Relevant bibliographies by topics / Turbulent entrainment

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Academic literature on the topic 'Turbulent entrainment'

Author: Grafiati
Published: 4 June 2021
Last updated: 18 February 2022

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Journal articles on the topic "Turbulent entrainment"

1

Shrinivas, Ajay B., and Gary R. Hunt. "Confined turbulent entrainment across density interfaces." Journal of Fluid Mechanics 779 (August 14, 2015): 116–43. http://dx.doi.org/10.1017/jfm.2015.366.

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In pursuit of a universal law for the rate of entrainment across a density interface driven by the impingement of a localised turbulent flow, the role of the confinement, wherein the environment is within the confines of a box, has to date been overlooked. Seeking to unravel the effects of confinement, we develop a phenomenological model describing the quasi-steady rate at which buoyant fluid is turbulently entrained across a density interface separating two uniform layers within the confines of a box. The upper layer is maintained by a turbulent plume, and the localised impingement of a turbulent fountain with the interface drives entrainment of fluid from the upper layer into the lower layer. The plume and fountain rise from sources at the base of the box and are non-interacting. Guided by previous observations, our model characterises the dynamics of fountain–interface interaction and the steady secondary flow in the environment that is induced by the perpetual cycle of vertical excursions of the interface. We reveal that the dimensionless entrainment flux across the interface $E_{i}$ is governed not only by an interfacial Froude number $\mathit{Fr}_{i}$ but also by a ‘confinement’ parameter ${\it\lambda}_{i}$, which characterises the length scale of interfacial turbulence relative to the depth of the upper layer. By deducing the range of ${\it\lambda}_{i}$ that may be regarded as ‘small’ and ‘large’, we shed new light on the effects of confinement on interfacial entrainment. We establish that for small ${\it\lambda}_{i}$, a weak secondary flow has little influence on $E_{i}$, which follows a quadratic power law $E_{i}\propto \mathit{Fr}_{i}^{2}$. For large ${\it\lambda}_{i}$, a strong secondary flow significantly influences $E_{i}$, which then follows a cubic power law $E_{i}\propto \mathit{Fr}_{i}^{3}$. Drawing on these results, and showing that for previous experimental studies ${\it\lambda}_{i}$ exhibits wide variation, we highlight underlying physical reasons for the significant scatter in the existing measurements of the rate of interfacial entrainment. Finally, we explore the implications of our results for guiding appropriate choices of box geometry for experimentally and numerically examining interfacial entrainment.
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Burridge, H. C., and G. R. Hunt. "Entrainment by turbulent fountains." Journal of Fluid Mechanics 790 (February 4, 2016): 407–18. http://dx.doi.org/10.1017/jfm.2016.16.

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Experimental measurements of entrainment by turbulent fountains from circular sources in quiescent uniform environments are presented. Our results span almost four orders of magnitude in the source Froude number ($0.004\leqslant \mathit{Fr}_{0}\leqslant 25$) and thereby encompass the entrainment across all classes of fountain behaviour identified to date. We identify scalings for the entrained volume flux $Q_{E}$, in terms of $\mathit{Fr}_{0}$ and the source volume flux $Q_{0}$, within a number of distinct Froude-number bands corresponding to each class of fountain. Additionally we identify a distinct class of new behaviour, as yet unreported, for $\mathit{Fr}_{0}\lesssim 0.1$.
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Ura, Masaru, and Nobuhiro Matsunaga. "ENTRAINMENT DUE TO MEAN FLOW IN TWO-LAYERED FLUID." Coastal Engineering Proceedings 1, no. 21 (January 29, 1988): 189. http://dx.doi.org/10.9753/icce.v21.189.

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The entrainment phenomena have been investigated across an interface between two-layered stratified flow induced by wind shear stress. The velocities of mean flow, turbulence and entrainment have been measured under three different conditions of water surface by using a wind-wave tank. When the entrainment velocity ue is expressed on the basis of the turbulent quantities at the interface, the turbulent entrainment coefficient E ( = ue/u) is given by E = A-(egl/u2)-3I1 ( A = 0.7). Here Eg, u and 1 are the effective buoyancy, the turbulence intensity and the integral lengthscale of turbulence at the interface, respectively. This result coincides with the relationship of entrainment due to oscillating grid turbulence, in which the mean flow does not exist. When, for the practical purpose, the estimation of ue is made by using the mean velocity Um and the depth h of mixed layer, Em ( - Ue/Um ) = Am•(egh/Um 2)"3/2 is derived from the transformation of E = A-(egl/u2)-3/2. There holds Am = A-Tf between Am and Tf, Tf being a turbulence factor given by (u/Um)4•(1/h)-3/2. It has been found that this relationship is also valid in various types of two-layered stratified flows as well as the wind-induced two-layered flows.
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Abade, Gustavo C., Wojciech W. Grabowski, and Hanna Pawlowska. "Broadening of Cloud Droplet Spectra through Eddy Hopping: Turbulent Entraining Parcel Simulations." Journal of the Atmospheric Sciences 75, no. 10 (October 2018): 3365–79. http://dx.doi.org/10.1175/jas-d-18-0078.1.

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This paper discusses the effects of cloud turbulence, turbulent entrainment, and entrained cloud condensation nuclei (CCN) activation on the evolution of the cloud droplet size spectrum. We simulate an ensemble of idealized turbulent cloud parcels that are subject to entrainment events modeled as a random process. Entrainment events, subsequent turbulent mixing inside the parcel, supersaturation fluctuations, and the resulting stochastic droplet activation and growth by condensation are simulated using a Monte Carlo scheme. Quantities characterizing the turbulence intensity, entrainment rate, CCN concentration, and the mean fraction of environmental air entrained in an event are all specified as independent external parameters. Cloud microphysics is described by applying Lagrangian particles, the so-called superdroplets. These are either unactivated CCN or cloud droplets that grow from activated CCN. The model accounts for the addition of environmental CCN into the cloud by entraining eddies at the cloud edge. Turbulent mixing of the entrained dry air with cloudy air is described using the classical linear relaxation to the mean model. We show that turbulence plays an important role in aiding entrained CCN to activate, and thus broadening the droplet size distribution. These findings are consistent with previous large-eddy simulations (LESs) that consider the impact of variable droplet growth histories on the droplet size spectra in small cumuli. The scheme developed in this work is ready to be used as a stochastic subgrid-scale scheme in LESs of natural clouds.
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Lecoanet, Daniel, and Nadir Jeevanjee. "Entrainment in Resolved, Dry Thermals." Journal of the Atmospheric Sciences 76, no. 12 (November 20, 2019): 3785–801. http://dx.doi.org/10.1175/jas-d-18-0320.1.

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Abstract Entrainment in cumulus convection remains ill understood and difficult to quantify. For instance, entrainment is widely believed to be a fundamentally turbulent process, even though Turner pointed out in 1957 that dry thermals entrain primarily because of buoyancy (via a dynamical constraint requiring an increase in radius r). Furthermore, entrainment has been postulated to obey a 1/r scaling, but this scaling has not been firmly established. Here, we study the classic case of dry thermals in a neutrally stratified environment using fully resolved direct numerical simulation. We combine this with a thermal tracking algorithm that defines a control volume for the thermal at each time, allowing us to directly measure entrainment. We vary the Reynolds number (Re) of our thermals between laminar (Re ≈ 600) and turbulent (Re ≈ 6000) regimes, finding only a 20% variation in entrainment rate ε, supporting the claim that turbulence is not necessary for entrainment. We also directly verify the postulated ε ~ 1/r scaling law.
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Mistry, Dhiren, Jimmy Philip, James R. Dawson, and Ivan Marusic. "Entrainment at multi-scales across the turbulent/non-turbulent interface in an axisymmetric jet." Journal of Fluid Mechanics 802 (August 10, 2016): 690–725. http://dx.doi.org/10.1017/jfm.2016.474.

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We consider the scaling of the mass flux and entrainment velocity across the turbulent/non-turbulent interface (TNTI) in the far field of an axisymmetric jet at high Reynolds number. Time-resolved, simultaneous multi-scale particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) are used to identify and track the TNTI, and directly measure the local entrainment velocity along it. Application of box-counting and spatial-filtering methods, with filter sizes $\unicode[STIX]{x1D6E5}$ spanning over two decades in length, show that the mean length of the TNTI exhibits a power-law behaviour with a fractal dimension $D\approx 0.31{-}0.33$. More importantly, we invoke a multi-scale methodology to confirm that the mean mass flux, which is equal to the product of the entrainment velocity and the surface area, remains constant across the range of filter sizes. The results, within experimental uncertainty, also show that the entrainment velocity along the TNTI exhibits a power-law behaviour with $\unicode[STIX]{x1D6E5}$, such that the entrainment velocity increases with increasing $\unicode[STIX]{x1D6E5}$. In fact, the mean entrainment velocity scales at a rate that balances the scaling of the TNTI length such that the mass flux remains independent of the coarse-grain filter size, as first suggested by Meneveau & Sreenivasan (Phys. Rev. A, vol. 41, no. 4, 1990, pp. 2246–2248). Hence, at the smallest scales the entrainment velocity is small but is balanced by the presence of a very large surface area, whilst at the largest scales the entrainment velocity is large but is balanced by a smaller (smoother) surface area.
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Hallworth, Mark A., Jeremy C. Phillips, Herbert E. Huppert, and R. Stephen J. Sparks. "Entrainment in turbulent gravity currents." Nature 362, no. 6423 (April 1993): 829–31. http://dx.doi.org/10.1038/362829a0.

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Presley, John D., and James W. Telford. "Turbulent entrainment at an inversion." Pure and Applied Geophysics PAGEOPH 127, no. 1 (1988): 117–41. http://dx.doi.org/10.1007/bf00878694.

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Craske, John, Pietro Salizzoni, and Maarten van Reeuwijk. "The turbulent Prandtl number in a pure plume is 3/5." Journal of Fluid Mechanics 822 (June 8, 2017): 774–90. http://dx.doi.org/10.1017/jfm.2017.259.

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We derive a new expression for the entrainment coefficient in a turbulent plume using an equation for the squared mean buoyancy. Consistency of the resulting expression with previous relations for the entrainment coefficient implies that the turbulent Prandtl number in a pure plume is equal to 3/5 when the mean profiles of velocity and buoyancy have a Gaussian form of equal width. Entrainment can be understood in terms of the volume flux, the production of turbulence kinetic energy or the production of scalar variance for either active or passive variables. The equivalence of these points of view indicates how the entrainment coefficient and the turbulent Prandtl and Schmidt numbers depend on the Richardson number of the flow, the ambient stratification and the relative widths of the velocity and scalar profiles. The general framework is valid for self-similar plumes, which are characterised by a power-law scaling. For jets and pure plumes it is shown that the derived relations are in reasonably good agreement with results from direct numerical simulations and experiments.
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de Lozar, Alberto, and Juan Pedro Mellado. "Direct Numerical Simulations of a Smoke Cloud–Top Mixing Layer as a Model for Stratocumuli." Journal of the Atmospheric Sciences 70, no. 8 (August 1, 2013): 2356–75. http://dx.doi.org/10.1175/jas-d-12-0333.1.

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Abstract A radiatively driven cloud-top mixing layer is investigated using direct numerical simulations. This configuration mimics the mixing process across the inversion that bounds the stratocumulus-topped boundary layer. The main focus of this paper is on small-scale turbulence. The finest resolution (7.4 cm) is about two orders of magnitude finer than that in cloud large-eddy simulations (LES). A one-dimensional horizontally averaged model is employed for the radiation. The results show that the definition of the inversion point with the mean buoyancy of 〈b〉(zi) = 0 leads to convective turbulent scalings in the cloud bulk consistent with the Deardorff theory. Three mechanisms contribute to the entrainment by cooling the inversion layer: a molecular flux, a turbulent flux, and the direct radiative cooling by the smoke inside the inversion layer. In the simulations the molecular flux is negligible, but the direct cooling reaches values comparable to the turbulent flux as the inversion layer thickens. The results suggest that the direct cooling might be overestimated in less-resolved models like LES, resulting in an excessive entrainment. The scaled turbulent flux is independent of the stratification for the range of Richardson numbers studied here. As suggested by earlier studies, the turbulent entrainment only occurs at the small scales and eddies larger than approximately four optical lengths (60 m in a typical stratocumulus cloud) perform little or no entrainment. Based on those results, a parameterization is proposed that accounts for a large part (50%–100%) of the entrainment velocities measured in the Second Dynamics and Chemistry of the Marine Stratocumulus (DYCOMS II) campaign.
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Dissertations / Theses on the topic "Turbulent entrainment"

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Boga, Gabriele. "Numerical Experiments on Turbulent Entrainment." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/20559/.

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The aim of this thesis work is the study of the turbulent entrainment phenomenon in jets through numerical experiments. More specifically, an attempt to study the effect of engulfment and nibbling mechanisms separately was made. The flow chosen for the numerical experiments is the temporal planar jet. The idea behind these experiments is to study the spreading and the mixing of a passive scalar under the effect of two modified velocity fields. The first is a large-scale velocity field obtained through a filtering operation, while the second is a small-scale velocity field obtained subtracting the large-scale velocity field from the total one and then adding the mean velocity. Initially, the post-processing of a spatially developing planar jet, performed by Doctor Andrea Fregni and Professor Andrea Cimarelli, has been carried out in order to analyse the main features of spatially evolving jets compared with the temporal ones. A co-flow and a passive scalar are present in the simulation. The Reynolds number is set to Re = 3000 and the Schmidt number is Sc = 1. After this first step, a benchmark DNS of a temporal planar jet with Re = 3000 and Sc = 1 has been performed in order to evaluate the main differences with respect to the spatially evolving jet. Once the settings were validated, the numerical experiments with large and small scale velocity fields have been performed. The filter used in all the experiments is the box filter. The results of two different filter lengths are presented, the first is Δ = 1.5λcl and the second is Δ = 3λcl. Since λcl is function of time, the two filter lengths are themselves varying in time. The results of the experiments were then compared with those of the unfiltered solution. The passive scalar spread approximatively the same amount under the effect of the large-scale velocity fields and under the effect of the unfiltered velocity. On the other hand, the small-scale fluctuations have been proved to be important in the mixing process.
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Mickett, John B. "Turbulent entrainment fluxes within the eastern Pacific warm pool /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/11005.

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Witz, Matthew J. "Mechanics of particle entrainment in turbulent open-channel flows." Thesis, University of Aberdeen, 2015. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=225690.

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An advanced understanding of particle entrainment is required to optimise the design and maintenance of numerous open channel hydraulic systems and structures placed in these systems; including river channels and canals. This study is on particle entrainment (defined as the movement of a particle from a stationary position to being mobile in the flow). Three aspects of particle entrainment were identified as the focus of this work: First, the waiting time for an exposed particle to entrain under constant flow conditions. Second, the flow features responsible for the entrainment of an individual exposed particle. Third, the motion of an entrained particle immediately after entrainment. Waiting time was found to be highly sensitive to protrusion, with a small increase in protrusion resulting in a significant decrease in waiting time. Contrary to previous suggestions the waiting time to entrainment was found to be poorly described by an exponential distribution; instead Weibull or gamma distributions provide an improved fit in both qualitative and quantitative terms. Ensemble averaged flow fields at the point of entrainment were computed to determine the features responsible for entrainment. The data from the transverse vertical PIV plane indicated the presence of two counter-rotating vortices, with the boundary between the vortices located directly over the entrainment particle. The streamwise vertical PIV measurements showed the presence of a structure extending for a considerable distance in the streamwise direction, the length of which appeared to be independent of submergence. Further, the inclination of the downstream end of the structure appeared to increase with submergence. From the point of entrainment particle dffusion in all three coordinate directions displays an exponent significantly greater than that of ballistic diffusion. From the point of entrainment particle diffusion in all three coordinate directions displays an exponent significantly greater than that of ballistic diffusion. The results highlight the clear difference in the local scale between the diffusion of an already mobile particle with one starting from a position of rest.
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Cocconi, Giacomo. "Numerical investigation of turbulent/non-turbulent interface." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/5237/.

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The subject of this work is the diffusion of turbulence in a non-turbulent flow. Such phenomenon can be found in almost every practical case of turbulent flow: all types of shear flows (wakes, jet, boundary layers) present some boundary between turbulence and the non-turbulent surround; all transients from a laminar flow to turbulence must account for turbulent diffusion; mixing of flows often involve the injection of a turbulent solution in a non-turbulent fluid. The mechanism of what Phillips defined as “the erosion by turbulence of the underlying non-turbulent flow”, is called entrainment. It is usually considered to operate on two scales with different mechanics. The small scale nibbling, which is the entrainment of fluid by viscous diffusion of turbulence, and the large scale engulfment, which entraps large volume of flow to be “digested” subsequently by viscous diffusion. The exact role of each of them in the overall entrainment rate is still not well understood, as it is the interplay between these two mechanics of diffusion. It is anyway accepted that the entrainment rate scales with large properties of the flow, while is not understood how the large scale inertial behavior can affect an intrinsically viscous phenomenon as diffusion of vorticity. In the present work we will address then the problem of turbulent diffusion through pseudo-spectral DNS simulations of the interface between a volume of decaying turbulence and quiescent flow. Such simulations will give us first hand measures of velocity, vorticity and strains fields at the interface; moreover the framework of unforced decaying turbulence will permit to study both spatial and temporal evolution of such fields. The analysis will evidence that for this kind of flows the overall production of enstrophy , i.e. the square of vorticity omega^2 , is dominated near the interface by the local inertial transport of “fresh vorticity” coming from the turbulent flow. Viscous diffusion instead plays a major role in enstrophy production in the outbound of the interface, where the nibbling process is dominant. The data from our simulation seems to confirm the theory of an inertially stirred viscous phenomenon proposed by others authors before and provides new data about the inertial diffusion of turbulence across the interface.
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Drew, Brady Patterson. "Entrainment Characteristics of Turbulent Round Gas Jets Submerged in Water." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/76852.

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The entrainment process in two-phase buoyant jets differs significantly from their singlephase counterparts, and is not well understood. Entrainment models developed for singlephase flow are often used in two-phase jetting simulations, albeit with limited success. In this work, Particle Image Velocimetry (PIV) and shadowgraph flow visualization experiments have been conducted on submerged round gas jets of varying speeds and nozzle diameters with the goal of improving our understanding of the entrainment process in a two-phase (gas-liquid) jet. The total entrainment estimated using the PIV measurements is higher than the respective values suggested by a common empirical model developed for singlephase buoyant jets. A two-phase theoretical entrainment model used for comparison shows an overestimation of entrainment, but predicts the increase in the rate of entrainment with axial distance from the jet nozzle seen in the PIV results. This thesis also presents advances in PIV processing methodology that were developed concurrently with the entrainment research. The novel Spectral Phase Correlation (SPC) allows for particle displacement to be determined directly from phase information in the Fourier domain. Some of the potential benefits of the SPC explored here include (1) avoidance of errors introduced by spatial peak-finding routines; (2) use of a modal analysis that can be used to provide information such as correlation quality; and (3) introduction of a means of incorporating information from multiple image windows. At low image noise levels, the method performs as well as an advanced CC-based method. However, difficulties unwrapping the aliased phase information cause the SPC's performance to degrade at high noise levels.
Master of Science
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Holzner, Markus. "Experimental and numerical study on the small scale features of turbulent entrainment." kostenfrei, 2007. http://e-collection.ethbib.ethz.ch/view/eth:29729.

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Robertson, Zachary Burton Smith. "Deposition of Newtonian Particles Entrained in a Turbulent Axisymmetric Free Jet." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/31884.

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In the past 10 years there has been a significant amount of research into two-phase particle transport. The terrorist events of September 11, 2001 sparked a series of studies analyzing particle entrainment and deposition in turbulent airflows. One area of research needing further attention has been the study of particles entrained in axisymmetric air jets. An experimental rig was designed and built to study entrainment properties and deposition of Newtonian particles, after injection into a turbulent axisymmetric free air jet. Newtonian spherical particles, ranging from 1mm to 6mm in diameter, were injected into a turbulent airstream and blown through a nozzle into a large, open space. As the particles fell out of the jet stream, their linear distances, from nozzle to initial-ground-contact, were recorded and analyzed. The experiments conducted indicated particle size and density to be significant factors when considering Newtonian particle entrainment. Additionally, particle deposition distribution revealed a consistent positive skewness, as opposed to an expected Gaussian form. The data presented in this paper provide a starting point for understanding entrainment of Newtonian spherical particles in jets. The simple experimental rig geometry and results also provide an opportunity for computational fluid dynamics models to be validated, answering a call from the 2006 Annual Review of Fluid Mechanics.
Master of Science
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Ma, Jianmin. "Numerical analysis of flow structures and bed entrainment in turbulent open-channel flow." Thesis, Queen Mary, University of London, 2009. http://qmro.qmul.ac.uk/xmlui/handle/123456789/524.

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The results from a Direct Numerical Simulation (DNS) and a Large Eddy Simulation (LES) are employed to study the large-scale coherent structures and bed entrainment in the turbulent open-channel flow. The gravel bed is represented by a hexagonal arrangement of uniform spheres. The large-scale coherent structures are composed of a group of quasistreamwise vortices and asymmetric hairpin vortices. The meandering structures are shown to be longer than the length of the computational box, more than 20 times the effective flow depth in this study, and the width tends to be one order of magnitude smaller than the length. The signature of the large-scale motion is elongated local maximum of streamwise velocity. It is also found that these structures contribute substantially to both of the Reynolds Stress (RS) and the Turbulent Kinetic Energy (TKE). The entrainment of bed gravels is investigated by the three-dimensional analysis of the relationship between near-wall coherent structures and the force moments exerted on the particles. It is found that the spanwise drag moment (MD2) is of the same order of magnitude compared with the streamwise drag moment (MD1). The majority of MD2 originates from pressure whilst the viscous force plays as an important role as pressure for MD1. The contributions of the forces at different heights of the particle to MD1 and MD2 are explored. The quasi-streamwise vortices are strongly associated with MD2 and the ejections are shown to be more favorable for bed entrainment than the sweeps in this bed condition.
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Sebesta, Christopher James. "Modeling the Effect of Particle Diameter and Density on Dispersion in an Axisymmetric Turbulent Jet." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/31987.

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Creating effective models predicting particle entrainment behavior within axisymmetric turbulent jets is of significant interest to many areas of study. Research into multiphase flows within turbulent structures has primarily focused on specific geometries for a target application, with little interest in generalized cases. In this research, the entrainment characteristics of various particle sizes and densities were simulated by determining the distribution of particles across a surface after the particles had fallen out of entrainment within the jet core. The model was based on an experimental set-up created by Lieutenant Zachary Robertson, which consists of a particle injection system designed to load particles into a fully developed pipe [1]. This pipe flow then exits into an otherwise quiescent environment (created within a wind tunnel), creating an axisymmetric turbulent round jet. The particles injected were designed to test the effect of both particle size and density on the entrainment characteristics. The data generated by the model indicated that, for all particle types tested, the distribution across the bottom surface of the wind tunnel followed a standard Gaussian distribution. Experimentation yielded similar results, with the exception that some of the experimental trials showed distributions with significantly non-zero skewness. The model produced results with the highest correlation to experimentation for cases with the smallest Stokes number (small size/density), indicating that the trajectory of particles with the highest level of interaction with the flow were the easiest to predict. This was contrasted by the high Stokes number particles which appear to follow standard rectilinear motion.
Master of Science
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10

Papanicolaou, Athanasios N. "The Role of Turbulence on the Initiation of Sediment Motion." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30591.

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The present study examines the role of turbulence on the incipient motion of sediment. For this purpose, well-controlled experiments are performed at the laboratory in a tilting flume. In these tests glass beads of the same size and density are used as the testing material to isolate the role of turbulence. State of the art equipment are used during the course of this study. Specifically, a 3-D Laser Doppler Velocimetry system is employed to measure the instantaneous velocity components at different points near the vicinity of a ball while the ball motion is monitored with a video camera. An image analysis program is developed here to analyze the motion of the particles within a test area. To examine the importance of the different stress components in the entrainment of sediment, five tests of different packing configuration are performed. Specifically three different roughness regimes are examined namely, the isolated, the wake interference, and the skimming flow. The results reveal that the instantaneous normal stress in the streamwise direction is the most dominant component of the instantaneous stress tensor. The backbone of this study is the development of a methodology to link the effects of turbulence with the commencement of sediment motion. It is considered that the metastable bursting cycle (i.e. sweeps, ejections, inward and outward interactions) is responsible for the sediment entrainment. And that the sediment entrainment, if any, occurs within a bursting period. The main concept behind the determination of the critical conditions is that the probability of the entrainment of sediment (effect) is equal to the probability of occurrence of these highly energetic turbulent events that have magnitude greater than the critical (cause). The probability of sediment entrainment is computed by means of the image analysis tool. The balance of moments is obtained here to determine the minimum moment that is required for the commencement of sediment motion. The balance of moments yields the deduction of a new variable that is used to describe the probability of occurrence of the different turbulent events. This variable is the summation of the instantaneous normal stresses in the streamwise and vertical direction. It is shown here that a two-parameter gamma density function describes quite well the statistical behavior of this variable. The results that are obtained from the existing model suggest that the present methodology can adequately describe the commencement of sediment motion. It is shown here that the traditionally used shear stress term uw may not be the appropriate measure for the determination of the critical conditions.
Ph. D.
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Books on the topic "Turbulent entrainment"

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Crawford, G. B. On the turbulent diffusion of air bubbles. Boulder, Colo: U.S. Dept. of Commerce, National Oceanic and Atmospheric Administration, Environmental Research Laboratories, Wave Propagation Laboratory, 1988.

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Crawford, G. B. On the turbulent diffusion of air bubbles. Boulder, Colo: U.S. Dept. of Commerce, National Oceanic and Atmospheric Administration, Environmental Research Laboratories, Wave Propagation Laboratory, 1988.

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Kamada, Ray. Amending the w* velocity scale for surface layer, entrainment zone, and baroclinic shear in mixed forced/free turbulent convection. Monterey, Calif: Naval Postgraduate School, 1992.

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The entrainment rate for a row of turbulent jets. [Cleveland, Ohio]: National Aeronautics and Space Administration, Lewis Research Center, 1990.

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Chanson, Hubert. Air Bubble Entrainment in Free-Surface Turbulent Shear Flows. Academic Press, 1996.

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Air Bubble Entrainment in Free-Surface Turbulent Shear Flows. Elsevier, 1996. http://dx.doi.org/10.1016/b978-0-12-168110-4.x5000-0.

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Chanson, Hubert. Air Bubble Entrainment in Free-Surface Turbulent Shear Flows. Academic Press, 1996.

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Chanson, Hubert. Air Bubble Entrainment in Free-surface Turbulent Flows. Experimental Investigations. University of Queensland Press, 1995.

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Book chapters on the topic "Turbulent entrainment"

1

Townsend, A. A. "Entrainment in Free Turbulent Flows." In Advances in Turbulence 2, 109–12. Berlin, Heidelberg: Springer Berlin Heidelberg, 1989. http://dx.doi.org/10.1007/978-3-642-83822-4_18.

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Netterville, Dennett D. J. "Entrainment and Plume Rise in Turbulent Winds." In Air Pollution Modeling and Its Application VIII, 681–93. Boston, MA: Springer US, 1991. http://dx.doi.org/10.1007/978-1-4615-3720-5_79.

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Pollard, Andrew. "Turbulent Round Jet Entrainment—A Historical Perspective." In 50 Years of CFD in Engineering Sciences, 269–94. Singapore: Springer Singapore, 2020. http://dx.doi.org/10.1007/978-981-15-2670-1_8.

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Redondo, J. M., and C. Yague. "Plume Entrainment in Stratified Flows." In Recent Research Advances in the Fluid Mechanics of Turbulent Jets and Plumes, 209–22. Dordrecht: Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-011-0918-5_13.

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McClimans, T. A. "Entrainment/Detrainment along River Plumes." In Recent Research Advances in the Fluid Mechanics of Turbulent Jets and Plumes, 391–99. Dordrecht: Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-011-0918-5_24.

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Mazellier, Nicolas, Francesco Stella, and Azeddine Kourta. "Analysis of Turbulent Entrainment in Separating/Reattaching Flows." In Fluid-Structure-Sound Interactions and Control, 255–60. Singapore: Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-33-4960-5_40.

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Chen, Jacqueline H. "The Effect of Compressibility on Conserved Scalar Entrainment in a Plane Free Shear Layer." In Turbulent Shear Flows 8, 297–311. Berlin, Heidelberg: Springer Berlin Heidelberg, 1993. http://dx.doi.org/10.1007/978-3-642-77674-8_21.

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Taveira, Rodrigo M. R., Carlos B. da Silva, and J. C. F. Pereira. "Turbulent Entrainment in Jets: The role of Kinetic Energy." In Springer Proceedings in Physics, 561–64. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-03085-7_135.

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Apperley, L. W., and A. J. Raudkivi. "The entrainment of sediments by the turbulent flow of water." In Sediment/Water Interactions, 39–49. Dordrecht: Springer Netherlands, 1989. http://dx.doi.org/10.1007/978-94-009-2376-8_5.

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Gordon, Eliott B., and Isaac Greber. "The Entrainment Rate for a Row of Turbulent Circular Jets." In Instabilities and Turbulence in Engineering Flows, 307–16. Dordrecht: Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-011-1743-2_17.

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Conference papers on the topic "Turbulent entrainment"

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van Reeuwijk, Maarten, Pietro Salizzoni, and John Craske. "Turbulent entrainment in jets and plumes." In THMT-15. Proceedings of the Eighth International Symposium On Turbulence Heat and Mass Transfer. Connecticut: Begellhouse, 2015. http://dx.doi.org/10.1615/ichmt.2015.thmt-15.240.

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DAHM, W. A., and P. E. DIMOTAKIS. "MEASUREMENTS OF ENTRAINMENT AND MIXING IN TURBULENT JETS." In 23rd Aerospace Sciences Meeting. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1985. http://dx.doi.org/10.2514/6.1985-56.

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Souders, David T., and C. W. Hirt. "Modeling Entrainment of Air at Turbulent Free Surfaces." In World Water and Environmental Resources Congress 2004. Reston, VA: American Society of Civil Engineers, 2004. http://dx.doi.org/10.1061/40737(2004)187.

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Ghasemi, Abbas, Vesselina Roussinova, Ronald Barron, and Ram Balachandar. "Analysis of Entrainment at the Turbulent/Non-Turbulent Interface of a Square Jet." In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-65355.

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Particle image velocimetry measurements are carried out to study the entrainment at the interface between the non-turbulent and turbulent regions in a square jet. Jet Reynolds number based on the hydraulic diameter of the jet is 50,000. Measurements cover up to 25 diameters downstream of the nozzle exit using five horizontal field-of-views in the central plane of the jet. The turbulent/non-turbulent interface is identified using a velocity criterion and a suitable thresholding method. Using vorticity and swirling strength it is shown that the turbulent/non-turbulent interface separates the rotational and irrotational regions of the flow. Instantaneous velocity vector field superimposed with the turbulent/non-turbulent interface are presented. The relation between the vortex cores in the vicinity of the turbulent/non-turbulent interface and the contractions and expansions noticed in the jet velocity field are explained. Entrainment into the jet is evaluated at each axial distance by identifying the points falling inside the turbulent region of the jet. Compared to a round jet, the square jet entrains more ambient fluid. In addition, normal volume fluxes going through the turbulent/non-turbulent interface of the square jet are found to be larger compared to that of a round jet.
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Drew, Brady, John Charonko, and Pavlos Vlachos. "Liquid Entrainment by Round Turbulent Gas Jets Submerged in Water." In ASME-JSME-KSME 2011 Joint Fluids Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajk2011-11015.

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Entrainment characteristics of two-phase flow (liquid-gas) buoyant jets differ significantly from their single-phase flow counterparts. Past studies have not adequately described the mechanisms that cause the gas jet to entrain liquid from its surroundings and expand. In this work, Particle Image Velocimetry (PIV) and shadowgraph flow visualization experiments have been conducted on submerged round gas jets of varying speeds and nozzle diameters with the goal of improving our understanding of the processes of entrainment and expansion in a two-phase jet. We hypothesize that liquid is entrained into the gas column through (1) shear entrainment due to instabilities at the interface between the fast-moving gas jet and stagnant liquid, and (2) convective entrainment that occurs when the jet begins to pinch off and transform into a bubbly plume. The total entrainment estimated using the PIV measurements is higher than the respective values that single-phase buoyant jet theory suggests, especially at low jet speeds. This may be an effect of increased convective entrainment as the jet slows down. The shadowgraph flow visualization experiments provide valuable information pertaining to the structure of the jet and the interfacial dynamics.
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Nakagawa, Masaki, and Werner Dahm. "Compressibility effects on entrainment and mixing in supersonic planar turbulent wakes." In 30th Fluid Dynamics Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1999. http://dx.doi.org/10.2514/6.1999-3582.

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Kumagai, Ichiro, Kakeru Taguchi, Chiharu Kawakita, Tatsuya Hamada, and Yuichi Murai. "Air Entrainment and Bubble Generation by a Hydrofoil in a Turbulent Channel Flow." In ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ajkfluids2019-5457.

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Abstract Air entrainment and bubble generation by a hydrofoil bubble generator for ship drag reduction have been investigated using a small high-speed channel tunnel with the gap of 20 mm in National Maritime Research Institute (NMRI). A hydrofoil (NACA4412, chord length = 40 mm) was installed in the channel and an air induction pipe was placed above the hydrofoil. The flow rate of the entrained air was quantitatively measured by thermal air flow sensors at the inlet of the air induction pipe. The gas-liquid flow around the hydrofoil was visualized by a backlight method and recorded by a high-speed video camera. As the flow velocity in the channel increased, the negative pressure generated above the suction side of the hydrofoil lowered the hydrostatic pressure in the channel, then the atmospheric air was entrained into the channel flow. The entrained air was broken into small air bubbles by the turbulent flow in the channel. The threshold of air entrainment, the air flow rate, and gas-liquid flow pattern depends on Reynolds number, angle of attack (AOA), and hydrofoil type. We identified at least three modes of air entrainment behavior: intermittent air entrainment, stable air entrainment, and air entrainment with a ventilated cavity. At high flow speed in our experimental condition (9 m/s), a large volume of air bubbles was generated by this hydrofoil system (e.g. air flow rate was 50 l/min for NACA4412 at AOA 16 degrees), which has a high potential to reduce ship drag.
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Ma, Fanhua, Chuanli Liu, Deming Jiang, and Longbao Zhou. "Study on Validation of Turbulent Entrainment Combustion Model for Spark-Ignition Engines." In International Fuels & Lubricants Meeting & Exposition. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 1994. http://dx.doi.org/10.4271/941935.

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Nakagawa, Masaki, and Werner Dahm. "Mach number effects on entrainment and mixing in supersonic planar turbulent wakes." In 38th Aerospace Sciences Meeting and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2000. http://dx.doi.org/10.2514/6.2000-664.

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Xu, Duo, and Jun Chen. "Experimental Study of Mixing and Entrainment in a Horizontal Turbulent Stratified Jet." In ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting collocated with the ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/fedsm2014-21871.

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The mixing efficiency, flux Richardson number Rif, is investigated in a horizontally injected turbulent stratified jet with a co-existence of stable and unstable stratifications. The high resolution experimental data from a developed laser-based technique show the statistical relationship between Rif and the gradient Richardson number Rig. In addition, the data are used to study the development of entrainment by two approaches, and compared with theoretical predictions.
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Reports on the topic "Turbulent entrainment"

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Kamada, R. F. Amending the W* Velocity Scale for Surface Layer, Entrainment Zone, and Baroclinic Shear in Mixed Forced/Free Turbulent Convection. Fort Belvoir, VA: Defense Technical Information Center, March 1992. http://dx.doi.org/10.21236/ada250389.

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Freedland, Graham. Entrainment Processes for a Jet in Cross-flow: The Quantification of Turbulent Contributions and their Importance on Accurate Modeling. Portland State University Library, January 2000. http://dx.doi.org/10.15760/etd.7490.

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Harcourt, Ramsey R. Impact of Typhoons on the Western Pacific Ocean DRI: Numerical Modeling of Ocean Mixed Layer Turbulence and Entrainment at High Winds. Fort Belvoir, VA: Defense Technical Information Center, September 2010. http://dx.doi.org/10.21236/ada542500.

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Harcourt, Ramsey R. Impact of Typhoons on the Western Pacific Ocean DRI: Numerical Modeling of Ocean Mixed Layer Turbulence and Entrainment at High Winds. Fort Belvoir, VA: Defense Technical Information Center, September 2012. http://dx.doi.org/10.21236/ada590609.

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Harcourt, Ramsey R. Impact of Typhoons on the Western Pacific Ocean (ITOP) DRI:Numerical Modeling of Ocean Mixed Layer Turbulence and Entrainment at High Winds. Fort Belvoir, VA: Defense Technical Information Center, September 2013. http://dx.doi.org/10.21236/ada591722.

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Harcourt, Ramsey R. Impact of Typhoons on the Western Pacific Ocean (ITOP) DRI: Numerical Modeling of Ocean Mixed Layer Turbulence and Entrainment at High Winds. Fort Belvoir, VA: Defense Technical Information Center, September 2013. http://dx.doi.org/10.21236/ada599038.

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