Academic literature on the topic 'Lagrangian decorrelation time scales'
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Journal articles on the topic "Lagrangian decorrelation time scales"
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Watteaux, R., G. Sardina, L. Brandt, and D. Iudicone. "On the time scales and structure of Lagrangian intermittency in homogeneous isotropic turbulence." Journal of Fluid Mechanics 867 (March 25, 2019): 438–81. http://dx.doi.org/10.1017/jfm.2019.127.
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We present a study of Lagrangian intermittency and its characteristic time scales. Using the concepts of flying and diving residence times above and below a given threshold in the magnitude of turbulence quantities, we infer the time spectra of the Lagrangian temporal fluctuations of dissipation, acceleration and enstrophy by means of a direct numerical simulation in homogeneous and isotropic turbulence. We then relate these time scales, first, to the presence of extreme events in turbulence and, second, to the local flow characteristics. Analyses confirm the existence in turbulent quantities of holes mirroring bursts, both of which are at the core of what constitutes Lagrangian intermittency. It is shown that holes are associated with quiescent laminar regions of the flow. Moreover, Lagrangian holes occur over few Kolmogorov time scales while Lagrangian bursts happen over longer periods scaling with the global decorrelation time scale, hence showing that loss of the history of the turbulence quantities along particle trajectories in turbulence is not continuous. Such a characteristic partially explains why current Lagrangian stochastic models fail at reproducing our results. More generally, the Lagrangian dataset of residence times shown here represents another manner for qualifying the accuracy of models. We also deliver a theoretical approximation of mean residence times, which highlights the importance of the correlation between turbulence quantities and their time derivatives in setting temporal statistics. Finally, whether in a hole or a burst, the straining structure along particle trajectories always evolves self-similarly (in a statistical sense) from shearless two-dimensional to shear bi-axial configurations. We speculate that this latter configuration represents the optimum manner to dissipate locally the available energy.
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Bos, Wouter J. T. "On the anisotropy of the turbulent passive scalar in the presence of a mean scalar gradient." Journal of Fluid Mechanics 744 (March 10, 2014): 38–64. http://dx.doi.org/10.1017/jfm.2014.60.
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AbstractWe investigate the origin of the scalar gradient skewness in isotropic turbulence on which a mean scalar gradient is imposed. The problem of the advection of an anisotropic scalar field is reformulated in terms of the advection of an isotropic vector field. For this field, triadic closure equations are derived. It is shown how the scaling of the scalar gradient skewness depends on the choice of the time scale used for the Lagrangian decorrelation of the vector field. The persistent anisotropy in the small scales for the third-order statistics is shown to be perfectly compatible with Corrsin–Obukhov scaling for second-order quantities, since second- and third-order scalar quantities are governed by a different triad correlation time scale. Whereas the inertial range dynamics of second-order scalar quantities is governed by the Lagrangian velocity correlation time, the third-order quantities remain correlated over a time related to the large-scale dynamics of the scalar field. It is argued that this time is determined by the average time it takes for a fluid particle to travel between ramp-cliff scalar structures.
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Martins, Luís Gustavo N., Gervásio A. Degrazia, Otávio C. Acevedo, Franciano S. Puhales, Pablo E. S. de Oliveira, Claudio A. Teichrieb, and Samuel M. da Silva. "Quasi-Experimental Determination of Turbulent Dispersion Parameters for Different Stability Conditions from a Tall Micrometeorological Tower." Journal of Applied Meteorology and Climatology 57, no. 8 (August 2018): 1729–45. http://dx.doi.org/10.1175/jamc-d-17-0269.1.
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AbstractTurbulent wind data measured by sonic anemometers installed at various heights on a 140-m-tall micrometeorological tower located at a coastal site are used to obtain vertical profiles of the velocity standard deviations σi, Lagrangian decorrelation local time scales TLi, and eddy diffusivities Kα for distinct stability conditions. The novelty of the study lies in the use of turbulent data directly measured over the extension of the atmospheric surface layer at a coastal site for that purpose. Furthermore, the approach employs the Hilbert–Huang transform to determine the wind energy spectral peak frequencies. These are applied to the asymptotic spectral equation from Taylor statistical diffusion theory to obtain the turbulent dispersion parameters, which are shown to generally agree well with those provided by a classical autocorrelation approach. For neutral and stable situations the vertical profiles of momentum eddy diffusivities agree well with those derived from the spectral and autocorrelation method. Additionally, the turbulent integral time scales and eddy diffusivities determined by the method at a coastal location are found to overestimate those predicted from analytical expressions based on continental field observations. The turbulence parameters found are suitable to be employed in air pollution dispersion models.
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Surcel, Madalina, Isztar Zawadzki, and M. K. Yau. "A Study on the Scale Dependence of the Predictability of Precipitation Patterns." Journal of the Atmospheric Sciences 72, no. 1 (January 1, 2015): 216–35. http://dx.doi.org/10.1175/jas-d-14-0071.1.
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Abstract A methodology is proposed to investigate the scale dependence of the predictability of precipitation patterns at the mesoscale. By applying it to two or more precipitation fields, either modeled or observed, a decorrelation scale can be defined such that all scales smaller than are fully decorrelated. For precipitation forecasts from a radar data–assimilating storm-scale ensemble forecasting (SSEF) system, is found to increase with lead time, reaching 300 km after 30 h. That is, for , the ensemble members are fully decorrelated. Hence, there is no predictability of the model state for these scales. For , the ensemble members are correlated, indicating some predictability by the ensemble. When applied to characterize the ability to predict precipitation as compared to radar observations by numerical weather prediction (NWP) as well as by Lagrangian persistence and Eulerian persistence, increases with lead time for most forecasting methods, while it is constant (300 km) for non–radar data–assimilating NWP. Comparing the different forecasting models, it is found that they are similar in the 0–6-h range and that none of them exhibit any predictive ability at meso-γ and meso-β scales after the first 2 h. On the other hand, the radar data–assimilating ensemble exhibits predictability of the model state at these scales, thus causing a systematic difference between corresponding to the ensemble and corresponding to model and radar. This suggests that either the ensemble does not have sufficient spread at these scales or that the forecasts suffer from biases.
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Buligon, Lidiane, Gervásio A. Degrazia, Charles R. P. Szinvelski, and Antonio G. Goulart. "Algebraic Formulation for the Dispersion Parameters in an Unstable Planetary Boundary Layer: Application in the Air Pollution Gaussian Model." Open Atmospheric Science Journal 2, no. 1 (August 12, 2008): 153–59. http://dx.doi.org/10.2174/1874282300802010153.
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An alternative formulation for the dispersion parameters in a convective boundary layer is presented. The development consists of a simple algebraic relation for the dispersion parameters, originated from the fitting of experimental data, in which the turbulent velocity variances and the Lagrangian decorrelation time scales are derived from the turbulent kinetic energy convective spectra. Assuming homogeneous turbulence for elevated regions in an unstable planetary boundary layer (PBL), the present approach, which provides the dispersion parameters, has been compared to the observational data as well as to results obtained by classical complex integral formulations. From this comparison yields that the vertical and lateral dispersion parameters obtained from the simple algebraic formulas reproduce, in an adequate manner, the spread of contaminants released by elevated continuous source in an unstable PBL. Therefore, the agreement with dispersion parameters available by an integral formulation indicates that the hypothesis of using an algebraic formulation as a surrogate for dispersion parameters in the turbulent convective boundary layer is valid. In addition, the algebraic vertical and lateral dispersion parameters were introduced into an air pollution Gaussian diffusion model and validated with the concentration data of Copenhagen experiments. The results of such Gaussian model, incorporating the algebraic dispersion parameters, are shown to agree with the measurements of Copenhagen.
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IJZERMANS, RUTGER H. A., ELENA MENEGUZ, and MICHAEL W. REEKS. "Segregation of particles in incompressible random flows: singularities, intermittency and random uncorrelated motion." Journal of Fluid Mechanics 653 (April 13, 2010): 99–136. http://dx.doi.org/10.1017/s0022112010000170.
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The results presented here are part of a long-term study in which we analyse the segregation of inertial particles in turbulent flows using the so called full Lagrangian method (FLM) to evaluate the ‘compressibility’ of the particle phase along a particle trajectory. In the present work, particles are advected by Stokes drag in a random flow field consisting of counter-rotating vortices and in a flow field composed of 200 random Fourier modes. Both flows are incompressible and, like turbulence, have structure and a distribution of scales with finite lifetime. The compressibility is obtained by first calculating the deformation tensor Jij associated with an infinitesimally small volume of particles following the trajectory of an individual particle. The fraction of the initial volume occupied by the particles centred around a position x at time t is denoted by |J|, where J ≡ det(Jij) and Jij ≡ ∂xi(x0, t)/∂x0,j, x0 denoting the initial position of the particle. The quantity d〈ln|J|〉/dt is shown to be equal to the particle averaged compressibility of the particle velocity field 〈∇ · v〉, which gives a measure of the rate-of-change of the total volume occupied by the particle phase as a continuum. In both flow fields the compressibility of the particle velocity field is shown to decrease continuously if the Stokes number St (the dimensionless particle relaxation time) is below a threshold value Stcr, indicating that the segregation of particles continues indefinitely. We show analytically and numerically that the long-time limit of 〈∇ · v〉 for sufficiently small values of St is proportional to St2 in the flow field composed of random Fourier modes, and to St in the flow field consisting of counter-rotating vortices. If St > Stcr, however, the particles are ‘mixed’. The level of mixing can be quantified by the degree of random uncorrelated motion (RUM) of particles which is a measure of the decorrelation of the velocities of two nearby particles. RUM is zero for fluid particles and increases rapidly with the Stokes number if St > Stcr, approaching unity for St ≫ 1. The spatial averages of the higher-order moments of the particle number density are shown to diverge with time indicating that the spatial distribution of particles may be very intermittent, being associated with non-zero values of RUM and the occurrence of singularities in the particle velocity field. Our results are consistent with previous observations of the radial distribution function in Chun et al. (J. Fluid Mech., vol. 536, 2005, p. 219).
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Buckley, Martha W., Tim DelSole, M. Susan Lozier, and Laifang Li. "Predictability of North Atlantic Sea Surface Temperature and Upper-Ocean Heat Content." Journal of Climate 32, no. 10 (April 30, 2019): 3005–23. http://dx.doi.org/10.1175/jcli-d-18-0509.1.
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Abstract Understanding the extent to which Atlantic sea surface temperatures (SSTs) are predictable is important due to the strong climate impacts of Atlantic SST on Atlantic hurricanes and temperature and precipitation over adjacent landmasses. However, models differ substantially on the degree of predictability of Atlantic SST and upper-ocean heat content (UOHC). In this work, a lower bound on predictability time scales for SST and UOHC in the North Atlantic is estimated purely from gridded ocean observations using a measure of the decorrelation time scale based on the local autocorrelation. Decorrelation time scales for both wintertime SST and UOHC are longest in the subpolar gyre, with maximum time scales of about 4–6 years. Wintertime SST and UOHC generally have similar decorrelation time scales, except in regions with very deep mixed layers, such as the Labrador Sea, where time scales for UOHC are much larger. Spatial variations in the wintertime climatological mixed layer depth explain 51%–73% (range for three datasets analyzed) of the regional variations in decorrelation time scales for UOHC and 26%–40% (range for three datasets analyzed) of the regional variations in decorrelation time scales for wintertime SST in the extratropical North Atlantic. These results suggest that to leading order decorrelation time scales for UOHC are determined by the thermal memory of the ocean.
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Bley, Sebastian, Hartwig Deneke, and Fabian Senf. "Meteosat-Based Characterization of the Spatiotemporal Evolution of Warm Convective Cloud Fields over Central Europe." Journal of Applied Meteorology and Climatology 55, no. 10 (October 2016): 2181–95. http://dx.doi.org/10.1175/jamc-d-15-0335.1.
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AbstractThe spatiotemporal evolution of warm convective cloud fields over central Europe is investigated on the basis of 30 cases using observations from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on board the geostationary Meteosat platforms. Cloud fields are tracked in successive satellite images using cloud motion vectors. The time-lagged autocorrelation is calculated for spectral reflectance and cloud property fields using boxes of 16 × 16 pixels and adopting both Lagrangian and Eulerian perspectives. The 0.6-μm reflectance, cloud optical depth, and water path show a similar characteristic Lagrangian decorrelation time of about 30 min. In contrast, significantly lower decorrelation times are observed for the cloud effective radius and droplet density. It is shown that the Eulerian decorrelation time can be decomposed into an advective component and a convective component using the spatial autocorrelation function. In an Eulerian frame cloud fields generally decorrelate faster than in a Lagrangian one. The Eulerian decorrelation time contains contributions from the spatial decorrelation of the cloud field advected by the horizontal wind. A typical spatial decorrelation length of 7 km is observed, which suggests that sampling of SEVIRI observations is better in the temporal domain than in the spatial domain when investigating small-scale convective clouds. An along-track time series of box-averaged cloud liquid water path is derived and compared with the time series that would be measured at a fixed location. Supported by previous results, it is argued that this makes it possible to discriminate between local changes such as condensation and evaporation on the one hand and advective changes on the other hand.
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Degrazia, Gervasio, Domenico Anfossi, Haroldo Fraga De Campos Velho, and Enrico Ferrero. "A Lagrangian Decorrelation Time Scale in the Convective Boundary Layer." Boundary-Layer Meteorology 86, no. 3 (March 1998): 525–34. http://dx.doi.org/10.1023/a:1000734626931.
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Sumata, Hiroshi, Frank Kauker, Michael Karcher, Benjamin Rabe, Mary-Louise Timmermans, Axel Behrendt, Rüdiger Gerdes, et al. "Decorrelation scales for Arctic Ocean hydrography – Part I: Amerasian Basin." Ocean Science 14, no. 1 (March 2, 2018): 161–85. http://dx.doi.org/10.5194/os-14-161-2018.
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Abstract. Any use of observational data for data assimilation requires adequate information of their representativeness in space and time. This is particularly important for sparse, non-synoptic data, which comprise the bulk of oceanic in situ observations in the Arctic. To quantify spatial and temporal scales of temperature and salinity variations, we estimate the autocorrelation function and associated decorrelation scales for the Amerasian Basin of the Arctic Ocean. For this purpose, we compile historical measurements from 1980 to 2015. Assuming spatial and temporal homogeneity of the decorrelation scale in the basin interior (abyssal plain area), we calculate autocorrelations as a function of spatial distance and temporal lag. The examination of the functional form of autocorrelation in each depth range reveals that the autocorrelation is well described by a Gaussian function in space and time. We derive decorrelation scales of 150–200 km in space and 100–300 days in time. These scales are directly applicable to quantify the representation error, which is essential for use of ocean in situ measurements in data assimilation. We also describe how the estimated autocorrelation function and decorrelation scale should be applied for cost function calculation in a data assimilation system.
Dissertations / Theses on the topic "Lagrangian decorrelation time scales"
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Degrazia, Franco Caldas. "Derivação de escalas de tempo lagrangeanas dependentes da distância da fonte : uma aplicação na dispersão de contaminantes na camada limite planetária neutra e estável." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/148024.
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Existe uma variedade de modelos de dispersão de poluentes, em geral, os modelos gaussianos são usados em todo o mundo por agências ambientais com intuito de regulação. O modelo CALPUFF é um deles. Neste estudo, _e avaliada a influência de escalas de tempo de descorrelação no sistema de modelagem CALPUFF, sob condições atmosféricas neutras. Para fazer isso uma nova parametrização das escalas de tempo descorrelação é proposta. Uma distribuição espectral de um perfil de velocidade euleriana e uma for- mutação da evolução das escalas temporais de descorrelação Lagrangiana são utilizadas como os mecanismos forçantes na dispersão turbulenta, numa camada limite dominada pelo cisalhamento do vento. O desempenho do modelo foi estabelecido com a comparação das concentrações superficiais do experimento Over-Land Alongwind Dispersion. Emissões de fontes em linha foram avaliadas com o modelo CALPUFF com distintas formas de inicialização. Um segundo modelo também foi testado, normalmente utilizado para estudar e prever o impacto ambiental e validar parametrizações turbulentas. É o modelo estocástico de partículas Lagrangiano LAMBDA. Também neste estudo, os resultados do modelo LAMBDA e CALPUFF enfatizam a capacidade da nova derivação de escalas de tempo em representar o comportamento estocástico desconhecido do fenômeno da dispersão de poluentes.There exists a variety of pollution of dispersion models and in general, Gaussian models are used worldwide by environmental agencies in regulatory applications. The CALPUFF model is one of them. In this study, the in uence of decorrelation time scales in the CALPUFF modeling system under neutral conditions is evaluated. To do this a new parameterization of decorrelation time scales is proposed. A spectral distribution of an Eulerian velocity pro le and a formulation of the evolution of the Lagrangian decorrela- tion timescales are used as the forcing mechanisms (shear-dominated boundary layer) for the turbulent dispersion. The model performance was established by comparing ground- level concentrations with Over-Land Alongwind Dispersion experimental results. Line source emissions was evaluated using the CALPUFF model with different forms of the initialization. A second model was also tested, normally used to study and predict the environmental impact and validate turbulent parameterizations. Is the stochastic La- grangian dispersion model LAMBDA (Ferrero and Anfossi, 1998). Also in this study the model LAMBDA and CALPUFF results emphasized the ability of the new derivation of decorrelation time scales to represent the unknown stochastic behavior.
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Hsu, Chiao-Chu, and 許喬筑. "Prediction of Lagrangian Time Scales for Carrier Phase in Single-Phase and Droplet-Loading Two-Phase Mixing Layers." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/12506857543826698963.
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碩士國立成功大學
航空太空工程學系
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Turbulent dispersion of the dispersed-phase elements in two-phase flows can be performed by probabilistic computation of the particle’s spatial distribution. It requires Lagrangian autocorrelation function of particle,RLpi , to quantify the trajectory variance of particle. However, experimental data on the Lagrangian velocity autocorrelation of particles is too almost nonexistent. It is questionable whether or not the of the carrier fluid in two-phase flow could be represented by those obtained from the single-phase flow. The Eulerian fluid velocity correlations in the single-phase and two-phase mixing layer flows are calculated from the raw data of the velocity measurements made in the experimental work of Wang and coworkers. Based on the simulation results and the experimental data, the relationship between Lagrangian and Eulerian integral time scales can be obtained. It is found that the Lagrangian time scale of the carrier phase in the two-phase case is different from that in the single-phase due to the change of the turbulence structure through the existence of the dispersed-phase elements. 1.1 前言 1 1.2 文獻回顧 3 1.3 研究目標 7 第二章 理論模式與數值方法 8 2.1 probabilistic Lagrangian method與實驗數據的整理 8 2.2 自相關函數與時間積分尺度 12 2.3 實驗設備 16 2.4 物理模式 18 2.4.1 連續相方程式 18 2.4.2 分散相方程式 18 2.5 數值方法 19 2.5.1 邊界條件 19 2.5.2 求解程序 20 第三章 結果與討論 22 3.1 數值模擬結果 22 3.2 常數C3的範圍分布 23 3.2.1 單相流 24 3.2.2 兩相流之連續相 24 3.3 顆粒的Stokes number 25 3.4 Lagrangian時間尺度之預測 28 第四章 結論與建議 30 參考文獻 32
Book chapters on the topic "Lagrangian decorrelation time scales"
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"Appendix C: Eulerian and Lagrangian Turbulence Scales." In Concentration Fluctuations and Averaging Time in Vapor Clouds, 153–55. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2010. http://dx.doi.org/10.1002/9780470937976.app3.
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Beris, Antony N., and Brian J. Edwards. "Poisson Brackets in Continuous Media." In Thermodynamics of Flowing Systems: with Internal Microstructure. Oxford University Press, 1994. http://dx.doi.org/10.1093/oso/9780195076943.003.0009.
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Now that we have defined the necessary thermodynamic quantities in chapter 4, we can turn back to the consideration of the dynamics of various physical systems. In order to apply a Poisson bracket to macroscopic transport phenomena, it is first necessary to rewrite the bracket (3.3-3) in a form which is suitable for continuum-mechanical considerations. As the number of particles increases to infinity, the transition is made from the specification of a very large number of discrete particle trajectories, xi(t), i=1,2,...,N, N→∞, to the determination of a single, continuous, vector function, Y(r,t), indicating the position of a fluid particle at time t which at a reference time t=0 was at position r, i.e., Y(r,0)=r. This is called a Lagrangian or material description. Alternatively, an Eulerian or spatial description can be used according to which the flow kinematics are completely specified through the determination of the velocity vector field, v(x,t), indicating the velocity of a fluid particle at a fixed spatial position, x, and time, t. (Truesdell [1966, p. 17] notes that the Lagrangian/Eulerian terminology is erroneous, however.) In this chapter, we shall use both descriptions to tackle the problem of ideal (inviscid) fluid flow and to arrive at a Poisson bracket for each case. The dissipative system will be considered in chapter 7. Once again, the concept of time and length scales is very important in determining when the experimenter views the system in consideration as a continuum entity. In chapter 3, we studied the dynamics of a system of discrete particles bouncing around with our time scale implicitly set on the order of the mean free time of the particles between collisions, ζ, and the length scale on the order of the mean free path, λ. As the number of particles approaches infinity, however, we note that certain averages, such as the velocity and the energy of the system, are practically constant on such a small time scale. Since the number of particles is so large, it is almost impossible to get any detailed information about the system as a whole by looking at individual particles because the number of the degrees of freedom is horrendous.
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Gross, Alan G. "Brian Greene: The Speculative Sublime." In The Scientific Sublime. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780190637774.003.0009.
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Charles Dodgson warned a child correspondent of the dangers of living in the looking-glass world of mathematicians like himself, the high price of consistently believing “six impossible things before breakfast”: . . . Don’t be in such a hurry to believe next time—I’ll tell you why—If you set to work to believe everything you will tire out the muscles of the mind, and then you’ll be so weak you won’t be able to believe the simplest true things. Only last week a friend of mine set to work to believe Jack-the-giant-killer. He managed to do it, but he was so exhausted by it that when I told him it was raining (which was true) he couldn’t believe it, but rushed out into the street without his umbrella, the consequence of which was his hair got seriously damp, and one curl didn’t recover its right shape for nearly two days. . . . In all his books, Brian Greene is our tour guide on a journey into his particular looking-glass world—string theory, an exercise in the speculative sublime, a sublime only for aficionados, certainly not for you and me. Here is the abstract of an article cited a respectable 201 times: . . . We show that a string-inspired Planck scale modification of general relativity can have observable cosmological effects. Specifically, we present a complete analysis of the inflationary perturbation spectrum produced by a phenomenological Lagrangian that has a standard form on large scales but incorporates a string-inspired short distance cutoff, and find a deviation from the standard result. We use the de Sitter calculation as the basis of a qualitative analysis of other inflationary backgrounds, arguing that in these cases the cutoff could have a more pronounced effect, changing the shape of the spectrum. Moreover, the computational approach developed here can be used to provide unambiguous calculations of the perturbation spectrum in other heuristic models that modify trans-Planckian physics and thereby determine their impact on the inflationary perturbation spectrum. Finally, we argue that this model may provide an exception to constraints, recently proposed by Tanaka and Starobinsky, on the ability of Planck-scale physics to modify the cosmological spectrum. . . .
Conference papers on the topic "Lagrangian decorrelation time scales"
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Pini, A., L. Grandoni, G. Leuzzi, P. Monti, F. Maicu, and F. De Pascalis. "Evaluation of Lagrangian time scales and turbulent diffusivities by GPS equipped drifters." In 2017 IEEE Workshop on Environmental, Energy, and Structural Monitoring Systems (EESMS). IEEE, 2017. http://dx.doi.org/10.1109/eesms.2017.8052687.
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Huilier, Daniel G. F. "Relationships Between Lagrangian and Eulerian Scales: A Review." In ASME 2002 Joint U.S.-European Fluids Engineering Division Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/fedsm2002-31294.
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The purpose of the present communication is to summarize the state-of-the art knowledge of the existing relationships between Eulerian and Lagrangian statistics in the literature. It will focus on integral scales, especially the classical Eulerian scales (such as those classically obtained from a fixed hot-wire or LDA control volume), the interesting moving Eulerian time scale (that obtained by a sensor which would move with the mean velocity) and the Lagrangian integral scale, most important for Lagrangian turbulent diffusion and dispersion simulations.
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Huilier, Daniel G. F. "Estimates Between Lagrangian and Eulerian Integral Scales: Theoretical, Experimental and Numerical Aspects." In ASME 2002 International Mechanical Engineering Congress and Exposition. ASMEDC, 2002. http://dx.doi.org/10.1115/imece2002-33808.
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The purpose of the present communication is to summarize the state-of-the art knowledge of the existing relationships between Eulerian and Lagrangian statistics in the literature. It will focus on integral scales, especially the classical Eulerian scales (such as those classically obtained from a fixed hot-wire or LDA control volume), the interesting moving Eulerian time scale (that obtained by a sensor which would move with the mean velocity) and the Lagrangian integral scale, most important for Lagrangian turbulent diffusion and dispersion simulations.
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Huilier, Daniel. "Why Are Relationships Between Lagrangian and Eulerian Scales Necessary for Gas-Particle Flow Modeling?" In ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45727.
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Simulation of Gas-Particle flows can be fulfilled by Lagrangian modeling of the dispersed phase. Each type of Lagrangian method, Monte-Carlo/Eddy Interaction or Markov Chain models, needs the knowledge of Lagrangian scales associated with the turbulent flow under consideration and the type of particle dispersing in the gas carrier flow. Unfortunately, Lagrangian quantities (as well the interesting moving Eulerian time scale, that given by a sensor which would move with the mean fluid velocity) are still difficult to be obtained directly by most experimental measurement techniques (except by very recent techniques such as PIV.PTV.), contrary to Eulerian scales scales, such as those classically obtained from a fixed hot-wire or LDA control volume. It is therefore of great importance to have available accurate relationships between Eulerian and Lagrangian scales, based on fluid flow properties as well as particle characteristics.
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Marchioli, Cristian, Maurizio Picciotto, and Alfredo Soldati. "Quantification of Particle and Fluid Scales in Particle-Laden Turbulent Channel Flow." In ASME 2006 2nd Joint U.S.-European Fluids Engineering Summer Meeting Collocated With the 14th International Conference on Nuclear Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/fedsm2006-98164.
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In this work, we study the dispersion of inertial particles in fully-developed turbulent channel flow to evaluate the relationship between particle and fluid time scales, and to identify suitable scales for parametrization of near-wall particle behavior. Direct Numerical Simulation (DNS) and Lagrangian particle tracking are used to build a complete and homogeneous dataset which covers a large target parameter space and includes statistics of particle velocity and particle concentration at steady state. Our results show that the Lagrangian integral time scale of the fluid is adequate to characterize particle wall deposition and that such fluid time scale will be different when sampled at the position of either fluid particles or inertial particles. Differences become particularly evident in the range 5 < St < 25. These observations can be crucial to improve the accuracy of engineering models for particle deposition.
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Rybalko, Michael, Eric Loth, and Dennis Lankford. "LES Sub-Grid Diffusion for Lagrangian Particles." In ASME 2008 Fluids Engineering Division Summer Meeting collocated with the Heat Transfer, Energy Sustainability, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/fedsm2008-55207.
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A continuous random walk (CRW) turbulent diffusion model was developed for Lagrangian particles within flow fields simulated by hybrid RANS/LES methodologies. For RANS flow-fields, the conventional time-scale and length-scale constants were determined by the turbulence intensity and dissipation values computed by the single-phase solver with a k-ω (Menter SST) model and subsequent comparison with turbulent particle diffusion experimental results of Snyder & Lumley (1971). This allowed validation against data for four particle types ranging from hollow glass to copper shot in grid-generated turbulence. The stochastic diffusion model was then extended to utilize the Nichols-Nelson k-ω hybrid RANS-LES turbulence model in a more complex turbulent flow resulting from the unsteady, three dimensional wake of a cylinder at Mach number of 0.1 and Reynolds number (ReD) of 800. The gas flow was computed with a 5th-order upwind-biased scheme. Throughout the wake, the sub-grid random walk model yielded good predictions of particle diffusion as compared with DNS. Also, these results indicate that crossing trajectory effects and inertia-based drift corrections are critical to handling a variety of particle Stokes numbers as well as regions of non-homogeneous turbulence, even when most of the kinetic energy is captured with the resolved-scales of an LES approach.
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Waindim, Mbu, and Datta V. Gaitonde. "Results and Analysis of Implicit Large Eddy Simulations of Equilibrium Spatially Developing Turbulent Boundary Layers at Multiple Mach Numbers." In ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting collocated with the ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/fedsm2014-21391.
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Equilibrium turbulent flat plate boundary layers with time invariant statistics were obtained at Mach numbers 1.7, 2.3, and 2.9. These are to be used as the initial condition for Large Eddy Simulations (LES) or Direct Numerical Simulations (DNS) of shock wave/turbulent boundary layer interactions utilizing a body force-based method. The results obtained are supplemented by an analysis of the mean and statistical properties of the respective boundary layers. The spanwise extent of the domain required to allow adequate decorrelation between the centerline and the boundaries is investigated by extensively probing the flowfields obtained. This is done to quantify the coherent structures of the turbulent flow. Specifically, two point correlations and integral length scales are used to investigate spanwise decorrelation distances in an attempt to pick a computational domain which is large enough to permit decorrelation downstream but small enough to minimize computational costs. It is shown that by examining the precursor events in the upstream region, namely the generalized stability criterion, it is possible to provide estimates for the force field parameters necessary for transition for a given flow, with only a small portion of the domain in the neighborhood of the trip. The technique is made even more efficient by investigating the possibility of determining these parameters using a two-dimensional simulation. Additionally, the three flow fields obtained are surveyed to confirm that they are suitable for subsequent SBLI simulations. We check that (i)they possess the expected turbulent characteristics and (ii)there is no signature of the tripping mechanism.
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Mansoori, Z., A. Dadashi, M. Saffar-Avval, F. Behzad, and G. Ahmadi. "Three-Dimensional Simulation of Turbulent Gas-Solid Flow and Heat Transfer in a Pipe." In ASME 2009 Fluids Engineering Division Summer Meeting. ASMEDC, 2009. http://dx.doi.org/10.1115/fedsm2009-78007.
Full textAbstract:
Three-dimensional simulation of turbulent gas-solid flow with heat transfer for a vertical pipe is performed in this study and the results are presented. The approach is based on an Eulerian/Lagrangian four-way interaction formulation considering turbulent hydrodynamic and thermal intensities and time scales equations. Inter-particles and particle-wall interactions are accounted for with an inelastic collision model. Numerical model validation is performed for an upward pipe gas-solid flow with constant wall heat transfer.
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Xu, Baopeng, Ya Liu, and Rong Xie. "Large Eddy Simulation of a Realistic Gas Turbine Combustor." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-57512.
Full textAbstract:
This paper proposes a large eddy simulation approach for the modeling of combusting flow with spray in realistic gas turbine combustors. A one equation subgrid model is used to model the effect of the unresolved subgrid scales on the resolved large scales. Subgrid combustion is modeled by an extended eddy dissipation model in which the filtered reaction rate is controlled by the turbulent mixing rate between the fine structures and the surrounding fluids. An Eulerian-Lagrangian approach is used to model the two-phase spray flow, and spray particles are tracked by a two-way coupling Lagrangian approach. Then the proposed approach is applied to simulate a combusting spray flow in an industrial annular combustor. The objectives of this study are to demonstrate its capability to investigate the complex flow and combustion dynamics in realistic gas turbine combustors. The predicted instantaneous and time averaged fields of velocity, temperature, pressure, fuel mass fraction are investigated. The precessing vortex core caused by the swirling flow as well as pressure oscillations is examined. The predicted results nicely reproduce the flow, spray and combustion dynamics and successfully capture the main features of the studied combustor, such as the processing vortex core. Finally, the predicted exit temperature and the total pressure loss are compared with experimental data and good agreements are obtained.
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Fragoso, Mauricio da Rocha, Francisco Alves dos Santos, Leonardo M. Marques da Cruz, Ju´lio A. C. Pellegrini, Tatiana Mafra, Arcilan Trevenzoli Assireu, and Bruna Nogueira Cerrone. "Real-Time Ocean Monitoring Through Lagragian Drifters During an Offshore Drilling Operation." In ASME 2008 27th International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2008. http://dx.doi.org/10.1115/omae2008-57807.
Full textAbstract:
MONDO Project is a surface ocean monitoring program for offshore operations never done before in Brazilian waters. It consisted on the periodic deployment of satellite tracked ocean drifters that provides real-time surface ocean currents and temperature data. Throughout September–November 2007, 40 satellite tracked ocean drifters were deployed at Santos Basin, located at the Brazilian Southeastern Ocean Bight. The results of this project can be used to study a wide range of subjects about ocean dynamics such as eddy activity, predictability, lagrangian integral scales, diffusivity, wind influence, etc. This paper is focused on eddies activities and ocean dynamics predictability. It can be observed that the number of anticyclonic eddies is a little higher than cyclonic ones during 2007 spring and that they present high values of relative vorticity (O(±10−5 s−1)). The rotation period lies between 16 days (anticyclonic) and 21days (cyclonic), with tangential velocities around 0.4 m/s. Comparison with data measured by drifters and altimetry showed good results, which indicates that a more extensive analysis about eddies in this region using altimetry data should provide relevant results. The methods of non-linear analysis applied to MONDO Project data allowed to estimate the predictability of the phenomena within Rossby radius scale (∼30 km). The results indicate that the prediction errors tend to double for periods greater than 3 days. It is suggested also that at least 4 variables should be considered in modeling studies on this region.