Search results for "Turbulence"
showing 10 items of 378 documents
Turbulence structure and implications in exchange processes in high-amplitude vegetated meanders: Experimental investigation
2018
Aquatic plants in rivers interact with flow and exert an important role in maintaining suitable habitat and ecological equilibrium. Understanding turbulence structure in the presence of vegetation is important with respect to environmental processes, such as sediment transport and mixing of transported quantities. Literature indicates that mass and momentum exchanges in the presence of vegetation are strongly influenced by the sequence of coherent structures which form between vegetated and non-vegetated zones. In the present paper we investigate turbulence structure and coherent motion in high-curvature channels with submerged vegetation. The analysis is performed with the aid of detailed …
Wave dynamics and turbulence in multimode optical systems
2021
The subject of this thesis essentially focuses on the experimental and theoretical study of optical turbulence in different types of nonlinear media. The first part of the manuscript is devoted to the study of thermalization and condensation of optical waves during their propagation in graded-index multimode fibers. The analysis based on the wave turbulence theory reveals that the disorder inherent to light propagation in an optical fiber induces a significant acceleration of the process of optical thermalization, which can clarify the mechanism of certain regimes of spatial beam cleaning recently reported in the literature. We show experimentally that the optical field relaxes during its p…
A Comparison of Direct Numerical Simulation and Turbulence Models for Liquid Metal Free Convection in Volumetrically Heated Enclosures
1999
Asymptotic Analysis of a Slightly Rarefied Gas with Nonlocal Boundary Conditions
2011
In this paper nonlocal boundary conditions for the Navier–Stokes equations are derived, starting from the Boltzmann equation in the limit for the Knudsen number being vanishingly small. In the same spirit of (Lombardo et al. in J. Stat. Phys. 130:69–82, 2008) where a nonlocal Poisson scattering kernel was introduced, a gaussian scattering kernel which models nonlocal interactions between the gas molecules and the wall boundary is proposed. It is proved to satisfy the global mass conservation and a generalized reciprocity relation. The asymptotic expansion of the boundary-value problem for the Boltzmann equation, provides, in the continuum limit, the Navier–Stokes equations associated with a…
Computational and experimental studies of the flow field near the beam entrance window of a liquid metal target
2014
Abstract After the first world liquid metal target has been successfully operated at the SINQ facility at the Paul Scherrer Institut (PSI) for 6 months. The idea of having a reliable target with a bypass flow for cooling the beam entrance window, but with the bypass flow not driven by a separate pump, was examined within the project called LIMETS (Liquid Metal Target for SINQ). In designing of liquid metal targets, turbulence modelling is of high importance due to lack in methods for measuring the spatial distribution of flow and turbulence characteristics. In this study, validation of different turbulence models were performed in water model with hemispherical geometry using particle image…
Hydraulic analysis of EU-DEMO divertor plasma facing components cooling circuit under nominal operating scenarios
2019
Within the framework of the Work Package DIV 1 – “Divertor Cassette Design and Integration” of the EUROfusion action, a research campaign has been jointly carried out by University of Palermo and ENEA to investigate the steady state thermal-hydraulic behaviour of the DEMO divertor cassette cooling circuit, focussing the attention on its Plasma Facing Components (PFCs). The research campaign has been carried out following a theoretical-computational approach based on the Finite Volume Method and adopting the commercial Computational Fluid-Dynamic code ANSYS-CFX. A realistic model of the PFCs cooling circuit has been analysed, specifically embedding each Plasma Facing Unit (PFU) cooling chann…
Effect of a Passive Tuned Mass Damper on Offshore Installation of a Wind Turbine Nacelle
2021
Abstract Although the installation of offshore wind turbines takes place in calm seas, successful mating of wind turbine components can be challenging due to the relative motions between the two mating parts. This work investigates the effect of a passive tuned mass damper on the mating processes of a nacelle for a 10-megawatt (MW) offshore wind turbine. A nacelle with lifting wires and a monopile with a mass damper are respectively modelled using the multibody formulation in the HAWC2 program. A single mass damper is tuned to target at the first natural period of the monopile and is coupled to the main program using a dynamic link library. Afterwards, numerical simulations were carried out…
Turbulence structure and coherent motion in a straight laboratory flume
2012
Evolution of coherent turbulent structures and relation with bed-forms formation in a straight flume
2008
The present paper describes some results of experimental work carried out in a rectilinear flume to investigate the interactions between flow turbulence and sediment motion. The analysis is conducted through the comparison between the periodicity of turbulent structures evolving along the channel and the wavelength of bed forms (alternate bars) forming on the bed. The occurrence of turbulent events (inward interaction, ejection, sweep and burst) has been verified through the conditioned quadrant analysis. The quantitative information about the spatial and temporal scale of the events has been obtained through the space-time correlations of the conditioned data. The analysis essentially high…
Experimental investigation of the evolution of secondary motion in a large amplitude meandering flume
2008
The development of secondary motion along open-channel bends strongly affects the bed deformation and the channel plane evolution. Recent experimental results obtained at the apex section of a large amplitude meandering flume have confirmed that besides the main central circulation cell a second counter-rotating cell develops near the free surface of the outer bank. In the light of such results, in this work the attention is devoted to the analysis of the evolution of the observed secondary motion along whole bend. The analysis is conducted on the basis of flow velocity data collected in five transversal sections along half wave-length of the same large amplitude meandering flume.