Turbulent Deposition Research Articles

Turbulence and sediment deposition in a channel with floating vegetation

Floating canopies of vegetation alter the vertical profile of flow velocity within and below canopies, which in turn impacts sediment deposition below canopies. This study explored the impacts of channel-average velocity (U0), vegetation density (a), and relative flow depth (hg/H, where hg is the height of the free flow region below the floating canopy and H is the entire flow depth) on the longitudinal distributions of near-bed turbulent kinetic energy (TKE) and sediment deposition in a channel with a floating vegetation canopy. Below a floating canopy, sediment deposition was correlated with the near-bed TKE. For the low-density and low-velocity cases, sediment deposition was spatially uniform across the entire channel because the near-bed TKE was lower than the critical value for sediment resuspension. As the vegetation density and channel-average velocity increased, the near-bed TKE increased and surpassed the critical TKE, which caused resuspension and reduced deposition below the canopy relative to the upstream reference. For the same vegetation density and channel-average velocity, a lower relative flow depth (hg/H) produced a higher below-canopy depth-averaged velocity and near-bed TKE, resulting in less deposition below the canopy. A model was proposed for predicting the longitudinal evolution of near-bed TKE based on the predicted flow velocity below the canopy throughout the channel. The longitudinal evolution of deposition below a floating canopy was predicted by combining the predicted near-bed TKE with the deposition probability. The predicted near-bed TKE and deposition matched laboratory measurements. Finally, the proposed model can be used to predict the longitudinal profile of deposition below a real Eichhornia crassipes canopy.

The CHIMERE chemistry-transport model v2023r1

Abstract. A new version of the CHIMERE model is presented. This version contains both computational and physico-chemical changes. The computational changes make it easy to choose the variables to be extracted as a result, including values of maximum sub-hourly concentrations. Performance tests show that the model is 1.5 to 2 times faster than the previous version for the same setup. Processes such as turbulence, transport schemes and dry deposition have been modified and updated. Optimization was also performed for the management of emissions such as anthropogenic and mineral dust. The impact of fires on wind speed, soil properties and leaf area index (LAI) was added. Pollen emissions, transport and deposition were added for birch, ragweed, olive and grass. The model is validated with a simulation covering Europe with a 60 km × 60 km resolution and the entire year of 2019. Results are compared to various measurements, and statistical scores show that the model provides better results than the previous versions.

A CFD numerical simulation of particle deposition characteristics in automobile tailpipe: power abatement pathways

The study of the movement of pollutants through ducts facilitates the assessment and control of ambient air quality problems (AQ). Among other things, understanding the deposition and distribution of particulate matter in elbows is important for practical engineering applications. In this study, the turbulent flow field and particle deposition in a 90° bend is investigated using RANS simulation. The RNG k-ε turbulence model was employed to calculate the airflow flow field and the discrete phase model (DPM) was used to simulate the particle phase motion. Where for the discrete phase, the Discrete Random Wander (DRW) model was considered and the deposition of particles with sizes of 1, 3, 5, 10, 20, and 40 μm in the flow field was investigated separately. Grid-independent validation of the models used in the simulations was performed. The effects of inlet velocity, particle size, and direction of gravity on the flow field and particle deposition in the elbow were considered. The results show that the flow field in the bend is strongly influenced by the above parameters. Among them, the turbulent disturbance in the bend section is the most intense, with high turbulent energy value, and it is also the region with the largest energy loss. The inlet velocity is negatively correlated with the deposition rate, and the particle size is positively correlated with the deposition rate.

Emplacement of shocked basement clasts during crater excavation in the Ries impact structure

In the Aumühle quarry of the Ries impact structure, moderately shocked clasts from the Variscan basement occur sandwiched between overlying suevite and components derived from the Mesozoic sedimentary cover of the underlying Bunte Breccia without distinct shock effects. We analyzed the clasts by optical microscopy, scanning electron microscopy (SEM/EDS/EBSD), and Raman spectroscopy to unravel their emplacement relation to the overlying suevite and the sediment-rock clasts of the Bunte Breccia. Clasts sizes range up to few decimeters and are embedded in a fine-grained lithic matrix; no impact-melt fragments are observed. Amphibolite clasts contain maskelynite with few lamellar remnants of feldspar, indicating shock pressures of 28–34 GPa. Amphiboles have cleavage fractures and (1¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\overline{1}$$\\end{document}01) mechanical twins suggesting differential stresses > 400 MPa. Felsic gneiss components have optically isotropic SiO2 indicative of shock pressures ≈35 GPa. Metagranite cataclasite clasts contain shocked calcite aggregates and quartz with a high density of fine rhombohedral planar deformation features indicating shock pressures ≈20 GPa. The moderately shocked basement clasts originate from deeper levels of the transient cavity and lower radial distance to the center of the structure compared to the sediment-rock clasts. Both were ballistically ejected during crater excavation. In accordance with palaeo- and rock magnetic data, they were mixed during turbulent deposition at the top of the Bunte Breccia before the emplacement of suevite. The high amount of basement clasts below suevite and on top of the underlying Bunte Breccia is consistent with the commonly reported inverse stratigraphy in the Ries impact structure.Graphical

Numerical study of turbulent heat transfer and particle deposition in enhanced pipes with helical roughness

Large-eddy simulations of turbulent heat transfer and solid particle deposition in helically rib-roughened pipe flows have been performed for different Reynolds numbers Re and various particle diameters Dp. An Euler–Lagrange approach, using cyclic boundary conditions for the continuous and the dispersed phase, have been applied to achieve a fully developed turbulent flow. An adhesion and removal model have been added to the multiphase large-eddy simulations to take into account the physical effect of particle re-entrainment. The complex interactions between particle-laden turbulent flow and the structured pipe wall in multiple-started helically ribbed pipes are numerically investigated with regard to heat transfer, pressure loss, and particulate deposition. The results of the Nusselt numbers Nu, friction factors fd, and particle deposition rates Ṅd are presented for each geometry variant. For same Reynolds numbers Re, significant differences of those values have been observed for the differently structured pipes.

Thermal and Structural History of Impact Ejecta Deposits, Ries Impact Structure, Germany

AbstractThe Ries impact structure (Germany) contains well‐preserved ejecta deposits consisting of melt‐free lithic breccia (Bunte Breccia) overlain by suevite. To test their emplacement conditions, we investigated the magnetic properties and microstructures of 26 polymict breccia clasts and a stratigraphic profile from the clasts into the suevite at the Aumühle quarry. Remanent magnetization directions of the Bunte Breccia clasts fall into two groups: those whose directions mostly lie parallel to the reversed field during impact carried mostly by magnetite, and those whose directions vary widely among each clast carried by titanohematite. Basement clasts containing titanohematite acquired a chemical remanent magnetization (CRM) during the ejection process and then rotated during turbulent deposition. Clasts of sedimentary rocks grew magnetite after turbulent deposition, with CRM directions lying parallel to the paleofield. Suevite holds a thermal remanent magnetization carried by magnetite, except for ∼12 cm from the contact with the Bunte Breccia, where hematite concentrations increase due to hydrothermal alteration. These observations lead us to propose a three‐stage model of (a) turbulent deposition of the melt‐free breccia with clast rotation <580°C, (b) deposition of the overlying suevite, which acted as a semi‐permeable barrier that confined hot (<300°C) oxidizing fluids to the permeable breccia zone, and (c) prolonged hydrothermal activity producing further alteration which ended before the next geomagnetic reversal. Basement outcrops have significantly different magnetic properties than the Bunte Breccia basement clasts with similar lithology. Two basement blocks situated near the inner ring may have been thermally overprinted up to 550°C.

Study of poly-disperse aerosols deposition in turbulent flow with different Reynolds numbers

The turbulent deposition mechanism is one of the main mechanisms of aerosol deposition in nuclear power plant tubes. An experimental study of poly-disperse aerosol deposition in a horizontal tube is conducted, where the nominal Reynolds number (Re) is in a range of 3600–200,000. The aerosol deposition velocity first increases and then decreases with the increase of Res, and at high Re, particle rebound occurs during aerosol deposition in the tube. When the Re is low, the aerosol deposition velocity increases with the increase of aerosol diameter. When the Re is greater than 60,000, the deposition velocity first increases and then decreases with the increase of aerosol diameter due to particle surface rebound. A new aerosol deposition model has been developed by establishing the energy conservation equation of the rebounded particles in the viscous sublayer. The calculated results of the new model are in good agreement with these experimental results, and the error between the aerosol deposition velocity calculated by the model and experimental results is between −60% and 150%.

Effect of room size, shape, AC placement, and air leakage on indoor airborne viral transmission

We conducted Euler–Lagrange Reynolds-Averaged Navier–Stokes simulations with statistical overloading to investigate the effect of room shape, air-condition (AC) location, and the presence of an open window on indoor airborne viral transmission, particularly as it relates to the spatio-temporal distribution of viral-laden droplet nuclei. Two room geometries were considered with two different AC types positioned at different locations within each room. We considered the case of perfect filtration where pathogens can exit the room through ventilation, air leakage through an open window, turbulent wall deposition, and by gravitational settling onto the bottom floor. We observe the room-averaged concentration to decay at the rate estimated from the well-mixed model and therefore to be independent of room size and shape or AC type and placement. It is also independent of whether or not there is an open window. However, we find that the departure from well-mixedness, which has been quantified using a time- and source-to-sink separation-dependent correction function γ, is affected by room shape and AC placement. More specifically, indoor spaces where the AC is installed on one end of the room allow droplet nuclei ejected on one end of the room to travel longer distances before being removed from the room as opposed to indoor spaces in which the AC is installed at the center of the room. The present results allow generalization of a simple model for the accurate prediction of viral quanta inhaled by an individual in any indoor environment.

Characterization of size-segregated particles' turbulent flux and deposition velocity by eddy correlation method at an Arctic site

Abstract. Estimating aerosol depositions on snow and ice surfaces and assessing the aerosol lifecycle in the Arctic region is challenged by the scarce measurement data available for particle surface fluxes. This work aims at assessing the deposition velocity of atmospheric particles at an Arctic site (Ny-Ålesund, Svalbard islands) over snow, during the melting season, and over dry tundra. The measurements were performed using the eddy covariance method from March to August 2021. The measurement system was based on a condensation particle counter (CPC) for ultrafine particle (UFP; < 0.25 µm) fluxes and an optical particle counter (OPC) for evaluating particle size fluxes in the accumulation mode (ACC; 0.25 < dp < 0.7 µm) and quasi-coarse mode (CRS; 0.8 < dp < 3 µm). Turbulent fluxes in the ultrafine particle size range were prevalently downward, especially in summertime. In contrast, particle fluxes in the accumulation and quasi-coarse mode were more frequently positive, especially during the colder months, pointing to surface sources of particles from, for example, sea spray, snow sublimation, or local pollution. The overall median deposition velocity (Vd+) values were 0.90, 0.62, and 4.42 mm s−1 for UFP, ACC, and CRS, respectively. Deposition velocities were smaller, on average, over the snowpack, with median values of 0.73, 0.42, and 3.50 mm s−1. The observed velocities differ by less than 50 % with respect to the previous literature in analogous environments (i.e. ice/snow) for particles in the size range 0.01–1 µm. At the same time, an agreement with the results of predictive models was found for only a few parameterizations, in particular with Slinn (1982), while large biases were found with other models, especially in the range 0.3–10 µm, of particle diameters. Our observations show a better fit with the models predicting a minimum deposition velocity for small-accumulation-mode particle sizes (0.1–0.3 µm) rather than for larger ones (about 1 µm), which could result from an efficient interception of particles over snow surfaces which are rougher and stickier than the idealized ones. Finally, a polynomial fit was investigated (for the ACC-CRS size range) to describe the deposition velocity observations which properly represents their size dependence and magnitude. Even if this numerical fit is driven purely by the data and not by the underlying chemical–physical processes, it could be very useful for future model parameterizations.

Aerosol turbulent deposition characteristics under small and micro-scaled leakage paths

The small and micro-scaled leakage path of steel containment has a retention effect on aerosol penetration under accident conditions, which is important for estimating radioactive release into the environment. Turbulent deposition mechanism may play an important role in aerosol retention in the leakage path. In this paper, experimental study on aerosol turbulent deposition is carried out in capillaries and a rectangular channel. The mass concentration and size distribution of aerosol are measured, and dimensionless analysis of experimental data are carried out. The results show that the dimensionless deposition velocity increases with the quadratic relationship of the dimensionless particle relaxation time under the condition of eddy diffusion-impaction regime. An empirical correlation has been established with Re and Kn to predict the turbulent deposition velocity, which is verified by additional experiments and is applicable to the characteristic size in range of 47 μm to 1000 μm, and the Re number of 700 to 3400.

Simulation of Turbulent Flow Structure and Particle Deposition in a Three-Dimensional Heat Transfer Duct with Convex Dimples

In engineering applications, dust deposition on the heat transfer channel greatly reduces the efficiency of heat transfer. Therefore, it is very significant to study the characteristics of particle deposition for thermal energy engineering applications. In this study, the Reynolds stress model (RSM) and the discrete phrase model (DPM) were used to simulate particle deposition in a 3D convex-dimpled rough channel. A discrete random walk model (DRW) was used for the turbulent diffusion of particles, and user-defined functions were developed for collisions between particles and walls. An improved deposition model of rebound between particles was developed. The flow structure, secondary flow, temperature distribution, Q criterion, and particle deposition distribution in the convex-dimpled rough channel were analyzed after a study of the grid independence and a numerical validation. The results showed that these mechanisms affected the flow structure in the flow field. For tiny particles (dp ≤ 10 μm), the presence of convex dimples promoted their deposition. The rates of particle deposition in the presence of convex dimples were 535, 768, 269, and 2 times higher than in smooth channels (particle sizes of 1, 3, 5, and 10 μm, respectively). However, for large particles (dp > 10 μm), although the presence of convex dimples had a certain effect on the location distribution of particle deposition, it had little effect on the deposition rates of large particles, which were 0.99, 0.98, 0.97 and 0.96 times those in the smooth channel, respectively.

Numerical simulation of turbulent flow and particle deposition in heat transfer channels with concave dimples

The efficiency of heat transfer will be significantly reduced if airborne particles deposit in the heat transfer channel. Better understandings on particle deposition characteristics in heat exchanger channel are crucial for the energy efficiency improvement. In this study, the particle deposition in a three-dimensional dimpled rough channel was simulated using the Reynolds stress model (RSM) and discrete particle model (DPM). For the turbulent diffusion of particles, the random walk model (DRW) was employed, and for the particle–wall contact, user-defined functions(UDF) are developed in this study to achieve motions such as bouncing and deposition of particles. Grid independence testing and numerical verification were followed by an analysis and study of the flow structures, secondary flow, temperature distribution, and particle deposition distribution in the dimpled rough channel. On the turbulent structure and particle deposition characteristics, the impacts of several significant parameters, including particle size, airflow velocity, the ratio of dimple depth to inner diameter (h/d), and the ratio of inner diameter of dimple to distance between dimples (d/s), were examined. The findings demonstrate that the primary mechanisms influencing the deposition characteristics of particles in dimpled channels are gravity deposition, thermophoresis force distribution, turbulence structure, secondary flow, and particle inertia, and the effects of these mechanisms change significantly with particle size. For small particles (dp ≤ 10 μm), the presence of dimples will encourage deposition; however, for large particles (dp > 10 μm), the presence of dimples will only have a little impact on the distribution of where the particles are deposited.

Measurements of Ice Crystal Fluxes from the Surface at a Mountain Top Site

New observations of anomalously high cloud ice crystal concentrations at the Jungfraujoch research station (Switzerland, 3.5 km a.s.l.) are presented. High-resolution measurements of these ice crystals using a high-speed 2D imaging cloud particle spectrometer confirm that the concentrations far exceed those expected from any known primary ice production mechanisms and are at temperatures well below those for known secondary ice production processes to contribute. The most likely explanation is due to a strong surface source generated by the interaction of turbulent deposition of supercooled droplets to fragile ice-covered snow surfaces. This process enhances the detachment of crystal fragments wherein the smaller size mode is turbulently re-suspended even at low wind speeds below expected blowing snow thresholds. These then continue to grow, adding significantly to the ice crystal number concentrations whose size and habit is determined by the transport time between the ice crystal source and measurement location and liquid water profile within the cloud. We confirm, using eddy covariance measurements of ice particle number fluxes, that the likely source is significantly far upwind to preclude flow distortion effects such that the source plume has homogenised by the time they are measured at the mountain top summit.

Fully-resolved numerical simulations of the turbulent flow and particle deposition in a cubical cavity with two pairs of differentially heated opposed walls at Rayleigh number 3.6 × 109

Fully-resolved numerical simulations of the turbulent flow and particle deposition in a cubical cavity with two pairs of differentially heated opposed walls at Rayleigh number 3.6 × 109

Synthesis of Epitaxial MoS2/MoO2 Core-Shell Nanowires by Two-Step Chemical Vapor Deposition with Turbulent Flow and Their Physical Properties.

MoO2 nanowires (NWs), MoO2/MoS2 core-shell NWs, and MoS2 nanotubes (NTs) were synthesized by the turbulent flow chemical vapor deposition of MoO2 using MoO3, followed by sulfurization in the sulfur gas flow. The involvement of MoO x suboxide is suggested by density functional theory (DFT) calculations of the surface energies of MoO2. The thickness of the MoS2 layers can be controlled by precise tuning of sulfur vapor flow and temperatures. MoS2 had an armchair-type winding topology due to the epitaxial relation with the MoO2 NW surface. A single ∼ few-layer MoO2/MoS2 core-shell structure showed photoluminescence after the treatment with a superacid. The resistivities of an individual MoO2 NW and a MoS2 NT were measured, and they showed metallic and semiconducting resistivity-temperature relationships, respectively.

Velocity, Turbulence, and Sediment Deposition in a Channel Partially Filled With a Phragmites australis Canopy

AbstractLaboratory experiments examined the longitudinal evolution of near‐bed velocity, turbulent kinetic energy (TKE), and net deposition in a model Phragmites australis canopy occupying 1/3 of the channel width. The canopies were constructed from model P. australis with real morphology and a solid volume fraction between 0.003 and 0.018. An exponential model was modified to predict the longitudinal evolution of near‐bed velocity inside the canopy, from which the near‐bed TKE can be predicted. By combining the predicted TKE and a deposition probability, we proposed a model to predict the distribution of net deposition inside the canopy. The predicted velocity, TKE, and deposition were in good agreement with the measurements. Relative to an upstream reference, the net deposition within the canopy was enhanced when two conditions were met: the in‐canopy, near‐bed TKE was smaller than the critical value for resuspension, and resuspension took place in the bare channel. Above a critical vegetation density (defined by a critical solid volume fraction ϕc), the spatially‐averaged deposition inside P. australis surpassed that in the adjacent bare channel. The proposed model provides a way to estimate ϕc. Relative to the upstream reference, deposition inside the canopy was always diminished over some fraction of the flow adjustment distance, Ld (distance from canopy leading edge to fully developed flow). When the canopy length was greater than 0.4 Ld, canopy‐averaged deposition was enhanced relative to the bare channel. Finally, for the same canopy length, differences in plant morphologies did not have a strong impact on the in‐canopy deposition distribution.

Large-eddy-simulation study on turbulent particle deposition and its dependence on atmospheric-boundary-layer stability

Abstract. It is increasingly recognized that atmospheric-boundary-layer stability (ABLS) plays an important role in eolian processes. While the effects of ABLS on particle emission have attracted much attention and been investigated in several studies, those on particle deposition have so far been less well studied. By means of large-eddy simulation, we investigate how ABLS influences the probability distribution of surface shear stress and hence particle deposition. Statistical analysis of the model results reveals that the shear stress can be well approximated using a Weibull distribution, and the ABLS influences on particle deposition can be estimated by considering the shear stress fluctuations. The model-simulated particle depositions are compared with the predictions of a particle-deposition scheme and measurements, and the findings are then used to improve the particle-deposition scheme. This research represents a further step towards developing deposition schemes that account for the stochastic nature of particle processes.

Role of a Nanocomposite Pour Point Depressant on Wax Deposition in Different Flow Patterns from the Perspective of Crystallization Kinetics.

Wax deposition is one of the core issues affecting flow assurance studies of crude oil pipelines, particularly with deep and ultradeep water conditions. Nanocomposite pour point depressants (NPPDs) provide a novel and effective strategy for inhibiting wax deposition and have recently attracted increasing research attention. Although recent advances have been made in understanding the performance and mechanism of NPPDs, the effect of flow pattern remains an open question. In this paper, deposition thicknesses of waxy oils with different flow patterns and NPPD dosages were obtained using a flow loop experimental device. It was found that the NPPD used in the current work can effectively inhibit the formation of wax deposition layers in different flow patterns. The Avrami model-focused beam reflectance measurement and polarizing microscope experiment method were used to characterize crystallization kinetics parameters and mesoscopic structure parameters of wax crystals. The consistency of results from Avrami equation fitting parameters, wax crystal morphology, and particle number supported the validity of crystallization kinetics analysis. The mechanisms of NPPD in different flow regimes were discussed. The inhibition of laminar and turbulent deposition layers by NPPD was attributed to the improvement of wax crystal morphology and the reduction of wax crystal number, respectively. This has important consequences for our understanding of the utilization and mechanism of nanocomposite pour point depressants.

Numerical study on targeted delivery of magnetic drug particles in realistic human lung

Inhalation of medical drug particles through human airway is widely utilized for the remedy of lung diseases. Due to the complexities of airway morphology, flow turbulence and particle deposition, the drug delivery efficiency to the morbid region of lung is always unsatisfactory. In this research, a 3D anatomically accurate human airway model from oral cavity to lung is reconstructed, and the large eddy simulation-discrete phase model (LES-DPM) is adopted to simulate the airway flow and drug particles transport. To improve the particle delivery to the targeted region of the left lung, a magnetic drug targeting (MDT) system is established. It is found that the LES-DPM in conjunction with MDT system is an effective tool to study airway flow patterns and magnetic particle deposition features. Moreover, the magnetic source layout, magnetic particle size and magnetic field intensity all have significant impacts on the particle deposition efficiency in the left lung. Optimal combination factors for drug particle delivery results are successfully achieved. The total deposition efficiency of magnetic particles in the left lung can be increased to more than 5 times. This work not only could provide a better understanding of air-particle dynamics, but also could contribute toward improved strategies for more efficient drug delivery in the realistic human lungs.

Numerical simulation of the effects of sandy water on regulator labyrinth channel in micro-sprinkler systems

Abstract The effects of sandy water on the W-shaped labyrinth channel of micro-sprinkler irrigation systems with large flowrate were investigated using Computational Fluid Dynamics (CFD). Using ANSYS FLUENT software and different inflow conditions (e.g., pressure, velocity, sediment concentration, and sand particle diameter), internal turbulent multiphase flow and sand deposition were simulated by the Eulerian multiphase flow model. Particle erosion in the labyrinth channel was calculated by the Discrete Phase Model (DPM). The results show that vortex movements and shear actions at the boundary layer cause self-flushing in the channel. The location of sand particle deposits and the turbulent dissipation rate are related to the operating pressure, which is optimal at 300 kPa. The erosion rate of the channel wall is proportional to the inflow sediment concentration but has no obvious relationship with inflow velocity. Based on the movement regulation of sand particles in the labyrinth channel, recommendations on filtration requirements and operating pressure of irrigation systems are proposed.