Download or read book Observations of Entrainment Processes in Axisymmetric Turbulent Jets written by Claude Strope and published by . This book was released on 1992 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Investigations on the Turbulent Entrainment Process in an Axisymmetric Jet written by Marc Wolf and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Entrainment Processes for a Jet in Cross Flow written by and published by . This book was released on 2020 with total page 193 pages. Available in PDF, EPUB and Kindle. Book excerpt: A jet in cross flow (JICF) is examined experimentally by injecting a stream of air into crossing fluid with an aim into quantifying entrainment process and downstream evolution. The behavior of JICF is important to fields ranging from turbine-blade cooling to smokestack pollution and volcanic eruption dynamics. Existing simplified volcanic plume models are tested; most importantly, the near-field contributions of complex interconnected vortex systems, which present significant uncertainties because they assume negligible turbulence. While jets in irrotational cross-flow have been investigated, this analysis has focused on the interaction between a turbulent jet in low and highly turbulent cross-flow created by an active grid. Instantaneous velocity fields were collected over seven planes using particle image velocimetry (PIV). A center-plane (x-y) and six planes parallel to the floor (x-z) highlight the interaction and resulting vortex systems. Various jet-to-cross-flow velocity ratios, Rv, were collected for each plane, which allow for computation of mean statistics and Reynolds stresses. Analysis was focused in five stages: a) identification of differences in the development of the jet across various inflow conditions, b) analysis of the vortex systems through transport and critical points analysis, c) decomposition of the flow structures to identify and remove the highest-order contributions to turbulence kinetic energy and d) extraction of reduced order modeling closure terms and e) optimization of closure terms for the simplified one-dimensional model, Plumeria. These five stages provided a comprehensive description of the role of cross-flow turbulence on the development of JICF. Noteworthy findings include significant changes in wake recovery and the near-wake recirculation region that impacted near-field entrainment; increased entrainment for high cross-flow turbulence after the collapse of the potential core due to increased engulfment and viscous nibbling between turbulent fluids; the presence of shear layer and wake vortices through critical point analysis; and the absence of entrainment and shear layer expansion near the exit. Most importantly, the negligible entrainment near the exit and impact of small scale turbulent features that must be included for any specific model to yield reasonable predictions is highlighted. By laying the foundation for a more nuanced approach to JICF, it is possible to more precisely summarize the complex features observed in this work through simplified descriptions that can be of benefit to both engineering design and geophysical modeling.
Download or read book Turbulent Jets and Plumes written by Joseph Hun-wei Lee and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 391 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Recent Research Advances in the Fluid Mechanics of Turbulent Jets and Plumes written by P.A. Davies and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 513 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Turbulent Jets in the Presence of a Turbulent Ambient written by Amirhossein Afrooz and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Turbulent mixing, which leads to dilution or chemical reactions (including combustion) at a molecular level, is studied using a passive scalar. Khorsandi (2013) and Perez-Alvarado (2016) studied the velocity and concentration fields of an axisymmetric turbulent jet in zero mean flow, respectively, in a quiescent and turbulent ambient. The aim of the present study is to extend this work observing a turbulent jet released into a nearly homogeneous isotropic turbulent background with negligible mean flow created with a random jet array. The characteristic of the jet in a turbulent background flow is compared to that released into a quiescent background. Planar laser induced fluorescence (PLIF) is used for flow visualization and to quantify concentrations in cross-sections of turbulent jets with Reynolds numbers of 5800 and 10600 at axial distances between x/D of 20 and 70. The data was post-processed using MATLAB codes. Flow visualisation shows that the jet cross-section has greater variation in position and shape when released into a turbulent ambient, due to the larger eddies of the turbulence distorting the jet path and the smaller eddies distorting the jet cross-section, until at some downstream distance the turbulence results in the breakup of the jet (zero mean jet velocity). The increased variability of the jet is seen in time traces of the centreline concentration. The jet cross-sections are spatially averaged to determine the rate of decrease of the concentration and increase of the jet half width with axial distance. Normalized centreline concentration varies with normalized axial distance as x-1 in a quiescent ambient and with x-1.7 for the jet with Re = 10600 and x-2.1 for the jet with Re = 5800 in the turbulent ambient. The normalized jet half width varies with normalized axial distance as x1 in a quiescent ambient and with x1.2 for jet Re = 10600 and x1.4 for jet Re = 5800 in the turbulent ambient. The position of the centre of mass of the jet cross-sections indicated a greater meandering of the jet path with downstream distance (Re = 10600). The radius of gyration of the jet was used to identify the growth in width of the cross-section independent of the meandering of the jet path. The normalized radius of gyration of the jet varied as x1.8 for the jet released in both quiescent and turbulent ambient, however the magnitude was greater in the turbulent ambient with a greater increase for the lower Reynolds number jet. The downstream evolution of the cross-sectional shape factor also indicated the greater disruption of the cross-section in the turbulent ambient. Lastly, the decay in the time averaged centreline concentration was compared to that of the centreline velocity and was found to decrease more gradually in the turbulent ambient. In summary, the turbulence in the ambient progressively breaks up the jet structure and distorts the jet path resulting in a faster rate of decay of the jet, which is greater for jets with lower Reynolds number." --
Download or read book Three Theoretical Investigations of Turbulent Jets written by Jung-Tai Lin and published by . This book was released on 1971 with total page 102 pages. Available in PDF, EPUB and Kindle. Book excerpt: Tracings: 12.20.
Download or read book Turbulent jets in confined spaces application in mixing ventilation experimental and numerical studies written by Taghi Karimipanah and published by . This book was released on 1996 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book 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 published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: "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"--
Download or read book The Theory of Turbulent Jets written by Genrikh Naumovich Abramovich and published by . This book was released on 1963 with total page 660 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Entrainment by Turbulent Jets of Air written by James Roger Connell and published by . This book was released on 1973 with total page 162 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Entrainment and Turbulence in Axisymmetric Buoyant Jets written by Jean Benedict Noelting and published by . This book was released on 1983 with total page 382 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Turbulent Jets written by N. Rajaratnam and published by Elsevier. This book was released on 1976-01-01 with total page 315 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulent Jets
Download or read book Experiments on Entrainment Mixing and Chemical Reactions in Turbulent Jets at Large Schmidt Number written by Werner Johann Anton Dahm and published by . This book was released on 1985 with total page 322 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Entrainment Rate for a Row of Turbulent Jets written by Eliott B. Gordon and published by . This book was released on 1986 with total page 256 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Entrainment Rate for a Row of Turbulent Jets written by Mary Virginia Nash and published by . This book was released on 1984 with total page 118 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Effect of Background Turbulence on the Scalar Field of a Turbulent Jet written by Alejandro Perez Alvarado and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "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." --
