenta en el marco de la selección de la configuración de la fachada una cuantificación general de la contribución de la fachada ventilada a la eficiencia energética de los edificios. En segundo lugar, se realizan dos simulaciones para analizar dos ubicaciones diferentes del edificio caso de estudio. La evaluación de la influencia de los edificios circundantes en el comportamiento de la ventilación natural del edificio caso de estudio se realiza mediante la utilización de modelos CFD validados. Se proponen distintos parámetros y visualizaciones para la evaluación cuantitativa y cualitativa de cada solución. A continuación se selecciona la mejor ubicación con respecto al comportamiento de la ventilación natural en el edificio caso de estudio. Finalmente, la investigación concluye con la construcción a escala real del edificio caso de estudio. Se valida con éxito la simulación CFD del interior del edificio utilizada desde la etapa de diseño. También se verifica con éxito el comportamiento de la ventilación natural del edificio. Además, se analizan las condiciones de confort interiores mediante la evaluación de los siguientes índices: riesgo de corrientes de aire (DR por sus siglas en inglés "draught risk"), voto promedio previsto (PMV por sus siglas en inglés "predicted mean vote") y el porcentaje previsto de personas insatisfechas (PPD por sus siglas en inglés "predicted percentage of dissatisfied people"). Los resultados muestran que el uso de la ventilación natural permite alcanzar, de manera más energéticamente eficiente, lasDurant les últimes dècades els agents involucrats en el disseny d'edificis utilitzen estratègies fiables de disseny que els permeten aprofitar els recursos naturals de l'entorn amb l'objectiu d'augmentar l'eficiència energètica dels edificis així com promoure el desenvolupament sostenible i generar valor afegit per la societat. Aquesta tesi proposa una estratègia fiable de disseny d'edificis per a millorar la seva eficiència energètica mitjançant l'ús de la ventilació natural (NV per les sigles en anglès "natural ventilation"). L'estratègia consisteix a avaluar la solució arquitectònica més adequada tenint en compte les condicions ambientals i l'entorn dels edificis amb l'objectiu de maximitzar l'ús de la ventilació natural des de la fase inicial del seu disseny. En aquesta tesi s'aplica l'estratègia de disseny a un cas d'estudi real i particular. L'estratègia de disseny es basa en l'ús d'un codi numèric comercial que resol les equacions de la mecànica de fluids (CFD per les sigles en anglès "computational fluid dynamics"). El programari CFD simula les característiques que influeixen en la ventilació natural i prediu el seu comportament en els edificis abans de la seva construcció. Aquesta tècnica numèrica permet la visualització del flux d'aire en els edificis. A més, el programari permet calcular paràmetres que són analitzats i comparats posteriorment per triar la solució arquitectònica que supose un millor comportament de la ventilació natural. Pel que fa a totes les decisions arquitectòniques possibles, la investigació es centra en la selecció de la ubicació de l'edifici i de la configuració de les obertures de la façana. En primer lloc, s'analitza la viabilitat de l'estratègia de disseny en una regió determinada: la zona costanera Mediterrània de la Comunitat Valenciana. La regió es caracteritza per les condicions uniformes del vent predominant durant l'estació càlida. A continuació, s'utilitza una simulació de CFD validada per analitzar qualitativament i quantitativament la influència dels edificis circumdants en els fluxos del vent a través i al voltant dels edificis circumdants. L'objectiu és comparar diferents posicions dels buits de la façana per seleccionar l'alternativa que millor aprofite els recursos de ventilació natural disponibles. A més, en el marc de la selecció de la configuració de la façana es presenta una quantificació general de la contribució de la façana ventilada a l'eficiència energètica dels edificis. En segon lloc, es realitzen dues simulacions per analitzar dues ubicacions diferents de l'edifici cas d'estudi. L'avaluació de la influència dels edificis circumdants en el comportament de la ventilació natural de l'edifici cas d'estudi es realitza mitjançant la utilització de models CFD validats. Es proposen diferents paràmetres i visualitzacions per a l'avaluació quantitativa i qualitativa de cada solució. A continuació es selecciona la millor ubicació pel que fa al comportament de la ventilació natural a l'edifici cas d'estudi. Finalment, la investigació conclou amb la construcció a escala real de l'edifici cas d'estudi. Es valida amb èxit la simulació CFD de l'interior de l'edifici utilitzada des de l'etapa de disseny. També es verifica amb èxit el comportament de la ventilació natural de l'edifici. A més, s'analitzen les condicions de confort interiors mitjançant l'avaluació dels següents índexs: risc de corrents d'aire (DR per les sigles en anglès "draught risk"), mitjana de vots previstos (PMV per les sigles en anglès "predicted mean vote") i el percentatge previst de persones insatisfetes (PPD per les sigles en anglès "predicted percentage of dissatisfied people"). Els resultats mostren que l'ús de la ventilació natural permet assolir, de manera més energèticament eficient, les condicions de confort.Mora Pérez, M. (2017). Computational fluid dynamics (CFD) applied to buildings sustainable design: natural ventilation. Case study [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86208TESISCompendi

Using large eddy simulation to model buoyancy-driven natural ventilation

The use of Large Eddy Simulation (LES) for modelling air flows in buildings is a growing area of Computational Fluid Dynamics (CFD). Compared to traditional CFD techniques, LES provides a more detailed approach to modelling turbulence in air. This offers the potential for more accurate modelling of low energy natural ventilation which is notoriously difficult to model using traditional CFD. Currently, very little is known about the performance of LES for modelling natural ventilation, and its computational intensity makes its practical use on desk top computers prohibitive. The objective of this work was to apply LES to a variety of natural ventilation strategies and to compile guidelines for practitioners on its performance, including the trade-off between accuracy and cost

Innovative Modelling Approaches for the Design, Operation and Control of Complex Energy Systems with Application to Underground Infrastructures

The ventilations systems play a key role in underground infrastructures for health and safety of occupants during normal operation as well as during accidents. Their performances are affected by selection of the optimal design, operation and control that is investigated by predicting air flow. The calculation of ventilation flows and their interaction with fires can be done with different modelling approaches that differ in the accuracy and in the required resources. The 3D computational fluid dynamics (CFD) tools approximate the flow behaviour with a great accuracy but they require high computational resources. The one dimensional (1D) models allow a compact description of the system with a low computational time but they are unsuitable to simulate thermal fluid-dynamic scenarios characterized by turbulence and gradients. Innovative tools are necessary in order to make the analysis and optimization of these systems possible and accurate in a reasonable time. This can be achieved both with appropriate numerical approaches to the full domain as the model order reduction techniques and with the domain decompositions methods as the multiscale physical decomposition technique. The reduced order mode techniques as the proper orthogonal decomposition (POD) is based on the snapshots method provides an optimal linear basis for the reconstruction of multidimensional data. This technique has been applied to non-dimensional equations in order to produce a reduced model not depending on the geometry, source terms, boundary conditions and initial conditions. This type of modelling is adapted to the optimization strategies of the design and operation allowing to explore several configuration in reduced times, and for the real time simulation in the control algorithms. The physical decomposition achieved through multiscale approaches uses the accuracy of the CFD code in the near field e.g. the region close to the fire source, and takes advantage of the low computational cost of the 1-D model in the region where gradients in the transversal direction are negligible. In last years, the multiscale approach has been proposed for the analysis of tunnel ventilation. Among the several CFD codes used in this field, the Fire Dynamic Simulator (FDS) is suitable for the multiscale modelling. This is an open source CFD package developed by NIST and VTT and presents the HVAC routine in which the conservation equations of mass, energy and momentum are implemented. Currently, the HVAC module does not allow one to consider heat and mass transfer, which significanltly limits the applications. For these reasons a multiscale simulator has been created through the fully integration of a 1D continuity, momentum, energy and mass transport equation in FDS modifying its source codes. The multiscale simulator thus obtained, is based on a direct coupling by means of a Dirichlet-Neumann strategy. At each 1-D-CFD interface, the exchange flow information occurs prescribing thermo-fluid dynamic boundary conditions. The 1-D mass transport equation computes the diffusion of the exhaust gas from the CFD domain and the relative concentration that is particularly interesting in the case of back layering of smoke. The global convergence of the boundary conditions at each 1-D-CFD interface has been analyzed by monitoring the evolution of thermo-fluid dynamic variables (temperature, velocity, pressure and concentration. The multiscale simulator is suitable for parametric and sensitivity studies of the design and the operation ventilation and fire safety systems. This new tool will be available for all the scientific community. In this thesis, Chapter 1 provides a general introduction to the role of the system ventilation in underground infrastructures and to the innovative modelling strategies proposed for these systems. Chapter 2 offers a description of the 1D network modelling, its fluid-dynamic application to the Frejus tunnel and its thermal application to ground heat exchangers. In Chapter 3, the proper orthogonal decomposition method is presented and its application to the optimal control of the sanitary ventilation for the Padornelo Tunnel is discussed. To demonstrate the applicability of POD method in other fields, boreholes thermal energy storage systems have been considered in same chapter. In particular, a multi-objective optimization strategy is applied to investigate the optimal design of these system and an optimization algorithm for the operation is proposed. Chapter 4 describes the multiscale approach and the relative simulator. The new open tool is used for modeling the ventilation system of the Monte Cuneo road tunnel in case of fire. Results show that in the case of the current configuration of the ventilation system, depending on the atmospheric conditions at portals, smoke might not be fully confined. Significant improvements in terms of safety conditions can be achieved through increase of in smoke extraction, which requires the installation of large dumpers and of deflectors on the jet fans. The developed tool shows to be particularly effective in such analysis, also concerning the evaluation of local conditions for people evacuation and fire-brigades operation

An Experimental and Theoretical Investigation of Novel Aircraft Drag Reduction

Air transportation is an important part of the world’s economic and indispensable transportation system. The major institutions in the world and the aviation authorities are well aware of the demanding expectations of the public for cheaper transportation cost and at the same time the need to reduce the negative impact of aircraft or air-transportation system on the atmosphere which include noise around airports and global warming to attain sustainability, reduction in the emission of green-house gases such Nitrogen oxides (x) and Carbon di-oxide. In order to achieve such a balance in the future, a strategy is required to match competitive excellence dedicated to meeting the demands of society while at the same time being cost effective for the airline companies and operating aviation authorities. Such a vision or concept cannot be realised without making further technological breakthroughs in engineering fields such as Aerodynamics and other discipline including materials and structures. Improving aircraft aerodynamic performance will have a direct impact on helping to implement these goals. Improving aircraft drag capabilities remains one of the big challenges faced by manufacturers of transport aircraft. It is known that for a typical transport aircraft drag, the induced drag amounts to about 40% of the total drag at cruise flight conditions and about 80 –90 percent of the total drag during aircraft take off. The skin friction drag constitute approximately one half of the total Aircraft drag at cruise flight configuration making up most of the remaining percentage of drag at cruise condition. The use of winglets or other wing-tip devices as a drag reduction device play a significant role in improving aircraft performance by acting as passive devices to reduce drag and enhance aircraft performance. In this thesis, four novel spiroid drag reduction devices are presented which were designed and optimised using STAR-CCM+ Optimate + which uses the SHERPA search algorithm as its optimisation tool. The objective of the optimisation process was set to maximise the lift-to-drag ratio. A low fidelity mesh model was used during the optimisation and the results were verified by using high-fidelity physics and mesh model. The developed devices showed an improve CL/CD ratio of up to 11 percent and improved CL by up to 7 percent while reducing CD by up to 4 percent with an 18 - 24 percent reduction in induced drag observed as well. The devices showed consistency in performance at several Mach numbers and angles of attacks. Thus, suggesting that such devices could be used over a wide range of flight regimes on aircraft or UAVs. The study also successfully demonstrated the capability to using this optimisation process in the design and development of such devices. Furthermore, a numerical investigation and wind tunnel verification study was performed on a wing tip turbine to ascertain the aerodynamic performance modification of using such a device at several Mach numbers, angles of attack, propeller rpms and sensitivity of propeller nacelle positions at the wing tip. The obtained results revealed a trend on the nacelle position to achieve the most improved aerodynamic performance. A CL/CD ratio improvement of up to 7 percent, CL modification of approximate 4 percent and CD reduction of up to 4 percent were achieved. In addition to demonstrate an appreciation of some of the wider implication of installing wing tip devices, a flutter analysis on a rectangular clean wing with added variable mass at the wing tip was performed. The result showed that the added masses had no significant implication on the flutter characteristics of the wing

Analysis of night-time climate in plastic-covered grenhouses

Este trabajo analiza el clima nocturno del invernadero. EL objeto del estudio es el invernadero de plástico sin calefacción, cuyo clima se estudia utilizando modelos CFD, modelos basados en los balance de energía (ES) y s datos experimentales. El fin es doble, por un lado se trata de analizar y comprender el clima nocturno del invernadero, y proponer soluciones a los problemas relacionados con las altas tasas de humedad. Por otro lado se investigan nuevos métodos de simulación del clima del invernadero, métodos basados en el uso conjunto o acoplamiento de modelos CFD y ES , y también basados en la técnica de optimización. El Capitulo 1 introduce el contexto general y los objetivos que plantea el trabajo. El Capitulo 2 estudia el clima nocturno en un invernadero de capa sencilla. Para ello desarrolla un modelo CFD que incluye una UDF (User Define Function) para calcular la tasa de condensación. Una vez validado el modelo se analiza el comportamiento del invernadero bajo distintas condiciones de contorno.. El Capitulo 3 analiza una solución para combatir las bajas temperaturas nocturnas, la pantalla térmica. Los efectos de la pantalla se analizan mediante el uso del CFD. Se lleva a cabo una comparación completa entre el invernadero de capa sencilla y el invernadero con pantalla. El capitulo proporciona información detallada sobre el clima del invernadero y presenta un estudio paramétrico del efecto de la temperatura equivalente del cielo y la cesión de calor desde el suelo en el clima del invernadero con pantalla térmica. EL Capitulo 4 presenta un nuevo método para optimizar el diseño del invernadero. El método se basa en el acoplamiento de dos algoritmos de optimización que operan con el modelo ES. A su vez el modelo ES está conectado con el modelo CFD. El objetivo es doble, por un lado introducir una nueva manera de optimizar el diseño del invernadero, y por el otro lado tratar de resolver uno de los problemas evidenciados en el capítulo 2. El resultado muestra que un material de cubierta de alto poder de reflexión del infrarrojo lejano aportaría mejorías relevantes al clima del invernadero. El Capitulo 5 presenta un modelo acoplado para el estudio del clima del invernadero. EL CFD se utiliza para proporcionar las tasas de ventilación y los coeficientes convectivos al modelo ES. Esta técnica se utiliza para estudiar los efectos de diferentes estrategias de ventilación sobre el régimen de humedad con diferentes condiciones externas. Finalmente, el Capitulo 6 resume las conclusiones y propone algunos temas para futuras investigacionesThis work studied night-time greenhouse climate. The focus was on unheated plastic greenhouses and analyses were carried out using CFD models, Energy balance (ES) models and experimental data. The aims were twofold: on the one hand, it was intended to analyse and understand night-time greenhouse climate and propose solutions to the high-humidity issue. On the other hand, the aim was to investigate novel simulation approaches based on the coupling of CFD and ES models as well as the use of optimisation algorithms to study greenhouse climate. Chapter 1 is an introductory chapter which includes the general context and overall research objectives. Chapter 2 studies night-time climate in single-layer greenhouses by means of CFD. The model is validated and condensation User Defined Function (UDF) is introduced which accounted for the condensation rate found on the inner face of the greenhouse cover. Chapter 3 studies a commonly used solution to the issue of low night-time temperature. A thermal screen was analysed by means of CFD simulations. A thorough comparison was made between single-layer and screened greenhouses and detailed information was provided in order to build a framework for taking decisions as to whether to use a screen or not. Chapter 4 introduces a novel approach to optimizing greenhouse design; the approach relies on two optimization algorithms linked to an ES model which was coupled to a CFD model. The aim of the study was twofold: on the one hand to introduce a method offering a general approach for optimizing greenhouse design and on the other, to attempt to solve one of the issues highlighted in Chapter 2. It was shown that using a highly reflective covering material would have a theoretically significant impact on greenhouse performance. Chapter 5 introduces a coupled model for studying greenhouse climate. The CFD was used to provide the ventilation rate and convective coefficients for the ES model. This approach was applied to study the effects of different ventilation strategies on humidity under different outside air conditions. Finally Chapter 6 summarizes the conclusions and proposes themes for future research