Download or read book Effect of Background Turbulence on an Axisymmetric Turbulent Jet written by Babak Khorsandi 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 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." --
Download or read book Simultaneous Velocity temperature Measurements for the Quantification of the Effect of Background Turbulence on the Mixing Within a Turbulent Jet written by Fanny Legay and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Turbulent jets are commonly encountered flows, which frequently transport a scalar and occur in both natural and man-made settings (e.g. pollutants being dispersed from a smokestack into the atmosphere; injection of reactants into a combustor). In the majority of such contexts, the jet issues into an environment that is turbulent – a factor that plays a key role in the jet’s subsequent evolution, yet one that has been the subject of little study. The objective of this work was therefore to quantify the (longitudinal and radial) velocity and scalar fields of an axisymmetric turbulent jet of heated air emitted into a turbulent background.To this end, turbulent coflows with three different levels of turbulence intensity were generated in a wind tunnel by means of passive and active grids and a flow-conditioning circuit was designed and built to generate the axisymmetric jet of heated air. Emphasis was placed on simultaneous measurements of the velocity and temperature fields, with the aim of both quantifying and further understanding the mixing of jets within a turbulent environment. Hot-wire anemometry and cold-wire thermometry were employed, using a combined hot- and cold-wire probe that was designed and built for this purpose. Simultaneous measurements of the jet’s velocity and temperature fields were made at various downstream positions and for four jet-to-coflow velocity ratios.Measurements of the velocity and temperature fields, and the combined velocity-scalar statistics, showed that the background turbulence accelerated the evolution of the jet, by increasing both the rate at which the velocity and scalar fields decay in magnitude and broaden in width with increasing downstream distance. Moreover, the effective “destruction” of the average jet was observed under certain conditions. Spectral analyses suggested that the entrainment mechanism occurs at intermediate scales for low levels of background turbulence, but that large scales of the background turbulence play a significant role when the intensity of the background turbulence increases (for the cases studied herein). Probability density functions demonstrated that (i) a larger range of instantaneous velocities throughout the jet, and (ii) the presence of cold air deeper into the jet were observed due to the background turbulence. Conditional expectations suggested that axial velocity fluctuations transport larger radial velocity (momentum) and temperature fluctuations, and that the radial transport of temperature fluctuations was enhanced when the intensity of the background turbulence increased"--
Download or read book The Effect of Exit Conditions on the Development of an Axisymmetric Turbulent Free Jet written by Stanely James Kleis and published by . This book was released on 1974 with total page 408 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Generation and Suppression of Turbulence in an Axisymmetric Turbulent Jet in the Presence of an Acoustic Influence written by Evgeniĭ Vladimirovich Vlasov and published by . This book was released on 1974 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Application of Some Turbulence Models to the Computation of an Axisymmetric Jet in Streaming Flow written by S. Biringen and published by . This book was released on 1974 with total page 44 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 Axisymmetric Turbulent Jets and Wakes that are Self preserving written by William Martin Vogel and published by 1974 [c1975]. This book was released on 1974 with total page 288 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Dynamics of Non Spherical Particles in Turbulence written by Luis Blay Esteban and published by Springer. This book was released on 2019-08-13 with total page 163 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book studies the dynamics of 2D objects moving through turbulent fluids. It examines the decay of turbulence over extended time scales, and compares the dynamics of non-spherical particles moving through still and turbulent fluids. The book begins with an introduction to the project, its aims, and its relevance for industrial applications. It then discusses the movement of planar particles in quiescent fluid, and presents the numerous methodologies used to measure it. The book also presents a detailed analysis of the falling style of irregular particles, which makes it possible to estimate particle trajectory and wake morphology based on frontal geometry. In turn, the book provides the results of an analysis of physically constrained decaying turbulence in a laboratory setting. These results suggest that large-scale cut-off in numerical simulations can result in severe bias in the computed turbulent kinetic energy for long waiting times. Combining the main text with a wealth of figures and sketches throughout, the book offers an accessible guide for all engineering students with a basic grasp of fluid mechanics, while the key findings will also be of interest to senior researchers.
Download or read book Turbulence Measurements in Axisymmetric Jets of Air and Helium written by N. R. Panchapakesan and published by . This book was released on 1991 with total page 226 pages. Available in PDF, EPUB and Kindle. Book excerpt: A turbulent round jet of air discharging into quiescent air was studied experimentally. X-wire hot-wire probes mounted on a moving shuttle were used to eliminate rectification errors due to flow reversals in the intermittent region of the jet. Moments of velocity fluctuatuions up to fourth order were measured to characterize turbulent transport in the jet and to evaluate current models for triple moments that occur in the Reynolds stress equations. Fourth moments were very well described in terms of second moments by the quasi-gaussian approximation across the entire jet including the intermittent region. Profiles of third moments were found to be significantly different from earlier measurements. The Basic triple moment model that inlcluded turbulent production and models for the dissipations and the return to isotropy part of the pressure correlations was found to be unsatisfactory. When mean-strain production and a model for rapid pressure correlations were also included, predictions were satisfactory in the fully turbulent region.
Download or read book Reynolds Number Effects on the Mixing Behavior of Axisymmetric Turbulent Jets written by William M. Pitts and published by . This book was released on 1991 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Environmental Hydraulics Volume 1 written by Georgos C. Christodoulou and published by CRC Press. This book was released on 2022-03-07 with total page 716 pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the last two decades environmental hydraulics as an academic discipline has expanded considerably, caused by growing concerns over water environmental issues associated with pollution and water balance problems on regional and global scale. These issues require a thorough understanding of processes related to environmental flows and transport phenomena, and the development of new approaches for practical solutions. Environmental Hydraulics includes about 200 contributions from 35 countries presented at the 6th International Symposium on Environmental Hydraulics (Athens, Greece, 23-25 June 2010). They cover the state-of-the-art on a broad range of topics, including: fundamentals aspects of environmental fluid mechanics; environmental hydraulics problems of inland, coastal and ground waters; interfacial processes; computational, experimental and field measurement techniques; ecological aspects, and effects of global climate change. Environmental Hydraulics will be of interest to researchers, civil/environmental engineers, and professional engineers dealing with the design and operation of environmental hydraulic works such as wastewater treatment and disposal, river and marine constructions, and to academics and graduate students in related fields.
Download or read book Environmental Hydraulics Two Volume Set written by George C. Christodoulou and published by CRC Press. This book was released on 2010-06-09 with total page 1288 pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the last two decades environmental hydraulics as an academic discipline has expanded considerably, caused by growing concerns over water environmental issues associated with pollution and water balance problems on regional and global scale. These issues require a thorough understanding of processes related to environmental flows and transport
Download or read book Computations of an Axisymmetric Turbulent Free Jet written by Shawn Douglas Givler and published by . This book was released on 1994 with total page 442 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Prediction of an Axisymmetric Turbulent Jet by a Three equation Model of Turbulence written by S. Biringen and published by . This book was released on 1975 with total page 53 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Multiwave Interactions in Turbulent Jets written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-07 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nonlinear wave-wave interactions in turbulent jets were investigated based on the integrated energy of each scale of motion in a cross section of the jet. The analysis indicates that two frequency components in the axisymmetric mode can interact with other background frequencies in the axisymmetric mode, thereby amplifying an enormous number of other frequencies. Two frequency components in a single helical mode cannot, by themselves, amplify other frequency components. But combinations of frequency components of helical and axisymmetric modes can amplify other frequencies in other helical modes. The present computations produce several features consistent with experimental observations such as: (1) dependency of the interactions on the initial phase differences, (2) enhancement of the momentum thickness under multifrequency forcing, and (3) the increase in background turbulence under forcing. In a multifrequency-excited jet, mixing enhancement was found to be a result of the turbulence enhancement rather than simply the amplification of forced wave components. The excitation waves pump energy from the mean flow to the turbulence, thus enhancing the latter. The high frequency waves enhance the turbulence close to the jet exit, but, the low frequency waves are most effective further downstream. Mankbadi, Reda R. Glenn Research Center NASA ORDER C-99066-G; RTOP 505-62-21...
Download or read book The Effects of External and Self Excitations on Axisymmetric Jet Turbulence and Noise written by M. Abbas Zaqir Hasan and published by . This book was released on 1987 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt:
