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16 results on '"Steiros, K."'

1. Self-regulating turbulence

Author

Steiros, K.

Subjects
Physics - Fluid Dynamics
Abstract

A landmark of out-of-equilibrium physics is Kolmogorov's phenomenological theory of turbulence. However, the past 20 years have provided evidence of a new, universal type of turbulence cascade, which does not abide to Kolmogorov physics. To address this issue, we revise the classical Kolmogorov cascade, by superimposing on it a mechanism of active information exchange between large and small scales. The new theory yields predictions for the dissipation rate, integral length scale and turbulence kinetic energy, as well as a criterion for the transition of the system from the new, to the classical physics in decaying turbulence. The assumptions and predictions are validated using large-scale simulations and data from the literature., Comment: 10 pages, 8 figures

Published
2021

2. Recirculation regions in wakes with base bleed

Author

Steiros, K, Bempedelis, N, and Ding, L

Subjects
Physics - Fluid Dynamics
Abstract

The appearance of detached recirculation regions in wakes with base bleed determines the aerodynamic properties of many natural organisms and technological applications. In this work we introduce an analytical model which captures certain key dimensions of the recirculation region in the wake of porous plates of infinite aspect ratio, along with the porosity range \ks{over which} it exists, when vortex shedding is absent or suppressed. The model is used to interpret why the recirculation region (i) emerges, (ii) migrates away from the body with increasing base bleed, (iii) disappears at a critical bleed and (iv) is partially insensitive to variations in the Reynolds number. The model predictions show considerable agreement with data from laboratory experiments and numerical simulations. exists. The predictions show considerable agreement with data from laboratory experiments and numerical simulations., Comment: 12 pages, 9 figures

Published
2020
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3. Turbulent shear flow without vortex shedding, Reynolds shear stress and small-scale intermittency.

Author

Steiros, K., Obligado, M., Bragança, P., Cuvier, C., and Vassilicos, J.C.

Subjects
COHERENT structures, TURBULENT shear flow, REYNOLDS stress, PARTICLE image velocimetry, PROPER orthogonal decomposition
Abstract

This work presents an experimental investigation of the effects of vortex shedding suppression on the properties and recovery of turbulent wakes. Four plates, properly modified so that they produce different vortex shedding strengths, are tested using high speed particle image velocimetry and hot-wire anemometry, and analysed using spectral proper orthogonal decomposition, mean-flow linear stability analysis and various turbulence statistics. When present, vortex shedding is found to exhibit a characteristic frequency that scales with the mean shear, providing a link between the mean flow and the main turbulent motion. To achieve full suppression of shedding, we combine the effects of porosity and fractal perimeter. The mean shear is then decreased to the point where the flow becomes convectively unstable and shedding vanishes. In that case, the onset of self-similarity is delayed, compared with the case with vortex shedding, and appears after another large-scale structure, the secondary vortex street, emerges. It is also found that both large- and small-scale intermittency are starkly reduced when shedding is absent. A simple theoretical representation of the wake dynamics explains the evolution of the wake properties and its connection to the coherent structures in the flow. [ABSTRACT FROM AUTHOR]

Published
2025
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13. Local velocity measurements in the Shrek experiment at high reynolds number

Author

Christophe Baudet, Michel Bon-Mardion, Patrick Bonnay, Braslau, A., Bernard Castaing, Francesca Chillà, Laurent Chevillard, François Daviaud, Pantxo Diribarne, Bérengère Dubrulle, Davide Durì, Davide Faranda, Basile Gallet, Mathieu Gibert, Alain Girard, Bernard Hébral, Thierry Lehner, Moukharski, I., Jean-Paul Moro, Philippe-Emmanuel Roche, Bernard Rousset, Eléonore Rusaouën, Saint-Michel, B., Julien Salort, E-W, Saw, Steiros, K., Wiertel-Gasquet, C., Laboratoire des Écoulements Géophysiques et Industriels [Grenoble] (LEGI), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS), Service des Basses Températures (SBT ), Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut de Recherche Interdisciplinaire de Grenoble (IRIG), Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Systèmes Physiques Hors-équilibre, hYdrodynamique, éNergie et compleXes (SPHYNX), Service de physique de l'état condensé (SPEC - UMR3680), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Institut Rayonnement Matière de Saclay (IRAMIS), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, Laboratoire de Physique de l'ENS Lyon (Phys-ENS), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS), Hélium : du fondamental aux applications (NEEL - HELFA), Institut Néel (NEEL), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS), Laboratoire Univers et Théories (LUTH (UMR_8102)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Service de Thermo-hydraulique et de Mécanique des Fluides (STMF), Département de Modélisation des Systèmes et Structures (DM2S), CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Delft University of Technology (TU DELFT), Delft University of Technology, ANR-09-BLAN-0094,SHREK,Superfluide à Haut Reynolds en Ecoulement de von Karman(2009), European Project: 312778,EC:FP7:INFRA,FP7-INFRASTRUCTURES-2012-1,EUHIT(2013), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA), Université Grenoble Alpes (UGA)-Institut de Recherche Interdisciplinaire de Grenoble (IRIG), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), HELFA - Hélium : du fondamental aux applications, Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF), PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), CEA-Direction de l'Energie Nucléaire (CEA-DEN), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-CEA-Direction de l'Energie Nucléaire (CEA-DEN), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF), École normale supérieure - Lyon (ENS Lyon)-Centre National de la Recherche Scientifique (CNRS)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon, Hélium : du fondamental aux applications (HELFA), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7), GIRARD, Dominique, Blanc - Superfluide à Haut Reynolds en Ecoulement de von Karman - - SHREK2009 - ANR-09-BLAN-0094 - Blanc - VALID, and European High-performance Infrastructures in Turbulence - EUHIT - - EC:FP7:INFRA2013-04-01 - 2017-03-31 - 312778 - VALID

Subjects
[PHYS]Physics [physics], [PHYS] Physics [physics]
Abstract

International audience; We report preliminary results obtained using new local velocity probes in the Superfluid Helium high REynold number von Kármán flow (SHREK) experiment for different forcing conditions. The presentation will focus on the validation of the signals obtained from a hot-wire and a total head pressure tube in both normal and superfluid phases of liquid helium.

Published
2015

15. Power consumption and form drag of regular and fractal-shaped turbines in a stirred tank.

Author

Steiros, K., Bruce, P. J. K., Buxton, O. R. H., and Vassilicos, J. C.

Subjects
ENERGY consumption, TURBINES, WIND tunnels, HYDRAULIC machinery, FRACTAL analysis, FLUID dynamics
Abstract

Previous wind-tunnel measurements have shown that fractal-shaped plates have increased drag compared to square plates of the same area. In this study, the power consumption and drag of turbines with fractal and rectangular blades in a stirred tank are measured. Power number decreases from rectangular to fractal impellers by over 10%, increasingly so with fractal iteration number. Our results suggest that this decrease is not caused by the wake interaction of the blades, nor solely by the wake interaction with the walls either. Pressure measurements on the blades' surface show that fractal blades have lower drag than the rectangular ones, opposite to the wind tunnel experiment results. All tested blades' center of pressure radius increases with Re, while their drag coefficient decreases, a possible effect of the solid body rotation expansion with Re. Spectral analysis of the pressure signal reveals two peaks possibly connected to the blades' roll vortices. © 2016 American Institute of Chemical Engineers AIChE J, 63: 843-854, 2017 [ABSTRACT FROM AUTHOR]

Published
2017
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16. Balanced nonstationary turbulence.

Author

Steiros K

Abstract

Kolmogorov's 1941 (K41) framework remains central to the understanding of turbulent flows. However, in unsteady turbulence, K41's critical equilibrium assumption is expected to hold in an asymptotic manner, as the Reynolds number and wave numbers tend to infinity, rendering K41 not strictly valid at finite wave numbers. This work proposes a generalization of K41 for out-of-equilibrium effects and cascades far from initial conditions. The main result is a correction to the -5/3 law for out-of-equilibrium eddies, unrelated to intermittency effects. Experimental and numerical evidence is provided in support of the theoretical results.

Published
2022
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