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Letteratura scientifica selezionata sul tema "Analogie de Reynolds"

Autore: Grafiati

Pubblicato: 5 ottobre 2024

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Articoli di riviste sul tema "Analogie de Reynolds"

Ghosh, Bikramaditya, Krishna M.C., Shrikanth Rao, Emira Kozarević e Rahul Kumar Pandey. "Predictability and herding of bourse volatility: an econophysics analogue". Investment Management and Financial Innovations 15, n. 2 (25 giugno 2018): 317–26. http://dx.doi.org/10.21511/imfi.15(2).2018.28.

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Financial Reynolds number works as a proxy for volatility in stock markets. This piece of work helps to identify the predictability and herd behavior embedded in the financial Reynolds number (time series) series for both CNX Nifty Regular and CNX Nifty High Frequency Trading domains. Hurst exponent and fractal dimension have been used to carry out this work. Results confirm conclusive evidence of predictability and herd behavior for both the indices. However, it has been observed that CNX Nifty High Frequency Trading domain (represented by its corresponding financial Reynolds number) is more predictable and has traces of significant herd behavior. The pattern of the predictability has been found to follow a quadratic equation.

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de Roode, Stephan R., Peter G. Duynkerke e A. Pier Siebesma. "Analogies between Mass-Flux and Reynolds-Averaged Equations". Journal of the Atmospheric Sciences 57, n. 10 (maggio 2000): 1585–98. http://dx.doi.org/10.1175/1520-0469(2000)057<1585:abmfar>2.0.co;2.

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Deckelman, Steven, Jennifer Graetz e Tyler Russell. "A multiplicative analogue of the Reynolds operator and construction of invariants". Rocky Mountain Journal of Mathematics 45, n. 4 (agosto 2015): 1107–18. http://dx.doi.org/10.1216/rmj-2015-45-4-1107.

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Gaviglio, J. "Reynolds analogies and experimental study of heat transfer in the supersonic boundary layer". International Journal of Heat and Mass Transfer 30, n. 5 (maggio 1987): 911–26. http://dx.doi.org/10.1016/0017-9310(87)90010-x.

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McKeon, B. J., e J. F. Morrison. "Asymptotic scaling in turbulent pipe flow". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 365, n. 1852 (16 gennaio 2007): 771–87. http://dx.doi.org/10.1098/rsta.2006.1945.

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The streamwise velocity component in turbulent pipe flow is assessed to determine whether it exhibits asymptotic behaviour that is indicative of high Reynolds numbers. The asymptotic behaviour of both the mean velocity (in the form of the log law) and that of the second moment of the streamwise component of velocity in the outer and overlap regions is consistent with the development of spectral regions which indicate inertial scaling. It is shown that an ‘inertial sublayer’ in physical space may be considered as a spatial analogue of the inertial subrange in the velocity spectrum and such behaviour only appears for Reynolds numbers R + >5×10 3 , approximately, much higher than was generally thought.

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Radkevich, E. V., E. A. Lukashev e O. A. Vasil’eva. "Hydrodynamic instabilities and nonequilibrium phase transitions". Доклады Академии наук 486, n. 5 (20 giugno 2019): 537–42. http://dx.doi.org/10.31857/s0869-56524865537-542.

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For laminar-turbulent transition model is built reconstruction of the initial stage of instability as a nonequilibrium phase transition, the mechanism of which is diffusion stratification. It is shown that the Gibbs free energy deviations from the homogeneous state (relative to the instability under consideration) is an analogue Ginzburg-Landau potentials. Numerical experiments were performed. Self-excitation of a homogeneous state by edge control condition of increasing speed. Under external influence (increase in speed at the input), there is a transition to chaos through bifurcations of period doubling, when the internal control parameter (analogue of the Reynolds number) changes, like the Feigenbaum period doubling cascade.

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CHILDRESS, STEPHEN, SAVERIO E. SPAGNOLIE e TADASHI TOKIEDA. "A bug on a raft: recoil locomotion in a viscous fluid". Journal of Fluid Mechanics 669 (12 gennaio 2011): 527–56. http://dx.doi.org/10.1017/s002211201000515x.

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The locomotion of a body through an inviscid incompressible fluid, such that the flow remains irrotational everywhere, is known to depend on inertial forces and on both the shape and the mass distribution of the body. In this paper we consider the influence of fluid viscosity on such inertial modes of locomotion. In particular we consider a free body of variable shape and study the centre-of-mass and centre-of-volume variations caused by a shifting mass distribution. We call this recoil locomotion. Numerical solutions of a finite body indicate that the mechanism is ineffective in Stokes flow but that viscosity can significantly increase the swimming speed above the inviscid value once Reynolds numbers are in the intermediate range 50–300. To study the problem analytically, a model which is an analogue of Taylor's swimming sheet is introduced. The model admits analysis at fixed, arbitrarily large Reynolds number for deformations of sufficiently small amplitude. The analysis confirms the significant increase of swimming velocity above the inviscid value at intermediate Reynolds numbers.

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Zhao, Shuo, Xiaoping Chen, Yuting Yang e Dengsong Huang. "Effects of Viscosity Law on High-Temperature Supersonic Turbulent Channel Flow for Chemical Equilibrium". Processes 12, n. 2 (24 gennaio 2024): 256. http://dx.doi.org/10.3390/pr12020256.

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Direct numerical simulations of temporally evolving high-temperature supersonic turbulent channel flow for chemical equilibrium were conducted with a Mach number of 3.0, a Reynolds number of 4880, and a wall temperature of 1733.2 K to investigate the influence of the viscosity law. The mean and fluctuating viscosity for the mixture rule is higher than that for Sutherland’s law, whereas an opposite trend is observed in the mean temperature, mean pressure, and dissociation degree. The Trettel and Larsson transformed mean velocity, the Reynolds shear stress, the turbulent kinetic energy budget, and the turbulent Prandtl number are insensitive to the viscosity law. The semilocal scaling that take into account local variation of fluid characteristics better collapses the turbulent kinetic energy budget. The modified strong Reynolds analogies provide reasonably good results for the mixture rule, which are better than those for Sutherland’s law. The streamwise and spanwise coherencies for the mixture rule are stronger and weaker than those for Sutherland’s law, respectively. The relationship between viscosity and species components can help to identify the traveling wave packet.

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Yim, Eunok, e Paul Billant. "Analogies and differences between the stability of an isolated pancake vortex and a columnar vortex in stratified fluid". Journal of Fluid Mechanics 796 (11 maggio 2016): 732–66. http://dx.doi.org/10.1017/jfm.2016.248.

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In order to understand the dynamics of pancake shaped vortices in stably stratified fluids, we perform a linear stability analysis of an axisymmetric vortex with Gaussian angular velocity in both the radial and axial directions with an aspect ratio of ${\it\alpha}$. The results are compared to those for a columnar vortex (${\it\alpha}=\infty$) in order to identify the instabilities. Centrifugal instability occurs when $\mathscr{R}>c(m)$ where $\mathscr{R}=ReF_{h}^{2}$ is the buoyancy Reynolds number, $F_{h}$ the Froude number, $Re$ the Reynolds number and $c(m)$ a constant which differs for the three unstable azimuthal wavenumbers $m=0,1,2$. The maximum growth rate depends mostly on $\mathscr{R}$ and is almost independent of the aspect ratio ${\it\alpha}$. For sufficiently large buoyancy Reynolds number, the axisymmetric mode is the most unstable centrifugal mode whereas for moderate $\mathscr{R}$, the mode $m=1$ is the most unstable. Shear instability for $m=2$ develops only when $F_{h}\leqslant 0.5{\it\alpha}$. By considering the characteristics of shear instability for a columnar vortex with the same parameters, this condition is shown to be such that the vortex is taller than the minimum wavelength of shear instability in the columnar case. For larger Froude number $F_{h}\geqslant 1.5{\it\alpha}$, the isopycnals overturn and gravitational instability can operate. Just below this threshold, the azimuthal wavenumbers $m=1,2,3$ are unstable to baroclinic instability. A simple model shows that baroclinic instability develops only above a critical vertical Froude number $F_{h}/{\it\alpha}$ because of confinement effects.

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JIMÉNEZ, JAVIER, SERGIO HOYAS, MARK P. SIMENS e YOSHINORI MIZUNO. "Turbulent boundary layers and channels at moderate Reynolds numbers". Journal of Fluid Mechanics 657 (2 giugno 2010): 335–60. http://dx.doi.org/10.1017/s0022112010001370.

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The behaviour of the velocity and pressure fluctuations in the outer layers of wall-bounded turbulent flows is analysed by comparing a new simulation of the zero-pressure-gradient boundary layer with older simulations of channels. The 99 % boundary-layer thickness is used as a reasonable analogue of the channel half-width, but the two flows are found to be too different for the analogy to be complete. In agreement with previous results, it is found that the fluctuations of the transverse velocities and of the pressure are stronger in the boundary layer, and this is traced to the pressure fluctuations induced in the outer intermittent layer by the differences between the potential and rotational flow regions. The same effect is also shown to be responsible for the stronger wake component of the mean velocity profile in external flows, whose increased energy production is the ultimate reason for the stronger fluctuations. Contrary to some previous results by our group, and by others, the streamwise velocity fluctuations are also found to be higher in boundary layers, although the effect is weaker. Within the limitations of the non-parallel nature of the boundary layer, the wall-parallel scales of all the fluctuations are similar in both the flows, suggesting that the scale-selection mechanism resides just below the intermittent region, y/δ = 0.3–0.5. This is also the location of the largest differences in the intensities, although the limited Reynolds number of the boundary-layer simulation (Reθ ≈ 2000) prevents firm conclusions on the scaling of this location. The statistics of the new boundary layer are available from http://torroja.dmt.upm.es/ftp/blayers/.

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Più fonti

Tesi sul tema "Analogie de Reynolds"

Ben, Nasr Ouissem. "Numerical simulations of supersonic turbulent wall-bounded flows". Phd thesis, INSA de Rouen, 2012. http://tel.archives-ouvertes.fr/tel-01059805.

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This work deals with spatially-evolving supersonic turbulent boundary layers over adiabatic and cold walls at M∞ = 2 and up to Re0 ≈ 2600 using 3 different SGS models. The numerical methodology is based on high-order split-centered scheme to discretize the convective fluxes of the Navier-Stokes equations . For the adiabatic case, it is demonstrated that all SGS models require a comparable minimum grid-refinement in order to capture accurately the near-wall-turbulence. Overall, the models exhibit correct behavior when predictiong the dynamic properties, but show different performances for the temperature distribution in the near-wall region. For the isothermal case, it is found that the compressibility effects are not enhanced due to the wall cooling. As expected, the total temperature fluctuations are not negligible in the near-wall region. The study shows that the anti-correlation linking both velocity and temperature fields, derived from the Morkovin's hypothesis, is not satisfied.

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Celep, Muhittin. "Τransitiοn dans les cοuches limites supersοniques : simulatiοns numériques directes et cοntrôle par stries". Electronic Thesis or Diss., Normandie, 2024. http://www.theses.fr/2024NORMIR15.

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Dans les écoulements à haute vitesse, une traînée visqueuse élevée et des charges thermiques importantes sont des conséquences inhérentes sur les corps aérodynamiques. Ces effets augmentent de manière significative pendant la phase de transition lorsque la couche limite devient turbulente. Afin de réduire les risques de dommages mécaniques et de défaillances liées à la fatigue, des systèmes de protection thermique sont intégrés aux véhicules, ajoutant de la complexité aux aspects techniques et économiques de la conception. La solution réside dans l’acquisition d’une compréhension approfondie des mécanismes de transition et le développement de systèmes de contrôle pour prolonger la couche limite laminaire le long de la surface du véhicule. De nombreuses techniques de contrôle actives et passives peuvent être utilisées pour le contrôle de la transition, parmi lesquelles la méthode de l’emploi de stries émerge comme une approche particulièrement prometteuse. Cette méthode consiste à générer des stries étroitement espacées dans la direction de l’envergure, créant des zones alternées de haute et basse vitesse dans le champ d’écoulement. Bien que la méthode ait été testée récemment dans des écoulements supersoniques, démontrant son efficacité pour retarder la transition, sa pertinence doit être évaluée plus avant. Dans ce travail de recherche, des cas de DNS sont réalisés dans des régimes supersoniques et près-hypersoniques. Les stries sont introduites à l’aide d’une bande de soufflage/aspiration placée sur la paroi avant celle de la perturbation qui est utilisée pour déclencher la transition de manière “contrôlée”, forcée par une perturbation à une seule fréquence et longueur d’onde. L’enquête à Mach 2.0 confirme que les stries avec cinq fois la longueur d’onde fondamentale sont les plus bénéfiques pour le contrôle de la transition. De plus, le refroidissement améliore l’efficacité de la méthode, tandis que le chauffage détériore considérablement la capacité de contrôle des stries. La condition murale isotherme n’altère pas l’impact stabilisateur comparable de la déformation du flux moyen (DFM) et de la partie 3D du contrôle à Mach 2.0. Cependant, à Mach 4.5, tant le type d’instabilité que les caractéristiques des stries changent de manière significative. L’impact stabilisateur de la DFM devient presque absent, et la partie 3D du contrôle prédomine, les caractéristiques des stries n’étant plus considérées comme indépendantes de leur amplitude de perturbation initiale
In high-speed flows, elevated viscous drag and thermal loads are inherent outcomes over aerodynamic bodies. These effects escalate substantially during the transition phase when the boundary layer becomes turbulent. To mitigate potential mechanical damage and fatigue-related failures, thermal protection systems are integrated into vehicles, adding complexity to the technical and economic aspects of design. The solution lies in gaining a comprehensive understanding of transition mechanisms and developing control systems to prolong laminar boundary layer along the vehicle’s surface. Numerous active and passive control techniques can be employed for transition control, with the streak employment method emerging as a particularly promising approach. This method involves generating narrowly spaced streaks in the spanwise direction, creating alternating high and low-speed regions in the flow field. Although the method has only recently been tested in supersonic flows, demonstrating its effectiveness in delaying transition, its suitability needs to be assessed further. In this research work, direct numerical simulations are performed in supersonic and near-hypersonic regimes. Streaks are introduced through a blowing/suction strip placed at the wall prior to that of the perturbation which is used to trigger transition in a “controlled” fashion, forced by a single frequency and wavenumber disturbance. The investigation at Mach 2.0 confirms that streaks with five times the fundamental wavenumber are most beneficial for transition control. Additionally, cooling enhances the method’s effectiveness, while heating severely deteriorates the capability of control streaks. The isothermal wall condition does not alter the comparable stabilizing impact of the mean flow deformation (MFD) and the 3-D part of the control at Mach 2.0. However, at Mach 4.5, both the type of instability and the characteristics of the streaks change significantly. The stabilizing impact of the MFD becomes nearly absent, and the 3-D part of the control predominates, with the characteristics of the streaks no longer considered independent of their initial disturbance amplitude

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Reynolds, York [Verfasser]. "Singen und Kämpfen : die Kunst des klassischen Gesangs und die Kunst des waffenlosen Vollkontakt-Nahkampfstils Wing Tsun Kuen im Vergleich ihrer Körpertechniken im Hinblick auf ihre Analogien und einer gemeinsamen holistisch-generischen Tiefenstruktur / von York Reynolds". 2007. http://d-nb.info/986408700/34.

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Libri sul tema "Analogie de Reynolds"

R, Lang Peter, e Lombargo Frank S, a cura di. Atmospheric turbulence, meteorological modeling, and aerodynamics. Hauppauge, NY: Nova Science Publishers, 2009.

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Capitoli di libri sul tema "Analogie de Reynolds"

Avdeev, Alexander A. "Reynolds Analogy". In Mathematical Engineering, 417–66. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-29288-5_11.

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Simonson, J. R. "Forced convection: Reynolds analogy and dimensional analysis". In Engineering Heat Transfer, 101–23. London: Macmillan Education UK, 1988. http://dx.doi.org/10.1007/978-1-349-19351-6_7.

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Choi, K. S. "Breakdown of the Reynolds Analogy over Drag-Reducing Riblets Surface". In Advances in Turbulence IV, 149–54. Dordrecht: Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-011-1689-3_25.

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Kelly, G. M., J. M. Simmons e A. Paull. "Skin Friction Measurements and Reynolds Analogy in a Hypersonic Boundary Layer". In Shock Waves @ Marseille I, 299–304. Berlin, Heidelberg: Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/978-3-642-78829-1_48.

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Saha, Sujoy Kumar, Hrishiraj Ranjan, Madhu Sruthi Emani e Anand Kumar Bharti. "Numerical Simulation of Integral Roughness, Laminar Flow in Tubes with Roughness and Reynolds Analogy for Heat and Momentum Transfer". In Insert Devices and Integral Roughness in Heat Transfer Enhancement, 99–121. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-20776-2_5.

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Burmeister, L. C. "Reynolds analogy for mass transfer". In Experiments in Heat Transfer and Thermodynamics, 49–53. Cambridge University Press, 1994. http://dx.doi.org/10.1017/cbo9780511608346.011.

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Reynolds, Philip L. "Conjugal and Nuptial Symbolism in Medieval Christian Thought". In The Symbolism of Marriage in Early Christianity and the Latin Middle Ages. Nieuwe Prinsengracht 89 1018 VR Amsterdam Nederland: Amsterdam University Press, 2019. http://dx.doi.org/10.5117/9789462985919_ch02.

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Medieval scholars, clerics, and religious perceived important resemblances between marriage and the relationship between God or Christ and the Church or its individual members. They construed the divine–human relationship as a mystical marriage, but they also used such analogies to explain the laws and morality of human marriage and as the basis of the doctrine of marriage as one of the sacraments. This chapter explores the diversity of such comparisons. Having noted the limitations of symbolism as our overarching category, Reynolds proposes that the implicit common denominator within medieval thought was a notion of representation, that is, a resemblance posited between corresponding items on two hierarchically ordered planes, respectively spiritual or divine and corporeal or created. Lower things, construed as signs or figures, provided cognitive and rhetorical access to analogous higher things, whereas higher things could function analogically as exemplars that lower things were required to emulate. But these two vectors of comparison were not always coincident.

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Rout, Siddharth. "Early Advancements in Turbulence-Generated Noise Modelling: A Review". In Boundary Layer Flows - Advances in Modelling and Simulation [Working Title]. IntechOpen, 2023. http://dx.doi.org/10.5772/intechopen.1002433.

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Turbulent flows generate a broadband of acoustic noise, which can be extremely important. So, there is need for modelling the generation and propagation of acoustic energy in fluid flows, especially turbulent. This chapter reviews the research work conducted to identify and quantify the noise field generated in turbulent flows. The story starts with the journey of experimental identification and measurement of noise generated from vortices. Various analytical models there were developed, soon after, the popularity of turbulence generated is discussed. The base path-breaking research on quantifying noise generation from conservation laws including Navier–stokes equations is discussed and further used for approximation of acoustic intensity by acoustic analogy with electrostatic quadrupole near-field and far-field. With the development of computational numerical techniques flow field for complex geometries and higher fidelity became possible. The candidates for relevant computational methods are touched and integration with turbulent models is discussed. Finally, a case of simulation of noise generation for turbulent flow over airfoil using acoustic equations and Reynolds-averaged Navier-Stokes (RANS) turbulent model is reviewed.

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Williams, Howard. "Beowulf and Archaeology: Megaliths Imagined and Encountered in Early Medieval Europe". In The Lives of Prehistoric Monuments in Iron Age, Roman, and Medieval Europe. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780198724605.003.0012.

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Since the mid nineteenth century AD, the poem Beowulf has long been a quarry for inspiration, analogy and insight for those exploring the archaeology of Early Medieval Britain and Scandinavia (Cramp 1957; Hills 1997; Webster 1998; Owen-Crocker 2000). The dialogue of archaeology and poem has been employed to explore a range of Early Medieval social practices and structures: the production and circulation of weapons and armour through inheritance and gift-giving, the role of vessels and feasting practices, hall-building and ceremony, the hoarding of treasure, and various dimensions of funerary practice including barrow-burial, boat-burial, and cremation. In discussing many of these practices, scholars have recently pointed to the sense of the past in the poem as a practice-orientated form of social memory. Synergies have been identified between heroic poetry and the ceremonial use of material culture, monuments, architectures, and landscapes identified in poetry and archaeological evidence as distinct but related technologies of remembrance within the hierarchical Christian Anglo-Saxon kingdoms that emerge during the mid to late seventh century AD (Williams 1998; 2006; 2011a; 2011b; Owen-Crocker 2000; Semple 2013). In this fashion, the assertions of legitimacy and identities by Early Medieval elites, including their claims to land, power and people, were performed through the ritualized reuse, appropriation and naming of ancient monuments and their deployment within rituals and oral performances, including poetry (Semple 2013; see also Price 2010). The locations and immediate environs of major later Anglo-Saxon churches and elite residences, and the maritime and land routes connecting them, provided the dramaturgical and ritualized settings and media by which social memories were transmitted and reproduced. Landmarks such as ancient monuments were actively integrated through reuse for a variety of functions from burial to assembly (Williams 2006; Reynolds and Langlands 2011; Semple 2013). In particular, Sarah Semple’s (2013) important interdisciplinary survey and analysis of Anglo-Saxon perceptions and reuse of prehistoric monuments from the fifth to the eleventh centuries AD, identifies the variegated and shifting perceptions of prehistoric monuments revealed by later Anglo-Saxon texts, manuscript illustrations, place-names and archaeological evidence (see also Semple 1998; 2004).

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Atti di convegni sul tema "Analogie de Reynolds"

Jiang, Lei-Yong, e Ian Campbell. "Reynolds Analog in Combustor Modeling". In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-27017.

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Accurate temperature prediction is vital for the development of advanced combustion systems. The Reynolds analogy concept has been almost exclusively used in current turbulent reacting flow RANS simulations. In this paper, this hypothesis applied to a diffusion flame model combustor is discussed and assessed. Some of the numerical results obtained from a flamelet combustion model with the turbulence Prandtl/Schmidt number from 0.25 to 0.85 are presented, and compared with a benchmark experimental database. It is found that the turbulence Prandtl/Schmidt number has significant effect on the predicted temperature and species fields inside the combustor, as well as the temperature profile at the combustor wall. In contrast, its effect on the velocity field is insignificant in the range assessed. With the optimized turbulence Prandtl/Schmidt number, both velocity and scalar fields can be reasonably and quantitatively predicted. For the present configuration and operating conditions, the optimal Prandtl/Schmidt number is 0.5, lower than the commonly accepted values, ∼0.70. This study suggests that for accurate prediction of scalar transfers in turbulent reacting flows, the Reynolds analogy concept should be improved and new approaches should be developed.

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Abramov, Alexander, e Alexander Butkovskii. "Extended Reynolds analogy for the rarefied Rayleigh problem: Similarity parameters". In 31ST INTERNATIONAL SYMPOSIUM ON RAREFIED GAS DYNAMICS: RGD31. AIP Publishing, 2019. http://dx.doi.org/10.1063/1.5119671.

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Forooghi, Pourya, Franco Magagnato e Bettina Frohnapfel. "REYNOLDS ANALOGY IN TURBULENT FLOWS OVER ROUGH WALLS - A DNS INVESTIGATION". In International Heat Transfer Conference 16. Connecticut: Begellhouse, 2018. http://dx.doi.org/10.1615/ihtc16.cov.021429.

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Polkowski, Janusz W. "An Influence of the Thickness of a Laminar Sublayer and Mixing Length Model on the Skin Friction and Heat Transfer in the Boundary Layer Flow". In ASME 1987 International Gas Turbine Conference and Exhibition. American Society of Mechanical Engineers, 1987. http://dx.doi.org/10.1115/87-gt-68.

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An influence of the thickness of the laminar sub-layer and mixing length profile on skin friction and heat transfer in the incompressible boundary layer is studied. Solution of the momentum and energy equations for different algebraic expressions for the mixing length is presented. Relationships between the specific forms of Reynolds analogy and boundary conditions (temperature or heat flux) as well as the limitations of Reynolds analogy are discussed.

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De Maio, M. "DNS of momentum and heat transfer inside rough pipes". In Aerospace Science and Engineering. Materials Research Forum LLC, 2023. http://dx.doi.org/10.21741/9781644902677-7.

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Abstract. We carry out direct numerical simulation (DNS) of turbulent flow in pipes with a grit-blasted surface, to investigate both on momentum and heat transfer. A wide range of Reynolds numbers are considered, while maintaining a constant molecular Prandtl number of 0.7. The large relative roughness influences both the velocity and the temperature fields, indicating that the Reynolds analogy does not hold at high Reynolds bulk number.

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Som, Abhijit. "Generalized Reynolds Analogy: An Engineering Prospective of Thermo-Fluid Physics for Heat Exchanger Design". In ASME 2021 Power Conference. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/power2021-65820.

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Abstract In practical interest of Reynolds analogy for power and process industries, in a unified system approach an engineering prospective of thermo-fluid physics has been proposed by developing a theory of basic heat exchanger design and analysis. Needless to mention of excellent books on heat exchangers, this paper focuses on the novelty of heat exchanger, which in author’s view depends upon the possibility of energy exchange between two fluid streams at different temperatures. Since operation cannot be random, the principal act of design is to engineer a product such that it operates in specified manner to perform its desired function of de-energizing one stream by virtue of energizing the other. With law of the integral as the guiding principle of physics, it shall be made clear that energy exchange in the form of heat must be accompanied by energy transfer such that heat exchanger must operate due to simultaneous process of cooling and heating of the fluid streams with an intervening medium. To unlock the secret of steady operation a fundamental postulate concerning thermodynamic behavior of the system has been made by invoking zeroth law of thermodynamics. Remarkably, it lends itself a necessary and sufficient condition concerning proportionality between heat-flux and required temperature difference to yield fluids unique thermal response in relation to the heat transfer surface temperature. Consequently, far-reaching physical implications of the constant of proportionality on system design can be clearly exposed of with due consideration to Eulerian descriptions of conservation principles according to Newton’s mechanical theory. Consistently enough, because of thermal non-equilibrium, effectiveness of system design and off design performance warrants a fundamental theorem like one suggested by Reynolds concerning augmentation of thermal diffusion due to fluid motion. Accordingly, flow rates become critical operating parameters for thermal performance and pressure drop requirements. Furthermore, and most importantly, in support of the theorem an order magnitude analysis appears to be in order, to show the dependence of flow resistance and hence, system thermal response on fluid flow behavior in terms of non-dimensional parameters. As a result, it is made clear that development of design correlations for friction factor and non-dimensional heat transfer coefficient in terms of both Reynolds number and Prandtl number is an integral part of heat exchanger design process by gathering experimental data. Finally, generalized mathematical statement of Reynolds analogy has been obtained relating Stanton number with friction factor, which reduces to our familiar expression for Prandtl number of unity.

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Guerras Colo´n, Israel, Sandra Velarde-Sua´rez, Rafael Ballesteros-Tajadura, Jesu´s Manuel Ferna´ndez Oro e Jose´ Gonza´lez. "Noise Prediction in HVAC Squirrel-Cage Fans by Unsteady Reynolds Navier-Stokes Computation". In ASME-JSME-KSME 2011 Joint Fluids Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajk2011-23022.

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Small centrifugal and axial fans are used in automobile applications, as it is the case for HVAC systems for public transport. Typically, these fans are used to work at high speed (over 4000 rpm) and variable operation conditions, even at extreme off-design points. Flow instabilities, low efficiency and high levels of noise and vibrations appear in these machines due to these working characteristics and the need of low fabrication costs. However, lower noise levels are required today to improve the passengers comfort. Aiming to solve these problems, it is interesting to develop a computer application to predict the generated noise level (especially at the blade passing frequency BPF), which could be used during the design phase of the fans. In this paper, using Computational Fluid Dynamics (CFD) tools, the three-dimensional (3D) internal flow in a small squirrel-cage fan is computed unsteadily. Based upon the data acquired from the pressure fluctuations at the surfaces of 46 rotating blades and the volute tongue, the Ffowcs Williams-Hawkings analogy, which has been successfully applied in other types of turbomachines, is used to predict noise levels at the BPF. On the other hand, in order to validate the predicted numerical results, an experimental noise characterization in a semi-anechoic chamber using capacitive microphones and a real-time frequency analyzer is performed.

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Velarde-Suárez, Sandra, Rafael Ballesteros-Tajadura, Jesús Manuel Fernández Oro e José González. "Noise Prediction in HVAC Squirrel-Cage Fans by Unsteady Reynolds Navier-Stokes Computation". In ASME 2012 Fluids Engineering Division Summer Meeting collocated with the ASME 2012 Heat Transfer Summer Conference and the ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/fedsm2012-72502.

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Khalatov, Artem, e Vitaliy Onishchenko. "Heat Transfer and Surface Friction Downstream of a Dual Array of Dimples of a Different Shape". In ASME Turbo Expo 2008: Power for Land, Sea, and Air. ASMEDC, 2008. http://dx.doi.org/10.1115/gt2008-50022.

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The wide experimental program was carried out in the Institute for Engineering Thermophysics (Kiev, Ukraine) to study heat transfer and surface friction downstream of the dual array of dimples. The test section is the rectangular channel 34 mm height, 290 mm wide and 125 mm long. The unheated dual array of dimples was placed on the channel floor (bottom) wall upstream of the electrically heated test section. Inserts with dimples of spherical, cylindrical and square shape were tested at their relative depth h/D of 0.20 and 0.30. Projected (surface) diameter of dimples is 25.0 mm; the second row was placed in the staggered fashion with the downstream pitch Sx/D of 0.64. The span-wise spacing Sz/D is of 2.0 providing the second row exactly fills in the open span-wise gap between dimples in the first row. The inlet air speed was from 4.1 to 16.6 m/c, Reynolds number Re2H, based on the equivalent (hydraulic) channel diameter varied from 17,400 to 71,800, the inlet boundary layer thickness did not exceed 1.0 mm. According to shape factor measurements the turbulent flow existed in front of dimples for all flow conditions tested. Heat transfer measurements were performed over the center line downstream of the representative dimple placed in the first or second row. The Reynolds number Rex based on the downstream distance was ranged from 3,000 to 105,000. Based on measurements, the conclusion was made that immediately after dimple array (at Rex>3,000) heat transfer corresponds to the turbulent flow data for a smooth flat plate extended into the low Reynolds number area. The downstream heat transfer ratio Nux/Nu0 weakly depends on the dimple shape and depth. The downstream surface friction τw was measured over the central line beyond the dimple placed in the first or second row. The tube-in-flow technique was employed in these measurements. At low probe distances (x/D = 1.2–2.4) the surface friction coefficients locate between classic correlations for the laminar and turbulent flow (extended into the low Reynolds number area) for a smooth flat plate. At high probe distances (x/D > 4.16) the surface friction data agrees well with the classic turbulent flow correlation for the smooth flat plate. Close to the dimple downstream edge (x/D < 2.4) the Reynolds analogy factor is over the unity for all dimple depths and geometries, thus confirming the greater heat transfer increases compared with pressure drop growth. At higher distances, the Reynolds analogy factor is above or below the Reynolds analogy line (RAF = 1.0) depending on the dimple shape and depth. Comparisons on the Reynolds analogy factor magnitude were made in terms of the downstream distances from the dimple back edge.

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Zhao, Zhiqi, Lei Luo, Xun Zhou e Songtao Wang. "Effect of Coolant Mass Flow Rate of Dirt Purge Hole on Heat Transfer and Flow Characteristics at a Turbine Blade Tip Underside". In ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-76156.

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High thermal load on the turbine blade tip surface would lead to high temperature corrosion and severe structural damage. One method to reduce blade tip high thermal stress is to use cooler fluid from the compressor, that exists dirt purge hole mounted on the tip underside, for cooling purpose. In this study, internal serpentine cooling passage is modeled as a U bend channel with a sharp 180-deg turn with the dirt purge hole arranged at the tip-wall. The effect of the layout of dirt purge hole and varying coolant mass flow rate on flow structure, heat transfer on the tip-wall and friction factor of the U bend channel are numerically studied with Reynolds number ranging from 100,000 to 440,000. The results show that the vortex pair is forced to flow near the tip-wall while the increasing shearing effect induced by the vortex pairs increases the local heat transfer. With an increase mass flow rate of the dirt purge hole, the suction effect enhances the local heat transfer performance. However, the pressure loss is also increased accordingly at all Reynolds numbers. The augmentations with Reynold analogy performance and the thermal performance for 5.8% mass flow rate case is 12.5% and 12.7%, respectively, which reaches the highest performance augmentation compared to the smooth-tip channel.

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