Article

Experimental Study of Sand and Slurry Jets in Water

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Abstract

This paper presents the results of an experimental study of turbulent sand jets and sand-water slurry jets impinging vertically into a stagnant water body. The jets contained silica sand with a median diameter D(50) of 206 mu m, and with an initial concentration 0.60 by volume for the sand jets, and 0.055-0.124 by volume for the slurry jets. The jets had densimetric Froude numbers between 2.0 and 5.94. The sand concentration and velocity profiles were measured simultaneously using a novel fiber optical probe, up to a distance of 130d(o) for sand jets, and 65d(o) for slurry jets, where do is the jet diameter at the water surface. The jets were found to have self-similar Gaussian profiles. The centerline sand concentration within the jets was found to decrease rapidly, following trends similar to single phase plumes. The centerline sand velocity profile decreased significantly before reaching a plateau region. The "terminal" centerline sand velocity within this region varies somewhat depending upon sand mass flux, and is between 0.32 and 0.43 m/s. The spreading rates of the jets were found to vary with the particle Froude number. Within the sand jets and the higher Froude number slurry jet, the sand concentration had a smaller spreading rate than the velocity. The other slurry jets had equal concentration/velocity spreading rates. The momentum flux of the sand within the jets was found to decrease sharply, followed by a constant flux below a depth of 25 to 30 jet diameters.

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... Particle-laden turbulent jets have many engineering applications, such as in: marine bed capping, hydro-transport systems, and wastewater disposal (Balarac et al. 2007;Azimi et al. 2012a, b;Canton et al. 2017;Zhang et al. 2018). Several research studies have been performed to understand the dynamics of particles and flow configuration in solid-liquid, non-swirling turbulent jets (Brush 1962;Fan et al. 1990; Rahimipour and Wilkinson 1992;Mazurek et al. 2002;Tamburello and Amitay 2008;Virdung and Rasmuson 2007;Casciola et al. 2010;Hall et al. 2010;Azimi et al. 2011Azimi et al. , 2012aLau and Nathan 2014;Jayakumar and Abraham 2016;Azimi 2020, 2021;Janati and Azimi 2021a, b). The particle dynamics and particle-particle interactions in particle-laden turbulent jets are correlated with the initial inlet configurations, such as particle size, D 50 , initial particle concentration, c o , nozzle diameter, d o , and the initial velocity of particles, u o . ...
... The particle dynamics and particle-particle interactions in particle-laden turbulent jets are correlated with the initial inlet configurations, such as particle size, D 50 , initial particle concentration, c o , nozzle diameter, d o , and the initial velocity of particles, u o . Many laboratory experiments have been conducted in the past to study the evolution, mixing properties, turbulence attenuation/augmentation, and spreading rates of two-phase turbulent jets (Huai et al. 2013;Jiang et al. 2005;Virdung and Rasmuson 2007;Hall et al. 2010;Azimi et al. 2012a, b). ...
... Weisbrot et al. (1982) formulated the spreading rate of single-phase jets as a function of fluid velocity, u, and it was scaled using u −3/2 . The spreading rate in water jets has ranged between 0.104 and 0.115 and in slurry jets has ranged between 0.08 and 0.11 (Wang and Law 2002;Hall et al. 2010). Azimi et al. (2012b) indicated that the spreading rate of slurry jets can be correlated with the sand initial concentration as c o −3/2 . ...
Article
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A series of laboratory experiments was conducted to study particle dynamics and flow characteristics of vertically discharged sand-water swirling jets in stagnant water. The effects of swirling motion on variations of sand concentration, axial velocity, and mixing properties of sand-water swirling jets were studied by employing an advanced optical fiber probe (PV6). The axial and radial sand concentration and velocity were measured for sand-water swirling jets with limited and unlimited mass of sand particles. The availability of sand particles was quantified by the aspect ratio of sand mass to nozzle diameter. Sand mass and momentum fluxes were calculated from cross-sectional integration of sand concentration and velocity profiles to validate the measured data. A strong decay rate of momentum flux was observed along the recirculation zone and at a distance equal to 20 times the nozzle diameter. Prediction models were developed based on the measured data to estimate sand concentration and velocity of sand-water swirling jets with different swirling strengths. It was found that aspect ratio and swirling strength significantly impact the variations of axial concentration and velocity decay rates in sand-water swirling jets. Laboratory measurements indicated that the centerline sand concentration decreased at a higher rate in comparison with sand-water jets without a swirling motion. In addition, the centerline sand concentration and velocity significantly decreased by increasing the swirling strength. The spreading rate of sand-water swirling jets increased with increase in the swirling number. The radially averaged drag coefficient of particles at different cross sections was calculated by employing the momentum balance along the jet axis and the proposed models for prediction of sand velocity and concentration. It was found that the swirling motion of sand particles significantly increased the drag coefficient. The power spectral density results of sand-water swirling jets indicated that the sand phase attenuated the first peak signal in the frequency domain in comparison with the power spectral density results of single-phase swirling jets. Graphical abstract
... In cases where buoyancy becomes a predominant source of motion, the resulting flow is called a plume. Particle-laden jets with high initial momentum and particle concentration are commonly known as sand/slurry jets in the literature ( Hall et al., 2010 ;Azimi et al., 2012aAzimi et al., , 2012b. Further, gravitydriven sand jets with limited sand mass are known to form particle clouds in water. ...
... In addition, the mean velocity and sand concentration in solid-liquid (sand/slurry) jets and particle clouds are necessary to understand the anatomy of sand jets and particle clouds, as they evolve in the ambient and help explain ambient entrainment and mixing. Variations of sand concentration along the main axis of sand jets with Stoke numbers of 0.42 and 0.7 were found to be similar to single-phase jets ( Hall et al., 2010 ). However, the results obtained on sand jets with no initial water-phase momentum and with different particle sizes (i.e., S t = 0.46, 0.70, 1.46) indicated that particle size significantly changes the mean centerline axial velocity ( Azimi et al., 2011 ). ...
... A high-resolution data acquisition board (National Instrument, Austin, U.S.) was utilized to convert the analog voltage signals from a PV6 processing unit to digital signals. The fiber optic probe and the signal processing (PV6) unit have been successfully used in other fluidized bed studies, sand/slurry jets ( Hall et al., 2010 ;Azimi et al., 2015 ) and can be used in viscoplastic sand mixtures ( Azimi, 2015 ;2016 ;2017 ). The probe tip had a diameter of 4 mm, and contained two light sources and two light refracting optical sensors with a diameter of 1 mm each. ...
Article
Laboratory experiments were conducted to study the dynamics of particle clouds released vertically downward into stagnant water. The importance of nozzle diameter, sand particle mass, and particle size were studied in the form of an aspect ratio and Stokes number. The axial and radial profiles of sand concentration and velocity of particle clouds were measured by an accurate and robust optical probe (PV6). Empirical formulations were developed to explain the variations in sand concentration and velocity profiles. It was found that the zone of jet development was smaller in particle clouds than in single-phase water jets and sand jets. Laboratory measurements also indicated that the centerline sand concentration in particle clouds decreased with a slower rate in comparison to single-phase buoyant and sand jets. Important parameters such as mass, momentum fluxes, and drag and entrainment coefficients were calculated inside particle clouds to better understand the evolution of particle clouds in stagnant water. The radial variation of drag coefficient indicated a particle grouping effect in the core region of particle clouds where the drag coefficients decreased from 0.4 to less than 0.1. The entrainment coefficient decreased non-linearly in the radial direction. A new mathematical correlation was also developed to calculate the distribution of entrainment coefficient inside particle clouds. It was observed that the aspect ratio can significantly alter the radial entrainment coefficient in transverse directions. The inter-particle collision of particle clouds was evaluated by calculating the Bagnold number in both axial and radial directions. It was found that the inter-particle collision occurred for x/do ≤ 10 for St = 0.74 and for St = 0.52, and the Bagnold number values were smaller than 45 for x/do ≥ 20, indicating that a micro viscose regime controls the flow in these particle cloud dynamics.
... Turbulent jet, as a common phenomenon found in fluid engineering and a representative topic in fluid mechanics, has attracted considerable attention and received extensive investigation in the past several decades [1,12,18,25,34]. Previously reported focus is not only centered on single-phase jet flows but also on multi-phase jet flows which can be observed in a number of circumstances both in natural and engineering circumstances. ...
... A number of experimental investigations upon sediment-laden jets have been conducted [2,12,18,21,22,24,31]. In the early stage of these studies, Singamsetti [31] observed the axial velocity distribution of sediment-laden downward jets, and found that the axial velocity followed a self-similar Gaussian distribution based on the dimensional analysis in the zone of established flow. ...
... This difficulty has been partially solved recently. Hall et al. [12] developed a novel optical probe to measure concentration and velocity of particles simultaneously with initial sand concentration by volume as high as 0.124, which provides valuable observational data for the study of sediment-laden jets under high concentrations. ...
Article
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The drift velocity, defined as the velocity of individual phase relative to the water–sediment mixture, is a key variable in two-phase mixture model. In this paper, a relation for the drift velocity in sediment-laden jets, expressed as a power series of the nozzle Stokes number, was derived by using the perturbation approach. It shows that except the gravity and turbulent diffusion, effects of particle inertia, inter-phase interaction, and other forces contained in the first-order particle inertial corrections also play significant roles in sediment-laden jet flows. Based on the relation for the drift velocity, the velocity and concentration distribution were obtained from the similarity solutions for sediment-laden jets. The calculated concentration and velocity profiles agree well with the experimental observations in literature. Furthermore, analysis on the sediment diffusion coefficient shows that the fluid turbulence is not the only driving force for the sediment diffusion in sediment-laden jets; the effect of particle turbulence on the behavior of sediment-laden jets is also significant with the increasing of particle inertia.
... Slurry jets have wide applications in pumping industrial (e.g., mining or petroleum) tailings into settling tanks, dredging and land reclamation, discharging storm water and industrial waters that have solid particles, and etc. A number of experimental and numerical studies in this area have been reported (Brush 1962;Singansetti 1966;Awaya et al. 1985;Parthasarathy and Faeth 1987;Mazurek et al. 2002;Jiang et al. 2005;Hall et al. 2010). Usually, two injection ways were used, vertically upward and vertically downward. ...
... Previous experiments have indicated that the velocity and concentration of the solid phase across slurry jets follow self similar Gaussian distributions (Singansetti 1966;Jiang et al. 2005;Hall et al. 2010). In the slurry jets with dilute solid particles, Jiang et al. (2005) reported that the velocity and concentration of the liquid phase also 36 exhibit self similar Gaussian profiles. ...
... The spreading of the solid phase has been found to increase linearly along the axial direction (Brush 1962;Mazurek et al. 2002;Hall et al. 2010). Brush (1962) reported that the spreading rate of the velocity of the solid phase depended on the particle size. ...
... Many research studies have been devoted to investigating the mixing of turbulent sand jets and plumes of particles in ambient water ( Parthasarathy and Faeth 1987;Muste et al. 1998;Deguen et al. 2011;Azimi et al. 2012aAzimi et al. , 2014Azimi et al. , 2015Lai et al. 2016a, b;Moghadaripour et al. 2017). In sand jets, the interaction between two phases (i.e., sand and water) and particle-particle interactions considerably affect particle dynamics such as mean velocities of sand and water, solid-phase concentration distribution, flow entrainment, and turbulent fluctuations ( Sheen et al. 1994;Muste et al. 1998;Ruggaber 2000;Bush et al. 2003;Hall et al. 2010). Mixing dilute sand jets in water with low volumetric sand concentrations (c o ¼ 0.1-2.4%) ...
... Time-averaged velocities and turbulence intensities of both phases were measured close to the nozzle and at three cross sections of x=d o ¼ 8, 16, and 40, where x is the axial distance from nozzle. Effects of nozzle size and initial jet velocity on mean sand velocity and sand concentration were studied for sand jets (c o ¼ 60%) and slurry jets (c o ¼ 5.5-12.4%) in water ( Hall et al. 2010). It was found that the centerline particle velocity dropped rapidly with a rate of −1=3 and reached a plateau for x=d o > 64. ...
... They found that the normalized concentration decreased with x=d o up to x=d o ¼ 120. Numerical analysis of sand jets in water conducted by Azimi et al. (2011) also showed a good agreement with the experimental results ( Hall et al. 2010). ...
Article
Laboratory experiments were conducted to investigate the evolution of particle clouds in stagnant water. Nozzle size and released mass of particles were formed to an aspect ratio of Lo/do, where Lo is a length of sand particles occupied in a pipe with a nozzle diameter of do. Characteristic length and time scales of Li and τ* were found to classify the initial regime (sand jets), the transient regime (particle cloud with trailing stem), particle cloud without trailing stem, and swarm of particles. Image analysis indicated that the transition regime occurred for 1<τ*<5 and swarm of particles occurred for τ*>15, where τ* is the characteristic time scale for cloud classification. This classification was found to be applicable for 0.1375 mm ≤D50<0.507 mm, where D50 is the mean particle size. It was found that the formation of trailing stem can change the characteristics of transient particle clouds. Power law correlations were developed for progression depth, width, and frontal velocity of particle clouds with Lo/do using length and time scales based on initial parameters of particle clouds. The effect of particle size on evolution of particle clouds was considered using Stokes number St. Wider particle clouds were observed for small St because small particles have a higher tendency to follow water eddies. The effects of nondimensional release height of sand particles η on spreading of particle clouds were also investigated. A relatively wide range of η was tested for 1 ≤η ≤26.5. For small Lo/do (i.e., Lo/do ≤1.5), experimental results indicated a direct correlation between η and the width of particle clouds. An adverse relationship was found for 1.5<Lo/do<15.
... Experiments of Hall et al. (2010) showed that the fluid phase velocity, u f , and particle volume fraction, α, are well approximated by Gaussian profiles beyond the potential core (see later section for discussion of potential core). Jiang et al. (2005) also suggested that the particle phase velocity, u p , is a sum of u f and a settling velocity, W s , for dilute particle concentrations.At this point, it is assumed that the slip velocity, u s ðzÞ, is constant across a plume cross section (u s is in general not equal to W s ) and is applicable for a broader range of concentration, such that u p ¼ u f þ u s (the profiles are shown in Fig. 1), hence ...
... The k-ϵ mixture turbulence model was used to model the turbulence properties and the turbulent viscosity. The CFD predicted velocity and particle concentration were validated using the data of Hall et al. (2010). The results suggested that a uniform slip velocity across a cross section close to the source (but variable along the depth) is reasonable, even though the particle concentration is still high. ...
... Experiments of Hall et al. (2010) measured the velocity spreading rate of the fluid phase of a particle plume, varying parameters such as initial particle concentration, velocity, and nozzle diameter. They did not observe a systematic change in the spreading rate for the range of these parameters studied. ...
Article
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Integral models of single-phase plumes are often closed using the entrainment hypothesis, which assumes the entrainment velocity is proportional to a characteristic plume velocity, but the corresponding theoretical development for modeling particle plumes has received less attention. In this paper an integral model is developed by proposing a new spreading hypothesis for particle plumes, in which the fluid phase spreading rate is taken as that of a single-phase plume, whereas the particle phase spreading rate is a function of the particle phase and fluid phase average vertical velocity. The change in momentum flux of the particle and fluid phases are calculated by considering the cross-sectional integrated buoyant and drag forces acting on the particles, and their reaction force acting on the fluid. Mixing characteristics of the particle plume can then be determined. The model was validated by laboratory particle plume experiments conducted for various particle sizes and initial plume-to-particle-settling velocity ratios, as well as experiments in the literature. Centerline particle and fluid velocities, as well as particle concentrations were generally well predicted. The inferred entrainment coefficient for a particle plume and the importance of lift force are also discussed.
... Slurry jets have wide applications in pumping industrial (e.g., mining or petroleum) tailings into settling tanks, dredging and land reclamation, discharging storm water and industrial waters that have solid particles, etc. A number of experimental and numerical studies in this area have been reported[7,13,26,33,55,67,90]. Usually, two injection ways were used, vertically upward and vertically downward. ...
... Compared to singlephase jets, the adding of the solid phase will change the properties of the flow[89]. Previous experiments have indicated that the velocity and concentration of the solid phase across slurry jets follow self-similar Gaussian distributions[26,33,90]. In the slurry jets with dilute solid particles, Jiang et al.[33]reported that the velocity and concentration of the liquid phase also exhibit self-similar Gaussian profiles. ...
... However, this may not be valid for the slurry jets with high concentration solid particles. The spreading of the solid phase has been found to increase linearly along the axial direction[13,26,55]. Brush[13]reported that the spreading rate of the velocity of the solid phase db s dx depended on the particle size. ...
... Slurry jets have wide applications in pumping industrial (e.g., mining or petroleum) tailings into settling tanks, dredging and land reclamation, discharging storm water and industrial waters that have solid particles, etc. A number of experimental and numerical studies in this area have been reported [7,13,26,33,55,67,90]. Usually, two injection ways were used, vertically upward and vertically downward. ...
... Previous experiments have indicated that the velocity and concentration of the solid phase across slurry jets follow self-similar Gaussian distributions [26,33,90]. In the slurry jets with dilute solid particles, Jiang et al. [33] reported that the velocity and concentration of the liquid phase also exhibit self-similar Gaussian profiles. ...
... The spreading of the solid phase has been found to increase linearly along the axial direction [13,26,55]. Brush [13] reported that the spreading rate of the velocity of the solid phase db s dx depended on the particle size. ...
Chapter
Jets and plumes are common in our environment. Some examples of jets are: wastewater discharged from an outfall, emission from an aircraft or vehicle, and the eruption of volcano. Some examples of plumes are: the smoke from a chimney stack or cigarette, the thermal plumes from a fire, municipal wastewater or hot water discharged in deep water, and oil spill from sea bed. One of the most important features of jets or plumes is its ability of entraining ambient fluid to achieve self-dilution. This greatly triggers our interests to study jets and plumes. This book chapter is a review of the studies on turbulent jets and plumes, with a focus on the transport of conservative pollutants.
... A recent experimental investigation on highly concentrated slurry jets was conducted to observe the impact of particle-particle interaction on jet spreading and rate of change on the axial concentration (Hall et al. 2010). In this study, the averaged-particle velocity and concentration were measured using a novel optical probe for highly concentrated sand jets. ...
... This paper consists of two parts. In the first part, the results from the numerical simulation of the sand jets are compared with the experimental measurements of Hall et al. (2010). ANSYS CFX solver package (ANSYS 2009) with modified k-ε turbulent model and interparticle relations was applied for simulation of the water phase, and zero-equation model was used for simulation of the dispersed phase (ANSYS 2009). ...
... In the present numerical study, simulations were performed on a desktop computer with an Intel Pentium dual 2.8 GHz processor and RAM of 3 GB. The computation domain was similar to the laboratory experiment of sand jet in water (Hall et al. 2010). In Hall et al. experiments (2010), the nozzle sizes were 19 and 12.5 mm and located 75 mm above the water surface. ...
Article
Full-text available
Sand jets in water have extensive engineering applications. A detailed numerical modeling of sand jets in water was conducted at high initial sand concentration using a commercial computational fluid dynamics package (ANSYS CFX 11.0). The results of the numerical simulation were first compared with some recent laboratory experiments. Simulations were then conducted to investigate the effect of sand particle sizes on velocity distribution, concentration profile, and turbulent properties. Turbulent flow characteristics, such as turbulent kinetic energy, turbulence intensity, rate of energy dissipation, and turbulent eddy frequency, were evaluated and the trend compared with the previous studies in the literature. The location of maximum kinetic energy was found to be independent of particle size. The turbulent kinetic energy and rate of dissipation of the water phase decrease with increasing particle size. DOI:10.1061/(ASCE)EM.1943-7889.0000283. (C) 2011 American Society of Civil Engineers.
... Some experimental investigations were successful in partially measuring the characteristics of highly concentrated slurry jets. Hall et al. (2010) were able to measure sand-phase mean velocity and concentration of slurry jets with small particle size but, no turbulent measurements were made. They employed a fiber optic probe to make simultaneous measurements of both the sand particle velocities and concentrations along the axis of the jet and at different cross sections. ...
... The outer boundary of the domain was set as wall boundary condition with an outlet Parthasarathy and Faeth (1987) the injecting pipe reached the fully-developed pipe flow condition and the initial turbulence intensity of the water-phase was set as 3.7% with the initial length scale same as the pipe diameter (Ansys, 2009). Experimental study of Hall et al. (2010) was conducted in a large tank with dimensions of 2.10 Â 1.25 Â 1.16 m. According to the memory limitation and the axisymmetric behavior of the jets, the computational domain was reduced systematically to a smaller size (see Azimi et al., 2011 for detail). ...
... It is interesting to note that the mentioned shortcoming of the Coarse mesh became negligible at x/ d = 15, that is, the influence of the mesh resolution becomes less significant far from the nozzle. Capability of the model to simulate sand-phase axial velocity and volumetric particle concentration was validated with the laboratory experiments of Hall et al. (2010). The simulation results of the mean properties of sand-phase at different cross sections (x/ d = 12.9, 25.8 and 38.7) are shown in Fig. 6 triangle symbols represent the slurry jets with 8.6% and 12.4% sand concentration, respectively. ...
Article
The characteristics of sand–water slurry jets in water were investigated by a validated numerical model. Predictions of the main properties of the jet such as axial and radial velocities and particle concentration agreed well with laboratory measurements. The effect of sand particles on slurry jet spreading rate, axial velocity decay, decay of concentration and turbulence properties was studied, and the results were compared with the corresponding single-phase water jets and plumes. It was found that the width of slurry jets grows linearly from the nozzle up to a certain distance and then the growth rate became non-linear. At particle volume concentrations larger than 2.4% or with particle sizes larger than 505 μm, the spreading rate of sand phase was found to be only about one third of that of the water phase. Empirical formulations are proposed to describe the effects of controlling parameters on the axial velocity decay of slurry jets. Some integral properties were computed from numerical results such as entrainment and drag coefficients. The absolute entrainment coefficient was introduced and computational results indicated that slurry jets were more efficient in mixing than single-phase jets. From the computed values of drag coefficient, the grouping effect of particles was found to reduce the drag coefficient by half. Turbulent shear stresses of both sand-phase and water-phase were also estimated.
... Jiang et al. [1] conducted experiments and numerical simulations for predicting the settling dispersion process of fine sediments discharged into water. Jiang et al. [2], Mazurek et al. [3], and Hall et al. [4] conducted measurements of the properties (e.g., concentration and velocity profiles) of a jet of sand and slurries discharged into still water. For decades, the numerical simulation of multiphase flows (e.g., multiphase sand–water systems) has been on the basis of the conventional mesh-based methods (either Eulerian or Lagrangian) such as finite volume methods (FVM) and finite element (FEM) (e.g., [5,1]). ...
... Based on the flow conditions of the sand jet, four different cases are considered in this study (Table 1). Case 1 is selected to be comparable with the Hall et al. [4] experiments. The sand grains have a size of 0.002 m and a density of q s = 2550 kg/m 3 . ...
... It appears the model is able to predict the flow features of a turbulent sand jet. Fig. 9compares the experimental (by Hall et al. [4] and numerical centerline velocity , v cen , in different distances, d, from the water surface. To improve the oscillations in the numerical results, they are time averaged from t = 2 s to t = 4 s with 0.5 s intervals. ...
Article
Discharge of sand into water can be modeled as the multiphase flow of a non-Newtonian and a Newtonian fluid by treating the granular material as a continuum. The numerical modeling of this article is on the basis of the latest generation of computational methods, the mesh-free Lagrangian (particle) methods. In these methods, the solution domain is discretized by a set of nodes or particles, possessing the field variables and moving in a Lagrangian coordinates. This makes these methods the powerful tool for handling any deformation or fragmentation in interfaces, which is a usual problem in multiphase granular flow (e.g., sand–water systems). The Moving Particle Semi-implicit method (MPS) is used in this study. A multiphase non-Newtonian MPS approach is developed and applied to the case of sand discharge into still water. The results are validated using experimental measurements and analytical solutions to evaluate the accuracy of the model. The effects of flow conditions and rheological properties on the behaviour of sand discharge into water are also investigated.
... Jiang et al. [9] performed experiments to examine the characteristics of a sediment-laden jet with the sediment concentration at 0.19%. Hall et al. [7] extended this with the concentration in a range of 5.5 − 12.4%. Higher values up to 60% cases were investigated in [1,7]. ...
... Hall et al. [7] extended this with the concentration in a range of 5.5 − 12.4%. Higher values up to 60% cases were investigated in [1,7]. Besides particle concentration, studies were also carried out for other parameters such as particle size, initial jet velocity and nozzle diameter. ...
... Four laboratory experiments on slurry jets were originally conducted by Hall et al. (2010). In each experiment, the median particle size of sediment was s 0.206 mm d = , the density of water was Table 1, where d is the jet diameter at the nozzle, 0 u is the initial slurry jet velocity at the nozzle, s0 ϕ is the initial particle volume fraction, and St is the Stokes number. ...
... As can be seen from these figures, when the slurry jet has a larger Stokes number, it spreads less radially. To plot the data in a dimensionless form, dimensional considerations were used to predict the main characteristics of the jets (Hall et al 2010). Fig. 11 is a normalized plot of the centerline particle streamwise velocity for slurry jets, where the depth x is normalized by the length scale dFr (Fr is the Froude number), and scx u is the centerline particle streamwise velocity of the slurry jet. ...
Article
Slurry jets in a static uniform environment were simulated with a two-phase mixture model in which flow-particle interactions were considered. A standard k-ε turbulence model was chosen to close the governing equations. The computational results were in agreement with previous laboratory measurements. The characteristics of the two-phase flow field and the influences of hydraulic and geometric parameters on the distribution of the slurry jets were analyzed on the basis of the computational results. The calculated results reveal that if the initial velocity of the slurry jet is high, the jet spreads less in the radial direction. When the slurry jet is less influenced by the ambient fluid (when the Stokes number St is relatively large), the turbulent kinetic energy k and turbulent dissipation rate ε, which are relatively concentrated around the jet axis, decrease more rapidly after the slurry jet passes through the nozzle. For different values of St, the radial distributions of streamwise velocity and particle volume fraction are both self-similar and fit a Gaussian profile after the slurry jet fully develops. The decay rate of the particle velocity is lower than that of water velocity along the jet axis, and the axial distributions of the centerline particle streamwise velocity are self-similar along the jet axis. The pattern of particle dispersion depends on the Stokes number St. When St = 0.39, the particle dispersion along the radial direction is considerable, and the relative velocity is very low due to the low dynamic response time. When St = 3.08, the dispersion of particles along the radial direction is very little, and most of the particles have high relative velocities along the streamwise direction.
... An optical probe with a hardware data processing unit (PV6) was used to measure sand velocities and concentrations. The optical probe has been verified to measure velocity and concentration by many researchers for fluidized bed studies (Liu et al., 2003a(Liu et al., , 2003b and vertically downward sand-water jets (Hall et al., 2010). The probe is capable of measuring instantaneous velocity and concentration and needs to be positioned perpendicular to the main direction of the flow. ...
... The measured signal voltage is converted to sand concentration using the calibration curves. Detailed information about the principles of the optical probe and measurement techniques were provided in Hall et al. (2010). ...
... Within the jet core, two regions have been identified, the suspension region where the sediment particles are in suspension by the jet flow, and the settling region where the settling velocity exceeds the fluid velocity (Jiang et al., 2005). Hall et al. (2010) suggested that the exit densimetric Froude number is the main factor affecting the distributions of the fluid and sediment. The nozzle densimetric Froude number F, which gives an estimate of the intensity of the sediment-laden jet was then defined in the study of Huai et al. (2012). ...
Article
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Wastewater disposal through the dumping of spoil and sludge into the river, lake, or ocean is typically in the form of a sediment‐laden jet. The inorganic and organic solids from the effluent settling close to the source often result in the formation of sludge banks which can have a damaging effect on the marine ecosystem. Therefore, predicting the transport and deposition of sediment‐laden wastewater jet flows has been a focus of intense research for decades. In this paper, we discussed the fundamental understanding of sediment‐laden jets and the progress made in their predictions. We also highlighted some of the pertinent research challenges revealed by the previous studies and identified some key research issues that need to be addressed to achieve sustainable marine wastewater disposal in the face of increasing river, lake, and marine pollution.
... A few relevant environmental interests are settling sediment, volcanic eruption columns, carbon dioxide marine sequestration plumes, gas bubbles, and oil droplets from oil well explosions (Baines & Sparks, 2005;Dannberg & Sobolev, 2015;Freeth & Kay, 1987;Huppert & Neufeld, 2014;Macdonald et al., 2002;Socolofsky et al., 2011;Wang et al., 2016). Previous numerical simulation (Azimi et al., 2011(Azimi et al., , 2012El-Amin et al., 2010;Ivanov et al., 2020) and laboratory (Hall et al., 2010;Pierre & Jayamumi, 1995;Seol et al., 2007) studies have investigated the effects of particle size on the mean flow characteristics of sediment plumes. In recent years, the distribution of suspended sediment concentration in open channel has also been studied. ...
Article
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Deep sewage discharge leads to inestimable damage to the ambient water (lakes, oceans and reservoirs), which has caused widespread social concern. In the current paper, a three‐dimensional (3D) buoyancy plume model for deep sewage discharge was developed. It simulates sediment‐laden flow with the effects of temperature and salinity differences. Taking the turbulent diffusion coefficient of salinity (αsal) as the calibration parameter, a comparison between the RNG k‐ε and the standard k‐ε models was performed. The proposed model was verified well and agreement with experiment, which proved that the RNG model with the αsal value of 0.4 was the optimal calibration. Then the model was applied to quantify the behavior of the buoyant plume in the ambient fluid (salt water) with respect to different contours of turbulent kinetic energy (k), temperature, salinity and sediment. The dimensionless centerline trajectory positions and boundary positions of them were determined. The results indicated that the discharge of low‐salinity sediment‐bearing water influenced the deep ambient water spatially, both near the free surface and in the vertical plane. Different diffusion and spreading shapes (butterfly, Ginkgo biloba, bean) can be observed on the surface. Accurately evaluating the impact of deep discharge on ambient water has great significance for maintaining healthy and sustainable environments in offshore areas, deep lakes and reservoirs.
... Previous laboratory (Hall et al. 2010) and numerical (Azimi, Zhu & Rajaratnam 2011 studies have investigated the influence of particle size, particle concentration and nozzle size on the mean flow characteristics of sediment plumes. These authors considered fine to medium sized sand with diameters in the 0.1-0.8 ...
Article
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Turbulence statistics in a negatively buoyant multiphase plume - Volume 896 - Ankur D. Bordoloi, Chris C. K. Lai, Laura Clark, Gerardo V. Carrillo, Evan Variano
... In the present research, researchers mainly take the mixture model as the main research method. The particle model is also used to study the solid-liquid two-phase flow, but its application to the turbine simulation has rarely been reported [13][14][15]. In this paper, the particle model and the inhomogeneous model are used to simulate and analyze the solid-liquid two-phase flow of the HL240 turbine using the ANSYS-CFX fluid analysis software. ...
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To solve unstable operating and serious wearing of a hydraulic turbine in its overflow parts under solid-liquid two-phase flow, a particle model software and an inhomogeneous model in CFX are used to simulate the hydraulic turbine to understand the wearing of overflow parts and the external characteristics under the solid-liquid two-phase flow. Eleven different conditions at different densities and concentration have been calculated. The simulation results show that the volume distribution of solid particles is larger at the turn of the volute and nose end, resulting in the serious wear in this area. Due to uniform flow at the butterfly edge of volute under solid-liquid two-phase flow, the wear at the entrance of guide vane, the inlet of the blade and the outlet in the shroud is more serious than in other sections. Meanwhile, the collision between the solid phase particles and the overflow components is more intense under solid-liquid two-phase flow in the rotor which can lead to cavitation especially in the outlet and shroud of the blade. In addition, with the increase of density and concentration of solid particles the inlet and outlet pressure difference gradually rises, causing the efficiency loss of the hydraulic turbine.
... Usually, flume sediment experiments are carried out by loading a prescribed rate and composition of sediment at the inlet or through recirculating a given sediment that is pre-laid to the flume. Dry sand load is to deliver the prepared sediment using a feeder connected with vibrating belt [18,19]. Wet loading is to inject prepared sediment slurry to the flume at inlet [20,21]. ...
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Fine sediment transport is currently attracting increasing attentions owing to its importance in the dynamics of sediment-contaminant interaction in the fluvial environment downstream of dams, which calls for more detailed and accurate flume experiments. However, because of inaccurate loading and undesired recirculation of fine sediment in the usual short laboratory flumes, such experiments are often unrepeatable and unreliable. In this technical note, we propose a new sediment feeder, to load dry sediment sample at the inlet, and a pressurized sediment filter, to screen the sediment out at the outlet, to implement a clear-water supply system for the flumes. It can improve fine sediment experiments not only by accurate loading but also through preventing undesired sediment recirculation, which can interfere and even modify the designated upstream input conditions. These devices have been constructed and tested, shown to be practical, simple and effective. Using them together can also provide a way to reclaim all the samples of experimental sediment that are of crucial importance for repeat and multiple tests for different contamination with a given sediment without losing the prescribed composition and other properties. This implementation is especially suitable for simulating fine particle affinity contaminant transport in fluvial turbulent flows in low sediment concentrations.
... The numerical methods used in this study were validated in previous work [1] against the experimental data of Hall et al. [28]. In the validation, the numerical results of particle velocity and particle concentration at some stand-off distances are used to compare with corresponding experimental data. ...
Article
When entrained into a carrier flow, such as liquid or gas, sand particles are able to interact with material surfaces strongly, which may cause serious erosion damage. How particle size affects the erosion characteristics, such as erosion pattern, erosion rate, erosion mechanism and erosion profile remains largely unexplored. In this study, we perform both experiments and numerical simulations to study the effects of particle size on those factors. In the experimental setup, a wet erosion test-rig is used, in which the flow speed of a mixture of sand particles and water is set to be 30 m/s and the different average sand particle sizes of 50, 80, 150, 350, 450 and 700 μm are taken. The experimental results show that there is a transition in the erosion profile from a "W" shape to a "U" shape with increasing the sand particle size. The sample surface profiles obtained from the experiments are then used to create geometry models for our numerical simulations. The simulation results are in good agreement with experimental measurements in terms of erosion rate and erosion pattern. Importantly, the simulations show that the larger sand particles able to dig deeper into the sample surface than smaller particles, providing a cogent explanation for the observed transition. The present work highlights the important role of particle size in affecting the erosion pattern, erosion rate, erosion mechanism and eroded profile.
... In the study of the sediment-laden jet, Hall et al. (2010) suggested that the exit densimetric Froude number was the main contributor to the distributions of water and sand. The exit densimetric Froude number, which gives an estimate of the intensity of the sediment-laden jet, ...
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Sediment-laden jets were simulated with an Eulerian two-phase model that implements Euler-Euler coupled governing equations for fluid and solid phases. Both flow-particle and particle-particle interactions were considered in this model. A modified k-ε turbulence model was chosen to close the fluid phase equations. The computational results compared well with previous laboratory measurements. The characteristics of the flow fields of the two phases and the influences of hydraulic and geometric parameters on the distribution of the sediment-laden jet were analyzed on the basis of computational results. The calculation results reveal that if the initial velocity of the sediment-laden jet is high, the jet is sprayed higher and spreads further in the radial direction. The turbulent kinetic energy k and turbulent dissipation rate ε, whose decay rates are higher than that of the jet velocity, decrease rapidly after the sediment-laden jet enters the nozzle. For different values of the exit densimetric Froude number F, the profiles of deposited sediment and the axial distributions of the jet velocity, density deficit and turbulent kinetic energy are self-similar on a certain jet axis. The decay rate of the sand velocity is higher than that of water velocity along the axis of the sediment-laden jet, and if the sediment particle has a higher settling velocity, it has higher inertia and spreads less radially.
... sil.ab.ca) with a mean diameter of D 50 = 0.21 mm and density of q s = 2540 kg/m 3 were added gradually to the foam mixture to form a sand-foam mixture. The uniformity of particle sizes was evaluated by fitting the sand particle size distribution data with the lognormal probability curves [23,24]. Sand particle sizes were considered uniform since the geometric standard deviation r g = D 84 /D 50 = D 50 /D 16 was found to be smaller than 1.35 [25]. ...
... The capability of the numerical multiphase flow modeling method used in this study is validated by comparing with experimental data of Hall et al. [57]. In the validation, the numerical results of particle velocity and particle concentration at some standoff distances are used to compare with experimental data. ...
Article
Material erosion under a multiphase flow is a very complex process influenced by many parameters. Understanding physical mechanisms and establishing governing laws for predicting the erosion rate are of great importance to alleviate or even avoid erosion damage in engineering applications. In this paper, we perform a combined numerical and experimental study to understand how the evolution of material surface induced by erosion can inversely affect the multiphase flow characteristics and erosion mechanisms on the surface. A water-sand erosion test-rig system is used to obtain the surface profiles, erosion rates and surface patterns of stainless steel under a water-sand multiphase flow. A multiphase flow model and an erosion model are combined to obtain the flow profile, erosion rate and erosion pattern. To gain insights into the multiphase flow and erosion mechanism changes due to the surface evolution induced by the erosion process, we take the surface profiles obtained from our testing samples at different stages of experiments to create geometry models for our numerical simulations. The numerical results are in good agreement with experimental results for erosion rate and erosion pattern as well as erosion mechanism. Through systematic numerical simulations, we clearly reveal the detailed changes in multiphase flow characteristics and erosion mechanisms arising from the surface evolution. The present work shows that the erosion process is very sensitive to the change of the test sample surface resulting from the change in erosion mechanism, highlighting the need to include the surface evolution in erosion modeling.
... There is as yet little experimental data on particle-laden buoyant jet discharges, especially their bottom interactions. In their experimental study of the dynamics of particle-laden jets in stagnant ambient water, [62,79] did not include boundary interactions. Though the role of the ambient hydrodynamics on the discharges is prevalent after such interactions [12], the impingement position may shift significantly in strong ambient currents [60]. ...
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In this paper, the authors review the current state of the science on the dynamics of gravity currents generated by positively and negatively buoyant jet discharges from submerged round outfalls (i.e., a point source) in inland and coastal waters. Specifically, this article focuses on describing gravity currents occurring at both the bottom boundary and the free surface of the receiving fluid. The manmade discharge operations generating both types of gravity currents and their significance to sustainability of the surrounding hydro-environment are first described. The authors then summarize the flow regimes characteristics of these discharges before becoming gravity currents and how those flow regimes influence the dynamics of the gravity currents. The gravity current dynamics in the calm receiving waters are then analyzed. This analysis is followed by an analysis of the influence of the hydrodynamic forces (e.g., currents, turbulence, waves) on the dynamics of gravity currents. Finally, the authors review quantitative modeling approaches for different forms of gravity current, and identify the current knowledge gaps and research needs.
... The behaviour of these jets is determined by the size, concentration and density of the suspended particles. A number of experimental and numerical studies have been conducted to investigate the hydrodynamic behaviour of steady-state particle-laden jets (Virdung and Rasmuson, 2007;Wang et al., 2009a;Hall et al., 2010;Gan and Nichels, 2010;Azimi et al., 2011) but less attention has been devoted to the study of the fronts of particle-laden jets with relatively high particle concentrations. ...
Article
An experimental study was conducted to examine the behaviour of a sand jet front in water and its associated fluid motions with different sand particle sizes and initial sand jet diameters. The shape of sand jet front was found to be directly related to the particle Reynolds number of sand particles. The frontal velocity along the centreline of the jet axis was measured and compared to that of single-phase buoyant jets and particle thermals. The jet front settling velocity of small particles was found to be as large as 5 times that of the individual particle settling velocity. The presence of particles and the additional momentum generated by particles were found to reduce the growth rate of the jet front width, compared with those of the single-phase buoyant jets and particle thermals. Evolution of vortices and their structure were extracted from velocity fields by employing Galilean velocity decomposition and a local vortex identification technique. It was shown that, radial convection velocity can change the shape of the vortices. Large radial convection velocity transformed the vortex from semi-circular shape to elongated ellipsoid vortex. Effect of particles on turbulence of the carrier phase was studied. It was found that smaller particles increase turbulence attenuation of the carrier phase. Effect of particles on the modulation of turbulence can be described by the Stokes number along the jet axis. A classification was made for solid–liquid and solid–gas turbulent jets and new formulations were proposed to show the correlation between Stokes number and the turbulence attenuation of particle-laden turbulent jets.
Article
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The motion of particle clouds (i.e., sediment clouds) usually can be found in engineering applications such as wastewater discharge, land reclamation, and marine bed capping. In this paper, a series of laboratory tests are conducted on coral sand to investigate the shape feature of the single particle and the mixing processes of the coral sand particle clouds. The shape of coral sand particle is measured and quantified. The experimental results demonstrate that the shape of coral sand particles tends to be spherical as the particle size decreases, and empirical equations were established to explain the variation of D 50 and f S,50 of coral sand. Compared with the silica sand, the evolution of the coral sand particle cloud still experiences three stages, but the threshold for the Reynolds number of particle clouds entering the next stage changes. Further, the normalized axial distance of the coral sand particle clouds is 58% smaller. The frontal velocity exhibits similar varying tendency for the coral sand particle cloud. Considering the difference in shape between coral sand particles and silica sand particles, a semi-empirical formula was proposed based on the original silica sand prediction formula by adding the shape factor and the experimental data of 122 µm⩽ D 50 ⩽842 µm. It can predict the frontal velocity of the coral sand particle clouds.
Chapter
A series of detailed laboratory experiments were conducted to investigate the effect of low-velocity ratios on the particle dynamics in vertically discharged sand-water coaxial jets in stagnant water. The core and the surrounded annular nozzle diameters were do = 6 mm and da = 12 mm, respectively. Sand particles with a median diameter of 0.389 mm and an initial concentration of 60% by volume were issued through the annular nozzle. Different core water discharges were tested providing a Reynolds number range between 6622 and 11,919. The sand concentration and velocity were measured by implementing an accurate optical fiber probe (PV6) in axial and radial directions. The effects of velocity ratio (Ru) were studied to understand the dynamics of particles and momentum transfer for Ru < 0.5. In a distance less than 5 times of nozzle diameter, the decay rate of axial velocity and concentration of sand particles was found to be independent of velocity ratio. However, in the zone of flow development, the velocity decay rate of coaxial sand-water jets was higher than particle clouds and similar to single-phase water jets. It was found that the decay rate of sand concentration is lower than particle clouds and similar to slurry jets. The role of sand particles in turbulence augmentation and inter-scale coherent structures of the jet was also investigated using the Spectral Proper Orthogonal Decomposition method (SPOD). The SPOD method was used to decompose the flow into energy-ranked coherent structures and extract the energy spectra. It was found that a considerable portion of the turbulence kinetic energy is stored in low-frequency modes for velocity ratios smaller than 0.16. The Kelvin–Helmholtz (KH) type wave packets were observed in low frequencies and the first ten modes were found to be associated with the annular nozzle.
Article
Detailed laboratory experiments were performed to study the dynamics and mixing properties of vertically discharged sand-water coaxial jets in stagnant water. The effects of velocity ratio on the fluid dynamics of two-phase coaxial jets were studied. The axial and radial distributions of sand concentration and velocity were measured with an advanced optical fiber probe (PV6), and sand concentration and velocity measurements were formulated based on flow characteristics. The experimental results demonstrated that the axial velocity and concentration decay rate along the mixing zone, a length approximately six times greater than the nozzle diameter, were independent of the velocity ratio, Ru. Beyond the initial mixing zone, the axial decay rate of sand concentration increased with increasing velocity ratio and became similar to the concentration decay rate of slurry jets. The axial velocity decay of sand-water coaxial jets indicated an inverse relationship with velocity ratio: velocity decay rates decreased with increasing Ru. Experimental observations of sand-water coaxial jets showed that the spreading rate of coaxial jets decreased with increasing velocity ratio; for the coaxial jet with the highest Ru, the spreading rate reached the spreading rate of slurry jets. The integral quantities of jets such as mass and momentum fluxes were calculated using sand concentration and velocity profiles. Average drag coefficients were calculated using momentum balance and proposed equations for sand velocity and concentration. The variations of drag coefficient and interparticle collision parameter indicated that the particle grouping effect reduced the drag coefficient in sand-water coaxial jets with lower velocity ratios. The axial variations of the interparticle collision parameter indicated a strong correlation with velocity ratio. The strong correlation between velocity ratio and the mixing properties of sand-water coaxial jets suggests the velocity ratio is an effective design parameter to control and optimize particle mixing in stagnant water.
Experiment Findings
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The study of sand-laden turbulent jet is one of the interest areas for researchers in the field of hydraulics as it has many important engineering applications such as marine bed capping, mining operations, hydro-transport, dredging material disposal, and discharge of domestic and industrial wastewater. Several in-depth studies have been conducted previously focusing on various parameters. In this paper, results from a simple experimental study have been presented. Sand jet of same sized particle diameter has been used during the whole experiment. Three types of nozzle diameters and for each diameter of nozzle different sets of sand masses have been used for the study. The optical probe has been used in six different positions to register the voltage data and thus to facilitate sand particle frontal velocity calculation. The last position of the probe has been set depth enough to ensure that the sand particle has attained its terminal velocity in most cases. Several experiments have been conducted to see the effect of nozzle diameter and sand mass on sand particle frontal velocity.
Article
Laboratory experiments were conducted to investigate the dynamics of oblique particle cloud in stagnant water. Previous laboratory studies on vertically downward particle clouds indicated the importance of nozzle diameter do and mass of sand particles in form of an aspect ratio of Lo/do where Lo is the length of occupied sand particle in a pipe. In addition, particle size plays an important role in mixing capability of particle clouds. 30 laboratory experiments were carried out to consider the effects of Lo/do, particle size D50, angle of release θ, and release height H. In order to generalize the outcome of the present study, both particle size and release height were normalized to form Stokes number St and release number η. Three classes of particle size were identified for 0<St<1 and a relatively wide range of aspect ratio 0.8≤Lo/do≤40.1 was formed by changing the mass of sand particles. To consider the effects of release angle and release height, four release angles of θ=15o, 30o, 45o, and 60o were chosen and three release numbers of η=8.5, 13.2, and 17 were selected. Trajectories of particle clouds were identified based on the position of cloud front. Empirical formulations were developed to model the path of the frontal head of oblique particle clouds. Using a theoretical approach, the location of particle fall out was estimated within ±10% accuracy. Variations of the frontal velocity of particle clouds in vertical direction were investigated and an empirical equation was proposed based on dimensional analysis to predict the frontal velocity at different initial conditions. Mixing efficiency of particle clouds was characterized by entrainment coefficient αe. The entrainment coefficients of particle clouds were computed using the theoretical entrainment hypothesis. It was found that the Stokes number can significantly alter the mixing capability of particle clouds. The influence of controlling parameters on particle-particle interactions can be studied by estimating the drag reduction due to particle grouping effects. The averaged drag coefficients Cd of particle clouds were calculated from momentum equation and a semi-empirical model was proposed to estimate the drag reduction of particle clouds. Significant drag reduction occurred in particle clouds in comparison with individual particles.
Article
Laboratory experiments were conducted to study the dynamics of sand jets passing through two immiscible fluids. Different oil layer thicknesses, nozzle diameters, and sand masses were employed. Evolution of oily sand jets with time was investigated using image processing and boundary visualization techniques. Different shapes of the frontal head and trailing wave section were observed and cloud formation was classified into different categories based on Reynolds number, normalized oil layer thickness, and evolution time. It was found that the effect of Reynolds number on evolution of oily sand jets was more significant than the other parameters. Width and frontal velocity of oily sand jets were measured at different times. It was observed that oily sand jets became unstable after a distance of ten times larger than the nozzle diameter. Instability of oily sand jets caused intense spreading with a spreading rate of 0.4. The thin layer of oil encapsulated sand cluster was ruptured due to excess shear stress and caused bursting of the frontal head into a cloud of sand particles. Three different bursting mechanisms were observed and a correlation was found between the densimetric Froude number and the normalized bursting time. Data mining and boundary visualization techniques were used to model oily sand jets. Model trees were developed to classify and predict the growth of oily sand jets at different conditions. Modeling results indicated that the Model tree can predict the growth of sand jets with an uncertainty of ±8.2%, ±6.8%, and ±8.7% for width, velocity, and distance, respectively.
Article
Sediment-laden turbulent buoyant jets are commonly found in natural and engineered environments. Examples include volcanic eruptions, deep sea hydrothermal vents, discharge of partially-treated wastewater, and dredging operations. A horizontal sediment buoyant jet is characterized by a horizontal momentum jet, rising plume, and a horizontal surface gravity current. The settling of particles from a sediment buoyant jet depends on the complex interaction of particles with turbulent fluctuations and the mean flow-in particular particle reentrainment due to the external irrotational flow induced by the jet. A three-dimensional (3D) stochastic particle tracking model is proposed to predict the sedimentation from an arbitrarily inclined sediment-laden buoyant jet in a stagnant ambient. The simple model predicts the entire 3D jet flow field via a coupling of semianalytical models for the mean flow as well as turbulent fluctuations. The mean flow for the turbulent buoyant jet and the surface gravity current are determined using well-validated integral models, while the external jet-induced irrotational flow field is computed by a distribution of point sinks along the jet trajectory. Turbulent velocity fluctuations are modeled by a Lagrangian particle velocity autocorrelation function that mimics the trapping and loitering of sediment particles in turbulent eddies. The turbulent fluctuations are stochastically generated from a self-similar profile of the turbulent kinetic energy derived from computational fluid dynamics (CFD) solution of jets and plumes. Predictions of the particle tracking model are in excellent agreement with experimental data over the entire jet-plume regime for a wide range of particle sizes (58-621 μm) and properties. The model provides physical insight in delineating the modes of sediment fall out. The fraction of sediment mass fall-out from the jet lower boundary is found to be a function of the ratio between the jet momentum-buoyancy length scale ls = M3/4o/B1/2o and the momentum-settling length scale lm = M1/2o/ws, where Mo and Bo are the source momentum and buoyancy fluxes, and ws is the particle settling velocity in quiescent fluid. The particle distribution in the vertical centerline plane of the buoyant jet is also well-predicted. The model does not require any a priori adjustment of sediment settling velocity or particle re-entrainment rate.
Article
By changing the inlet edge blade shape of the plane to get different degrees of the back swept blade, simulating the back swept degree of 40°, 65°and 90° of axial flow pump blades and original prototype blades pump of the three-dimensional solid-liquid two-phase flow channel to get the characteristic curves and distributions of solid particles within the impeller. Characteristic curves show that the back swept angle will reduce the efficiency and head of the pump, which means the reduction grows with the growth angle. With the increase of the particle diameter, the particle moves backward to the pressure surface, therefore the solid phase volume fraction increases, meanwhile the solid phase volume fraction at the suction surface near the hub of the inlet side also increases; with the increase of particle volume fraction, the solid phase volume fraction at the pressure surface reduces and the solid phase volume fraction at the suction surface of the blade increases. It is predictable that the solid phase moves according to the angle between the radial direction and the solid phase velocity direction. The smaller the angle is the more obvious the radical flow is and the bigger the backswept angle is, then the solid phase is more difficult to contact with the blade suction surface than the pressure surface. When the sweep angle is small, the degree of radial flow is the major factor affecting the distribution of the solid phase on the pressure surface of the blade, otherwise when the sweep angle is large, the sweep angle would be the major factor, the greater the sweep angle, the smaller volume fraction of the solid phase on the pressure surface of the blade. Because the 90°sweep angle is large enough, and the radial flow at the suction surface is the smallest, when the back swept angle is 90° the solid phase volume fraction is small and uniform at the suction surface and the pressure surface near the rim of the blade, severe local wear can be avoided. When the swept angle is 40° and 65°, the solid phase volume fraction on the pressure surface near the rim of the blade is large. So it will easily lead to severe wear. In order to verify the correctness of the simulated results, the 65° back swept blade model is compared with the back swept blade of the sludge axial flow pump in the Nanjing Jiangxin island sewage treatment plant, meanwhile the swept angle of the blade is also close to 65°. The actual operating condition of the back swept impeller is complex, and the particle concentration and diameter may not be uniform, but according to the 2.3 and 2.4 sections, the impact of the particle concentration and diameter on the distribution of the solid phase on the blade is small, the solid volume fraction is just changing in on the original position with the particle diameter and the concentration changes. So the wear leaf diagram of the back swept blade can be comprised with the solid phase distribution of the simulation results. Based on the above, increase the back swept angel can reduce the solid volume on the pressure surface of the blade and the 90° back swept angle condition is better than that of 40° and 65° according to the solid volume.
Article
3D simulation was performed for the solid-liquid two-phase turbulent flow in centrifugal pumps using particle model and inhomogeneous model separately by ANSYS-CFX software. The k-ε turbulence model was applied to predict the liquid-phase, while an algebraic equation known as the dispersed phase zero equation was adopted to predict the solid-phase. At wall boundaries, for the so-lid-phase the free slip wall conditions was used for mass and momentum. The slip velocity and the fraction volume of solid particles on the wall of flow-passage parts were studied. The computational results were compared with the results of the corresponding literature. It is found that solid particles mainly accumulated near the wall of the exit of volute. There are three places where slip velocity of solid particles is relatively high and erosion of walls is more serious. Such as the head of blade near front shroud and the blade trailing edge, also the shroud part close to the back pressure side of blade. With these two models respectively, the CFD simulation can accurately simulate solid-liquid two-phase turbulent flow.
Article
Three-dimensional simulation was performed for the solid-liquid two-phase turbulent flow in centrifugal pumps with particle model and inhomogeneous model separately by ANSYS-CFX software. k-ε turbulence model was applied to predict the liquid-phase, and an algebraic equation known as the dispersed phase zero equation was adopted to predict the solid-phase. All wall boundaries were set as free slip wall conditions. Under the fraction volume of 0.1, the effect of the different diameters (0.1 mm, 0.25 mm, 0.5 mm and 0.75 mm) of solid particles on the slip velocity on the wall of flow-passage parts was studied. The results show that the slip velocity of solid particles increases along with the increase of the particle diameter. And solid particles gradually accumulate near the wall of press surface. There are three places where slip velocity of solid particles is larger and erosion of wall is more serious, such as the head of blade and the blade trailing edge, also the shroud part close to the back pressure side of blade.
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Some practical design tips and important recommendations are given to minimize the negative effect of discharge of wastewater laden with solid particles via submarine outfall. This study emphasizes the role of respecting the hydraulic conditions in the outfall to prevent sedimentation in the outfall or their accumulation in adjacent areas; also it includes the ways used to improve the outfall hydraulic capacity that decreases with time. The diagnostics and remediation procedures of mixing zones are discussed, especially in the case of previous toxic discharge that results in toxic sediments at the bed load. A literature review of techniques used to assess sediment quality near discharge points and locate effluent-affected sediment deposit is presented that include using acoustic profiles and images, chemical analysis, toxicity tests and multivariate indicators.
Article
Three-dimensional simulation was performed for the solid-liquid turbulent flow in swept-back double blades sewage pump with Particle model and SIMPLEC algorithm using ANSYS-CFX software. The coupling of impeller and volute is established using multiple reference frame. The k-ε double turbulence model was applied to predict the liquid-phase, and an algebraic named the dispersed phase zero equation was adopted to predict the solid-phase. Under the solid volume fraction of 5%, 10%, 15% and 20%, the effect of five different solid particle diameters (0.2, 0.4, 0.6, 0.8, 1.0 mm) on the particle distribution in the pump, solid particle slip velocity, the wear and tear of flow components, and the influence law of pump hydraulic overall performance were studied. Under the so-lid volume fraction of 5%, 10%, 15%, 20%. The results show that with the increase of solid volume fraction, particle trajectory is biased toward the back of suction side. Slip velocity of solid particle is significantly increased on pressure side and back shroud near the suction side's trailing edge, indicating wear of the wall is exacerbated, therefore, the shroud should be thickened in design phase. In addition, solid particle size and solid volume fraction have an influence on the pump hydraulic overall performance in different degrees: the hydraulic head and pump efficiency drops with the increase of particle side, while the hydraulic head increases and pump efficiency declines with the increase of so-lid volume fraction. According to the test results, the efficiency of model pump can reach 80% with 11 m head at rated condition. The design of sewage pump meets the requirements, and has reached the leading level in domestic design. ©, 2015, Editorial Department of Journal of Drainage and Irrigation Machinery Engineering. All right reserved.
Article
Horizontally discharging jets laden with sediment particles are investigated numerically. The computation of the fluid phase is conducted by Large Eddy Simulation (LES) while Lagrangian particle tracking is used to calculate the motion of sediment particles. Both momentum and buoyant discharge cases of sediment-laden jets are simulated. The computational results reveal that the advecting large eddies are responsible for the formation and the transport of high-concentration particle patches in the jet flows. For a horizontally discharging buoyant jet, it is observed that there exists a significant correlation of particle abundance and high turbulence intensity in the lower outer layer of the jet flow when its trajectory is deflected by buoyancy. The investigation of the instantaneous vorticity fields shows that the particle transport in horizontal sediment jets are large associated with the large eddies in the flow.
Article
A horizontally discharging buoyant jet laden with sediment particles is studied experimentally. Simultaneous measurements of the fluid and particle velocity fields are made with a two-camera PIV technique. The fluid phase is marked by small fluorescent particles which when excited by laser light, emit light of different wavelengths to the light scattered by the solid sediment particles. Similar to a particle-free buoyant jet, it is observed that buoyancy plays a main role of governing the flow mechanisms in the bending zone of a sediment-laden buoyant jet, where the locations of maximum velocity magnitude and the locations of maximum turbulence intensity are on different parts of a jet cross-section. It is found that regions of particle abundance and high turbulence intensity reside coincidently at the lower and outer layer of the jet in its bending zone. In the momentum-dominated zone, the action of buoyancy already modifies the cross-sectional profiles of fluid velocity and turbulence and the jet centerline trajectory is slightly bent upwards from the initial horizontal direction. The jet turbulence is suggested to play the role of suspending the particles within the jet. At low particle concentrations, the mean velocity field of the fluid phase is not affected much by the presence of sediment particles, but the turbulence property is more susceptible to variations in the initial particle concentration.
Article
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We have performed an experimental campaign in the laboratory on the near field behavior of inclined negatively buoyant jets, issuing from a circular sharp-edged orifice, in order to investigate the symmetry properties of this phenomenon. The velocity measurements were obtained via a non intrusive image analysis technique, namely Feature Tracking Velocimetry. We present here both first and second order statistics, showing that the asymmetry of inclined negatively buoyant jets cannot be considered only a far field feature of this phenomenon, as it arises very close to the release point.
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Sand jet in non-Newtonian viscoplastic fluid is associated with a number of industrial and engineering applications, including sand capping for the reclamation of oilsands tailings ponds and sediment deposition into soft mud. In this study, several experiments were carried out by depositing circular sand jets vertically into viscoplastic fluids, known as Laponite gel. The deformation regimes of sand jets in the gel were investigated. The yield-gravity parameter of the deformed sand drop in the gel was computed.
Article
This note presents the results of an experimental study of circular sand jets in air from three nozzles of diameter of 19.2, 31.1 and 63.8 mm. It was found that the frontal speeds of the sand jets and the steady sand jet velocity accelerate due to gravity with negligible air resistance. The sand velocity does not appear to be affected by sand particle sizes for the three sizes tested. The diameters of sand jets, as they travel downwards, decrease and gradually approach an asymptotic value after a distance of 120 times of the initial jet diameter. The sand concentration in the jet decreases as the distance from the nozzle increases. Waves were observed at the periphery of the sand jet and some preliminary results of wave speed and wavelength are reported.
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The axial and radial velocity components w and u, and the concentration c of a Rhodamine 6G dye were measured simultaneously in a turbulent buoyant jet, using laser-Doppler anemometry combined with a recently developed laser-induced-fluorescence concentration measurement technique. These non-intrusive techniques enable measurements in a region of plume motion where conventional probe-based techniques have had difficulties. The results of the study show that the asymptotic decay laws for velocity and concentration of a tracer transported by the flow are verified experimentally in both jets and plumes. The momentum and volume fluxes and the mean dilution factor are determined in dimensionless form as a function of the normalized distance from the flow source. Contradictory results from earlier experimental plume investigations concerning the decay laws of w and c and the plume width ratio bc/bw are discussed. The turbulence properties and the transition from momentum-driven jets to buoyancy-driven plumes are presented. The turbulence is found to scale with the mean flow as predicted by dimensional analysis and self-similarity. Buoyancy-produced turbulence is found to transport twice as much tracer as jet turbulence. Although velocity statistics in jets and plumes are found to be highly self-similar there is a strong disparity in the distribution of tracer concentration in the two flows. This occurs in the time-average mean flows as well as the r.m.s. turbulent quantities. Instantaneous concentration fluctuations are found to exceed time averages by as much as a factor of 3. The experimental results should provide a reasonable basis for validation of computer models of axisymmetric plumes.
Article
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This paper investigates the influence of inter-particle collisions on the particle phase variables in the configuration of a free turbulent round jet laden with solids, i.e., considering the so-called four-way coupling. As a result, and due to the absence of walls confining the flow, the effects of particle–particle interactions start to be relevant for larger mass loading ratios when compared with confined flows, such as those occurring in pipes or channels. Interestingly, the particle phase fields are modified similarly to what happens in the previous confined flows: the profile of mean axial velocity flattens and the turbulence tends to be more isotropic when inter-particle collisions are taken into account. However, the associated mechanisms are slightly different.
Article
The sediment laden buoyant jets with a certain fall velocity of particles are analyzed theoretically, assuming similarities for both velocity and sediment concentration profiles, and using Prandtl's mixing-length theory, for two-dimensional and axisymmetric cases. The jets are shown to be divided into three regions: nonbuoyant region, plume region, and settling region which causes only in an axisymmetric case. The numerical solutions show that the particle laden jet performs like a pure jet near the jet source, as the initial momentum is predominant. For the two-dimensional jet, the jet becomes asymptotic to the negative buoyant plume of finite velocity which is expressed in terms of jet sediment flux.
Article
An investigation of the instantaneous particle concentration at the centerline of a turbulent channel flow has been conducted. The concentration field was obtained by digitizing photographs of particles illuminated by a spanwise laser sheet and identifying individual particles. The resulting distribution was then compared to the expected distribution for the same number of particles randomly distributed throughout the volume. Significant departures from randomness have been found and the differences are strongly dependent on the time constants of the particles. Five different particle classes were investigated and the maximum departure from randomness was found when the ratio of the particle’s aerodynamic response time to the Kolmogorov time scale of the flow was approximately one. The length scales of the particle clusters were found to change with the particle size. The correlation dimension was used to produce a single parameter describing the degree of concentration regardless of the scale on which it occurs. The spacing between particle clusters was also investigated and found to be much larger than the scales on which concentration occurs.
Article
This Technical Note presents photographic observations of turbulent sand jets in water. Four sands, with mean diameters ranging from 0.17 to 1.47 mm. were used in combination with three nozzles of 8, 12.7 and 25.4 mm diameter. It was found that the linear growth rate of these sand jets increases with the parameter F0 which is proportional to the ratio of the momentum flux of the sand jet at the nozzle to buoyant force on the sand particles. For the largest value of F0 equal to about 15, the growth rate of the sand jet was 0.19 which is about 20% larger than that of turbulent water jets with Reynolds number larger than about 10,000.
Article
In this study, we investigated a vertical dilute sediment-laden jet both experimentally and theoretically. First, an instantaneous whole-field velocimetry tool, particle image velocimetry, was applied to measure the sediment and fluid mean and fluctuating velocities of a downward sediment-laden jet at the same time. Subsequently, an analysis was performed based on two-phase conservation equations for both downward and upward jets. The analysis shows that the mean sediment velocity can be taken as the sum of fluid velocity and the settling velocity in both cases. For the downward jets, the decay rate of the centerline sediment concentration increases with the sediment settling velocity while decreases with the initial discharge velocity. The zone of flow establishment for the sediment velocity is found to be longer than that of the fluid. For the upward jets, the maximum rise of the sediment particles and their deposition distribution on the ground were derived theoretically. The predicted results compare well to the experimental data in the literature.
Article
The interaction of a particle-laden jet (ReUe=6600) with a single synthetic jet or a continuous control jet located upstream of the main jet exit (i.e., within the main jet nozzle) was examined experimentally using PIV and PTV. A reduction technique was used to calculate 3-D flow fields from multiple 2-D measurement planes to study the complex 3-D interactions. The synthetic jet was shown to influence the particles both directly and indirectly through the manipulation of the carrier fluid’s drag force on the particles. The synthetic jet impulse directly vectors the particles away from the synthetic jet, while the formation of large vortical structures indirectly affects the particles, spreading throughout the measurement domain. By comparison, a continuous control jet only vectors the particles away from itself. The lowest Stokes number particles respond similarly to the carrier fluid, while higher Stokes number particles are less responsive to the control and only follow the strong vortical structures (i.e., higher circulation), which suggests that the preferential concentration concept depends on both the Stokes number as well as the strength of the coherent structures.
Article
The dispersion of particles in turbulent flows is poorly understood. Previous approaches to this problem have been found to be inadequate for nonisotropic turbulent flows. An approach involving a new physical concept is presented. This approach assumes that coherent vortex structures control the particle dispersion process in free shear flows. A simple computational model employing Stuart's vortices is used to simulate particle motion in a two-dimensional free shear layer. The results of this simulation are in reasonable agreement with previous experiments. For the first time, experimental observations indicating particle dispersion rates greater than fluid dispersion rates in free shear flows can be plausibly explained.
Article
A study was made of the diffusion of glass beads in a submerged axisymmetric jet in order to compare the characteristics of the diffusion of sediment with those of the diffusion of momentum in free-turbulence shear flow. A vertical ¬-inch jet of sediment-laden water was directed downward into a relatively large cylindrical tank of still water. Small concentrations of nearly spherical glass beads, both within and above the Stokes range in size, were introduced into the recirculating system. The effiux velocity of the jet was maintained at 20 ft/sec or more to lessen the relative importance of the fall velocity of the individual particles. Concentration profiles of the sediment were measured at various downstream sections in the zone of established flow and were compared with the velocity profiles at the same sections. The diffusion characteristics of the sediment-laden water were analyzed by use of the approximate theories derived for clear water jets. The results are applied to the suspended-load equation presently used for two-dimen- sional flow in open channels. Certain conclusions are drawn as to the propriety of the assumptions pertaining to the fall velocity and sediment diffusion used in deriving this equation.
Article
The interaction of solid particles with the temporal features of a turbulent flow has direct relevance to problems in particle and spray combustion and the processing of particulate solids. The object of the present study was to examine the behaviour of particles in a jet dominated by vortex ring structures. An axisymmetric air jet laden with 55 μm glass particles was forced axially with an acoustic speaker to organize the vortex ring structures rolling up in the free shear layer downstream of the nozzle exit. Visualization studies of forced and unforced flow with Reynolds number of the order of 20000 were completed using a pulsed copper vapour laser. Instantaneous photographs and videotapes of strobed forced flow show that particles become clustered in the saddle regions downstream of the vortex rings and are propelled away from the jet axis by the outwardly moving flow in these regions. Phase-averaged spatial distribution of particle number density computed from digitized photographs and phase-averaged particle velocity measurements yield further evidence that local particle dispersion and concentration are governed by convection due to large-scale turbulence structures. The large-scale structures and convection mechanisms were shown to persist for particle-to-air mass loading ratios up to 0.65.
Article
The development of a second-order integral model for a round turbulent buoyant jet is reported based on new experimental data on turbulent mass and momentum transport. The mean and turbulent characteristics of a round vertical buoyant jet covering the full range from jets to plumes were investigated using a recently developed combined digital particle image velocimetry (DPIV) and planar laser-induced fluorescence (PLIF) system. The system couples the two well-known techniques to enable synchronized planar measurements of flow velocities and concentrations in a study area. The experimental results conserved the mass and momentum fluxes introduced at the source accurately with closure errors of less than 5%. The momentum flux contributed by turbulence and streamwise pressure gradient was determined to be about 10% of the local mean momentum flux in both jets and plumes. The turbulent mass flux, on the other hand, was measured to be about 7.6% and 15% of the mean mass flux for jets and plumes respectively. While the velocity spread rate was shown to be independent of the flow regime, the concentration-to-velocity width ratio λ varied from 1.23 to 1.04 during the transition from jet to plume. Based on the experimental results, a refined second-order integral model for buoyant jets that achieves the conservation of total mass and momentum fluxes is proposed. The model employs the widely used entrainment assumption with the entrainment coefficient taken to be a function of the local Richardson number. Improved prediction is achieved by taking into account the variation of turbulent mass and momentum fluxes. The variation of turbulent mass flux is modelled as a function of the local Richardson number. The turbulent momentum flux, on the other hand, is treated as a fixed percentage of the local mean momentum flux. In addition, unlike most existing integral models that assume a constant concentration-to-velocity width ratio, the present model adopts a more accurate approach with the ratio expressed as a function of the local Richardson number. As a result, smooth transition of all relevant mean and turbulent characteristics from jet to plume is predicted, which is in line with the underlying physical processes.
Article
By combining aspects of optical fiber probes used to determine local particle concentrations and local particle velocities and by rapid signal processing, it is shown that a single probe can determine local instantaneous particle fluxes. Providing a transparent cover to prevent a “blind zone” is shown to be critical in improving the probe performance and linearity. A simple mechanistic model is successful in predicting the performance of the optical system. The results of the probe are validated using particles glued onto both a rotating disk and a flat vibrating surface.
Article
The novel parallel three-fiber optical probe described in Part I of this article is applied to determine simultaneously local instantaneous solids volume concentration, velocity, and flux in multiphase suspensions. Radial distributions of local particle concentration, velocity, and flux and their fluctuations in a high-density circulating fluidized bed (HDCFB) are presented. A strong correlation exists between fluctuations of local particle velocity and particle concentration. The optical probe is shown to provide a means of evaluating alternative measurement techniques that have commonly been employed in earlier studies.
Article
To investigate the behaviour of inter-particle collision and its effects on particle dispersion, direct numerical simulation of a three-dimensional two-phase turbulent jet was conducted. The finite volume method and the fractional-step projection algorithm were used to solve the governing equations of the gas phase fluid and the Lagrangian method was applied to trace the particles. The deterministic hard-sphere model was used to describe the inter-particle collision. In order to allow an analysis of inter-particle collisions independent of the effect of particles on the flow, two-way coupling was neglected. The inter-particle collision occurs frequently in the local regions with higher particle concentration of the flow field. Under the influence of the local accumulation and the turbulent transport effects, the variation of the average inter-particle collision number with the Stokes number takes on a complex non-linear relationship. The particle distribution is more uniform as a result of inter-particle collisions, and the lateral and the spanwise dispersion of the particles considering inter-particle collision also increase. Furthermore, for the case of particles with the Rosin–Rammler distribution (the medial particle size is set d50 = 36.7 μm), the collision number is significantly larger than that of the particles at the Stokes number of 10, and their effects on calculated results are also more significant.
Article
The structure of turbulent, dilute, particle-laden water jets, submerged in still water, was studied both experimentally and theoritically. Nonintrusive measurements were made of mean and fluctuating phase velocities and particle number fluxes. Analysis was used to help interpret the measurements, considering three limiting cases, as follows: (1) locally-homogeneous flow, where relative velocities between the phases are ignored; (2) deterministic separated flow, where relative velocities are considered, but particle/turbulence interactions are ignored; and (3) stochastic separated flow, where both phenomena are considered using random-walk methods. The locally-homogeneous flow approximation was more effective than for past work involving larger density ratios between the phases; however, stochastic analysis yielded best agreement with measurements. Effects of enhanced drag (due to high relative turbulent intensities of particle motion) and effects of particles on liquid turbulence properties (turbulence modulation), were observed. Several recent proposals for treating these phenomena were examined; however, none appears to be adequate for reliable general use.
Article
The effect of particle size on two-phase turbulent jet flow structure is studied in the present experimental investigation. Polystyrene solid particles of 210, 460, and 780 μm were used. The particles' mass loading ratios ranged from 0 to 3.6. The flow Reynolds number was 2 ‘ 104, which was based on the pipe nozzle diameter and the fluid-phase centerline velocity at the nozzle exit. A two-color laser-Doppler anemometer (LDA), combined with the amplitude discrimination method and the velocity filter method, was employed for measurement. The measurement range of the jet flow was from the initial pipe exit to 90D downstream. Results are presented for the mean velocities of particle and fluid phases, the flow's turbulent intensities and the flow's Reynolds stresses. The energy spectra and the correlation functions of the two-phase jet flow were also obtained by using another one-component He-Ne LDA system.
Article
"This is an authorized facsimile and was produced by microfilm-xerography in 1969 by University Microfilms, a Xerox company, Ann Arbor, Michigan, U.S.A."--Prelim. p. Thesis (Ph. D.)--University of Iowa, 1965. Includes bibliographical references (leaves 88-93).
Article
The present study investigates the gas-particle two-phase flow in the turbulent plane jet by solving the two-dimensional and compressible flow fields numerically using direct-numerical-simulation technique. The flow fields are spatially developing, but we focus our study on the evolution of coherent vortex structures and dispersion patterns of particles in the near field at different Stokes numbers. The initial symmetric mode of flow changes its shape to the asymmetric mode after about three convection periods as the flow moves downstream. The concessive paring processes between two and three vortex structures are observed. The predicted mean velocity profiles show self-similar behavior and coincide well with previous experimental data. The profiles of turbulent intensity and Reynolds shear stress also display self-similar characteristics in the further downstream regions. The local-focusing phenomena of particles occur in the quasicoherent dispersion structure of particles. The higher density distribution at the outer boundary of large-scale vortex structure characterizes the dispersion pattern of particles at the Stokes numbers of order of unity. Furthermore, these particles disperse largely along the lateral direction and show the nonuniform distribution of concentration. For the particles at the Stokes number of 0.01, the dispersion along the lateral direction is considerable due to the small aerodynamics response time, but the particles are distributed evenly in the flow field. Particles at the Stokes numbers of 10 and 50 disperse much less along the lateral direction with the even density distribution. These results support the previous conclusions on the dispersion of particles in the free shear flows.