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Journal articles on the topic 'Turbulentné modely'

Author: Grafiati
Published: 4 June 2021
Last updated: 1 February 2022

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1

Souza, José Francisco Almeida de, José Luiz Lima de Azevedo, Leopoldo Rota de Oliveira, Ivan Dias Soares, and Maurício Magalhães Mata. "TURBULENCE MODELING IN GEOPHYSICAL FLOWS – PART I – FIRST-ORDER TURBULENT CLOSURE MODELING." Revista Brasileira de Geofísica 32, no. 1 (March 1, 2014): 31. http://dx.doi.org/10.22564/rbgf.v32i1.395.

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ABSTRACT. The usage of so-called turbulence closure models within hydrodynamic circulation models comes from the need to adequately describe vertical mixing processes. Even among the classical turbulence models; that is, those based on the Reynolds decomposition technique (Reynolds Averaged Navier-Stokes – RANS), there is a variety of approaches that can be followed for the modeling of turbulent flows (second moment) of momentum, heat, salinity, and other properties. Essentially, these approaches are divided into those which use the concept of turbulent viscosity/diffusivity in the modeling of the second moment, and those which do not use it. In this work we present and discuss the models that employ this concept, in which the viscosity can be considered constant or variable. In this latter scenario, besides those that use the concepts of mixture length, the models that use one or two differential transport equations for determining the viscosity are presented. The fact that two transport equations are used – one for the turbulent kinetic energy and the other for the turbulent length scale – make these latter ones the most complete turbulent closure models in this category. Keywords: turbulence modeling, turbulence models, first-order models, first-order turbulent closure. RESUMO. A descrição adequada dos processos de mistura vertical nos modelos de circulação hidrodinâmica é o objetivo dos chamados modelos de turbulência, os quais são acoplados aos primeiros. Mesmo entre os modelos clássicos de turbulência, isto é, aqueles que se baseiam na técnica de decomposição de Reynolds (Reynolds Averaged Navier-Stokes – RANS), existe uma variedade de abordagens que podem ser seguidas na modelagem dos fluxos turbulentos (segundos momentos) de momentum, calor, salinidade e outras propriedades. Fundamentalmente estas abordagens dividem-se entre aquelas que utilizam o conceito de viscosidade/ difusividade turbulenta na modelagem dos segundos momentos, e aquelas que não o utilizam. Nesse trabalho são apresentados e discutidos os modelos que empregam este conceito, onde a viscosidade pode ser considerada constante ou variável. No caso variável, além daqueles que utilizam o conceito de comprimento de mistura, são ainda apresentados os modelos que utilizam uma ou duas equações diferenciais de transporte para a determinação da viscosidade. O fato de empregar duas equações de transporte, uma para a energia cinética turbulenta e outra para a escala de comprimento turbulento, fazem destes últimos os mais completos modelos de fechamento turbulento desta categoria. Palavras-chave: modelagem da turbulência, modelos de turbulência, modelos de primeira ordem, fechamento turbulento de primeira orde
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2

Rincón-Díaz, Carlos A., and José Albors-Garrigós. "Sustaining strategies in RTOs. A contingent model for understanding RTOs’ perfomance." Dirección y Organización, no. 50 (July 1, 2013): 74–84. http://dx.doi.org/10.37610/dyo.v0i50.433.

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The objectives of this paper are to propose a contingent model linking context, organizational and performance variables, and to identify barriers that Research and Technology Organisations have to overcome to work with companies. Fur thermore, there is discussion of the best practices that Research and Technology Organisations carry out in order to develop competitive advantages and adjust to turbulent environments. This research was based on a field study of 14 Research and Technology Organisations in the Valencian Community and 13 Research and Technology Organisations in the Basque Country. The study identifies certain factors which could improve their performance to address properly changes in their environment and become more competitive.Keywords: research and technology organisations (RTOs), innovation strategies, turbulent environment, RTO challenges.Estrategias de sostenimiento de los Centros Tecnológicos. Un modelo contingente para entender su desempeñoResumen: Los objetivos de este trabajo son proponer un modelo contingente que relaciona variables de contexto, organizacionales y de resultado, e identificar las barreras que los Centros Tecnológicos encuentran para trabajar con empresas y las buenas prácticas llevan a cabo para desarrollar ventajas competitivas y adaptarse en entornos turbulentos. Esta investigación se baso en un estudio de catorce Centros tecnológicos de la Comunidad Valenciana y trece Centros Tecnológicos del País Vasco. El estudio propone algunos factores a mejorar para que los Centros Tecnológicos afronten adecuadamente los cambios en su entorno y sean más competitivos.Palabras clave: centros tecnológicos (CT), estrategias de innovación, entorno turbulento, retos de los centros tecnológicos.
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3

Antunes do Carmo, José S., A. Temperville, and Fernando J. Seabra-Santos. "Fricción y tensión tangencial por fondo con ola y corriente." Ingeniería del agua 10, no. 2 (June 1, 2003): 177. http://dx.doi.org/10.4995/ia.2003.2583.

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Se calcula la tensión tangencial debido a ola y corriente mediante un modelo numérico con cierre turbulento K-L, donde K es la energía cinética turbulenta y L es la escala longitudinal de turbulencia. Se obtiene el coeficiente de fricción parametrizado para el caso de flujo turbulento rugoso, siguiendo a Soulsby et al. (1994) y se amplía al caso de flujo turbulento liso. La comparación de estos resultados con otros existentes en la literatura, especialmente los proporcionados por Tanaka y Thu (1994) muestra un buen ajuste.Se propone una nueva parametrización de la serie temporal de la tensión tangencial que incluye el coeficiente de fricción local obteniéndose mejores resultados que aplicando la parametrización propuesta por Soulsby et al. (1994).
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4

Navas-Montilla, A., J. Murillo, and P. García-Navarro. "Modelos de simulación de alto orden para la resolución de fenómenos de propagación de ondas en flujos de lámina libre con turbulencia." Ingeniería del agua 23, no. 4 (October 31, 2019): 275. http://dx.doi.org/10.4995/ia.2019.12169.

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<p>En este trabajo se presenta una herramienta de simulación basada en la resolución transitoria de grandes remolinos (URANS o DA-LES) para flujos turbulentos de aguas poco profundas en los que la turbulencia es predominantemente horizontal. El aspecto fundamental del modelo es la combinación de una discretización de alto orden en espacio y tiempo con una modelización de los efectos en el flujo promedio de las escalas turbulentas no resueltas. El modelo propuesto garantiza con precisión de máquina el equilibrio hidrostático (propiedad well-balanced) gracias a la utilización de una formulación del flujo numérico que incluye los términos fuente en la resolución del problema de Riemann derivativo en las paredes de las celdas. Se presenta una validación del modelo utilizando datos de literatura para un experimento de laboratorio que involucra un flujo de aguas poco profundas sobre una isla cónica, que da lugar a la generación de una calle de vórtices aguas abajo de la isla. Los resultados numéricos muestran que el modelo propuesto es capaz de reproducir fenómenos turbulentos bidimensionales, proporcionando un mayor nivel de detalle que la aproximación RANS tradicional.</p>
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5

Masamoto, Kai, Masayuki Takahashi, and Shinnosuke Obi. "MoP-12 Experimental Study on the Turbulent Flow in a Simplified HDD Model." Proceedings of JSME-IIP/ASME-ISPS Joint Conference on Micromechatronics for Information and Precision Equipment : IIP/ISPS joint MIPE 2015 (2015): _MoP—12–1_—_MoP—12–3_. http://dx.doi.org/10.1299/jsmemipe.2015._mop-12-1_.

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6

Sengupta, Samiran, P. K. Vijayan, K. Sasidharan, and V. K. Raina. "ICONE19-43613 TURBULENT MIXING INSIDE THE CHIMNEY MODEL OF A POOL TYPE RESEARCH REACTOR." Proceedings of the International Conference on Nuclear Engineering (ICONE) 2011.19 (2011): _ICONE1943. http://dx.doi.org/10.1299/jsmeicone.2011.19._icone1943_248.

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7

Sventitskiy, Alexander E., and Vladlen A. Zazimko. "THE NUMERICAL MODEL OF MULTIPLE SUPERSONIC TURBULENT JETS OF DIFFERENT GAS COMPOSITION(Multiple Jet)." Proceedings of the International Conference on Jets, Wakes and Separated Flows (ICJWSF) 2005 (2005): 273–78. http://dx.doi.org/10.1299/jsmeicjwsf.2005.273.

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8

Mueller, Michael E., and Venkat Raman. "Model form uncertainty quantification in turbulent combustion simulations: Peer models." Combustion and Flame 187 (January 2018): 137–46. http://dx.doi.org/10.1016/j.combustflame.2017.09.011.

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9

Fischer Filho, João Alberto, Yane De Freitas Da Silva, Alexandre Barcellos Dalri, Luiz Fabiano Palaretti, José Renato Zanini, and Anderson Prates Coelho. "CARACTERIZAÇÃO HIDRÁULICA DE GOTEJADORES DE FLUXO TURBULENTO." IRRIGA 23, no. 2 (October 9, 2018): 380–89. http://dx.doi.org/10.15809/irriga.2018v23n2p380-389.

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CARACTERIZAÇÃO HIDRÁULICA DE GOTEJADORES DE FLUXO TURBULENTO JOÃO A. FISCHER FILHO; YANE DE FREITAS DA SILVA; ALEXANDRE B. DALRI; LUIZ FABIANO PALARETTI; JOSÉ R. ZANINI E ANDERSON PRATES COELHO Departamento de Engenharia Rural, Universidade Estadual Paulista – Câmpus Jaboticabal, Via de Acesso Professor Paulo Donato Castelane, Vila Industrial, Jaboticabal, SP, Brasil. E-mail: joaofischer16@gmail.com, yanefsilva@gmail.com, dalri@fcav.unesp.br. lfpalaretti@fcav.unesp.br, jrzanini@fcav.unesp.br, anderson_100ssp@hotmail.com 1 RESUMO Na avaliação do desempenho hidráulico de quatro modelos de gotejadores não autocompensantes foi utilizada uma bancada de ensaios com capacidade para 25 gotejadores de cada modelo. Cada modelo foi submetido a diferentes pressões (p), determinando-se assim a vazão média (q), o coeficiente de variação de fabricação (CVf) e a equação característica do gotejador (q versus p). Posteriormente foram determinados, em condições de campo, em uma área plana, os coeficientes de uniformidade de Christiansen (CUC) e de distribuição (CUD) para 16 gotejadores de cada modelo avaliado. Foi adotado delineamento inteiramente casualizado com quatro repetições e teste de Tukey para comparação das médias de CUC e CUD. Os quatro modelos, operando nas pressões nominais, apresentaram vazões de, respectivamente, 2,22; 1,30; 1,45 e 1,93 L h-1 e CVf médio de, respectivamente, 1,30%; 3,61%; 2,65% e 3,97%, sendo caracterizados como de excelente e média uniformidade. Os quatro modelos enquadraram-se em regime de escoamento turbulento, com valores de expoente “x” da equação característica do gotejador variando entre 0,4714 e 0,5174e coeficientes de determinação R2 superiores a 99%. Os valores de CUC e CUD diferiram estatisticamente e foram, em média, superiores a 90% e, destacando positivamente os gotejadores Driptech e Dripline. Palavras–chave: equação característica, irrigação por gotejamento, uniformidade FISCHER FILHO, J. A.; SILVA, Y. F.; DALRI, A. B.; PALARETTI, L. F.; ZANINI, J. R.; COELHO, A. P. HYDRAULIC CHARACTERIZATION OF TURBULENT FLOW DRIPPERS 2 ABSTRACT In the evaluation of hydraulic performance of four models of not self-compensating drippers was used a bench of tests with capacity for 25 drippers of each model. Each model was subjected to different pressures (p), thus determining the mean flow rate (q), the coefficient of manufacturing variation (CVf) and the characteristic equation of the dripper (q versus p). Subsequently, the Christiansen (CUC) and distribution (CUD) uniformity coefficients for 16 drippers of each evaluated model were determined under field conditions in a flat area. A completely randomized design with four repetitions and Tukey’s test were used to compare means of CUD and CUC. The four models, operating at nominal pressures, had flow rates of, respectively, 2.22; 1.30; 1.45 and 1.93 L h-1 and mean CVf of, respectively, 1.30%; 3.61%; 2.65% and 3.97%, being characterized as having excellent and average uniformity. The four models were fitted under a turbulent flow regime, with exponent values "x" of the characteristic equation of the dripper varying between 0.4714 and 0.5174, and R2 determination coefficients above 99%. The values of CUC and CUD differed statistically and were, on average, higher than 90% and, in particular, the Driptech and Dripline drippers. Keywords: characteristic equation, drip irrigation, uniformity
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10

Tamaru, Akihiro, and Shinnosuke Obi. "MoP-11 Large Eddy Simulation for Turbulent Flow in a simplified HDD Model using OpenFOAM." Proceedings of JSME-IIP/ASME-ISPS Joint Conference on Micromechatronics for Information and Precision Equipment : IIP/ISPS joint MIPE 2015 (2015): _MoP—11–1_—_MoP—11–3_. http://dx.doi.org/10.1299/jsmemipe.2015._mop-11-1_.

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11

Whitehead, J. A., and Wei Wang. "A Laboratory Model of Vertical Ocean Circulation Driven by Mixing." Journal of Physical Oceanography 38, no. 5 (May 1, 2008): 1091–106. http://dx.doi.org/10.1175/2007jpo3805.1.

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Abstract A model of deep ocean circulation driven by turbulent mixing is produced in a long, rectangular laboratory tank. The salinity difference is substituted for the thermal difference between tropical and polar regions. Freshwater gently flows in at the top of one end, dense water enters at the same rate at the top of the other end, and an overflow in the middle removes the same amount of surface water as is pumped in. Mixing is provided by a rod extending from top to bottom of the tank and traveling back and forth at constant speed with Reynolds numbers &gt;500. A stratified upper layer (“thermocline”) deepens from the mixing and spreads across the entire tank. Simultaneously, a turbulent plume (“deep ocean overflow”) from a dense-water source descends through the layer and supplies bottom water, which spreads over the entire tank floor and rises into the upper layer to arrest the upper-layer deepening. Data are taken over a wide range of parameters and compared to scaling theory, energetic considerations, and simple models of turbulently mixed fluid. There is approximate agreement with a simple theory for Reynolds number &gt;1000 in experiments with a tank depth less than the thermocline depth. A simple argument shows that mixing and plume potential energy flux rates are equal in magnitude, and it is suggested that the same is approximately true for the ocean.
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12

Lipatnikov, Andrei N., and Jerzy Chomiak. "Flame Speed Closure Model of Premixed Turbulent Combustion : Further Development and Validation(S.I. Engines, Flame Propagation)." Proceedings of the International symposium on diagnostics and modeling of combustion in internal combustion engines 2004.6 (2004): 583–90. http://dx.doi.org/10.1299/jmsesdm.2004.6.583.

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13

Gershgorin, Boris, and Andrew J. Majda. "Quantifying Uncertainty for Climate Change and Long-Range Forecasting Scenarios with Model Errors. Part I: Gaussian Models." Journal of Climate 25, no. 13 (July 1, 2012): 4523–48. http://dx.doi.org/10.1175/jcli-d-11-00454.1.

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Abstract Information theory provides a concise systematic framework for measuring climate consistency and sensitivity for imperfect models. A suite of increasingly complex physically relevant linear Gaussian models with time periodic features mimicking the seasonal cycle is utilized to elucidate central issues that arise in contemporary climate science. These include the role of model error, the memory of initial conditions, and effects of coarse graining in producing short-, medium-, and long-range forecasts. In particular, this study demonstrates how relative entropy can be used to improve climate consistency of an overdamped imperfect model by inflating stochastic forcing. Moreover, the authors show that, in the considered models, by improving climate consistency, this simultaneously increases the predictive skill of an imperfect model in response to external perturbation, a property of crucial importance in the context of climate change. The three models range in complexity from a scalar time periodic model mimicking seasonal fluctuations in a mean jet to a spatially extended system of turbulent Rossby waves to, finally, the behavior of a turbulent tracer with a mean gradient with the background turbulent field velocity generated by the first two models. This last model mimics the global and regional behavior of turbulent passive tracers under various climate change scenarios. This detailed study provides important guidelines for extending these strategies to more complicated and non-Gaussian physical systems.
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14

Scase, M. M., and R. E. Hewitt. "Unsteady turbulent plume models." Journal of Fluid Mechanics 697 (March 12, 2012): 455–80. http://dx.doi.org/10.1017/jfm.2012.77.

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AbstractFour existing integral models of unsteady turbulent plumes are revisited. We demonstrate that none of these published models is ideal for general descriptions of unsteady behaviour and put forward a modified model. We show that the most recent (top-hat) plume model (Scase et al. J. Fluid Mech., vol. 563, 2006, p. 443), and the earlier (Gaussian) plume models (Delichatsios J. Fluid Mech., vol. 93, 1979, p. 241; Yu Trans. ASME, vol. 112, 1990, p.186), are all ill-posed. This ill-posedness arises from the downstream growth of short-scale waves, which have an unbounded downstream growth rate. We show that both the top-hat and the Gaussian (Yu) models can be regularized, rendering them well-posed, by the inclusion of a velocity diffusion term. The effect of including this diffusive mechanism is to include a vertical structure in the model that can be interpreted as representing the vertical extent of an eddy. The effects of this additional mechanism are small for steady applications, and cases where the plume forcing can be considered to follow a power law (both of which have been studied extensively). However, the inclusion of diffusion is shown to be crucial to the general initial-value problem for unsteady models.
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15

Uchaikin, V. V. "Nonlocal Turbulent Diffusion Models." Journal of Mathematical Sciences 253, no. 4 (February 11, 2021): 573–82. http://dx.doi.org/10.1007/s10958-021-05255-z.

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16

Goldberg, Uriel C., Barna L. Bihari, and Sekaripuram V. Ramakrishnan. "Model for turbulent backflows." AIAA Journal 30, no. 2 (February 1992): 557–59. http://dx.doi.org/10.2514/3.10954.

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17

Abe, Ken-ichi. "Advanced Algebraic Model for Turbulent Diffusion Vector in Two-Equation Turbulence Models." AIAA Journal 39, no. 11 (November 2001): 2216–18. http://dx.doi.org/10.2514/2.1221.

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18

Abe, Ken-ichi. "Advanced algebraic model for turbulent diffusion vector in two-equation turbulence models." AIAA Journal 39 (January 2001): 2216–18. http://dx.doi.org/10.2514/3.14988.

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19

Zhou, Lei, Ming Jia, Chun Long Xu, Qiang Zhou, and Jun Han. "Application of the Algebraic Subgrid Turbulent Kinetic Energy Model in LES Model." Advanced Materials Research 347-353 (October 2011): 2576–81. http://dx.doi.org/10.4028/www.scientific.net/amr.347-353.2576.

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In this study the dynamic Smagorinsky model (DSM model) and an algebraic model for the subgrid turbulent kinetic energy have been implemented into KIVA3VLES code to investigate the atomization and evaporation processes of diesel spray in a constant volume vessel. Based on the experimental results of the liquid and vapor phase distributions as well as the results obtained by the differential subgrid scale kinetic energy (K-equation) model, the paper reveals the influence of the turbulent kinetic energy model on the fuel spray prediction. Computational results show that by combining the DSM model and the algebraic subgrid turbulent energy model, the turbulent diffusion of droplets can be reasonably simulated, the liquid penetration and the predicted liquid and fuel vapor mass fraction contours are close to the experiment results. At the same time, the turbulent kinetic energy given by the DSM model is in agreement with the results by the K-equation model, but with less computational cost..
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Aizawa, Kai, Susumu Terakado, Masashi Komada, Hidenori Morita, Richard DeJong, and Steve Sorenson. "Turbulent model validations with CFD/wind tunnel test and application to SEA for wind noise prediction." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, no. 6 (August 1, 2021): 175–86. http://dx.doi.org/10.3397/in-2021-1330.

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Wind noise is becoming to have a higher priority in automotive industry. Several past studies investigated whether SEA can be utilized to predict wind noise by applying a turbulent spectrum model as the input. However, there are many kinds of turbulent models developed and the appropriate model for input to SEA is still unclear. Due to this, this paper focuses on clarifying an appropriate turbulent model for SEA simulation. First, the input turbulent pressure spectrum from five models are validated with wind tunnel tests and CFD. Next, a conventional numerical approach is used to validate models from the aspect of response accuracy. Finally, turbulent models are applied to an SEA model developed for a wind tunnel, and the SEA response is validated with test data. From those input/response validations, an appropriate turbulent model is investigated.
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Baratta, Mirko, and Stefano d'Ambrosio. "Further Investigation of RNG k-ε Model Capabilities in the Simulation of In-Cylinder Turbulent Flows(Computation Technology)." Proceedings of the International symposium on diagnostics and modeling of combustion in internal combustion engines 2004.6 (2004): 33–41. http://dx.doi.org/10.1299/jmsesdm.2004.6.33.

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22

Biferale, L., D. Pierotti, and F. Toschi. "Helicity advection in turbulent models." Le Journal de Physique IV 08, PR6 (October 1998): Pr6–131—Pr6–137. http://dx.doi.org/10.1051/jp4:1998618.

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23

Pope, Stephen B. "Simple models of turbulent flows." Physics of Fluids 23, no. 1 (January 2011): 011301. http://dx.doi.org/10.1063/1.3531744.

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Cheng, Baolian. "Review of turbulent mixing models." Acta Mathematica Scientia 29, no. 6 (November 2009): 1703–20. http://dx.doi.org/10.1016/s0252-9602(10)60012-4.

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Biferale, L., D. Pierotti, and F. Toschi. "Helicity transfer in turbulent models." Physical Review E 57, no. 3 (March 1, 1998): R2515—R2518. http://dx.doi.org/10.1103/physreve.57.r2515.

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26

Meyer, Daniel W., and Patrick Jenny. "Micromixing models for turbulent flows." Journal of Computational Physics 228, no. 4 (March 2009): 1275–93. http://dx.doi.org/10.1016/j.jcp.2008.10.019.

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27

Adem, J., V. M. Mendoza, and E. E. Villanueva. "Three-months extended and seasonal forecast of sea surface temperature anomalies for thermodynamic climate prediction." Geofísica Internacional 39, no. 2 (April 1, 2000): 189–99. http://dx.doi.org/10.22201/igeof.00167169p.2000.39.2.276.

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La ecuación de conservación de energía térmica aplicada a la capa de mezcla oceánica se utiliza para la predicción de las anomalías de la temperatura de la superficie del mar y de sus cambios mensuales para periodos extendidos de tres meses, así como para la predicción estacional de estas anomalías en los océanos Pacífico y Atlántico del Hemisferio Norte. La ecuación incluye el transporte horizontal de calor por corrientes oceánicas y por remolinos turbulentos, así como calentamiento por radiación de onda corta y larga, evaporación y calor sensible cedido a la atmósfera por transporte turbulento vertical. En este trabajo llevamos a cabo una verificación de las predicciones para el periodo de junio 1980 a mayo 1984; los resultados muestran que este modelo tiene cierta habilidad en la predicción de las anomalías de la temperatura de la superficie del mar de gran escala y de sus cambios mensuales para periodos extendidos de tres meses, así como en la predicción estacional de estas anomalías.
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Souza, José Francisco Almeida de, José Luiz Lima de Azevedo, Leopoldo Rota de Oliveira, Ivan Dias Soares, and Maurício Magalhães Mata. "INCORPORATION OF NEW TURBULENT CLOSURE SCHEMES IN THE PRINCETON OCEAN MODEL (POM)." Revista Brasileira de Geofísica 31, no. 1 (March 1, 2013): 17. http://dx.doi.org/10.22564/rbgf.v31i1.243.

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One of the most challenging issues in oceanography is the simulation of the mixing processes, which are responsible for diffusion of momentum, heat, salt, sediments etc. In the modeling of flow, the hydrodynamic model simulates the properties of the mean flow while the turbulence model, coupled to the first, is responsible for simulating the mixing processes. In this article it is used the Princeton Ocean Model (POM), which includes the well known turbulent closure model q2 − q2L of Mellor & Yamada (1982), level 2.5. To add flexibility to the modeling, the k − ε and k − ω models, which belong to the same class of models, are incorporated into the POM and two test cases, one involving the deepening of the oceanic mixed layer and the other addressing the estuarine circulation, are carried out to allow the quality assessment of the models implementation in the computer code. The tests indicated that the model implementation was adequate. Comparing with the original model available in the Princeton Ocean Model, the results showed that the model k − ε tends to overestimate the mixed layer, while the model k − ω underestimates it, within an acceptable range of tolerance. In terms of estuarine circulation, the k − ε and k − ω models showed a greater capacity of mixing at the bottom of the estuarine mixing zone and also at the surface layer.RESUMO: Uma das questões mais desafiadoras em oceanografia é a simulação dos processos de mistura, responsáveis pela difusão de momentum, calor, sal, sedimentos etc. Na modelagem de escoamentos, o modelo hidrodinâmico simula as propriedades do escoamento médio, enquanto o modelo de turbulência, acoplado ao primeiro, é o responsável por simular os processos de mistura. Nesse artigo é utilizado o Princeton Ocean Model (POM), o qual traz acoplado o conhecido esquema de fechamento turbulento q2 − q2L de Mellor & Yamada (1982), n´ıvel 2.5. Para adicionar flexibilidade à modelagem, os modelos k − ε e k − ω, da mesma categoria de modelos, são incorporados ao POM e dois casos-teste, um envolvendo o aprofundamento da camada de mistura oceânica e o outro a circulação estuarina, são realizados para permitir a avaliação da qualidade da implementação dos modelos no código computacional. Os testes indicaram que a implementação dos modelos foi adequada. Tendo como referência o modelo original do POM, os resultados mostraram que o modelo k − ε tende a superestimar a camada de mistura, enquanto o k − ω a subestima, numa faixa aceitável de tolerância. Em termos de circulação estuarina, os modelos k − ε e k − ω apresentaram uma maior capacidade de mistura tanto no fundo da zona de mistura estuarina como na camada superficial.Palavras-chave: modelos de turbulência, processos de mistura, modelos a duas equações, camada de mistura, circulação estuarina.
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29

Salari, Mahmoud, Mohammad Mehdi Rashidi, Emad Hasani Malekshah, and Masoud Hasani Malekshah. "Numerical analysis of turbulent/transitional natural convection in trapezoidal enclosures." International Journal of Numerical Methods for Heat & Fluid Flow 27, no. 12 (December 4, 2017): 2902–23. http://dx.doi.org/10.1108/hff-03-2017-0097.

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Purpose Because the local Re numbers, ratio of inertia to viscous forces, are not same at different regions of the enclosures, the present study aims to deal with the influences of using the turbulent/transition models on numerical results of the natural convection and flow field within a trapezoidal enclosure. Design/methodology/approach The three-dimensional (3D) trapezoidal enclosure with different inclined side walls of 75, 90 and 105 degrees are considered, where the side walls are heated and cooled at Ra = 1.5 × 109 for all cases. The turbulent models of the k-ε-RNG, k- ω-shear-stress transport (SST) and the newly developed transition/turbulent model of Reθ-γ-transition SST are utilized to analyze the fluid flow and heat transfer characteristics within the enclosure and compared their results with validated results. Findings Comprehensive comparisons have been carried out for all cases in terms of flow and temperature fields, as well as turbulent quantities, such as turbulent kinetic energy and turbulent viscosity ratio. Furthermore, the velocity and thermal boundary layers have been investigated, and the approximate transition regions for laminar, transitional and turbulent regimes have been determined. Finally, the heat transfer coefficient and skin friction coefficient values have been presented and compared in terms of different turbulent models and configurations. The results show that the transition/turbulence model has better prediction for the flow and heat fields than fully turbulent models, especially for local parameters for all abovementioned governing parameters. Originality value The originality of this work is to analyze the 3D turbulent/transitional natural convection with different turbulence/transition models in a trapezoidal enclosure.
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30

TAKAGI, Kenji, Motohiko YAMADA, and Yasushi UEMATSU. "Comparison of Numerical Methods and Various Turbulent Models for Local Wind Simulation Model." Wind Engineers, JAWE 1997, no. 72 (1997): 59–72. http://dx.doi.org/10.5359/jawe.1997.72_59.

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31

Laín, S., and C. A. Grillo. "Comparison of turbulent particle dispersion models in turbulent shear flows." Brazilian Journal of Chemical Engineering 24, no. 3 (September 2007): 351–63. http://dx.doi.org/10.1590/s0104-66322007000300005.

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32

Wilcox, David C. "Multiscale model for turbulent flows." AIAA Journal 26, no. 11 (November 1988): 1311–20. http://dx.doi.org/10.2514/3.10042.

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33

Perrone, D., G. Nigro, and P. Veltri. "A SHELL MODEL TURBULENT DYNAMO." Astrophysical Journal 735, no. 2 (June 17, 2011): 73. http://dx.doi.org/10.1088/0004-637x/735/2/73.

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34

Canuto, V. M. "Turbulent Convection: A New Model." International Astronomical Union Colloquium 130 (1991): 27–32. http://dx.doi.org/10.1017/s0252921100079355.

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AbstractWe use the latest models of turbulence to compute a new expression for the turbulent convective flux, Fc. The new values of Fc are up to ten times larger than those given by the mixing length theory, MLT. Astrophysical considerations indicate that the new model fares better with observational data than the MLT.
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35

DUBOVIKOV, M. S. "DYNAMICAL MODEL OF TURBULENT EDDIES." International Journal of Modern Physics B 07, no. 27 (December 15, 1993): 4631–45. http://dx.doi.org/10.1142/s0217979293003796.

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Dynamical equations for the velocities and temperature fluctuations of turbulent eddies are presented. In the right side of the equation for the velocities are the external force, the turbulent force caused by interactions with larger-scale eddies, and the viscous force caused by interactions with smaller-scale eddies. The structure of the equation for the temperature fluctuations is analogous. The forces are specified on the basis of the well-known Wyld diagram technique of stochastic hydrodynamics so that the theory does not contain free parameters. The basic equations of the theory are approximately equivalent to Navier-Stokes equations and are particularly effective in the limit of very large Reynolds number. Turbulent convection is considered as an example of application of the basic equations.
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36

Ward, P., N. Collings, and N. Hay. "A Comparison of Simple Models of Turbulent Droplet Diffusion Suitable for Use in Computations of Spray Flames." Journal of Engineering for Gas Turbines and Power 107, no. 3 (July 1, 1985): 690–94. http://dx.doi.org/10.1115/1.3239790.

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An exact analysis of the diffusion of droplets in turbulent flow, taking account of the random nature of the flow and the range of length and time scales, is very involved and the equations derived are not necessarily solvable. For this reason spray models have usually not included liquid turbulent diffusion effects. Simpler models of turbulent diffusion of droplets are compared in this paper and equations suitable for insertion into existing spray models that require little extra computational effort are derived.
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37

Varničić, Milica. "POSLOVNI MODELI U SEKTORU TRANSPORTA I LOGISTIKE." Zbornik radova Fakulteta tehničkih nauka u Novom Sadu 34, no. 07 (July 1, 2019): 1230–33. http://dx.doi.org/10.24867/03ds01varnicic.

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Poslovni modeli su često korišten pojam u poslovnoj praksi, gde se koriste za opisivanje i razumevanje suštine poslovanja. Kompanije su, u današnje vreme, primorane da posluju na globalnim tržištima u uslovima stalnih i turbulentnih promena u njihovom okruženju. Da bi se izdvojila od konkurencije svaka kompanija mora da ima jasnu sliku za budućnost o svom poslovanju, konkurentnoj situaciji i da poseduje uspešan poslovni model. Predmet ovog rada jeste analiza poslovnih modela, nihovih ključnih elemenata, te inovacija i evolucija istih u oblasti transporta i logistike.
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38

Buchler, J. Robert. "Nonlinear Pulsations of Convective Stellar Models." International Astronomical Union Colloquium 176 (2000): 343–55. http://dx.doi.org/10.1017/s0252921100058036.

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AbstractWe review the numerical modeling of the nonlinear pulsations of classical variable stars with hydro-codes that include the effects of turbulent convection. Despite their simplicity these turbulent convective recipes appear to remove many of the difficulties that radiative codes faced. In particular, the numerical modeling of double mode pulsations has become possible.
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39

Gatski, T. B., and C. G. Speziale. "On explicit algebraic stress models for complex turbulent flows." Journal of Fluid Mechanics 254 (September 1993): 59–78. http://dx.doi.org/10.1017/s0022112093002034.

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Explicit algebraic stress models that are valid for three-dimensional turbulent flows in non-inertial frames are systematically derived from a hierarchy of second-order closure models. This represents a generalization of the model derived by Pope (1975) who based his analysis on the Launder, Reece & Rodi model restricted to two-dimensional turbulent flows in an inertial frame. The relationship between the new models and traditional algebraic stress models – as well as anisotropic eddy viscosity models – is theoretically established. A need for regularization is demonstrated in an effort to explain why traditional algebraic stress models have failed in complex flows. It is also shown that these explicit algebraic stress models can shed new light on what second-order closure models predict for the equilibrium states of homogeneous turbulent flows and can serve as a useful alternative in practical computations.
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40

Demuren, A. O., and S. Sarkar. "Perspective: Systematic Study of Reynolds Stress Closure Models in the Computations of Plane Channel Flows (Data Bank Contribution)." Journal of Fluids Engineering 115, no. 1 (March 1, 1993): 5–12. http://dx.doi.org/10.1115/1.2910114.

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This paper investigates the roles of pressure-strain and turbulent diffusion models in the numerical calculation of turbulent plane channel flows with second-moment closure models. Only high Reynolds number models are considered. Three turbulent diffusion and five pressure-strain models are utilized in the computations. The main characteristics of the mean flow and the turbulent fields are compared against experimental data. All the features of the mean flow are correctly predicted by all but one of the Reynolds stress closure models. The Reynolds stress anisotropies in the log layer are predicted to varying degrees of accuracy (good to fair) by the models. It is found that, contrary to previous assertions, wall-reflection terms are not necessary to obtain the correct Reynolds stress anisotropy in the log-layer. The pressure-strain models determine the level of anisotropy in the log-layer, while the diffusion models strongly influence the rate of relaxation towards isotropy in the outer-layer. None of the models could predict correctly the extent of relaxation towards isotropy of the streamwise and lateral components of the Reynolds stresses in the wake region near the center of the channel. Results from direct numerical simulation are used to further clarify this behavior of the models.
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41

Fukami, Kai, Koji Fukagata, and Kunihiko Taira. "Super-resolution reconstruction of turbulent flows with machine learning." Journal of Fluid Mechanics 870 (May 7, 2019): 106–20. http://dx.doi.org/10.1017/jfm.2019.238.

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We use machine learning to perform super-resolution analysis of grossly under-resolved turbulent flow field data to reconstruct the high-resolution flow field. Two machine learning models are developed, namely, the convolutional neural network (CNN) and the hybrid downsampled skip-connection/multi-scale (DSC/MS) models. These machine learning models are applied to a two-dimensional cylinder wake as a preliminary test and show remarkable ability to reconstruct laminar flow from low-resolution flow field data. We further assess the performance of these models for two-dimensional homogeneous turbulence. The CNN and DSC/MS models are found to reconstruct turbulent flows from extremely coarse flow field images with remarkable accuracy. For the turbulent flow problem, the machine-leaning-based super-resolution analysis can greatly enhance the spatial resolution with as little as 50 training snapshot data, holding great potential to reveal subgrid-scale physics of complex turbulent flows. With the growing availability of flow field data from high-fidelity simulations and experiments, the present approach motivates the development of effective super-resolution models for a variety of fluid flows.
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42

Alhumairi, Mohammed, and Özgür Ertunç. "Active-grid turbulence effect on the topology and the flame location of a lean premixed combustion." Thermal Science 22, no. 6 Part A (2018): 2425–38. http://dx.doi.org/10.2298/tsci170503100a.

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Lean premixed combustion under the influence of active-grid turbulence was computationally investigated, and the results were compared with experimental data. The experiments were carried out to generate a premixed flame at a thermal load of 9 kW from a single jet flow combustor. Turbulent combustion models, such as the coherent flame model and turbulent flame speed closure model were implemented for the simulations performed under different turbulent flow conditions, which were specified by the Reynolds number based on Taylor?s microscale, the dissipation rate of turbulence, and turbulent kinetic energy. This study shows that the applied turbulent combustion models differently predict the flame topology and location. However, similar to the experiments, simulations with both models revealed that the flame moves toward the inlet when turbulence becomes strong at the inlet, that is, when Re? at the inlet increases. The results indicated that the flame topology and location in the coherent flame model were more sensitive to turbulence than those in the turbulent flame speed closure model. The flame location behavior on the jet flow combustor significantly changed with the increase of Re?.
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43

Miraskari, Mohammad, Farzad Hemmati, MY Alqaradawi, and Mohamed S. Gadala. "Linear stability analysis of finite length journal bearings in laminar and turbulent regimes." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 231, no. 10 (February 6, 2017): 1254–67. http://dx.doi.org/10.1177/1350650117691697.

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Dynamic coefficients of a finite length journal bearing are numerically calculated under laminar and turbulent regimes based on Ng–Pan–Elrod and Constantinescu models. Linear stability charts of a flexible rotor supported on laminar and turbulent journal bearings are found by calculating the threshold speed of instability associated to the start of instable oil whirl phenomenon. Local journal trajectories of the rotor-bearing system were found at different operating conditions solely based on the calculated dynamic coefficients in laminar and turbulent flow. Results show no difference between laminar and turbulent models at low loading while significant change of the size of the stable region was observed by increasing the Reynolds number in turbulent models. Stable margins based on the laminar flow at relatively low Sommerfeld numbers [Formula: see text] were shown to fall inside the unstable region and hence rendering the laminar stability curves obsolete at high Reynolds numbers. Ng-Pan turbulent model was found to be generally more conservative and hence is recommended for rotor-bearing design.
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44

Perot, J. Blair, Sasanka Are, and Xing Zhang. "Application of the Turbulent Potential Model to Unsteady Flows and Three-Dimensional Boundary Layers." International Journal of Rotating Machinery 9, no. 5 (2003): 375–84. http://dx.doi.org/10.1155/s1023621x03000356.

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The turbulent potential model is a Reynolds-averaged (RANS) turbulence model that is theoretically capable of capturing nonequilibrium turbulent flows at a computational cost and complexity comparable to two-equation models. The ability of the turbulent potential model to predict nonequilibrium turbulent flows accurately is evaluated in this work. The flow in a spanwise-driven channel flow and over a swept bump are used to evaluate the turbulent potential model's ability to predict complex three-dimensional boundary layers. Results of turbulent vortex shedding behind a triangular and a square cylinder are also presented in order to evaluate the model's ability to predict unsteady flows. Early indications suggest that models of this type may be capable of significantly enhancing current numerical predictions of turbomachinery components at little extra computational cost or additional code complexity.
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45

Nie, Tao, and Wei Qiang Liu. "CFD Turbulent Model and Grid Dependency of Hypersonic Aerodynamic Heating Calculation Accuracy." Applied Mechanics and Materials 291-294 (February 2013): 1636–39. http://dx.doi.org/10.4028/www.scientific.net/amm.291-294.1636.

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Four turbulent models are introduced. The hypersonic aerodynamic heating calculation results by Shear Stress Transport (SST) turbulent model of different grid scale shows that near wall y+ spacing approximate to one third of the upper limit prescribed by turbulent model. Then, the comparison of the hypersonic aerodynamic heating calculation results by different turbulent model and the test data shows that SST turbulent model can give an enough accurate result.
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46

Villaret, C., and A. G. Davies. "Modeling Sediment-Turbulent Flow Interactions." Applied Mechanics Reviews 48, no. 9 (September 1, 1995): 601–9. http://dx.doi.org/10.1115/1.3023148.

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Models of widely differing complexity have been used in recent years to quantify sediment transport processes for engineering applications. This paper presents a review of these model types, from simple eddy viscosity models involving the “passive scalar hypothesis” for sediment predication, to complex two-phase flow models. The specific points addressed in this review include, for the suspension layer, the bottom boundary conditions, the relationship between the turbulent eddy viscosity and particle diffusivity, the damping of turbulence by vertical gradients in suspended sediment concentration, and hindered settling. For the high-concentration near-bed layer, the modeling of particle interactions is discussed mainly with reference to two-phase flow models. The paper concludes with a comparison between the predictions of both a classical, one-equation, turbulence k-model and a two-phase flow model, with “starved bed” experimental data sets obtained in steady, open-channel flow.
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47

Takeshi, Suzuki, and Sakai Yasuhiko. "1156 NUMERICAL SIMULATION OF REACTIVE TURBULENT SCALAR MIXING LAYER BY THE RANDOM FOURIER MODES METHOD AND LAGRANGIAN MOLECULAR MIXING MODEL." Proceedings of the International Conference on Jets, Wakes and Separated Flows (ICJWSF) 2013.4 (2013): _1156–1_—_1156–6_. http://dx.doi.org/10.1299/jsmeicjwsf.2013.4._1156-1_.

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48

Ferrey, P., and B. Aupoix. "Behaviour of turbulence models near a turbulent/non-turbulent interface revisited." International Journal of Heat and Fluid Flow 27, no. 5 (October 2006): 831–37. http://dx.doi.org/10.1016/j.ijheatfluidflow.2006.03.022.

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49

Ryu, Young-Hee, Jong-Jin Baik, and Sang-Hyun Lee. "A New Single-Layer Urban Canopy Model for Use in Mesoscale Atmospheric Models." Journal of Applied Meteorology and Climatology 50, no. 9 (September 2011): 1773–94. http://dx.doi.org/10.1175/2011jamc2665.1.

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AbstractA new single-layer urban canopy model for use in mesoscale atmospheric models is developed and validated. The urban canopy model represents a built-up area as a street canyon, two facing buildings, and a road. In this model, the two facing walls are divided into sunlit and shaded walls on the basis of solar azimuth angle and canyon orientation, and individual surface temperature and energy budget are calculated for each wall. In addition, for better estimation of turbulent energy exchange within the canyon, a computational fluid dynamics model is employed to incorporate the effects of canyon aspect ratio (height-to-width ratio) and reference wind direction on canyon wind speed. The model contains the essential physical processes occurring in an urban canopy: absorption and reflection of shortwave and longwave radiation, exchanges of turbulent energy and water between surfaces (roof, two facing walls, and road) and adjacent air, and heat transfer by conduction through substrates. The developed urban canopy model is validated using datasets obtained at two urban sites: Marseille, France, and Basel, Switzerland. The model satisfactorily reproduces canyon air temperatures, surface temperatures, net radiation, sensible heat fluxes, latent heat fluxes, and storage heat fluxes for both sites. Extensive experiments are conducted to examine the sensitivities of the urban surface energy balance to meteorological factors and urban surface parameters. The reference wind speed is found to be a more crucial meteorological factor than the reference air temperature in altering urban surface energy balance, especially for weak winds. The urban surface energy balance is most sensitive to the roof albedo among urban surface parameters. The roof fraction, canyon aspect ratio, and ratio of roughness length for momentum to that for heat for the roof play important roles in altering urban surface energy balance.
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50

Farah, Amjad, Maxim Kinakin, Glenn Harvel, and Igor Pioro. "ICONE19-43492 STUDY OF SELECTED TURBULENT MODELS FOR SUPERCRITICAL WATER HEAT TRANSFER IN VERTICAL BARE TUBES USING CFD CODE FLUENT-12." Proceedings of the International Conference on Nuclear Engineering (ICONE) 2011.19 (2011): _ICONE1943. http://dx.doi.org/10.1299/jsmeicone.2011.19._icone1943_197.

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