1,721,219 research outputs found
Protezione Contro i Fulmini : Valutazione del Rischio di Fulminazione e Protezione di Edifici e Strutture
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Exploitation of animal waste for electricity generation: an application to the Puglia Region (Italy)
No full textMechanisms for Selective Radial Dispersion of Microparticles in the Transitional Region of a Confined Turbulent Round Jet
No full textThe dispersion of particles of different diameters in a confined turbulent round jet is dominated by the local interactions between dispersed phase and large-scale, time dependent flow structures which populate the near-field of the jet. In this work, we address first the problem of identifying the flow structures which form in a three-dimensional, turbulent confined round jet, considering also the influence of the solid walls. Second, we examine particle dispersion specifically focusing on their preferential distribution. The three-dimensional, time dependent flow field is calculated using a finite-difference LES solver of the Navier-Stokes equations in a cylindrical reference frame, whereas the dispersion of particles is computed using a one-way coupling Lagrangian approach. The flow field is characterized by mutually interacting, transitional structures of different temporal and spatial scales. We investigate the behavior of particles, in turn characterized by different size and time-scales, with the object of examining their selective response to the various scales of the flow. Our analyses confirm that multiple organized structures grow up following different types of instability, and successively interact, creating the conditions for the developing of a three-dimensional vorticity field downstream the near-field of the jet. We show that the vortical structures interact selectively with the different size particles, producing different distribution patterns and dispersion rates qualitatively depending on the particle-to-fluid Stokes number. Following the model proposed previously, we complete the description of the particle dispersion mechanism based on the action of the large spanwise vortices, evidencing the effect of the secondary structures (ribs) on the smaller particles. We characterize the different distribution pattern of particle swarms and we analyze from a qualitative viewpoint particle dispersion behavior with the dynamics of the different transitional structures providing guidelines for dispersion control
Turbulent Flow and Dispersion of Inertial Particles in a Confined Jet Issued by a Long Cylindrical Pipe
No full textIn this work we examine first the flow field of a confined jet produced by a turbulent flow in a long cylindrical pipe issuing in an abrupt angle diffuser. Second, we examine the dispersion of inertial micro-particles entrained by the turbulent flow. Specifically, we examine how the particle dispersion field evolves in the multiscale flow generated by the interactions between the large-scale structures, which are geometry dependent, with the smaller turbulent scales issued by the pipe which are advected downstream. We use Large-Eddy-Simulation (LES) for the flow field and Lagrangian tracking for particle dispersion. The complex shape of the domain is modelled using the immersed-boundaries method. Fully developed turbulence inlet conditions are derived from an independent LES of a spatially periodic cylindrical pipe flow. The flow field is analyzed in terms of local velocity signals to determine spatial coherence and decay rate of the coherent KH vortices and to make quantitative comparisons with experimental data on free jets. Particle dispersion is analyzed in terms of statistical quantities and also with reference to the dynamics of the coherent structures. Results show that the particle dynamics is initially dominated by the KelvinHelmholtz (KH) rolls which form at the expansion and only eventually by the advected smaller turbulence scales
Time dependent fluid dynamics and Lagrangian tracking to model mixing in Rushton-impeller baffled-tank reactor
No full textThe object of this work is to investigate the role of large-scale convective structures in promoting mixing in a stirred tank. We focus on a standard geometry (uid particles. The three-dimensional, time-dependent, fully developed flow field is calculated with a computationally effcient procedure using a RANS solver with k–epsilon turbulence modeling and the $ow 8eld is assessed precisely against experimental data. Then, fluid parcels are tracked in the calculated flow field. Analyzing the trajectory of fluid parcels, the segregated regions within the flow are identified and mixing indicators are calculated (mixing time, circulation length and sojour
time distribution). A physical explanation is thus proposed to establish a link between large-scale mixing and complex fluid dynamics generated by the interactions of radial-discharge jet, ring vortices, and upper counter rotating vortex
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