Tesis sobre el tema "Turbulent fluxe"
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Gerbi, Gregory Peter. "Observations of turbulent fluxes and turbulence dynamics in the ocean surface boundary layer". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45778.
Texto completoIncludes bibliographical references (p. 110-119).
This study presents observations of turbulence dynamics made during the low winds portion of the Coupled Boundary Layers and Air-Sea Transfer experiment (CBLAST-Low). Observations were made of turbulent fluxes, turbulent kinetic energy, and the length scales of flux-carrying and energy-containing eddies in the ocean surface boundary layer. A new technique was developed to separate wave and turbulent motions spectrally, using ideas for turbulence spectra that were developed in the study of the bottom boundary layer of the atmosphere. The observations of turbulent fluxes allowed the closing of heat and momentum budgets across the air-sea interface. The observations also show that flux-carrying eddies are similar in size to those expected in rigid-boundary turbulence, but that energy-containing eddies are smaller than those in rigid-boundary turbulence. This suggests that the relationship between turbulent kinetic energy, depth, and turbulent diffusivity are different in the ocean surface boundary layer than in rigid-boundary turbulence. The observations confirm previous speculation that surface wave breaking provides a surface source of turbulent kinetic energy that is transported to depth where it dissipates. A model that includes the effects of shear production, wave breaking and dissipation is able to reproduce the enhancement of turbulent kinetic energy near the wavy ocean surface. However, because of the different length scale relations in the ocean surface boundary layer, the empirical constants in the energy model are different from the values that are used to model rigid-boundary turbulence. The ocean surface boundary layer is observed to have small but finite temperature gradients that are related to the boundary fluxes of heat and momentum, as assumed by closure models. However, the turbulent diffusivity of heat in the surface boundary layer is larger than predicted by rigid-boundary closure models. Including the combined effects of wave breaking, stress, and buoyancy forcing allows a closure model to predict the turbulent diffusivity for heat in the ocean surface boundary layer.
by Gregory Peter Gerbi.
Ph.D.
Dupland, Laure. "Modélisation de la turbulence thermique : modèles algébriques pour la prévision des flux de chaleur turbulents". Toulouse, ENSAE, 2005. http://www.theses.fr/2005ESAE0023.
Texto completoBrol, Keila Belquiz. "Modelagem e análise de selos de fluxo aplicados a máquinas rotativas". [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263055.
Texto completoDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: O desenvolvimento de modelos matemáticos que visam simular as características operacionais das máquinas rotativas é importante para representar uma variedade de fenômenos expressivos que se manifestam durante a operação, para tanto é necessário a modelagem dos componentes que caracterizam o comportamento dinâmico do sistema. Este trabalho tem por objetivo determinar os parâmetros físicos que integram os selos de fluxo de folga fixa e angular ao modelo global de sistemas rotativos. As rigidezes e os amortecimentos são obtidos através da solução de equações governantes para líquidos escoando em selos anulares pelo método clássico das perturbações de ordem máxima um e a solução da ordem zero permite demonstrar a variação da pressão e velocidade para as equações de ordem zero. Os resultados obtidos foram validados com os valores apresentados pela literatura. O resultado deste trabalho poderá ser aplicado na modelagem global de uma máquina rotativa, de modo a tornar a análise mais completa do conjunto girante
Abstract: The development of mathematical models designed to simulate operational characteristics is important to represent a wide variety of expressive phenomena that manifest during the operation, and therefore it is necessary the components modeling that characterize the system dynamic behavior. This study aims to determine the physical parameters that influence the flow seals to fixed angles and variables in the global rotating systems model. The stiffness and damping are obtained by solving the governing equations for fluid flowing in the annular seals using the classic perturbation method of maximal order one. The zero-order solution allows to demonstrate the pressure and speed variation to zero order. The results were validated with the similar tests reported in the literature. This work results are eligible to be applied to model a global rotating machine in order to make a more complete rotor analysis
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica
Salewski, Matthew. "Flux and dissipation of energy in the LET theory of turbulence". Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/4684.
Texto completoWeng, Wensong. "Turbulent air flow and fluxes over low hills". Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333317.
Texto completoKaye, Nigel Gregory. "Interaction of turbulent plumes". Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323741.
Texto completoThompson, Andrew F. "Eddy fluxes in baroclinic turbulence". Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2006. http://wwwlib.umi.com/cr/ucsd/fullcit?p3225998.
Texto completoTitle from first page of PDF file (viewed October 10, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 173-182).
Mickett, John B. "Turbulent entrainment fluxes within the eastern Pacific warm pool /". Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/11005.
Texto completoBernard, Donald Edward. "Optimization of Turbulent Prandtl Number in Turbulent, Wall Bounded Flows". ScholarWorks @ UVM, 2018. https://scholarworks.uvm.edu/graddis/824.
Texto completoCambra, Rémi. "Etude des flux turbulents à l'interface air-mer à partir de données de la plateforme OCARINA". Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLV024/document.
Texto completoExchanges of heat and momentum at the air-sea interface play a major role in the formation and the dynamics of water and air masses. In spite of decades of research, we still need to improve our knowledge of these exchanges, and more specifically our knowledge of turbulent fluxes, which are key variables in meteorological and climate models. In these models, sub-grid turbulent processes, thus turbulent fluxes also have to be modeled, which is mostly done with the Monin-Obukhov (1954, MOS hereafter) similarity theory. However, on the one hand, the use of a model implies that coefficients have to be adjusted. On the other hand, the model itself may require improvements. Unfortunately, obtaining flux estimates that have a good accuracy is a challenging effort, because of the intrusive effect of the platform, the limited accuracy the instruments, and because the instruments have their own sampling volume.Our study focuses on the estimation of turbulent fluxes at sea from measurements made with the new OCARINA platform (autonomous trimaran) during two campaigns : STRASSE 2012 and AMOP 2014. We analyze the characteristics of turbulence in the surface boundary layer, we estimate the turbulent fluxes by different methods, and compare the values of fluxes depending on environmental conditions, taking into account the sea state
Phordoy, Jacques. "Influence d'une transpiration sur un écoulement turbulent en canal, mesure des flux de chaleur". Toulouse, INPT, 1992. http://www.theses.fr/1992INPT108H.
Texto completoLitt, Maxime. "Etude de la couche de surface atmosphérique et des flux turbulents sur deux glaciers de montagne dans les Andes tropicales et les alpes Françaises". Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAU005/document.
Texto completoWe study turbulent fluxes of sensible and latent heat, that are a poorly-known and difficult term to measure over glaciers, with the help of two field campaigns deployed over the ablation zone of Zongo glacier (16°S, Bolivia, 4900-6000 m.a.s.l.) during the austral winter dry season and over the Saint-Sorlin glacier (French Alps, 45°N, 2600-3400 m.a.s.l.) during the boreal summer. A 6-m mast allowing for wind speed and air temperature vertical profile measurements was installed, along with 2-m masts holding eddy-covariance systems. The focus is on the temporal evolution of turbulent fluxes and the applicability of the aerodynamic profile method in the complex terrain of high mountains. The assumptions of the method are discussed by characterizing the wind regimes and the turbulence. We then compute fluxes and associated errors. Above Zongo glacier, under weak synoptic forcing, katabatic flows are observed from late afternoon to early morning, with a wind-speed maximum at around 2 m. Strong synoptic forcing roughly aligns with the glacier, leading to strong downslope flows for which no wind-speed maximum is observed. Most of the days around noon, upslope flows are observed. On Saint-Sorlin glacier in summer, flows associated with low-pressure systems coming from the west or Foehn events roughly align with the glacier, leading to strong downslope winds. Wind-speed maxima are observed night and day, ~50% of the time, when synoptic forcing is moderate. Upslope flows are observed 15% of the time, when synoptic forcing is weak. The surface layer is disturbed by outer-layer eddies in strong flows and by slow oscillations if katabatic flow prevails. These disturbances influence turbulent fluxes. Random errors on the fluxes derived from the profile method are mainly due to temperature uncertainties. Errors remain small on the mean fluxes. The surface layer is rarely deeper than 2 m on both glaciers and the profile method with measurements made above that height underestimates the surface fluxes by 20% to 70%. When a wind-speed maximum is observed, fluxes are underestimated even at 2 m. The influence on the fluxes of the surface-layer disturbances is not captured by the profile method, and fluxes are about 40% smaller than the eddy-covariance fluxes. The latter are affected by large random errors due to inadequate statistical sampling of large-scale eddies and are probably underestimated, mainly due to vertical wind speed underestimation (~15%) and to vertical flux divergence. Above Zongo glacier, due to the dry high-elevation air, sublimation (a few millimeters w. e. per day) is a large energy loss for the surface. Sensible heat flux is a large energy gain in strong nocturnal downslope flows (from 30 to 50 W m-2) and strong winds, due to a marked temperature inversion. When a wind-speed maximum is observed, low wind speeds cause small turbulent fluxes (from 5 to 20 W m-2). The sum of turbulent fluxes is small in those two cases because the fluxes are opposed in sign and the biases mostly compensate. In upslope flows, the sensible heat flux is small (<5 W m-2) due to near-neutral stratification, but latent heat losses remain large (around -25 to -35 W m-2), so that the net turbulent flux is large and the biases do not compensate. Above Saint-Sorlin glacier, the latent heat flux remains small because the air is generally humid, whereas the sensible heat flux can be large (~25 W m-2) when wind speed is high. The net flux is large when wind speed is high, and the biases on net turbulent fluxes derived from the profiles can be significant
Román, Cascón Carlos. "Variability of turbulent fluxes (momentum, heat andCO2) during Upwelling conditions. A case study". Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-303975.
Texto completoMätningar av flöden (impuls, värme, vattenånga och CO2) vid två olika höjder studerades med data från en mast på ön Östergarnsholm (i Östersjön) under en vecka, beräkningar av flödena gjordes med mätningar av atmosfäriska parametrar från samma mast samt data från två bojar på två olika platser. Man fann olika beteenden för de beräknade och uppmätta flödena. Direkt (sensibelt) värme visade högre korrelation mellan beräkningar och uppmätta sensibla värmeflöden . För CO2- flödet fann man inte detta samband. För alla flödena överensstämmer mätningarna bättre med beräknade flöden när de är gjorda under instabila förhållanden, vilket betyder att under dessa förhållanden representerar mätningarna i masten bättre området där bojarna är placerade. Den studerade perioden inkluderar en period med upvällning (upwelling) och en hög horisontell variabilitet i ytparametrar under den största delen av denna period. Detta visades genom jämförelser mellan de beräknade och de uppmätta flödena och även genom satellitmätningar. Det område uppvind masten där ytan påverkar flöden uppmätta i masten på en viss nivå kallas ”footprint area”, och denna footprint area förändras kontinuerligt på grund av det stora beroendet av skiktningen i atmosfären. Eftersom skiktningen under hela perioden förändrades från något stabilt till något instabilt, kan ytvariabiliteten även ses i variationen av uppmätta flöden på olika höjder. En viktig slutsats i studien är att beräkningar av flödena som görs med standardformler inte bör användas vid förhållanden med hög horisontell och vertikal variation av olika parameter (som havsytetemperatur och pCO2w), som till exempel under uppvällningssituationer och nära kusten, där phytoplankton markant kan påverka koncentrationen av CO2 vid ytan. Studien inkluderar meteorologiska, oceanografiska parametrar, flöden, samband med parametrar, överförings koefficienter, beroende av stabilitet och satellitbilder.
Flujos turbulentos (momento, calor sensible, calor latente y CO2) en 2 alturas diferentes fueron estudiadas usando medidas de una torre en la Isla de Östergarnsholm (Mar Báltico) durante una semana. Los flujos también fueron calculados usando formulaciones con medidas de la torre y de dos boyas ancladas en diferentes localizaciones. Diferentes características para los distintos flujos fueron encontradas. El flujo de calor latente muestra una relación más alta con los cálculos que el flujo de calor sensible. No se encontró esta relación para el flujo de CO2. También, todos los flujos medidos en la torre coinciden mejor con los flujos calculados cuando estos son hechos bajo condiciones de estratificación inestable, significando que la torre mide mejor el área donde son cogidas las medidas en las boyas (cerca de la torre). El periodo estudiado incluye un afloramiento costero y se encontró una alta heterogeneidad horizontal en la superficie del mar durante la mayoría de los periodos. Esto fue estudiado usando las comparaciones entre flujos calculados y medidos y también usando imágenes de satélite. El footprint area puede ser definido como el área a una distancia desde la torre hacia donde sopla el viento donde las condiciones de la superficie influyen las medidas del flujo de alguna cantidad en la torre, y este footprint area está continuamente cambiando debido a su alta dependencia con la estratificación. Durante todo el periodo la estratificación estuvo cambiando desde ligeramente estable a ligeramente inestable, y por ello la heterogeneidad de la superficie puede ser vista en la variabilidad de los flujos medidos a diferentes alturas. Una conclusión importante en este estudio es que los cálculos de los flujos usando formulaciones podrían no ser útiles cuando se espera una alta variabilidad de los diferentes parámetros (temperatura superficial del mar y pCO2w), como por ejemplo durante situaciones de afloramiento y también cerca de costa, donde el fitoplancton puede influenciar significativamente la concentración de CO2 en la superficie. Se presenta un amplio estudio, incluyendo parámetros meteorológicos y oceanográficos, comparaciones de flujos, relaciones con parámetros, coeficientes de transferencia, dependencias con la estratificación e imágenes de satélite.
Vigneron, Rémi. "Effets de gradients de pression sur des couches limites turbulentes supersoniques : calcul à l'aide d'une modélisation algèbrique des flux turbulents (A.S.M.)". Aix-Marseille 2, 1986. http://www.theses.fr/1986AIX22003.
Texto completoVigneron, Rémi. "Effets de gradients de pression sur des couches limites turbulentes supersoniques calcul à l'aide d'une modélisation algébrique des flux turbulents (A.S.M.) /". Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb376018135.
Texto completoSahlée, Erik. "The Influence of Waves on the Heat Exchange over Sea". Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-302874.
Texto completoSammanfattning av ”Våginflytandet på värmeutbytet över hav” Syftet med studien är att undersöka om det existerar ett våginflytande för värmeutbytet över hav och speciellt eventuellt våginflytande på utbyteskoefficienten CH (Stantons tal). Mätdata från Östergarnsholm utanför Gotland har använts. Denna mätstation har en stor sektor i vilken vindens anloppssträcka ostört är påverkad av hav. Data från perioden 1995–1999 har använts. Stantons tal CH beter sig annorlunda vid övergången från instabil till stabil skiktning beroende på havsytans tillstånd. Vid uppbyggande sjö gör CH ett ’hopp’ då det passerar neutral skiktning. För dyning finns inte detta hopp utan övergången är mycket mjukare. Denna skillnad observeras också hos det turbulenta värmeflödet. Baserat på definitionen av CH föreslås det att dess olika beteende för olika skiktning och vågtillstånd finns att söka i beteendet hos det turbulenta värmeflödet. En jämförelse av cospektrat för vertikal vind, w, och potentiell temperatur, θ, visar att där finns olikheter mellan uppbyggande sjö och dyning. Under instabila förhållanden och uppbyggande sjö domineras värmeflödet av storskaliga virvlar. Det existerar ingen signifikant skillnad i maximal värdets frekvens för olika grad av instabilitet. Dyningsfallen visar ett mer varierat beteende med en maximalvärdes frekvens som skiftar för olika stabilitetsområden. I studien undersöks också korrelationskoefficienten mellan longitudinal vind u, och vertikal vind w, Ru,w. Det visas att Ru,w är utsatt för ett visst våginflytande. Ru,w som en funktion av vågålder jämförs för neutral och icke-neutral skiktning. För dyning och icke-neutral skiktning så faller Ru,w snabbt till små värden nära noll. Detta resultat skiljer sig för neutral skiktning där Ru,w bara gör en svag minskning. Slutsatsen är att det krävs en viss mängd positivt värmeflöde och inaktiv turbulens för att se det kraftiga avtagandet hos korrelationskoefficienten.
Tullis, Stephen William. "Large eddy simulation of scalar flux in turbulent premixed flames". Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620081.
Texto completoLennartsson, Linda. "Influence of fog on stratification and turbulent fluxes over the ocean". Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-303768.
Texto completoSammanfattning av ”Påverkan av dimma på skiktningen och turbulenta flöden över hav” I detta arbete studeras ett fall av advektions dimma över Östersjön. Perioden undersökt är från den 5 till den 7 juni 1995. Mätmasten står på ön Östergarnsholm, en liten och låg ö utan träd utanför Gotland. Ur mätningarna fås bl.a. värmeflödet, relativa fuktigheten och temperaturen. På kvällen den 5 juni 1995 advekteras dimman in över Östergarnsholm. Detta ses både från att relativa fuktigheten stiger och att temperaturen sjunker. Innan dimman anlände var gränsskiktet stabilt skiktat. Denna skiktning ändrades snabbt till neutral då dimman når fram. Denna till synes neutrala skiktning visade sig efter noggrannare undersökning att inte alls vara neutral. Skiktet närmast marken upp till 15 meters höjd visade sig vara instabilt och däröver var det stabilt. Utifrån detta dras slutsatsen att dimman är låg endast 15 meter hög under denna period. Vid 12 tiden på dagen den 6 juni sjunker lufttemperaturen dramatiskt under ytvatten temperaturen samtidigt som relativa fuktigheten stiger upp till 100 %. Dimman är nu så pass tjock att den största delen av utstrålningen sker ifrån toppen vilket sänker luft temperaturen flera grader. Då stabiliteten undersöks visar den sig vara instabil skiktad ända upp till högsta mät nivån (28 meter). Antagandet görs att dimman är minst 30 meter djup. Även normaliserad standard avvikelse för temperaturen och den vertikala hastigheten undersöks för att ta reda på om de uppvisar samma variation som i det ostörda gränsskiktet.
Los, Sebastian Alexander. "Intermittent Turbulent Exchanges and Their Role in Vineyard Evapotranspiration". DigitalCommons@USU, 2019. https://digitalcommons.usu.edu/etd/7627.
Texto completoMaboni, Cristiano. "Fluxo de metano na atmosfera sobre uma cultura de arroz irrigado por inundação no sul do Brasil". Universidade Federal de Santa Maria, 2016. http://repositorio.ufsm.br/handle/1/9265.
Texto completoThe rice paddy is responsible for 12-16% of the anthropogenic emission of CH4 in the world. Brazil is one of most important rice paddy producer. The goal of this study is to understand the dynamics of methane exchange between rice paddy and the atmosphere in the south of Brazil. Two estimation techniques are used: eddy covariance and soil chamber. Data were obtained in a rice paddy farm in Cachoeira do Sul municipality. The total emission of methane in 2015-2016 rice paddy growing season (November 14, 2015 to April 16 2016) was 35.7 gCH4m−2. The solar radiation is the weather forcing that showed a higher correlation with methane emissions.
A produção de arroz irrigado por inundação é responsável por 12-26% de toda a emissão antropogênica de CH4 do mundo. O Brasil é um dos principais produtores de arroz irrigado por inundação. O objetivo deste estudo é compreender a dinâmica das trocas de metano entre o arroz irrigado por alagamento e a atmosfera no sul do Brasil. São utilizadas duas técnicas de estimativa de fluxos superficiais: Eddy Covariance e câmara de solo. Os dados foram obtidos sobre uma lavoura de arroz irrigado por inundação no município de Cachoeira do Sul. A emissão total de metano no arroz irrigado na safra de 2015-2016 (14 de novembro de 2015 a 16 de abril de 2016) foi de 35,7 gCH4m��2. A radiação solar é o forçante meteorológico que mostrou maior correlação com o fluxo de metano.
Johnson, Joseph C. "Turbulent heat flux measurements over the Greenland, Norwegian and Barents Seas". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA294129.
Texto completoThesis advisor(s): Peter S. Guest, Roland W. Garwood. "March 1995." Bibliography: p. 81-82. Also available online.
Swisher, Stacey Elaine. "Time-resolved heat flux measurements of the turbulent junction vortex system". Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-10312009-020052/.
Texto completoLowe, Steven J. "A parametric study of the momentum flux at the air-sea interface". Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-06102009-063110/.
Texto completoDaris, Thomas. "Étude des modèles de turbulence à quatre équations de transport pour la prévision des écoulements turbulents faiblement chauffés". Toulouse, ENSAE, 2002. http://www.theses.fr/2002ESAE0017.
Texto completoGalera, Larissa 1990. "Análise da influência das características geométricas de selos de fluxo aplicados a rotores". [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263035.
Texto completoDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: A análise dinâmica de rotores visa prever o comportamento e identificar desvios caracterizados por meio das respostas dinâmicas do conjunto, fornecendo indicadores de mau funcionamento ou diagnóstico de falhas, e minimizando os riscos de paradas imprevistas no sistema. O estudo dinâmico de máquinas rotativas deve ser realizado considerando a interação entre os componentes envolvidos na sua construção, como por exemplo, rotores, eixos, mancais, selos de fluxo e estruturas de suporte. Os selos de fluxo causam forças de reação que podem ser representadas por coeficientes dinâmicos. Este componente é o principal responsável por diferenças entre um modelo usando apenas eixo-mancal e a vibração real do sistema, como por exemplo, em bombas centrífugas. Dentro deste contexto, este trabalho tem por objetivo a determinação dos coeficientes dinâmicos de três tipos de selos planos, sendo eles: cilíndrico, cônico e escalonado, os quais serão integrados ao modelo global de sistemas rotativos, de modo a tornar a análise do conjunto girante mais completa. A análise dos selos de fluxo será realizada utilizando o método de volumes finitos para determinar a distribuição de velocidade circunferencial e de pressão ao longo do selo, que caracterizam as forças de reação. Estas, por sua vez, podem ser representadas em coeficientes de rigidez, amortecimento e inércia. Além disso, será verificada a influência de diversos parâmetros geométricos e operacionais nestes coeficientes. A inserção dos coeficientes dinâmicos dos selos planos e a análise do conjunto girante, a partir do pacote computacional Rotortest®, permitirá verificar a influência desses tipos de selos no sistema rotativo, analisando como este elemento modifica as características do conjunto e como acopla o eixo à fundação
Abstract: The dynamic analysis of rotors aims to predict its behavior and identify deviations characterized by the dynamic response of the set, providing malfunction indications or failure diagnosis, and minimizing the risk of having unexpected halts on the system. The dynamic study of rotating machines must be conducted by taking in account the interactions between the components involved in its construction, such as rotors, shafts, bearings, fluid seals, and support structures. The fluid seals cause reaction-forces, which can be represented for dynamic coefficients. This component is mainly responsible for the differences between a model using only a rotor-bearing and the actual vibration of the set, for example in centrifugal pumps. In this context, this work aims the determination of the dynamic coefficients of three types of plain seals, namely: straight, tapered, and stepped seals, which will be integrated with the global model of rotating systems, in order to make the analysis of the rotating set more complete. The fluid seals analysis will be accomplished through the finite volume method in order to determine the circumferential velocity and pressure distribution along the seal, which characterizes the reaction forces. Those can be, in turn, represented by stiffness, damping, and inertia coefficients. Besides, it will be verified the influence of several geometric and operational parameters on these coefficients. The insertion of the dynamic coefficients of plain seals and the analysis of the rotating set in the computational package Rotortest®, will verify the influence of these seals on the rotating system, analyzing how this element modify the set's characteristics and the coupling of the shaft to the foundation
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestra em Engenharia Mecânica
Rizzo, Luciana Varanda. "\"Os fluxos turbulentos de partículas e de compostos orgânicos voláteis, e a distribuição vertical de aerossóis na baixa troposfera da Amazônia\"". Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-28032007-165933/.
Texto completoThe Amazon tropical forest constitutes a complex ecosystem, in which the biosphere and the atmosphere are intrinsically related. To the natural biogenic sources, biomass burning emissions are summed up, changing significantly some aerosol characteristics, which in turn may affect important processes in the ecosystem. This work integrates observations of aerosol physical properties in Amazonia under two different conditions: i) turbulent transport between the forest canopy and the atmosphere (LBA/ZF2-2004 experiment); ii) evolution of biomass burning aerosol properties along the transport from the surface to the lower free troposphere (LBA/SMOCC-2202 experiment). Turbulent flux measurements were performed by eddy covariance in a tower at the Reserva Biológica de Cuieiras (AM), with an average particle flux of 0,05 106 m-2 s-1, denoting a net flux close to zero. During the day, particle emission was the predominant process, while the deposition dominated at night. Some events were associated to particle flux variability, such as: ascendant vertical gradients of coarse particles containing phosphorus and potassium at night; and events of abrupt increase in fine particles concentration also at night. Those events can be related to biogenic emissions. Isoprene and monoterpene fluxes (secondary organic aerosols precursors) reached, respectively, maximum values of 7.4 and 0.82 ?gC/m2/h around noon, without any apparent association with aerosol fluxes. Also, no clear events of nucleation were observed during the experiment. The aerosol vertical distribution were achieved from the compilation of 31 flights over impacted areas in Rondonia, and also over relatively clean areas on Western Amazon. Over the impacted areas, particle concentrations diminished with an average tax of 800 particles/cm3/km at the free troposphere. Vertical profiles showed that biomass burning aerosols have a tendency to accumulate at the top of the boundary layer, with possible optical implications at surface. Over impacted areas, an increase on particle average diameters, as well as on scattering and CCN activation efficiencies were observed at the free troposphere, possibly due to in cloud aerosol processes. Otherwise, over clean forest areas no significant differences on aerosol properties were observed inside the boundary layer and at the free troposphere. In this way, the two types of Amazonian aerosol particles were characterized in this work: biomass burning and natural biogenic particles. Results showed that biomass burning aging process affected significantly some physical properties of the aerosol population. As for biogenic particles, the biophysical mechanisms that govern their emission and deposition processed are still unclear, so that long range particle flux experiments are required for a better understanding of this issue.
Santos, Daniel Michelon dos. "VARIAÇÃO SAZONAL DA ACUMULAÇÃO E FLUXO NOTURNOS DE ESCALARES EM UMA PASTAGEM NA REGIÃO AMAZÔNICA". Universidade Federal de Santa Maria, 2010. http://repositorio.ufsm.br/handle/1/10257.
Texto completoAs acumulações verticais noturnas de dióxido de Carbono e de Radônio são investigadas em um sítio de pastagem na região Amazônica. Este sítio é caracterizado por forte estabilidade térmica durante a noite, que suprime uma boa porção da mistura turbulenta local, de forma que técnicas como a covariância dos vórtices apresentam dificuldades para a estimativa de fluxos turbulentos noturnos. A análise considera a variação sazonal dos perfis médios noturnos entre a estação úmida, de janeiro a junho e a seca, de julho a dezembro. Perfis de Radônio são analisados com o objetivo de se entender os processos que afetam os perfis de CO2 ao se comparar com um escalar independente e inerte. A análise também considera a direção do vento predominante durante a noite. Os resultados indicam que há uma grande diferença entre os fluxos e gradientes noturnos de CO2 entre as duas estações. Os gradientes verticais noturnos de CO2 entre os dois níveis mais altos da torre micrometeorológica freqüentemente são positivos, indicando aumento da concentração com a altura. Tais inversões são observadas com muito menos freqüência nos perfis de Radônio, que seguem a forma canônica de diminuição monotônica com a altura. Na estação seca as inversões de gradiente são mais freqüentes e estão, em geral, associadas à inversão da direção do fluxo vertical turbulento de CO2, indicando que no nível de medida há um transporte vertical para baixo deste escalar, o que proporciona convergência de fluxos e intensa acumulação junto à superfície. Uma análise coespectral mostra que este transporte para baixo ocorre nas maiores escalas temporais do movimento, sugerindo que esteja associado com transferências entre a floresta vizinha e a pastagem, na forma de fluxos de mesoescala. Os comportamentos médios sazonais são bem definidos, e uniformes ao longo da noite, mas estudos de caso mostram que estes processos são dominados por eventos específicos. Os fluxos de Radônio medidos em campanhas experimentais são utilizados para estimar os fluxos de CO2 através da relação entre os gradientes entre os dois escalares em seis noites, três em cada estação. A comparação com os fluxos determinados pela covariância dos vórtices é satisfatória na estação úmida, mas ruim na estação seca e os motivos são discutidos.
Schmid, Hans Peter Emil. "Spatial scales of sensible heat flux variability : representativeness of flux measurements and surface layer structure over suburban terrain". Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/29385.
Texto completoArts, Faculty of
Geography, Department of
Graduate
Eigenmann, Rafael Verfasser] y Thomas [Akademischer Betreuer] [Foken. "Free convection and turbulent fluxes over complex terrain / Rafael Eigenmann. Betreuer: Thomas Foken". Bayreuth : Universität Bayreuth, 2013. http://d-nb.info/1059353326/34.
Texto completoVendrame, Nadia. "Study of vegetation-atmosphere interactions over vineyards: CO2 fluxes and turbulent transport mechanics". Doctoral thesis, Università degli studi di Padova, 2017. http://hdl.handle.net/11577/3425729.
Texto completoLo studio delle interazioni tra vegetazione e atmosfera è oggi un tema di grande interesse nell’ottica di migliorare la comprensione della risposta delle piante alle variabili ambientali e la modellizzazione del loro ruolo nel cambiamento climatico globale. Particolare attenzione è di solito rivolta ai flussi di anidride carbonica (CO2) e, in genere, gli ecosistemi naturali come le foreste hanno ricevuto una maggiore attenzione. In questa ricerca sono state studiate le interazioni vegetatione-atmosfera su una coltura agraria importante per il bacino mediterraneo, quale il vigneto, focalizzandosi sul monitoraggio del bilancio annuale di carbonio e approfondendo lo studio della meccanica del trasporto turbulento che è alla base degli scambi di energia e materia. Il vigneto è un sistema complesso con diverse sorgenti e sink di scalari (vapore d’acqua, anidride carbonica, calore), in cui le due principali componenti, vite e suolo, compongono il flusso totale della canopy in un rapporto che varia nel corso dell’anno. Nei vigneti del Nord Italia, l’interfila è solitamente non lavorata e inerbita, giocando un ruolo importante nel bilancio del carbonio del sistema. In questo contesto, risulta cruciale la ripartizione dello scambio netto di CO2 dell’ecosistema (Net Ecosystem Exchange, NEE) nelle componenti suolo e vite. Nel corso di questa indagine, la NEE di un vigneto è stata monitorata per tre anni utilizzando la tecnica micrometeorologica dell’ eddy covariance (EC), mentre la misura dei flussi di CO2 al suolo è stata effettuata con camere (a cupola trasparente e oscura). Nel 2015, il bilancio annuale di carbonio del vigneto è stato di circa ‒ 80 g C m‒ 2 a‒ 1, dimostrando quindi la capacità di agire da sink, ma la maggior parte dell’assimilazione è risultata legata al suolo inerbito (‒ 60 g C m‒2 a‒1). In ogni caso, il sistema ha dimostrato un’elevata variabilità interannuale del bilancio del carbonio stagionale, in cui ondate di calore e periodi di siccità estivi hanno giocato un ruolo primario. Nella stagione 2014, caratterizzata da un regime di precipitazione abbondante, la NEE ha raggiunto il valore massimo di circa ‒ 250 g C m‒2. L’organizzazione del vigneto in filari determina una particolare dinamica del trasporto turbolento dentro canopy. Inoltre, la struttura morfologica del vigneto è altamente variabile durante il corso dell’anno, passando da una canopy praticamente vuota nel periodo di dormienza della vite a una situazione dove il fogliame è denso e concentrato nelle file al culmine della stagione vegetativa. L’influenza dello sviluppo della densità fogliare sulle statistiche della turbolenza è stato studiato installando un profilo verticale di anemometri ad ultrasuoni. Il flusso turbolento è risultato fortemente influenzato dalla struttura della canopy. Senza foglie, il regime turbolento è caratteristico di un flusso di parete, mentre con lo sviluppo completo del fogliame assume le proprietà tipiche di un flusso con mixing‒layer, sebbene il flesso al limite superiore della canopy sia poco accentuato, a causa della bassa densità fogliare del vigneto. Infine, è stata condotta un’analisi specifica delle strutture coerenti coinvolte nel trasporto di quantità di moto e sulle loro scale temporali. L’importanza di eventi discendenti che trasportano aria più veloce del flusso medio (sweeps) è aumentata nel corso della stagione. La durata media delle strutture coerenti dominanti è stato nell’ordine di 6 ‒ 10 s e, in questo caso, non è stata riscontrata nessuna chiara correlazione con lo sviluppo della struttura della canopy. Lo studio ha messo in evidenza l’importanza del monitoraggio a lungo termine degli scambi tra vegetazione e atmosfera, ma anche la complessità dei fenomeni di trasporto turbolento che li caratterizzano. Tuttavia, solo la piena comprensione della meccanica di questi processi può portare alla corretta interpretazione del ruolo della vegetazione nei cicli biogeochimici più fondamentali.
Didorally, Sheddia. "Prévision des flux de chaleur turbulents et pariétaux par des simulations instationnaires pour des écoulements turbulents chauffés". Thesis, Toulouse, ISAE, 2014. http://www.theses.fr/2014ESAE0015/document.
Texto completoThe improvement of aerothermal predictions is a major concern for aeronautic manufacturers. In line with this issue, SAS approaches are assessed on the prediction of wall and turbulent heat fluxes for heated-turbulent flows. This study also aims at evaluating these advanced URANS methods in regard to DRSM models and hybrid RANS/LES approaches as ZDES. Firstly, we proposed to combine the SAS approach and a DRSM model in order to better reproduce both resolved and modelled Reynolds stresses. This new model, called SAS-DRSM, was implemented in ONERA Navier-Strokes code elsA. Unsteady simulations of two heated turbulent flows encountered in an aircraft engine compartment were then performed to evaluate all the SAS models available in the code. These numerical studies demonstrated that SAS approaches improve prediction of the flows compared to classical URANS models. They lead to full 3D flows with many turbulent structures. These structures favour turbulent mixing and thus induce a better prediction of the wall heat fluxes. Moreover, the numerical simulations showed that SAS methods are more accurate than classical URANS models without increasing significantly calculation costs. SAS approaches are not able to resolve the smallest turbulent structures in relation to ZDES which provides better predictions. Finally, the investigation of the turbulent heat flux suggested that the constant turbulent Prendtl number assumption, that is characteristic of classical URANS models, may not be valid in some regions of the flow
Furst, Jonathan Joseph. "An Investigation of Vertical Turbulent Transport Processes in Coastal Regions Using Tower Observations". FIU Digital Commons, 2013. http://digitalcommons.fiu.edu/etd/814.
Texto completoSaid, Frédérique. "Etude expérimentale de la couche limite marine : structure turbulente et flux de la surface (expérience TOXANE-T)". Toulouse 3, 1988. http://www.theses.fr/1988TOU30022.
Texto completoBORGES, Camilla Kassar. "Estudo do comportamento dos fluxos de calor e massa no bioma caatinga na região semiárida da Paraíba". Universidade Federal de Campina Grande, 2017. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/1455.
Texto completoMade available in DSpace on 2018-08-15T13:45:50Z (GMT). No. of bitstreams: 1 CAMILLA KASSAR BORGES - TESE (PPGMet) 2017.pdf: 4598580 bytes, checksum: ef4afc927cf3418b3a0269f56b6304a5 (MD5) Previous issue date: 2017-08-23
Capes
Ambientes áridos e semiáridos correspodem a 1/3 da superfície terrestre, nessas localidades a água é elemento importante e limitante para o crescimento da vegetação e produtividade de biomassa do ecossistema. A região semiárida no Brasil compreende em torno de 11,5% do território nacional, onde 76% desta foi originalmente composta pelo bioma Caatinga, tendo o déficit hídrico como característica marcante, média pluviométrica inferior a 800 mm e temperaturas elevadas de médias anuais variando entre 25oC e 30oC. Pesquisas sobre a dinâmica dos fluxos de massa e energia nesses ambientes não têm recebido tanta atenção, apesar de serem especialmente vulneráveis às alterações ambientais. E, técnicas como a de eddy covariance (EC) tem contribuído para estimar a magnitude e padrões das trocas turbulentas entre o ecossistema e a atmosfera. Neste estudo micrometeorológico, para uma área de Caatinga densa (CD) e outra de Caatinga rala (CR), pertencentes ao Instituto Nacional do Semiárido (INSA) em Campina Grande – PB, durantes os anos 2013 e 2014, observou-se que o albedo (α) e o saldo de radiação (Rn) foram mais intensos na CR em comparação a CD, pois a magnitude da radiação de onda curta incidente esteve mais elevada nessa área. Constatou-se que a maior parte da radiação líquida converteu-se em fluxo de calor sensível (H), principalmente durante o período seco na CR, seguida do fluxo de calor latente (LE) e bem menor partição em fluxo de calor no solo (G), em geral cerca de 50% para H e 20% para LE. Constatou-se através do fechamento do balanço de energia que os fluxos turbulentos (H+LE) foram subestimados em relação à energia disponível à superfície (Rn-G), sendo que na CD essa discrepância foi maior chegando a ser superiores a 30%. O ecossitema nos dois locais de estudo atuou como sumidouros de CO2, sequestrando mais de 700 gC/m2 e 550 gC/m2 para a CD e CR, respectivamente.
Arid and semi-arid environments correspond to 1/3 of the terrestrial surface, in these localities water is an important and limiting element for vegetation growth and ecosystem biomass productivity. The semiarid region in Brazil comprises around 11.5% of the national territory, where 76% of this was originally composed by the Caatinga biome, with water deficit as a striking feature, average rainfall less than 800 mm and high temperatures of annual averages ranging between 25oC and 30oC. Research on the dynamics of mass and energy fluxes in these environments have not received much attention, although they are especially vulnerable to environmental change. And, techniques such as eddy covariance (EC) have contributed to estimating the magnitude and patterns of turbulent exchanges between the ecosystem and the atmosphere. In this micrometeorological study, for an area of dense Caatinga (DC) and another of sparse Caatinga (SC) belonging to the National Institute of the Semiarid (INSA) in Campina Grande - PB, during the 2013 and 2014 years, it was observed that the albedo (α) and the net radiation (Rn) were more intense in the SC compared to DC, since the magnitude of incident short wave radiation was higher in this area. It was found that most of the net radiation it converted to sensible heat flux (H), mainly during the dry period in the SC, followed by the latent heat flux (LE) and much smaller partition in soil heat flux (G), usually about 50% for H and 20% for LE. Through the energy balance closure, it was verified that the turbulent fluxes (H + LE) were underestimated in relation to the available energy to the surface (Rn-G), being that in the DC this discrepancy was greater and reaching more than 30%. The ecosystem at the two study sites acted as CO2 sinks, sequestering more than 700 gC/m2 and 550 gC/m2 for DC and SC, respectively.
Gengembre, Cyril. "Variabilité multi-échelles de la météorologie et des aérosols en situation littorale sous influence industrielle". Thesis, Littoral, 2018. http://www.theses.fr/2018DUNK0489/document.
Texto completoOn a site that is multi-influenced by urban and industrial emissions, the analysis of aerosol pollution, in the vicinity of sources, requires a multi-scale knowledge of atmospheric dynamics. A measurement campaign was developed in order to study the meteorological and micro-meteorological variability and the evolution of particles, in particular, submicronic evolution, during a one-year period.Oscillations of the aerosol concentration around the regional average were identified along the Dunkirk coastline, and were attributed to the local meteorological phenomena close to the industries. Recognition and machine learning methods using measurements by an ultrasonic anemometer and vertical wind profiles by a Doppler lidar, were implemented to define the variability of relevant phenomena in air pollution events : sea breeze, fog, front and storm. A six-years database analysis has highlighted a correlation between the annual sea breeze occurrence and the annual number of anticyclonic days. Furthermore, the annual fog frequency could be connected with the annual regional concentration of aerosols. Analysis of wind covariance revealed two contrasting situations, low-level and high-level turbulent fluxes. The fog and the sea breeze, with low-level fluxes, generate a high PM₁ pollution and are in favor of a high organic oxygenated aerosols concentration (secondary aerosols). High-level fluxes situations, favoring vertical exchanges, are associated with a large variability of sulfate aerosols. The long-term observation, made it possible to highlight the development of episodes of particulate pollution during local weather phenomena, owing to the local emissions, but also by taking into account the larger-scale pollution
Sahlée, Erik. "Fluxes of Sensible and Latent Heat and Carbon Dioxide in the Marine Atmospheric Boundary Layer". Doctoral thesis, Uppsala University, Department of Earth Sciences, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8184.
Texto completoOceans cover about 70% of the earth’s surface. They are the largest source of the atmospheric water vapour and act as enormous heat reservoirs. Thus in order to predict the future weather and climate it is of great importance to understand the processes governing the exchange of water vapour and heat between the ocean and atmosphere. This exchange is to a large extent mediated by turbulent eddies. Current numerical climate and weather forecast models are unable to resolve the turbulence, which means that the turbulent exchange needs to be simplified by using parameterizations.
Tower based measurements at the Östergarnsholm Island in the Baltic Sea have been used to study the air-sea turbulent exchange of latent and sensible heat and the heat flux parameterizations. Although the measurements are made at an island, data obtained at this site is shown to represent open ocean conditions during most situations for winds coming from the east-south sector. It is found that during conditions with small air-sea temperature differences and wind speeds above 10 m s-1, the structure of the turbulence is re-organized. Drier and colder air from aloft is transported to the surface by detached eddies, which considerably enhance the turbulent heat fluxes. The fluxes where observed to be much larger than predicted by current state-of-the-art parameterizations. The turbulence regime during these conditions is termed the Unstable Very Close to Neutral Regime, the UVCN-regime.
The global increase of the latent and sensible heat fluxes due to the UVCN-regime is calculated to 2.4 W m-2 and 0.8 W m-2 respectively. This is comparable to the current increase of the radiative forcing due to anthropogenic emissions of greenhouse gases, reported in Intergovernmental Panel on Climate Change fourth assessment report (IPCC AR4). Thus the UVCN-effect could have a significant influence when predicting the future weather and climate.
Lee, Hyunchang [Verfasser], Andreas [Akademischer Betreuer] Dreizler y Burak [Akademischer Betreuer] Atakan. "Thermographic PIV for Turbulent Flux Measurement / Hyunchang Lee. Betreuer: Andreas Dreizler ; Burak Atakan". Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2016. http://d-nb.info/1112332898/34.
Texto completoBateni, Sayed Mohyeddin. "Estimation of turbulent surface heat fluxes using sequences of remotely sensed land surface temperature". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/66850.
Texto completoCataloged from PDF version of thesis.
Includes bibliographical references (p. 330-366).
Fluxes of heat and moisture at the land-surface play a significant role in the climate system. These fluxes interact with the overlying atmosphere and influence the characteristics of the planetary boundary layer (e.g. temperature and water vapor content), ultimately influencing the presence and growth of low level clouds and precipitation. Nevertheless, there is currently no network of in situ sensors that can map these fluxes globally. Recently a number of studies have focused on the estimation of surface energy flux components based on the assimilation of land surface temperature (LST) within a variational data assimilation (VDA) framework. This study provides the theoretical basis for why sequences of LST contain the necessary information to estimate surface fluxes with minimal reliance on ancillary data and empirical parameterizations. Furthermore this study addresses one of the main drawbacks of the existing VDA models. They use the simple force-restore equation for soil heat diffusion as a physical constraint. The force-restore equation provides a simplified description of the LST dynamics. Also, its performance is highly affected by the specification of a deep ground temperature. These shortcomings cause significant errors in the diurnal dynamics of heat diffusion in the soil and ultimately the retrieval of components of surface energy balance. This study advances the VDA scheme by using the full heat diffusion equation as a constraint in lieu of the forcerestore approximation. The new VDA scheme is tested over several experimental field sites. The results show that inclusion of the heat diffusion equation decreases the phase error associated with the ground heat flux diurnal cycle, and improves surface heat flux estimation. The VDA scheme is further advanced by incorporating model uncertainty in order to account for measurement and model errors. Tests indicate that the VDA scheme with model uncertainty captures measurement errors as well as structural model errors. In order to provide coupled estimates of surface heat fluxes and vegetation dynamics, remotely sensed LST and fraction of photosynthetically active radiation are assimilated into a surface energy balance and a vegetation dynamics model. The application of the assimilation over West Africa shows that the scheme provides reliable estimates of important vegetation dynamics parameters that are required for understanding the role of plant phenology on surface energy balance and vice-versa.
by Sayed Mohyeddin Bateni.
Ph.D.
Sapkota, Deependra. "TRIPPING OF THE BOUNDARY LAYER DEVELOPMENT LENGTH OVER ROUGH AND FULLY TURBULENT SUBCRITICAL FLUME". OpenSIUC, 2015. https://opensiuc.lib.siu.edu/theses/1801.
Texto completoGullman-Strand, Johan. "Turbulence and scalar flux modelling applied to separated flows". Doctoral thesis, Stockholm : Department of Mechanics, Royal Institute of Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-92.
Texto completoSouza, Armando Alvarez de. "Simulação numérica do escoamento turbulento de jato de ar em fluxo cruzado". Instituto Tecnológico de Aeronáutica, 2007. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=450.
Texto completoBassit, Megalaa Gorg Abdelmassih. "Numerical and experimental study of steady and unsteady mixed convection flow in a cubical open cavity with the bottom wall heated". Doctoral thesis, Universitat Rovira i Virgili, 2016. http://hdl.handle.net/10803/396082.
Texto completoEn este estudio se analizan los experimentos y simulaciones numéricas del flujo de convección mixta en una cavidad cúbica situada en la parte inferior de un canal de sección cuadrada cuadrado. Los números de Reynolds en función de la velocidad media del flujo y la anchura del canal están en el rango 100≤Re≤1500 y el número de Richardson varía entre 0.1≤Ri≤10. La técnica PIV se ha utilizado para las medidas en un canal de agua. Se han llevado a cabo simulaciones numéricas tridimensionales con un código de volúmenes finitos de segundo orden, considerando la aproximación de Boussinesq ya que, en las condiciones experimentales utilizadas, la variación de las propiedades físicas con la temperatura no tiene influencia significativa en la topología general de flujo. En los rangos 100≤Re≤1500 y Ri≤0.1 el flujo es estacionario y consiste en un remolino situado en el interior de la cavidad cúbica que muestra velocidades mayores a medida que aumenta el número de Richardson. El flujo es no estacionario a Re = 100 y Ri = 10. Cerca de las paredes laterales se producen de forma alternada eyecciones de flujo, desde el interior de la cavidad hacia el canal, mientras que el flujo entra en la cavidad desde el canal a través de la parte central de la cavidad. Se ha utilizado una técnica de muestreo condicional para elucidar la estructura media de la evolución del flujo turbulento a Ri = 10. Se ha encontrado que las eyecciones de flujo persisten durante todo el rango de Reynolds analizado. Los números de Nusselt calculados están de acuerdo con los de las correlaciones reportadas en la literatura, válidas para cavidades bidimensionales.
In this study we analyze experiments and numerical simulations of steady and unsteady mixed convection flow in a cubical cavity located at the bottom of a square channel. The Reynolds numbers based on the mean flow velocity and the channel width are in the range 100≤Re≤1500 and the Richardson numbers vary within 0≤Ri≤10. Particle Image Velocimetry has been used for the measurements in a water channel. Three-dimensional direct numerical simulations have been carried out with a second order finite volume code considering the Boussinesq approximation since, for the experimental conditions considered, the variation of the physical properties with temperature has no significant influence on the overall flow topology. For 100≤Re≤1500 and Ri≤0.1 the flow is steady and it consists in a single roll that exhibits larger velocities as the Richardson number is increased. An unsteady periodic flow is found at Re=100 and Ri=10. Alternate flow ejections from the cavity to the channel occur near the lateral walls while the flow enters the cavity from the channel through the central part of the cavity. A conditional sampling technique has been used to elucidate the evolution of the mean unsteady turbulent flow at Ri=10. It has been found that the alternate flow ejections persist for all the Reynolds analyzed. The computed Nusselt numbers are in general agreement with a previously reported correlation, valid for two dimensional cavities of different aspects ratios.
Pianezze, Joris. "Modélisation de la structure verticale de la turbulence optique en milieu naturel". Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00830505.
Texto completoGamel, Hervé. "Caractérisation expérimentale de l'écoulement et de la dispersion autour d'un obstacle bidimensionnel". Thesis, Ecully, Ecole centrale de Lyon, 2015. http://www.theses.fr/2015ECDL0002/document.
Texto completoIn the last decades, there has been an increasing use of Computational Fluid Dynamics (CFD)simulations to evaluate the impact of atmospheric pollutants dispersion in within industrial and urban sites. Given the high geometrical complexity of these sites, these simulations are mainly performed adopting a Reynolds Averaged Navier-Stokes (RANS) approach and using k−e closure models. As is well known from previous studies, RANS k−e simulations are affected by some limitations that prevent them correctly reproducing the dynamics of the flow and the pollutant dispersion in complex geometrical configurations. The aim of the PhD is to provide a detailed experimental characterization of the flow and the turbulent dispersion around an idealized two-dimensional obstacle placed within a boundary layer flow. This is subsequently used to analyse the reliability of RANS closure models as predictive tools for the atmospheric dispersion of airborne pollutants. Initially we focus on the flow dynamics of a boundary layer flow developing over a rough wall and in the wake of a 2D obstacle. The velocity field is investigated experimentally by means of different measurement techniques, namely Hot Wire Anemometry (HWA), Laser Doppler Anemometry (LDA) and Stereo-Particle Imagery Velocimetry (PIV). A particular attention was devoted to the estimate of the turbulent viscosity nt as well as of the terms composing the turbulent kinetic energy budget (TKE), including its rate of dissipation e which was determined adopting different approaches. These measurements allowed us to analyse the accuracy of the parameterizations included in a standard k−e closure model. Our analysis show that a value of the coefficient Cμ = 0.09 leads to significant overestimation of nt in a boundary layer flow. Conversely, adopting Cμ = 0.09 provides a good agreement between modeled and direct estimates of nt in the wake of the obstacle. As a second step, we studied the dispersion of a passive scalar emitted by a ground level line source. To that purpose we measured the first four order moments of the concentration probability density function by mean of a flame ionization detector (FID). Furthermore, the coupling of the FID system with the LDA or HWA system allowed us to directly measure the turbulent mass transfer, i.e. the correlation between velocity and concentration fluctuations. The combination of these two techniques was carefully analyzed, in order to quantify eventual mutual disturbances of one measurement technique on the other. The measurements of the velocity/concentration correlations allowed us to determine experimentally the turbulent diffusivity Dt and the turbulent Schmidt number Sct , and therefore to test the accuracy of different closure models of the advection-distribution equation. Our results show that the value of the turbulent Schmidt number is approximately equal to 0.7 in most of the domain, except in the recirculation zone on the wake of the obstacle. Experimental data provide also a complete description of the spatial distribution of the concentration variance, and of the term composing its budget (with a focus on its dissipation). As for the velocity field, we test the reliability of different closure model proposed in the literature of the turbulent mass transfer terms, enlightening the shortcomings of simple gradient-law closer models
Ducousso, Nicolas. "Coexistence et interactions de la circulation décennale moyenne et des ondes et tourbillons transitoires dans l'océan Atlantique Nord". Brest, 2011. http://www.theses.fr/2011BRES2055.
Texto completoObservations of the ocean circulation reveal that the large-scale general circulation coexists with transient waves and coherent vortices. This thesis aims at characterizing some aspects of the interaction mechanisms, which link these kinds of motion. This objective encompasses two tasks: the first task is a critical review of the theoretical frameworks previously published in the literature; the second task consists of the analysis of a numerical simulation provided by the DRAKKAR team. The diagnostic s performed within the Temporal Residual Mean framework, as detailed by McDougall and Mclntosh (2001). Indeed, this framework provides a valuable perspective, as the constraint of the stratification and the quasi-adiabaticity of the ocean interior on the mean circulation and the interaction mechanisms is made explicit. The analysis illustrates these constraints by showing two things. First, the residual mean velocity is nearly aligned with the isopycnal surfaces and its diapycnal component is very weak. Second, the residual eddy fluxes of heat and salt are nearly aligned with the isopycnal surfaces and their intensity are significant in frontal areas only. Eddy diffusivities evaluated from the residual eddy fluxes are in partial accordance with values commonly found in the literature
Yun, Alexander. "Development and analysis of advanced explicit algebraic turbulence and scalar flux models for complex engineering configurations". Phd thesis, [S.l. : s.n.], 2005. http://elib.tu-darmstadt.de/diss/000579.
Texto completoSanz, Garcia Elena. "Influence de la micromorphologie de surface dans les échanges thermiques convectifs". Ecully, Ecole centrale de Lyon, 2007. http://www.theses.fr/2007ECDL0023.
Texto completoThis experimental thesis focuses on the understanding of heat transfer in a turbulent boundary layer. In particular we investigated the action of an ordered, three-dimensional and anisotropic roughness, which is completely immersed in the viscous sublayer of the turbulent boundary layer. A measurement technique has been developed in order to realize this study. This technique, based on thin film technology, has been tested and validated. Results show a measurable effect on the heat transfer coefficient, as well as on the mean velocity profiles. This effect is however not observed in a laminar boundary layer and it is quenched by an external freestream turbulence. Hence one can conclude that the observed effect is due to the interaction between the rough elements and the turbulent structures generated at the wall. An influence of this micro-roughness is also observed in the transition to turbulence of a laminar boundary layer. We also perform a statistical study of the heat transfer process in a turbulent boundary layer when subjected to freestream turbulence. The frequency spectra show a scaling law with a -7/3 exponent for the temperature in the immediate wake of the heated surface. The inertial range of the heat flux spectrum shows a dependence on the Reynolds number, with an exponent ranging from -5/3 to -7/3, as observed in the case of a homogeneous and isotropic turbulence in the presence of a mean temperature gradient
Gruber, Matthew. "A new sensitivity analysis and solution method for scintillometer measurements of area-average turbulent fluxes". Thesis, University of Alaska Fairbanks, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1547616.
Texto completoScintillometer measurements of the turbulence inner-scale length lo and refractive index structure function C2n allow for the retrieval of large-scale area-averaged turbulent fluxes in the atmospheric surface layer. This retrieval involves the solution of the non-linear set of equations defined by the Monin-Obukhov similarity hypothesis. A new method that uses an analytic solution to the set of equations is presented, which leads to a stable and efficient numerical method of computation that has the potential of eliminating computational error. Mathematical expressions are derived that map out the sensitivity of the turbulent flux measurements to uncertainties in source measurements such as lo. These sensitivity functions differ from results in the previous literature; the reasons for the differences are explored.
Babel, Wolfgang [Verfasser] y Thomas [Akademischer Betreuer] Foken. "Site-specific modelling of turbulent fluxes on the Tibetan Plateau / Wolfgang Babel. Betreuer: Thomas Foken". Bayreuth : Universität Bayreuth, 2013. http://d-nb.info/1059353237/34.
Texto completoSopkin, Kristin L. "Heat fluxes in Tampa Bay, Florida". [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002398.
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