323,425 research outputs found
A numerical investigation of high-Reynolds-number constant-volume non-Boussinesq density currents in deep ambient
No full textThe time-dependent behaviour of non-Boussinesq high-Reynolds-number density currents, released from a lock of height h0 and length x0 into a deep ambient and spreading over horizontal flat boundaries, is considered. We use two-dimensional Navier–Stokes simulations to cover: (i) a wide range of current-to-ambient density ratios, (ii) a range of length-to-height aspect ratios of the initial release within the lock (termed the lock aspect ratio λ=x0/h0) and (iii) the different phases of spreading, from the initial acceleration phase to the self-similar regimes. The Navier–Stokes results are compared with predictions of a one-layer shallow-water model. In particular, we derive novel insights on the influence of the lock aspect ratio (λ) on the shape and motion of the current. It is shown that for lock aspect ratios below a critical value (λcrit ), the dynamics of the current is significantly influenced by λ. We conjecture that λcrit depends on two characteristic time scales, namely the time it takes for the receding perturbation created at the lock upon release to reflect back to the front, and the time of formation of the current head. A comparison of the two with space–time diagrams obtained from the Navier–Stokes simulations supports this conjecture. The non-Boussinesq effect is observed to be significant. While the critical lock aspect ratio (λcrit ) is of order 1 for Boussinesq currents, its value decreases for heavy currents and increases significantly (up to about 20) for light currents. We present a simple analytical model which captures this trend, as well as the observation that for a light current the speed of propagation is proportional to λ1/4 when λ<λcrit
Diffusive author(s), cohesive author: Analysis of S/N (1994)
No full textThis study indicates the ways in which various aspects of the author(s) are brought forth in Dumb type’s performance art, the S/N production. Previous research has suggested a non-hierarchical organization of Dumb type and the absence of a “privileged author” in Dumb type’s collaborative work, S/N. However, the results that I have investigated from member’s interviews on the creative process of S/N along with my analysis of the recorded images of S/N, indicate a different aspect of the author(s). First, S/N was created through, so to speak, the collective ideas of the members of Dumb type. Further, S/N has at least nine quotations from previous performances, installations, and printed writings, besides the work-in-progress technique. Explicating one of the “author functions” as given by Michel Foucault, each text has plural subjects of the author. However, it has been revealed from members’ interviews that Teiji Furuhashi had a decision-making role in selecting the members’ ideas within the performance. Since then, S/N has had plural subjects of creation; however, Furuhashi is one of the subjects of creation along with the “privileged author.” S/N has plural authors (diffusive authors) yet at the same time, it has a “privileged author,” Teiji Furuhashi (cohesive author)
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Study of flow past elliptic and circular cylinders using direct numerical simulation
No full textFlow over elliptic cylinders can be considered prototypical of flow over a range of bluff bodies since the geometry allows one to study the effect of both thickness and angle-of-attack on the flow field. Therefore a careful study of this flow should provide valuable insight into the phenomenon of unsteady separation and the structure of bluff body wakes. With this in mind, a single-domain, spectral collocation technique has been developed to simulate the full three-dimensional incompressible flow over elliptic cylinders. Results of two- and three-dimensional simulations for a range of flow and geometric parameters are presented. The results are compared with available experimental and numerical data and it is found that important quantities like the Strouhal number and lift and drag coefficients match well with established values.It has been known for some time that two-dimensional numerical simulations of flow over nominally two-dimensional bluff bodies at Reynolds numbers for which the flow is intrinsically three-dimensional, lead to inaccurate prediction of the lift and drag forces. The details of the physical mechanisms that ultimately lead to the inaccurate prediction of surface pressure and consequently the lift and drag are still not clear. A detailed investigation has been performed and it is found that the over-prediction of mean drag force in two-dimensional simulations is directly related to higher Reynolds stresses in the wake.The mechanism by which streamwise vortical structures are generated in free-shear flows is not completely understood. Some studies attribute the generation to a core-instability mechanism whereas others attribute it to a braid-instability. The present simulation afford us an opportunity to investigate this issue in detail. For the wake of a circular cylinder, it is observed that streamwise structures are formed in the near wake both due to stretching of core vorticity which escapes out of the core and due to stretching of small scale streamwise vorticity already present outside the core.Made available in DSpace on 2011-05-07T13:33:33Z (GMT). No. of bitstreams: 2
license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5)
9624440.pdf: 8283282 bytes, checksum: 26699ff729b30f92af78e147a0ae0c2f (MD5)
Previous issue date: 1995Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:56:16Z
Item is restricted indefinitely.Restriction data tranferred 2014-07-01T11:26:17-05:00
Original Data
Group with Access UIUC Users [automated]
Release Date: none
Reason: ETDs are only available to UIUC Users without author permissionETDs are only available to UIUC Users without author permissionU of I Onl
Response of the wake of an isolated particle to isotropic turbulent cross-flow
No full textThe interaction of an isolated spherical particle with an isotropic turbulent cross-flow is considered using direct numerical simulations (DNS). The particle Reynolds number is varied from about 50 to 600 and the particle diameter is varied from about 1.5 to 10 times the Kolmogorov scale. The Taylor microscale of the freestream turbulent field considered here is 164. The DNS technique employed here is the first of its kind to address particle–turbulence interaction and it resolves the smallest scales in the freestream turbulent flow and the complex vortical structures in the particle wake. The primary objective of this paper is to present new results on the effect of the freestream turbulence on the particle wake and vortex shedding, and the modulation of freestream turbulence in the particle wake. The parameters of the present simulations are comparable to those of the experimental study by Wu and Faeth (1994a, 1994b), and agreement between the present computational results and the experimental measurement are presented. The effect of freestream turbulence on the mean and instantaneous wake structure is studied. ... [more]is peer reviewedMade available in DSpace on 2007-03-08T21:28:54Z (GMT). No. of bitstreams: 1
1047.pdf: 2751490 bytes, checksum: b7dd1e17f1445db29e82fbedfc37ab63 (MD5)
Previous issue date: 2004-03published or submitted for publicatio
Towards a universal criteria for turbulence suppression in dilute turbidity currents with non-cohesive sediments
No full textTurbidity currents exhibit fascinating physics as their sustained propagation depends on a tight interplay between the suspended sediments and turbulence. If resuspension dominates over deposition the intensity of the flow will increase, while if deposition dominates the flow turbulence can be completely damped inducing rapid settling of sediments and, eventually, flow extinction. This work explores the phenomenon whereby turbulence in a dilute turbidity current with non-cohesive sediments is abruptly extinguished owing to increasedsuspended sediment stratification. Three parameters control the flow dynamics: Reynolds number (Re_t), Richardson number (Ri_t) and sediment settling velocity (V_z). The condition for complete turbulence suppression can be expressed as a critical value for Ri_t V_z. Based on simulations, limited experiments and limited field data, the critical value appears to have a logarithmic dependence on Re_t.Fil: Cantero, Mariano Ignacio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Shringarpure, Mrugesh. University of Florida; Estados UnidosFil: Balachandar, S.. University of Florida; Estados Unido
Effect of turbulence on the drag and lift of a particle
No full textA direct numerical simulation (DNS) is used to study the effect of a freestream isotropic turbulent flow on the drag and lift forces on a spherical particle. The particle diameter is about 1.5 to 10 times the Kolmogorov scale, the particle Reynolds number is about 60 to 600, and the freestream turbulence intensity is about 10 to 25%. It is shown that the freestream turbulence does not have a substantial and systematic effect on the time-averaged mean drag. The standard drag correlation based on the instantaneous or mean slip velocity results in a reasonably accurate prediction of the mean drag obtained from the DNS. However, the accuracy of prediction of the instantaneous drag decreases with increasing particle size. For the smaller particles, the low frequency oscillations in the DNS drag are well captured by the standard drag, but for the larger particles significant differences exist even for the low frequency components. Inclusion of the added-mass and history forces, computed based on the fluid velocity at the center of the particle, does not improve the prediction. Different estimates of the fluid velocity seen by the particle are examined. It is shown that the mean drag is insensitive to the fluid velocity measured at the particle center, or obtained by averaging over a fluid volume of the order of the particle size. The fluctuations diminish as the size of the averaging volume increases. The effect of increasing freestream turbulence intensity for the same particle size is studied. Fluctuations in the drag and lift forces are shown to scale with the mean drag and freestream intensity. The standard drag without the added-mass and history forces provides the best approximation to the DNS result.is peer reviewedMade available in DSpace on 2007-03-08T21:29:10Z (GMT). No. of bitstreams: 1
1009.pdf: 1234933 bytes, checksum: 6991c3fec77416f82cf5c43ae8fe4ff1 (MD5)
Previous issue date: 2002-10published or submitted for publicatio
Control of turbulent transport in supercritical currents by three families of hairpin vortices
No full textWe elucidate the turbulent structure of supercritical gravity currents by means of highly resolved simulations that employ up to a billion grid points. Three families of hairpin vortices dominate the near-bed and interface layers of the current, with their generation mechanisms dictating their shape, orientation, and number density. The interaction of near-bed and lower-interface hairpins explains the weak inviscid lidlike behavior of the streamwise velocity maximum, while the upper-interface vortices are responsible for the substantially lower entrainment compared to turbulent wall jets.Fil: Salinas, Jorge Sebastián. University of Florida; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Balachandar, S.. University of Florida; Estados UnidosFil: Cantero, Mariano Ignacio. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin
- …
