The Dynamics Of An Axisymmetric Turbulent Jet And Of A Passive Scalar Patch In Ambient Turbulence Interpreted From The Passive Scalar Field Statistics
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The Dynamics Of An Axisymmetric Turbulent Jet And Of A Passive Scalar Patch In Ambient Turbulence Interpreted From The Passive Scalar Field Statistics
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Author : Rana Sahebjam
language : en
Publisher:
Release Date : 2022
The Dynamics Of An Axisymmetric Turbulent Jet And Of A Passive Scalar Patch In Ambient Turbulence Interpreted From The Passive Scalar Field Statistics written by Rana Sahebjam and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2022 with categories.
"The passive scalar field of an axisymmetric turbulent jet and an isokinetic jet in an approximately homogeneous isotropic turbulence (HIT) with negligible mean flow is studied experimentally. The present research builds on that of Khorsandi et al. 2013 and Perez-Alvarado 2016, who studied the velocity field and the passive scalar field of an axisymmetric turbulent jet in a turbulent ambient, respectively. The primary objective is to deduce the jet structure, and to study the jet mixing in the HIT ambient by following the meandering path of the jet, i.e. conditional on the jet centroid. The secondary objective, complementing the first, is to study the diffusion of a momentumless patch of a passive scalar in the HIT ambient.The effect of a turbulent ambient on the dynamics and mixing of the passive scalar field of an axisymmetric turbulent jet is investigated. The experiments were conducted either in a quiescent or a turbulent ambient. The turbulent ambient was generated by a random jet array to achieve an approximately zero-mean-flow HIT ambient in the measurement plane. Two jet Reynolds numbers of Re = 5800 and 10600 were studied. Planar laser-induced fluorescence was used to measure the concentrations of the passive scalar dye (Sc = 2000) at orthogonal cross-sections of the jet at axial distances of x/d = 20, 30, 40, 50, 60. The statistics of the passive scalar field were conditioned on the jet centroid and were compared to the Eulerian statistics and to those of the jet in a quiescent ambient. The use of the centroidal analysis allowed the structure of the jet in the HIT ambient to be deduced, for which a two-region model was proposed. In the first region, following the developing region of the jet, the ambient turbulence progressively disrupts the jet structure and results in a faster concentration decay compared to the quiescent ambient. At a critical downstream distance, where the relative turbulence intensity between the ambient and the jet (ξ = urms,HIT/ urms,jet ) exceeds 0.5, the HIT ambient has destroyed the jet structure and the second region starts. In the second region, the turbulent diffusion is the only mechanism to transport the passive scalar field. The first-order centroidal statistics of the scalar field show self-similarity and self-preservation before jet break-up. The width of the jet is larger in the HIT ambient compared to that in a quiescent ambient and grows with axial distance but remains unchanged beyond jet break-up. Using the present passive scalar data and the velocity data from Khorsandi et al. 2013, it is argued that the momentum-driven entrainment of the jet in the HIT ambient is reduced compared to that in a quiescent ambient, and that the entrainment ceases beyond the jet break-up. The entrainment of the smaller scales of the ambient turbulence leads to a wider range of centerline concentrations and rms concentrations within the jet, and they are hypothesized to increase local concentration gradients and reduce the jet mixing.Diffusion of a patch of a passive scalar in the HIT ambient is studied. A high-Sc number passive scalar dye (Sc = 2500) is released isokinetically from a large diameter jet (d = 29.97 mm), and an orthogonal view of the passive scalar field is obtained using planar laser-induced fluorescence. The temporal evolution of the scalar patch is due to molecular diffusion and to turbulent diffusion in a quiescent ambient and in the HIT ambient, respectively. Time-averaged statistics of the passive scalar field are assessed at t = 0.2, 1, 1.8, 2.6, 3.4 s using a centroidal analysis. The mean concentration decays quickly and the rms concentration increases within the scalar patch. Compared to the quiescent ambient case, a wider range of the concentrations is present at the centroid of the scalar field. The size of the scalar patch increases with time, which is attributed to an increasing turbulent diffusivity for times shorter than the integral time scale of the turbulence"--
Effect Of Background Turbulence On The Scalar Field Of A Turbulent Jet
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Author : Alejandro Perez Alvarado
language : en
Publisher:
Release Date : 2016
Effect Of Background Turbulence On The Scalar Field Of A Turbulent Jet written by Alejandro Perez Alvarado and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with categories.
"The effect of background turbulence on the scalar field of an axisymmetric turbulent jet is investigated experimentally. The present investigation builds on the work of Gaskin et al. (2004), who studied the concentration and velocity fields of a plane jet in a shallow coflow with different turbulence levels and Khorsandi et al. (2013), who studied the velocity field of an axisymmetric turbulent jet emitted into a turbulent background. Different driving algorithms for a large RJA were tested and the statistics of the turbulence generated downstream of the RJA were compared to characterize the algorithms' performance. Variations in the spatial configuration of jets operating at any given instant, as well as in the statistics of their on/off times were studied. The algorithm identified as RANDOM generated the closest approximation of zero-mean-flow homogeneous isotropic turbulence. The flow generated by the RANDOM algorithm had a relatively high turbulent Reynolds number (ReT = uTl/[nu] = 2360, where uT is a characteristic RMS velocity, l is the integral length scale of the flow, [nu] is the kinematic viscosity of the water) and the integral length scale (l = 11.6 cm) is the largest reported to date. Thus, RANDOM algorithm was used to generate the background turbulence for the investigation of scalar mixing within a turbulent jet.The effect of background turbulence on the mixing of a passive scalar within a turbulent jet at different Reynolds numbers was investigated. To this end, planar laser-induced fluorescence was employed to obtain concentration measurements of dye (disodium fluorescein, Schmidt number = 2000) within the jet. Two jet Reynolds numbers (Re=UjD/[nu], where Uj is the jet exit velocity, D is the nozzle diameter and [nu] is the kinematic viscosity of the jet fluid, water) were studied: 10600 and 5800. The resulting statistics of the scalar fields showed that the mean concentrations of jets emitted into turbulent backgrounds were lower than those of jets emitted into a quiescent background near the centerline. However, near the edges of the jet (r/x>0.15), the concentrations were higher for the jets issued into turbulent surroundings. The RMS concentrations of the jet emitted into a turbulent background significantly increased. Examination of the probability density functions of concentration revealed a higher degree of intermittency of the scalar field. The probability of low concentrations increased in the presence of background turbulence although the maximum concentrations were comparable to those of the jet emitted into a quiescent background. Flow visualizations revealed meandering of the jet issued into background turbulence, which is associated with the increased probability of lower concentrations and higher intermittency. Additionally, the widths of the jets emitted into a turbulent background were increased. For the lower jet Reynolds number, the described effects were more evident and the jet structure was destroyed by the background turbulence within the measurement region, resulting in flat radial profiles of both the mean and RMS concentrations. Comparison of the results of the scalar field with those of the hydrodynamic jet of Khorsandi et al. (2013) revealed a similar behavior of the two fields. However, the most significant difference was the larger radial extent of the profiles of mean and RMS concentrations, which resulted from the meandering of the jet and increased transport of scalar by turbulent diffusion. The flow visualizations suggest that the entrainment and mixing in the jet in a turbulent background changes with the destruction of jet structure, from jet driven entrainment to become potentially dominated by i) increased lateral advection of the jet by large scales of the background turbulence during the meandering of the jet, which is subsequently mixed by its smaller scales, and ii) turbulent diffusion that is significantly enhanced by the turbulent background." --
Mixing Of A Passive Scalar In Isotropic And Sheared Homogeneous Turbulence
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Author : E. Shirani
language : en
Publisher:
Release Date : 1981
Mixing Of A Passive Scalar In Isotropic And Sheared Homogeneous Turbulence written by E. Shirani and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1981 with categories.
In order to calculate the velocity and passive scalar fields in homogeneous turbulent flows, the three-dimensional, time-dependent equations of motion and the diffusion equation have been solved numerically.
The Structure And Dynamics Of The Vorticity And Passive Scalar Fields At Small Scales In Homogeneous Isotropic Turbulence
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Author : Gregory R. Ruetsch
language : en
Publisher:
Release Date : 1992
The Structure And Dynamics Of The Vorticity And Passive Scalar Fields At Small Scales In Homogeneous Isotropic Turbulence written by Gregory R. Ruetsch and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1992 with categories.
Simulation Of The Mixing Of A Passive Scalar In A Free Round Turbulent Jet
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Author : C.L. Lubbers
language : en
Publisher:
Release Date : 1997
Simulation Of The Mixing Of A Passive Scalar In A Free Round Turbulent Jet written by C.L. Lubbers and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1997 with categories.
Examining The Effects Of A Controled Turbulent Velocity Field On A Passive Scalar
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Author : Don O'Regan
language : en
Publisher:
Release Date : 2005
Examining The Effects Of A Controled Turbulent Velocity Field On A Passive Scalar written by Don O'Regan and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2005 with Turbulence categories.
Aspects Of Geometrical Statistics In Turbulence
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Author : Silvio Di Savino
language : en
Publisher:
Release Date : 2014
Aspects Of Geometrical Statistics In Turbulence written by Silvio Di Savino and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014 with categories.
Experiments On Passive Scalar Mixing In Turbulent Flows With Different Velocity And Scalar Field Boundary Conditions
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Author : Jason Lepore
language : en
Publisher:
Release Date : 2013
Experiments On Passive Scalar Mixing In Turbulent Flows With Different Velocity And Scalar Field Boundary Conditions written by Jason Lepore and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with categories.
The findings suggest that both the mean flow shear and turbulence intensity of the velocity field play an important role in determining the mixedness of the scalar field." --
Recent Research Advances In The Fluid Mechanics Of Turbulent Jets And Plumes
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Author : P.A. Davies
language : en
Publisher: Springer Science & Business Media
Release Date : 2012-12-06
Recent Research Advances In The Fluid Mechanics Of Turbulent Jets And Plumes written by P.A. Davies and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012-12-06 with Science categories.
Challenging problems involvrllg jet and plume phenomena are common to many areas of fundamental and applied scientific research, and an understanding of plume and jet behaviour is essential in many geophysical and industrial contexts. For example, in the field of meteorology, where pollutant dispersal takes place by means of atmospheric jets and plumes formed either naturally under conditions of convectively-driven flow in the atmospheric boundary layer, or anthropogenically by the release of pollutants from tall chimneys. In other fields of geophysics, buoyant plumes and jets are known to play important roles in oceanic mixing processes, both at the relatively large scale (as in deep water formation by convective sinking) and at the relatively small scale (as with plume formation beneath ice leads, for example). In the industrial context, the performances of many engineering systems are determined primarily by the behaviour of buoyant plumes and jets. For example, (i) in sea outfalls, where either sewage or thermal effluents are discharged into marine and/or freshwater environments, (ii) in solar ponds, where buoyant jets are released under density interfaces, (iii) in buildings, where thermally-generated plumes affect the air quality and ventilation properties of architectural environments, (iv) in rotating machinery where fluid jet~ are used for cooling purposes, and (v) in long road and rail tunnels, where safety and ventilation prcedures rely upon an understanding of the behaviour of buoyant jets. In many other engineering and oceanographic contexts, the properties of jets and plumes are of great importance.
Turbulent Jets And Plumes
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Author : Joseph Hun-wei Lee
language : en
Publisher: Springer Science & Business Media
Release Date : 2012-12-06
Turbulent Jets And Plumes written by Joseph Hun-wei Lee and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012-12-06 with Science categories.
Jets and plumes are shear flows produced by momentum and buoyancy forces. Examples include smokestack emissions, fires and volcano eruptions, deep sea vents, thermals, sewage discharges, thermal effluents from power stations, and ocean dumping of sludge. Knowledge of turbulent mixing by jets and plumes is important for environmental control, impact and risk assessment. Turbulent Jets and Plumes introduces the fundamental concepts and develops a Lagrangian approach to model these shear flows. This theme persists throughout the text, starting from simple cases and building towards the practically important case of a turbulent buoyant jet in a density-stratified crossflow. Basic ideas are illustrated by ample use of flow visualization using the laser-induced fluorescence technique. The text includes many illustrative worked examples, comparisons of model predictions with laboratory and field data, and classroom tested problems. An interactive PC-based virtual-reality modelling software (VISJET) is also provided. Engineering and science students, researchers and practitioners may use the book both as an introduction to the subject and as a reference in hydraulics and environmental fluid mechanics.