497 research outputs found
Turbulent channel flow simulation at friction Reynolds number Re_tau = 20,000
No full textDataset supports:
Sandham, N., Johnstone, R., and Jacobs, C. (2017). Surface-sampled simulations of turbulent flow at high Reynolds number. International Journal for Numerical Methods in Fluids.
Dataset from a turbulent channel flow simulation at friction Reynolds number Re_tau = 20,000. The modelling approach considers a single large eddy simulation (LES) combined with an array of non-space-filling quasi-direct numerical simulations (QDNSs).</span
Turbulent channel flow simulations at friction Reynolds number Re_tau = 4200
No full textDataset supports:
Sandham, N., Johnstone, R., and Jacobs, C. (2017). Surface-sampled simulations of turbulent flow at high Reynolds number. International Journal for Numerical Methods in Fluids.
Datasets from turbulent channel flow simulations at friction Reynolds number Re_tau = 4200. The modelling approach considers a single large eddy simulation (LES) combined with an array of non-space-filling quasi-direct numerical simulations (QDNSs).</span
The resilience of the logarithmic law to pressure gradients: evidence from direct numerical simulation
Get PDFWall-bounded turbulence in pressure gradients is studied using direct numerical simulation (DNS) of a Couette–Poiseuille flow. The motivation is to include adverse pressure gradients, to complement the favourable ones present in the well-studied Poiseuille flow, and the central question is how the scaling laws react to a gradient in the total shear stress or equivalently to a pressure gradient. In the case considered here, the ratio of local stress to wall stress, namely ?+, ranges from roughly 2/3 to 3/2 in the ‘wall region’. By this we mean the layer believed not to be influenced by the opposite wall and therefore open to simple, universal behaviour. The normalized pressure gradients p+ ? d\tau+/dy+ at the two walls are ?0.00057 and +0.0037. The outcome is in broad agreement with the findings of Galbraith, Sjolander & Head (Aeronaut. Quart. vol. 27, 1977, pp. 229–242) relating to boundary layers (based on measured profiles): the logarithmic velocity profile is much more resilient than two other, equally plausible assumptions, namely universality of the mixing length \ell=\?appa y and that of the eddy viscosity \nu_t =u_\tau \kappa y. In pressure gradients, with \tau+ \not= 1, these three come into conflict, and our primary purpose is to compare them. We consider that the K´arm´an constant \kappa is unique but allow a range from 0.38 to 0.41, consistent with the current debates. It makes a minor difference in the interpretation. This finding of resilience appears new as a DNS result and is free of the experimental uncertainty over skin friction. It is not as distinct in the (rather strong) adverse gradient as it is in the favourable one; for instance the velocity U+ at y+ =50 is lower by 3% on the adverse gradient side. A plausible cause is that the wall shear stress is small and somewhat overwhelmed by the stress and kinetic energy in the bulk of the flow. The potential of a correction to the ‘law of the wall’ based purely on p+ is examined, with mixed results. We view the preference for the log law as somewhat counter-intuitive in that the scaling law is non-local but also as becoming established and as highly relevant to turbulence modelling
Surface-sampled simulations of turbulent flow at high Reynolds number
No full textA new approach to turbulence simulation, based on a combination of large-eddy simulation (LES) for the whole flow and an array of non-space-filling quasi-direct numerical simulations (QDNS), which sample the response of near-wall turbulence to large-scale forcing, is proposed and evaluated. The technique overcomes some of the cost limitations of turbulence simulation, since the main flow is treated with a coarse-grid LES, with the equivalent of wall functions supplied by the near-wall sampled QDNS. Two cases are tested, at friction Reynolds number Reτ=4200 and 20,000. The total grid node count for the first case is less than half a million and less than two million for the second case, with the calculations only requiring a desktop computer. A good agreement with published DNS is found at Reτ=4200, both in terms of the mean velocity profile and the streamwise velocity fluctuation statistics, which correctly show a substantial increase in near-wall turbulence levels due to a modulation of near-wall streaks by large-scale structures. The trend continues at Reτ=20,000, in agreement with experiment, which represents one of the major achievements of the new approach. A number of detailed aspects of the model, including numerical resolution, LES-QDNS coupling strategy and sub-grid model are explored. A low level of grid sensitivity is demonstrated for both the QDNS and LES aspects. Since the method does not assume a law of the wall, it can in principle be applied to flows that are out of equilibrium
Retracted. “Direct numerical simulation of the Ekman layer: A step in Reynolds number, and cautious support for a log law with a shifted origin”
No full textA retraction of our findings in Ref. [1] is necessary. The numerical accuracy was not up to the required standards, allowing an error of about 0.3 in U+ in the buffer layer, and was insufficient to support the logarithmic law that was proposed. New results on two levels of finer grids are presented and found to be close, and to compare very well with the channel direct numerical simulation DNS results of Hoyas and Jiménez[2]. Conversely, the excellent agreement with an analytical fit to experiments proposed by Chauhan et al.[3], well into the range of several hundred for z+ is lost
The turbulent Ekman boundary layer over an infinite wind-turbine array
No full textA numerical simulation of a neutral turbulent Ekman layer containing an actuator disk array is performed, to improve the understanding of the coupling between the atmospheric boundary layer and large arrays of horizontal-axis wind turbines. An infinite array is represented by 64 disks in a periodic domain. The disks are represented by body forces and aligned with the time-dependent incoming flow. The same flow is also simulated with disks absent. Relative to the latter, the peak shear stress is doubled and located at the top of the disks; with a disk spacing of 5 diameters, the array efficiency is reduced to below 30%, in approximate agreement with the predictions of simple models approximating the turbines as roughness. The disks increase the boundary-layer depth, and the ratio of the ageostrophic to the geostrophic velocity component within the boundary layer, so that the Ekman spiral becomes more pronounced. These effects are required for the satisfaction of the global kinetic energy balance; the power output of the array is directly linked to the integral of the ageostrophic velocity over the boundary-layer depth. At disk height, the power extracted by the disks is locally balanced largely by the turbulent transport of mean flow kinetic energy. However, the increased turbulence kinetic energy production attributed to the disks is a large fraction of the power abstracted by them. The results suggest that mixed tower heights might be more efficient
2007 Colin Roderick Lecture
No full textLet me thank my audience for coming to listen to me today: let me thank the Foundation for Australian Literary Studies for inviting me to give this year’s Colin Roderick Lectures.<br />I like to think that Professor Roderick would have looked kindly on the choice of a lecturer drawn from the bleak, ambiguous demi-monde where journalism and literary endeavours meet - for he was involved, as many of you will know, during his days as an editor at Angus and Robertson, in the celebrated libel case in 1961 over “The Bandar-Log,” a novel, still unpublished, by the distinguished Canberra press gallery journalist, Alan Reid. Roderick’s own writings had a strong influence on me at a particular point in my path as an author: but the one act of his that resonates most strongly in my thoughts is the decision he made, 40 years ago, to establish a centre for the study of Australian writing here in the North.</jats:p
Polyphony and the anxiety of influence in the fiction of Henry James
Get PDFJames's fiction, especially in the Middle Phase, centres
on the figure of the artist and is characterized by, the two
interrelated aspects which previous criticism has largely
overlooked: the Bakhtinian 'polyphonic' -creation of
'author-thinkers'; and the conflict between ephebes and
precursors, for which Harold-Bloom's concept of 'the-anxiety of
influence' is the most illuminating model. Polyphony is the
narrative mode, and influence is the intra-artistic, theme.
These, as the Introduction to the thesis makes clear, are
rehearsed in James's inaugural novel, Roderick Hudson. Rowland
Mallet is an author-thinker, and his failure is caused by
authorial limitations. His monologism -is impaired by his
mistaking empathy for the authorial sympathy. Likewise,
Hudson's failure does not arise from a mercurial temperament,
but from a polyphonic shortcoming: not possessing the power of
fiction to contain the fiction of power in, his mentor. And the
relationships among the three artists - Gloriani, Hudson and
Singleton - perfectly exemplify the Bloomian-theme. It is these
two concepts, polyphony and influence, which are the major
preoccupation in the Middle Phase; as, the works chosen
demonstrate. These are a novella, a novel, and a number of
short stories all of which have been unjustifiably neglected.
Chapter One, on The Aspern Papers, argues that Tina Bordereau,
far from being, the artless victim seen by many critics,
actually challenges and defeats the narrator by the very form
of her narrative. Her 'realist' discourse undermines his
language of 'romance', and shows up its internal unstability.
Chapter Two is an extensive study of the critical reception of
The Tragic Muse. The most common areas of critical attention
have been its contemporary topicality, its relation to previous
novels on similar themes, and the possible genealogy of Gabriel
Nash. Those have all missed the core of the work. - Chapter Three
demonstrates how polyphony and the anxiety of influence make
the novel what it really is. Influence arises from the
juxtaposition of, and the wrestling between, artistic ephebes
and their precursors (Nick and Nash,, Miriam and Madame Carre).
The dialogic quality defined by Bakhtin is crucial to the
proper, and even-handed, characterization of all, the conflicts
in the novel. And since most of James's tales in the eighties
and nineties -are about 'masters - and acolytes, the anxiety of
influence remains central. Chapter Four is a study of 'The
Author of Beltraffiol' and 'The Lesson of the Master'. Again the
characters' manipulations are a crucial focus in a way that
G6rard Genette's terminology helps to illuminate. The fact that
the ephebe is the author-thinker emphasizes the inextricability
of the Bakhtinian and the Bloomian in James. Just as
polyphony offers a different focus for explicating the poetics
of James's fiction; so the ephebal conflict provides the basis
for a fresh perception of James's own artistic struggle
Rescate y conservación del Acervo Histórico del Palacio de Minería: Informe de las labores de conservación preventiva e intervenciones menores en material Bibliohemerográfico y actividades en apoyo al Acervo Histórico : octubre 2011 - febrero 2012
No full textEl presente informe tiene como finalidad dar constancia de los trabajos realizados en el Acervo Histórico del Palacio de Minería, por los restauradores Roderick Palacios, Isabel Ritter y Eleonora Cruz, pasantes de la Licenciatura en Restauración de Bienes Culturales como prestación de su servicio social.</p
The Bookshop of Black Queer Diaspora
No full textRoderick A. Ferguson is professor of Women’s, Gender, and Sexuality Studies at Yale University, and the author and editor of six books, including the groundbreaking Aberrations in Black: Toward a Queer of Color Critique (University of Minnesota, 2004). As the 2020 recipient of the Kessler Award, his influence on the field of LGBTQ studies has been acknowledged by the Center for LGBTQ Studies (CLAGS)
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