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  • Turbulence
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  • 1
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    KIT Scientific Publishing | KIT Scientific Publishing
    Publication Date: 2024-04-11
    Description: The transport of bacteria in turbulent river-like environments is addressed, where bacterial populations are frequently encountered attached to solids. This transport mode is investigated by studying the transient settling of heavy particles in turbulent channel flows featuring sediment beds. A numerical method is used to fully resolve turbulence and finite-size particles, which enables the assessment of the complex interplay between flow structures, suspended solids and river sediment.
    Keywords: Aquatic pollution ; Exact coherent structures ; Particle-laden flows ; Gewässerverschmutzung ; Exakte kohärente Strukturen ; Partikelströmungen ; Turbulence ; Sedimentation ; Turbulenz ; thema EDItEUR::T Technology, Engineering, Agriculture, Industrial processes::TN Civil engineering, surveying and building
    Language: English
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  • 2
    Publication Date: 2024-04-11
    Description: Soot formation in a laminar and a turbulent diffusion flame as well as the formation of iron oxide nanoparticles in an iron pentacarbonyl doped near stoichiometric H?/O?/Ar-premixed flame have been investigated numerically. The particular modus operandi of the simulated test cases is described. In the case of the turbulent flame the impact of the turbulent closure of the single particle source terms on particle size distribution is shown.
    Keywords: TP155-156 ; CFD ; Nanoparticles ; Turbulence ; reactive flows ; stochastic modelling ; Turbulenz ; stochastische Modellierung ; Nanopartikel ; reaktive Strömungen ; thema EDItEUR::T Technology, Engineering, Agriculture, Industrial processes::TC Biochemical engineering::TCB Biotechnology
    Language: German
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  • 3
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    Springer Nature | Springer International Publishing
    Publication Date: 2024-04-11
    Description: This open access book allows the reader to grasp the main bulk of fluid flow problems at a brisk pace. Starting with the basic concepts of conservation laws developed using continuum mechanics, the incompressibility of a fluid is explained and modeled, leading to the famous Navier-Stokes equation that governs the dynamics of fluids. Some exact solutions for transient and steady-state cases in Cartesian and axisymmetric coordinates are proposed. A particular set of examples is associated with creeping or Stokes flows, where viscosity is the dominant physical phenomenon. Irrotational flows are treated by introducing complex variables. The use of the conformal mapping and the Joukowski transformation allows the treatment of the flow around an airfoil. The boundary layer theory corrects the earlier approach with the Prandtl equations, their solution for the case of a flat plate, and the von Karman integral equation. The instability of fluid flows is studied for parallel flows using the Orr-Sommerfeld equation. The stability of a circular Couette flow is also described. The book ends with the modeling of turbulence by the Reynolds-averaged Navier-Stokes equations and large-eddy simulations. Each chapter includes useful practice problems and their solutions. The book is useful for engineers, physicists, and scientists interested in the fascinating field of fluid mechanics.
    Keywords: Incompressible fluid mechanics ; Navier-Stokes Equations ; Plane Irrotational Flows ; Turbulence ; Instability ; thema EDItEUR::T Technology, Engineering, Agriculture, Industrial processes::TG Mechanical engineering and materials::TGB Mechanical engineering ; thema EDItEUR::T Technology, Engineering, Agriculture, Industrial processes::TG Mechanical engineering and materials::TGM Materials science::TGMF Engineering: Mechanics of fluids
    Language: English
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  • 4
    Publication Date: 2021-03-10
    Description: In the framework of space weather, the understanding of the physical mechanisms responsible for the generation of ionospheric irregularities is particularly relevant for their effects on global positioning and communication systems. Ionospheric equatorial plasma bubbles are one of the possible irregularities. In this work, using data from the ESA Swarm mission, we investigate the scaling features of electron density fluctuations characterizing equatorial plasma bubbles. Results strongly support a turbulence character of these structures and suggest the existence of a clear link between the observed scaling properties and the value of the Rate Of change of electron Density Index (RODI). This link is discussed, and RODI is proposed as a reliable proxy for the identification of plasma bubbles.
    Description: This research received financial support from European Space Agency (ESA contract N. 4000125663/18/I-NB-“EO Science for Society Permanently Open Call for Proposals EOEP-5 BLOCK4” (INTENS)) and from the Italian MIUR-PRIN grant 2017APKP7T on “Circumterrestrial Environment: Impact of Sun–Earth Interaction”.
    Description: Published
    Description: 759
    Description: 2A. Fisica dell'alta atmosfera
    Description: JCR Journal
    Keywords: Turbulence ; Electron density irregularities ; Equatorial topside ionosphere ; Swarm constellation ; 01.02. Ionosphere
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
    Publication Date: 2021-05-12
    Description: The present work focuses on the analysis of the scaling features of electron density fluctuations in the mid- and high-latitude topside ionosphere under different conditions of geomagnetic activity. The aim is to understand whether it is possible to identify a proxy that may provide information on the properties of electron density fluctuations and on the possible physical mechanisms at their origin, as for instance, turbulence phenomena. So, we selected about 4 years (April 2014–February 2018) of 1 Hz electron density measurements recorded on-board ESA Swarm A satellite. Using the Auroral Electrojet (AE) index, we identified two different geomagnetic conditions: quiet (AE 〈 50 nT) and active (AE 〉 300 nT). For both datasets, we evaluated the first- and second-order scaling exponents and an intermittency coefficient associated with the electron density fluctuations. Then, the joint probability distribution between each of these quantities and the rate of change of electron density index was also evaluated. We identified two families of plasma density fluctuations characterized by different mean values of both the scaling exponents and the considered ionospheric index, suggesting that different mechanisms (instabilities/turbulent processes) can be responsible for the observed scaling features. Furthermore, a clear different localization of the two families in the magnetic latitude— magnetic local time plane is found and its dependence on geomagnetic activity levels is analyzed. These results may well have a bearing about the capability of recognizing the turbulent character of irregularities using a typical ionospheric plasma irregularity index as a proxy
    Description: Published
    Description: 6183
    Description: 2A. Fisica dell'alta atmosfera
    Description: JCR Journal
    Keywords: Turbulence ; High-latitude ionosphere ; electron density fluctuations ; Swarm constellation ; 01.02. Ionosphere
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 6
    Publication Date: 2021-05-12
    Description: We investigated the average polar patterns of ionospheric electron density and the corresponding patterns of scaling features as a function of interplanetary magnetic field orientation. The focus is on the Northern Hemisphere using electron density data recorded on-board ESA Swarm A satellite. The first- and second-order scaling exponents have been evaluated by means of the -order structure functions. We used electron density measurements over a period of 15 months from April 1, 2014 to June 30, 2015, which corresponds to the maximum of solar cycle 24 and which is characterized by an average value of the solar radio flux (F10.7) index equal to (140+/- 30) sfu. Electron density, first- and second-order scaling exponents have been mapped and discussed for four main IMF orientations provided by Bx and By components under conditions of high solar activity. Large spatial changes of the second-order scaling exponent pattern are observed with a steepening of the associated spectral exponent in correspondence with the nightside polar cap trailing edge. Intermittency, defined as the departure from linearity of the dependence of scaling exponents on moment order q, is also evaluated finding that it is generally higher near the equatorward boundary of the auroral oval than elsewhere. On the whole, the found patterns of the electron density first- and second-order scaling exponents suggest the occurrence of turbulence at the high latitudes.
    Description: Published
    Description: 105531
    Description: 2A. Fisica dell'alta atmosfera
    Description: JCR Journal
    Keywords: Polar ionosphere ; Turbulence ; Scaling feature ; Space weather ; Swarm satellite ; electron density ; 01.02. Ionosphere ; 01.03. Magnetosphere
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 7
    Publication Date: 2021-05-31
    Description: In the polar ionosphere, the electric field is characterized by broadband and power law spectral densities at small/short spatio-temporal scales, which support a possible turbulent nature of the electric field fluctuations. Here, we investigate the multifractal character of the full three-dimensional electric field in the polar ionosphere as recorded on board the first Chinese Seismo- Electromagnetic Satellite (CSES-01). The results of our analysis prove a clear different degree of multifractality of the electric field fluctuations approaching either the polar cap trailing edge or the auroral region. The observed differences in the multifractal character are interpreted in terms of the different natures of the particle precipitation in the polar cap and in the auroral region. A possible link between the multifractal nature of electric field fluctuations, parallel to the geomagnetic field, and filamentation of field aligned currents (FACs) is established
    Description: Contract ASI “LIMADOU Scienza+” n 2020-31-HH.0 PNRA18 00289-A “Space weather in Polar Ionosphere: the Role of Turbulence”.
    Description: Published
    Description: 646
    Description: 2A. Fisica dell'alta atmosfera
    Description: JCR Journal
    Keywords: auroral ionosphere ; electric field ; Turbulence ; Fractals ; 01.02. Ionosphere
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 8
    Publication Date: 2018-04-12
    Description: This paper attempts to explore the statistical scaling features of high-latitude geomagnetic field fluctuations at Swarm altitude. Data for this study are low-resolution (1 Hz) magnetic data recorded by the vector field magnetometer on board Swarm A satellite over 1 year (from 15 April 2014 to 15 April 2015). The first- and second-order structure function scaling exponents and the degree of intermittency of the fluctuations of the intensity of the horizontal component of the magnetic field at high northern latitudes have been evaluated for different interplanetary magnetic field orientations in the GSM Y-Z plane and seasons. In the case of the first-order structure function scaling exponent, a comparison between the average spatial distributions of the obtained values and the statistical convection patterns obtained using a Super Dual Auroral Radar Network dynamic model (CS10 model) has been also considered. The obtained results support the idea that the knowledge of the scaling features of the geomagnetic field fluctuations can help in the characterization of the different ionospheric turbulence regimes of the medium crossed by Swarm A satellite. This study shows that different turbulent regimes of the geomagnetic field fluctuations exist in the regions characterized by a double-cell convection pattern and in those regions near the border of the convective structures.
    Description: Published
    Description: 10548-10562
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Keywords: Turbulence ; geomagnetic field ; High-latitude ; F-region ; 05.07. Space and Planetary sciences ; 01.02. Ionosphere ; 04.05. Geomagnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 9
    Publication Date: 2022-04-22
    Description: The recent Chinese Seismo-Electromagnetic Satellite (CSES-01) provides a good opportunity to investigate some features of plasma properties and its motion in the topside ionosphere. Using simultaneous measurements from the electric field detector and the magnetometers onboard CSES-01, we investigate some properties of the plasma ExB drift velocity for a case study during a crossing of the Southern auroral region in the topside ionosphere. In detail, we analyze the spectral and scaling features of the plasma drift velocity and provide evidence of the turbulent character of the ExB drift. Our results provide an evidence of the occurrence of 2D ExB intermittent convective turbulence for the plasma motion in the topside ionospheric F2 auroral region at scales from tens of meters to tens of kilometers. The intermittent character of the observed turbulence suggests that the macro-scale intermittent structure is isomorphic with a quasi-1D fractal structure, as happens, for example, in the case of a filamentary or thin-tube-like structure. Furthermore, in the analyzed range of scales we found that both magnetohydrodynamic and kinetic processes may affect the plasma dynamics at spatial scales below 2 km. The results are discussed and compared with previous results reported in the literature.
    Description: Published
    Description: 1936
    Description: 2A. Fisica dell'alta atmosfera
    Description: JCR Journal
    Keywords: Turbulence ; Auroral ionosphere ; ExB plasma motion ; 01.02. Ionosphere
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 10
    Publication Date: 2022-05-25
    Description: Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 52 (2005): 1218-1219, doi:10.1016/j.dsr2.2005.03.003.
    Description: This is our response to a comment by Walter Eifler on our paper `A simple model for the short-time evolution of near-surface current and temperature profiles' (arXiv:physics/0503186, accepted for publication in Deep-Sea Research II ). Although Eifler raises genuine issues regarding our model's validity and applicability, we are nevertheless of the opinion that it is of value for the short-term evolution of the upper-ocean profiles of current and temperature. The fact that the effective eddy viscosity tends to infinity for infinite time under a steady wind stress may not be surprising. It can be interpreted as a vertical shift of the eddy viscosity profile and an increase in the size of the dominant turbulent eddies under the assumed conditions of small stratification and infinite water depth.
    Description: The work was funded by Research Council of Norway projects 127872/720 and 155923/700.
    Keywords: Temperature ; Current ; Turbulence ; Sea surface ; Mathematical modelling ; Profiling instrument
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Format: 85649 bytes
    Format: application/pdf
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