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Xie, Qing, Siheng Yang, Hao Cheng, Chi Zhang i Zhuyin Ren. "Predicting the ignition sequences in a separated stratified swirling spray flame with stochastic flame particle tracking". Journal of the Global Power and Propulsion Society 6 (12.10.2022): 279–89. http://dx.doi.org/10.33737/jgpps/153495.
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Stochastic flame particle tracking in conjunction with non-reacting combustor simulations can offer insights into the ignition processes and facilitate the combustor optimization. In this study, this approach is employed to simulate the ignition sequences in a separated dual-swirl spray flame, in which the newly proposed pairwise mixing-reaction model is used to account for the mass and energy transfer between the flame particle and the surrounding shell layer. Based on the flame particle temperature, the particle state can be classified in to burnt, hot gas, and extinguished. The additional state of hot gas is introduced to allow the flame particles with high temperature to survive from nonflammable region and then potentially to ignite the nearby favourable regions. The simulations of the separated stratified swirl spray flame reveal two different ignition pathways for flame stabilization. The first showed that some flame particles from the spark would directly enter the main recirculation zone resulting from the velocity randomness and then ignite both sides of the combustor simultaneously. The second showed that flame particles from the spark would ignite the traversed regions following the swirl motion inside the combustor. The predicted ignition sequences were compared with the evolution of flame morphology recorded by high-speed imaging from experiments, showing qualitative agreement.
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Echekki, T., i M. G. Mungal. "Particle Tracking in a Laminar Premixed Flame". Physics of Fluids A: Fluid Dynamics 2, nr 9 (wrzesień 1990): 1523. http://dx.doi.org/10.1063/1.4738844.
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Uranakara, Harshavardhana A., Swetaprovo Chaudhuri, Himanshu L. Dave, Paul G. Arias i Hong G. Im. "A flame particle tracking analysis of turbulence–chemistry interaction in hydrogen–air premixed flames". Combustion and Flame 163 (styczeń 2016): 220–40. http://dx.doi.org/10.1016/j.combustflame.2015.09.033.
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Weber, R., A. A. F. Peters, P. P. Breithaupt i B. M. Visser. "Mathematical Modeling of Swirling Flames of Pulverized Coal: What Can Combustion Engineers Expect From Modeling?" Journal of Fluids Engineering 117, nr 2 (1.06.1995): 289–97. http://dx.doi.org/10.1115/1.2817143.
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The present study is concerned with mathematical modeling of swirling pulverized coal flames. The attention is focused on the near burner zone properties of high-and low-NOx flames issued from an Aerodynamically Air Staged Burner of 3.4 MW thermal input. The swirling combusting flows are calculated using the k–ε model and second-order models of turbulence. The Eulerian balance equations for enthalpy and mass fractions of oxygen, volatiles, carbon monoxide and final combustion products (CO2 + H2O) are solved. The Lagrangian particle tracking is accompanied by appropriate models of coal devolatilization and char combustion. Nitric oxide emissions are calculated using a NOx post-processor for thermal-, prompt- and fuel-NO. The objective of this paper is to examine whether the engineering information required for designing industrial burners is obtainable through the mathematical modeling. To this end, the flame computations, including NO emissions, are compared with the measured in-flame data. The guidelines as to the combination of physical submodels and model parameters needed for quality predictions of different flame types are given. The paper is a shorter version of our recent ASME publication (Weber et al., 1993).
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XIE, Qing, Zhuyin REN i Ke WANG. "Modelling ignition probability with pairwise mixing-reaction model for flame particle tracking". Chinese Journal of Aeronautics 34, nr 5 (maj 2021): 523–34. http://dx.doi.org/10.1016/j.cja.2020.12.031.
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Lee, K. H., i C. S. Lee. "Effects of tumble and swirl flows on turbulence scale near top dead centre in a four-valve spark ignition engine". Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 217, nr 7 (1.07.2003): 607–15. http://dx.doi.org/10.1243/095440703322114988.
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The in-cylinder flowfield and the turbulence scale at the ignition timing play an important role in enhancing the propagation speed of the initial flame and the engine combustion. The aim of this work is to investigate the effect of tumble and swirl flows on the turbulence scale near the top dead centre in a four-valve spark ignition (SI) engine by an experimental method. In this study, various flowfields such as tumble and swirl flows were generated by intake flow control valves. For investigation of the flowfields, the single-frame particle tracking velocimeter (PTV) and the twocolour particle image velocimeter (PIV) techniques were developed to clarify the in-cylinder flow pattern during the intake stroke and the turbulence intensity near the spark plug during the compression stroke respectively. In addition, the flame propagation was visualized by an ICCD camera, and its images were analysed to compare the flowfields. From these experimental results, the effects of tumble and swirl flows on the turbulence scale and the flame propagation speed were clarified.
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Lewis, G. S., i B. J. Cantwell. "Instantaneous Two-Dimensional Velocity Field Measurements in a Periodic Flame Using Particle Tracking Velocimetry". Physics of Fluids 31, nr 9 (wrzesień 1988): 2388. http://dx.doi.org/10.1063/1.4738823.
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Liu, Kan, i David Liu. "Particle tracking velocimetry and flame front detection techniques on commercial aircraft debris striking events". Journal of Visualization 22, nr 4 (2.07.2019): 783–94. http://dx.doi.org/10.1007/s12650-019-00571-8.
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Rezk, Hegazy, Magdy M. Zaky, Mohemmed Alhaider i Mohamed A. Tolba. "Robust Fractional MPPT-Based Moth-Flame Optimization Algorithm for Thermoelectric Generation Applications". Energies 15, nr 23 (23.11.2022): 8836. http://dx.doi.org/10.3390/en15238836.
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Depending on the temperature difference between the hot and cold sides of the thermoelectric generator (TEG), the output performance of the TEG can be produced. This means that it is necessary to force a TEG based on robust maximum power point tracking (MPPT) to operate close to its MPP at any given temperature or load. In this paper, an improved fractional MPPT (IFMPPT) is proposed in order to increase the amount of energy that can be harvested from TEGs. According to the suggested method, fractional order control is used. A moth-flame optimizer (MFO) was used to determine IFMPPT’s optimal parameters. A comparison of the results obtained by the MFO is made with those obtained by a particle swarm optimizer, genetic algorithm, gray wolf optimizer, seagull optimization algorithm, and tunicate swarm algorithm in order to demonstrate MFO’s superiority. IFMPPT’s primary objective is to enhance dynamic responses and exclude steady-state oscillations. Consequently, incremental resistance and perturb and observe are compared with the proposed strategy’s performance. It was revealed that IFMPPT provides superior tracking results both in dynamic and steady-state conditions when compared with traditional methods.
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Fuyuto, Takayuki, Yoshiaki Hattori, Hayato Yamashita, Naoki Toda i Makoto Mashida. "Set-off length reduction by backward flow of hot burned gas surrounding high-pressure diesel spray flame from multi-hole nozzle". International Journal of Engine Research 18, nr 3 (28.07.2016): 173–94. http://dx.doi.org/10.1177/1468087416640429.
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The backward flow of the hot burned gas surrounding a diesel flame was found to be one of the factors reducing the set-off length (also called the lift-off length), that is, the distance from a nozzle exit into which a diffusion flame cannot intrude. In the combustion chamber of an actual diesel engine, the entrainment of the surrounding gas into a spray jet injected from a multi-hole nozzle is restricted by the combustion chamber walls and the adjacent spray jets, thus inducing the backward flow of the surrounding gas toward the nozzle exit. The emergence of this backward flow was measured by particle tracking velocimetry in the non-combusting condition. A new momentum theory for calculating the backward flow velocity was established by extending Wakuri’s momentum theory. Shadowgraph imaging in an optical engine successfully visualized the backward flow of the hot burned gas. The hot burned gas is re-entrained into the spray jet in the region of the set-off position and shortens the set-off length in comparison to that of a single free-spray flame which does not induce the backward flow.
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Yang, J., S. Kook, K. Kim i C. Kweon. "In-Flame And In-Cylinder Flow/Turbulence Measurements Near The Glow Plug Using Flame Image Velocimetry And Particle Image Velocimetry In An Optical Compression-Ignition Engine". Proceedings of the International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics 20 (11.07.2022): 1–19. http://dx.doi.org/10.55037/lxlaser.20th.94.
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The present study implements two diagnostic methods based on tracking of seeded olive oil droplets (PIV: particle image velocimetry) and pattern changes detected in high-speed flame movies (FIV: flame image velocimetry) in a small-bore optical diesel engine. For each measurement, a total of 100 engine cycles are recorded and processed to address the inherent cyclic variations. The ensemble-averaged flow fields and turbulence intensity distribution extracted from individual cycles via the spatial filtering method are discussed with a particular interest in the influence of glow plug on flow and turbulence, i.e. rigid body and fluid interaction. The PIV results show a swirl flow structure forms and rotates with its centre shifted towards the exhaust side, leading to an asymmetric swirl structure. By comparing a PIV laser plane tilted towards the glow plug and a 10 mm horizontal plane below the cylinder head with no glow flow-plug interaction, it is observed that the flow-plug interaction causes the flow winding around the plug tip to generate complex flow structures and new vortices downstream of the plug. The tilted plane and 10-mm plane show similar bulk flow magnitude distribution patterns; however, the flow-plug interaction generates high turbulence in the tilted plane right downstream of the plug tip where new vortices form, which lasts for a few crank angles. The spatially averaged flow magnitude and turbulence intensity are measured higher in the 10-mm plane where there is no flow-plug interaction, suggesting the increased turbulence is a localised behaviour. The flame-plug interaction is also investigated during the combustion event using the FIV method. The level of flame-plug interaction is adjusted by changing the inter-jet spacing angle of two nozzle holes with one case showing high interaction and the other displaying low interaction. From the FIV measurements, the most significant effect of the flame-plug interaction is observed as the further penetration of the wall bounced flame for the high interaction case. This is due to the glow plug as a rigid body blocking the swirl flow and promoting the flame penetration back towards the centre of the combustion chamber upon the piston-bowl wall impingement. The measured turbulence intensity is also higher thanks to the enhanced wall bounced flame in addition to more significant flame-plug interaction at the interface.
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GUO, Chen, Shengli CHANG, Wenjie ZHANG, Guangyi XIAO, Fei WANG i Tong BAO. "Research on velocity measurement method of rocket engine tail flame particle based on quantum filter and tracking algorithm". Optics and Precision Engineering 31, nr 16 (2023): 2352–61. http://dx.doi.org/10.37188/ope.20233116.2352.
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Guerra, Juan F., Ramon Garcia-Hernandez, Miguel A. Llama i Victor Santibañez. "A Comparative Study of Swarm Intelligence Metaheuristics in UKF-Based Neural Training Applied to the Identification and Control of Robotic Manipulator". Algorithms 16, nr 8 (21.08.2023): 393. http://dx.doi.org/10.3390/a16080393.
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This work presents a comprehensive comparative analysis of four prominent swarm intelligence (SI) optimization algorithms: Ant Lion Optimizer (ALO), Bat Algorithm (BA), Grey Wolf Optimizer (GWO), and Moth Flame Optimization (MFO). When compared under the same conditions with other SI algorithms, the Particle Swarm Optimization (PSO) stands out. First, the Unscented Kalman Filter (UKF) parameters to be optimized are selected, and then each SI optimization algorithm is executed within an off-line simulation. Once the UKF initialization parameters P0, Q0, and R0 are obtained, they are applied in real-time in the decentralized neural block control (DNBC) scheme for the trajectory tracking task of a 2-DOF robot manipulator. Finally, the results are compared according to the criteria performance evaluation using each algorithm, along with CPU cost.
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Qin, Dingyi, Qianyun Chen, Jing Li i Zhaohui Liu. "Effects of Pressure and Coal Rank on the Oxy-Fuel Combustion of Pulverized Coal". Energies 15, nr 1 (31.12.2021): 265. http://dx.doi.org/10.3390/en15010265.
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Pressurized oxy-fuel combustion technology is the second generation of oxy-fuel combustion technology and has low energy consumption and low cost. In this research, a visual pressurized flat-flame reaction system was designed. A particle-tracking image pyrometer (PTIP) system based on a high-speed camera and an SLR camera was proposed. Combining the experimental system and data-processing method developed, the ignition and combustion characteristics of a single coal particle between 69 and 133 μm in size were investigated. The results indicated that at atmospheric pressure, the ignition delay time of ShanXi (SX) anthracite coal was longer than that of ShenHua (SH) bituminous coal, while that of PRB sub-bituminous coal was the shortest. As the pressure rose, the ignition delay time of the PRB sub-bituminous coal and SX anthracite coal showed a continuous increasing trend, while the ignition delay time of SH bituminous coal showed a trend of first increasing and then decreasing. Moreover, pressure also affects the pyrolysis process of coal. As the pressure increases, it became more difficult to release the volatiles produced by coal pyrolysis, which reduced the release rate of volatiles during the ignition stage, and prolonged the release time and burning duration time of volatiles.
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Ma, H., S. Marshall, R. Stevens i R. Stone. "Full-bore crank-angle resolved imaging of combustion in a four-stroke gasoline direct injection engine". Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 221, nr 10 (1.10.2007): 1305–20. http://dx.doi.org/10.1243/09544070jauto542.
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The conventional Bowditch piston arrangement in an optical access engine limits the field of view to about half the bore area. By using a transparent crown (with a flat top) and incorporating a concave surface into the underside of the piston, then the piston crown acts as a diverging lens. Appropriate choice of the radius of curvature and the piston crown thickness provides an image of the full bore. There is of course optical distortion in the image but, since the piston position is known for each image, then it is comparatively simple to reconstruct undistorted images and videos. As an illustration of the technique, results are presented here for flame front tracking, and estimates of the combustion temperature and soot loading by a colour ratio pyrometry technique. This full-bore imaging technique is also applicable to many other optical diagnostic techniques. For a motored engine with particle imaging velocimetry and an optical cylinder liner, then the light sheet could enter either through the piston to illuminate a vertical plane or through the cylinder liner and be imaged through the piston. The choice of laser-based combustion diagnostic techniques would be limited by the transmission range of the piston window.
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Brunel, Marc, Lila Ouldarbi, Alexandre Fahy i Gaële Perret. "3D-Tracking of Sand Particles in a Wave Flume Using Interferometric Imaging". Optics 3, nr 3 (22.08.2022): 254–67. http://dx.doi.org/10.3390/opt3030025.
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We report the 3D-tracking of irregular sand particles in a wave flume using a cylindrical interferometric particle imaging set-up. The longitudinal position of each particle is deduced from the ellipticity of its speckle-like interferometric image. The size of a particle is determined from the analysis of the 2D Fourier transform of its defocused image. It is further possible to identify some rotation of the particles. Simulations accurately confirm the experimental determination of the different parameters (3D position and size of each particle).
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Tolpadi, A. K., I. Z. Hu, S. M. Correa i D. L. Burrus. "Coupled Lagrangian Monte Carlo PDF–CFD Computation of Gas Turbine Combustor Flowfields With Finite-Rate Chemistry". Journal of Engineering for Gas Turbines and Power 119, nr 3 (1.07.1997): 519–26. http://dx.doi.org/10.1115/1.2817015.
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A coupled Lagrangian Monte Carlo Probability Density Function (PDF)-Eulerian Computational Fluid Dynamics (CFD) technique is presented for calculating steady three-dimensional turbulent reacting flow in a gas turbine combustor. PDF transport methods model turbulence-combustion interactions more accurately than conventional turbulence models with an assumed shape PDF. The PDF transport equation was solved using a Lagrangian particle tracking Monte Carlo (MC) method. The PDF modeled was over composition only. This MC module has been coupled with CONCERT, which is a fully elliptic three-dimensional body-fitted CFD code based on pressure correction techniques. In an earlier paper (Tolpadi et al., 1995), this computational approach was described, but only fast chemistry calculations were presented in a typical aircraft engine combustor. In the present paper, reduced chemistry schemes were incorporated into the MC module that enabled the modeling of finite rate effects in gas turbine flames and therefore the prediction of CO and NOx emissions. With the inclusion of these finite rate effects, the gas temperatures obtained were also more realistic. Initially, a two scalar scheme was implemented that allowed validation against Raman data taken in a recirculating bluff body stabilized CO/H2/N2-air flame. Good agreement of the temperature and major species were obtained. Next, finite rate computations were performed in a single annular aircraft engine combustor by incorporating a simple three scalar reduced chemistry scheme for Jet A fuel. This three scalar scheme was an extension of the two scalar scheme for CO/H2/N2 fuel. The solutions obtained using the present approach were compared with those obtained using the fast chemistry PDF transport approach (Tolpadi et al., 1995) as well as the presumed shape PDF method. The calculated exhaust gas temperature using the finite rate model showed the best agreement with measurements made by a thermocouple rake. In addition, the CO and NOx emission indices were also computed and compared with corresponding data.
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Magnuson, Matthew, Terry Stilman, Shannon Serre, John Archer, Ryan James, Xiaoyan Xia, Mitchell Lawrence, Erin Tamargo, Hadas Raveh-Amit i Avi Sharon. "Part 2: Stabilization/Containment of Radiological Particle Contamination to Enhance First Responder, Early Phase Worker, and Public Safety". Applied Sciences 12, nr 8 (11.04.2022): 3861. http://dx.doi.org/10.3390/app12083861.
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The application of stabilization technologies to a radiologically contaminated surface has the potential for reducing the spread of contamination and, as a result, decreasing worker exposure to radiation. Three stabilization technologies, calcium chloride (CaCl2), flame retardant Phos-Chek® MVP-Fx, and Soil2OTM were investigated to evaluate their ability to reduce the resuspension and tracking of radiological contamination during response activities such as vehicle and foot traffic. Concrete pavers, asphalt pavers, and sandy soil walking paths were used as test surfaces, along with simulated fallout material (SFM) tagged with radiostrontium (Sr-85) applied as the contaminant. Radiological activities were measured using gamma spectrometry before and after simulated vehicle operation and foot traffic experiments, conducted with each stabilization technology and without application as a nonstabilized control. These measurements were acquired separately for each combination of surface and vehicle/foot traffic experiment. The resulting data describes the extent of SFM removed from each surface onto the tires or boots, the extent of SFM transferred to adjacent surfaces, and the residual SFM remaining on the tires or boots after each experiment. The type of surface and response worker actions influenced the stabilization results. For instance, when walked over, less than 2% of particles were removed from nonstabilized concrete, 4% from asphalt, and 40% of the particles were removed from the sand surface. By contrast, for vehicle experiments, ~40% of particles were again removed from the sand, but 7% and 15% from concrete and asphalt, respectively. In most cases, the stabilization technologies did provide improved stabilization. The improvement was related to the type of surface, worker actions, and stabilizer; a statistical analysis of these variables is presented. Overall, the results suggest an ability to utilize these technologies during the planning and implementation of response activities involving foot and vehicle traffic. In addition, resuspension of aerosolizable range SFM was monitored during walking path foot traffic experiments, and all stabilizing agents decreased the measured radioactivity, with the Soil2OTM decrease being 3 fold, whereas the CaCl2 and Phos-Chek MVP-Fx surfaces generated no detectable radioactivity. Overall, these results suggest that the stabilization technologies decrease the availability of particles respirable by response workers under these conditions.
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Abidalla, Wisam Abdulabbas, Ahmed Sami Naser i Mohsin J. Nasir. "Finding of Suitable Transportation Rate Formula by Using "Velocity - Height - Distance" for Bed Material Load". Mathematical Modelling of Engineering Problems 9, nr 2 (28.04.2022): 463–67. http://dx.doi.org/10.18280/mmep.090223.
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This research aims to find a suitable transportation rate formula for bed load. Laboratory experiments were conducted in a flume for monitoring and measuring the transportation of sediment particles (bed load) which move by jumping, rolling, or sliding within the flume. This study included two parts. The first part is experimenting using a flume and tracking the particles' movement by analysing the images taken by the camera. The measurements that have been taken are the amount of accumulated bed load particles at the end of the flume, which are distributed along a certain distance during a specific time, thus obtaining measuring data about the amount of accumulated bed load and values of moving distance and the required time for accumulating the particles at the flume end. The accumulated height of bed load is also measured. These experiments were conducted at different low-flow velocities. The second part includes the expression of a formula for bed load transportation rate, which is the product of multiplying the accumulated height of bed load by the velocity of bed load particles with distance at a certain time that was devised in the first part. Through the proposed method of obtaining the measurements in the first part Analysis of bed load particle velocity was done by using (π-theorem) from the results of experiments (Cv, V, ρ, ρS, µ, ds, L). To derive the formula of accumulated bed load height at flume end along a certain distance using Rayleigh’s method and using the results of the experiment (δ, V, g, ds). Finally, there can be found an expression of the bed load transportation rate formula. Checking was made for this formula, which was compared with other researchers' equations using statically measured. It was found that the derived formula was acceptable to calculate the transportation rate of bed load.
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van den Bremer, T. S., C. Whittaker, R. Calvert, A. Raby i P. H. Taylor. "Experimental study of particle trajectories below deep-water surface gravity wave groups". Journal of Fluid Mechanics 879 (20.09.2019): 168–86. http://dx.doi.org/10.1017/jfm.2019.584.
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Owing to the interplay between the forward Stokes drift and the backward wave-induced Eulerian return flow, Lagrangian particles underneath surface gravity wave groups can follow different trajectories depending on their initial depth below the surface. The motion of particles near the free surface is dominated by the waves and their Stokes drift, whereas particles at large depths follow horseshoe-shaped trajectories dominated by the Eulerian return flow. For unidirectional wave groups, a small net displacement in the direction of travel of the group results near the surface, and is accompanied by a net particle displacement in the opposite direction at depth. For deep-water waves, we study these trajectories experimentally by means of particle tracking velocimetry in a two-dimensional flume. In doing so, we provide visual illustration of Lagrangian trajectories under groups, including the contributions of both the Stokes drift and the Eulerian return flow to both the horizontal and the vertical Lagrangian displacements. We compare our experimental results to leading-order solutions of the irrotational water wave equations, finding good agreement.
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Alhusban, Zaid, i Manousos Valyrakis. "Assessing and Modelling the Interactions of Instrumented Particles with Bed Surface at Low Transport Conditions". Applied Sciences 11, nr 16 (9.08.2021): 7306. http://dx.doi.org/10.3390/app11167306.
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Sediment transport at near threshold to low transport stages (below the continuous transport) can still be affected by flow turbulence and its dynamics can benefit from further comprehensive studies. This study uses an instrumented particle embedded with micro electromechanical sensors (MEMS) to allow tracking the motions and forces acting on it, leading to and during its transport. Instrumented particle transport experiments were carried out at laboratory flume under a range of flow conditions. The probability distributions functions (PDFs) of bed load particle instantaneous velocities, hop distances and associated travel times (measured from start to stop of transport) were obtained for all the performed experiments with varying flow rates and particle density. The modelled distributions are useful and enable a deeper understanding of bed load sediment transport dynamics from a Lagrangian perspective. Furthermore, the results analyzed from the instrumented particle (including the particle’s transport mode) were validated using visual particle tracking methods (top and side cameras). The findings of this study demonstrate that for the range of turbulent flows trialed herein, the instrumented particle can be a useful, accessible, and low-cost tool for obtaining particle transport dynamics, having demonstrated satisfactory potential for field deployment in the near future.
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Wang, Dudou, Hongfu Qiang i Chao Shi. "A multiphase SPH framework for solving the evaporation and combustion process of droplets". International Journal of Numerical Methods for Heat & Fluid Flow 30, nr 3 (12.12.2019): 1547–75. http://dx.doi.org/10.1108/hff-08-2019-0666.
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Purpose This paper aims to introduce a two-dimensional smoothed particle hydrodynamics (SPH) framework for simulating the evaporation and combustion process of fuel droplets. Design/methodology/approach To solve the gas–liquid two-phase flow problem, a multiphase SPH method capable of handling high density-ratio problems is established. Based on the Fourier heat conduction equation and Fick’s law of diffusion, the SPH discrete equations are derived. To effectively characterize the phase transition problem, inspired by volume of fluid method, the concept of liquid phase mass fraction of the SPH particles is proposed. The one-step global reaction model of n-hexane is used for the vapor combustion. Findings The evaporation and combustion process of single droplet conforms to the law. The framework works out well when the evaporation of multiple droplets involves coalescence process. Three different kinds of flames are observed in succession in the combustion process of a single droplet at different inflow velocity, which agree well with the results of the experiment. Originality/value To the best of the authors’ knowledge, this is the first computational framework that has the capability to simulate evaporation and combustion with SPH method. Based on the particle nature of SPH method, the framework has natural advantages in interface tracking.
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Pouransari, H., H. Kolla, J. H. Chen i A. Mani. "Spectral analysis of energy transfer in turbulent flows laden with heated particles". Journal of Fluid Mechanics 813 (27.01.2017): 1156–75. http://dx.doi.org/10.1017/jfm.2017.2.
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In this study we consider particle-laden turbulent flows with significant heat transfer between the two phases due to sustained heating of the particle phase. The sustained heat source can be due to particle heating via an external radiation source as in the particle-based solar receivers or an exothermic reaction in the particles. Our objective is to investigate the effects of fluid heating by a dispersed phase on the turbulence evolution. An important feature in such settings is the preferential clustering phenomenon which is responsible for non-uniform distribution of particles in the fluid medium. Particularly, when the ratio of particle inertial relaxation time to the turbulence time scale, namely the Stokes number, is of order unity, particle clustering is maximized, leading to thin regions of heat source similar to the flames in turbulent combustion. However, unlike turbulent combustion, a particle-laden system involves a wide range of clustering scales that is mainly controlled by particle Stokes number. To study these effects, we considered a decaying homogeneous isotropic turbulence laden with heated particles over a wide range of Stokes numbers. Using a low-Mach-number formulation for the fluid energy equation and a Lagrangian framework for particle tracking, we performed numerical simulations of this coupled system. We then applied a high-fidelity framework to perform spectral analysis of kinetic energy in a variable-density fluid. Our results indicate that particle heating can considerably influence the turbulence cascade. We show that the pressure-dilatation term introduces turbulent kinetic energy at a range of scales consistent with the scales observed in particle clusters. This energy is then transferred to high wavenumbers via the energy transfer term. For low and moderate levels of particle heating intensity, quantified by a parameter $\unicode[STIX]{x1D6FC}$ defined as the ratio of eddy time to mean temperature increase time, turbulence modification occurs primarily in the dilatational modes of the velocity field. However, as the heating intensity is increased, the energy transfer term converts energy from dilatational modes to divergence-free modes. Interestingly, as the heating intensity is increased, the net modification of turbulence by heating is observed dominantly in divergence-free modes; the portion of turbulence modification in dilatational modes diminishes with higher heating. Moreover, we show that modification of divergence-free modes is more pronounced at intermediate Stokes numbers corresponding to the maximum particle clustering. We also present the influence of heating intensity on the energy transfer term itself. This term crosses over from negative to positive values beyond a threshold wavenumber, showing the cascade of energy from large scales to small scales. The threshold is shown to shift to higher wavenumbers with increasing heating, indicating a growth in the total energy transfer from large scales to small scales. The fundamental energy transfer analysis presented in this paper provides insightful guidelines for subgrid-scale modelling and large-eddy simulation of heated particle-laden turbulence.
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OHIWA, Norio, Yojiro ISHINO, Takanori TOMATSU i Ryuji YAMAKITA. "Magnifying and Tracking Observation of Micro PET Particles Passing through a Plane Premixed Flame Front". Journal of Thermal Science and Technology 2, nr 2 (2007): 212–23. http://dx.doi.org/10.1299/jtst.2.212.
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Park, Yong Sung, Philip L. F. Liu i I.-Chi Chan. "Contact line dynamics and boundary layer flow during reflection of a solitary wave". Journal of Fluid Mechanics 707 (13.07.2012): 307–30. http://dx.doi.org/10.1017/jfm.2012.280.
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AbstractIn this paper we present a set of wave flume experiments for a solitary wave reflecting off a vertical wall. A particle tracking velocimetry (PTV) technique is used to measure free-surface velocity and the velocity field in the vicinity of the moving contact line. We observe that the free surface undergoes the so-called rolling motion as the contact line moves up and down the vertical wall, and fluid particles on the free surface almost always flow toward the wall except at the end of the reflection process. As the contact line descends along the wall, wall boundary layer flows move in a downward direction and therefore the boundary layer acts like a conduit through which the surface-rolling-induced flow escapes from the meniscus. However, during the last phase of the reflection process flow reversal occurs inside the wall boundary layer. An approximate analytical solution is developed to explain the flow reversal feature. Very good agreement between the approximate theory and measured data is obtained. Because of the flow reversal, boundary layer flows collide with the surface-rolling-induced flows. The collision gives rise to a jet ejecting from the meniscus into the water body, which later evolves into a small eddy. It is noticed that the fluid particles in different regions such as the free stream, the free-surface boundary layer and the wall boundary layer, can be transported to other regions by passing through the meniscus.
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Krista, Larisza D., i Matthew Chih. "A DEFT Way to Forecast Solar Flares". Astrophysical Journal 922, nr 2 (1.12.2021): 218. http://dx.doi.org/10.3847/1538-4357/ac2840.
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Abstract Solar flares have been linked to some of the most significant space weather hazards at Earth. These hazards, including radio blackouts and energetic particle events, can start just minutes after the flare onset. Therefore, it is of great importance to identify and predict flare events. In this paper we introduce the Detection and EUV Flare Tracking (DEFT) tool, which allows us to identify flare signatures and their precursors using high spatial and temporal resolution extreme-ultraviolet (EUV) solar observations. The unique advantage of DEFT is its ability to identify small but significant EUV intensity changes that may lead to solar eruptions. Furthermore, the tool can identify the location of the disturbances and distinguish events occurring at the same time in multiple locations. The algorithm analyzes high temporal cadence observations obtained from the Solar Ultraviolet Imager instrument aboard the GOES-R satellite. In a study of 61 flares of various magnitudes observed in 2017, the “main” EUV flare signatures (those closest in time to the X-ray start time) were identified on average 6 minutes early. The “precursor” EUV signatures (second-closest EUV signatures to the X-ray start time) appeared on average 14 minutes early. Our next goal is to develop an operational version of DEFT and to simulate and test its real-time use. A fully operational DEFT has the potential to significantly improve space weather forecast times.
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Zepeda Mondragon, Hilda, Juan Antonio Garcia Aragon, Humberto Salinas Tapia i Bommanna G. Krishnappan. "Estimation of Fractal Dimension of Suspended Sediments from Two Mexican Rivers". Water 14, nr 18 (6.09.2022): 2774. http://dx.doi.org/10.3390/w14182774.
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Sampling programs for suspended sediment were carried out in the Usumacinta River and its tributary Grijalva River in Mexico during the years 2016 and 2017. Suspended sediment samples collected during these sampling programs were analyzed in the laboratory using a Rotating Annular Flume (RAF) fitted with a Particle Tracking Velocimetry (PTV) to obtain the 2D images of the suspended sediment particles as they were undergoing floc reconstruction, and subsequently using a glass settling column fitted with inline digital holography set up to obtain 3D holograms of the fully flocculated sediment particles. From these high-resolution hologram images, the fractal dimension of the flocculated sediment particles was obtained using the classical box-counting method and an improved Triangular box-counting method. The estimated fractal dimension of flocculated sediment, which is a measure of floc compactness and structure that control the settling velocity of flocculated sediment was used to validate two empirical models to estimate the fractal dimension in terms of the floc sizes of suspended sediments of these two rivers. It is shown in this study that the floc characteristic can be analyzed in laboratory experiments after floc reconstruction with the use of an RAF and it offers a viable alternative to the costly in-situ sampling that is often carried out in ocean research. The digital holography method employed in this research offers an efficient methodology to obtain the floc fractal dimension. Regarding the innovative aspects and new contribution to science, we can say that we have developed a laboratory protocol to test river waters to establish floc properties such as fractal dimensions of flocs in this research which will help to test river waters on a routine basis with manageable costs. We can also say that we have developed models to predict the relationship between floc fractal dimension and floc size, which did not exist before.
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Bartos, Daniel, Matthew Dunn, Mariano Sirignano, Andrea D'Anna i Assaad R. Masri. "Tracking the evolution of soot particles and precursors in turbulent flames using laser-induced emission". Proceedings of the Combustion Institute 36, nr 2 (2017): 1869–76. http://dx.doi.org/10.1016/j.proci.2016.07.092.
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Lin, Yen-Cheng, Hao-Che Ho, Tzu-An Lee i Hsin-Yu Chen. "Application of Image Technique to Obtain Surface Velocity and Bed Elevation in Open-Channel Flow". Water 14, nr 12 (13.06.2022): 1895. http://dx.doi.org/10.3390/w14121895.
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The frequency of droughts and floods is increasing due to the extreme climate. Therefore, water resource planning, allocation, and disaster prevention have become increasingly important. One of the most important kinds of hydrological data in water resources planning and management is discharge. The general way to measure the water depth and discharge is to use the Acoustic Doppler Current Profiler (ADCP), a semi-intrusive instrument. This method would involve many human resources and pose severe hazards by floods and extreme events. In recent years, it has become mainstream to measure hydrological data with nonintrusive methods such as the Large-Scale Particle Image Velocimetry (LSPIV), which is used to measure the surface velocity of rivers and estimate the discharge. However, the unknown water depth is an obstacle for this technique. In this study, a method combined with LSPIV to estimate the bathymetry was proposed. The experiments combining the LSPIV technique and the continuity equation to obtain the bed elevation were conducted in a 27 m long and 1 m wide flume. The flow conditions in the experiments were ensured to be within uniform and subcritical flow, and thermoplastic rubber particles were used as the tracking particles for the velocity measurement. The two-dimensional bathymetry was estimated from the depth-averaged velocity and the continuity equation with the leapfrog scheme in a predefined grid under the constraints of Courant–Friedrichs–Lewy (CFL). The LSPIV results were verified using Acoustic Doppler Velocimetry (ADV) measurements, and the bed elevation data of this study were verified using conventional point gauge measurements. The results indicate that the proposed method effectively estimated the variation of the bed elevation, especially in the shallow water level, with an average accuracy of 90.8%. The experimental results also showed that it is feasible to combine the nonintrusive imaging technique with the numerical calculation in solving the water depth and bed elevation.
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Azevedo, Sidney Gomes, Ana Luisa Farias Rocha, Ronald Zico de Aguiar Nunes, Camila da Costa Pinto, Ştefan Ţălu, Henrique Duarte da Fonseca Filho, Jaqueline de Araújo Bezerra i in. "Pulsatile Controlled Release and Stability Evaluation of Polymeric Particles Containing Piper nigrum Essential Oil and Preservatives". Materials 15, nr 15 (5.08.2022): 5415. http://dx.doi.org/10.3390/ma15155415.
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Considerable efforts have been spent on environmentally friendly particles for the encapsulation of essential oils. Polymeric particles were developed to encapsulate the essential oil from Piper nigrum based on gelatin and poly–ε–caprolactone (PCL) carriers. Gas Chromatography ((Flame Ionization Detection (GC/FID) and Mass Spectrometry (GC/MS)), Atomic Force Microscopy (AFM), Nanoparticle Tracking Analysis (NTA), Confocal Laser Scanning Microscopy (CLSM), Attenuated Total Reflectance–Fourier-transform Infrared Spectroscopy (ATR–FTIR), and Ultraviolet–Visible (UV–VIS) spectroscopy were used for the full colloidal system characterization. The essential oil was mainly composed of β-caryophyllene (~35%). The stability of the encapsulated systems was evaluated by Encapsulation Efficiency (EE%), electrical conductivity, turbidity, pH, and organoleptic properties (color and odor) after adding different preservatives. The mixture of phenoxyethanol/isotialzoni-3-one (PNE system) resulted in enhanced stability of approximately 120 and 210 days under constant handling and shelf-life tests, respectively. The developed polymeric system presented a similar controlled release in acidic, neutral, or basic pH, and the release curves suggested a pulsatile release mechanism due to a complexation of essential oil in the PCL matrix. Our results showed that the developed system has potential as an alternative stable product and as a controlling agent, due to the pronounced bioactivity of the encapsulated essential oil.
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Itay, Uri, i Dan Liberzon. "Lagrangian Kinematic Criterion for the Breaking of Shoaling Waves". Journal of Physical Oceanography 47, nr 4 (kwiecień 2017): 827–33. http://dx.doi.org/10.1175/jpo-d-16-0289.1.
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AbstractAn experimental study was conducted with the aim of validating the Lagrangian kinematic criterion (LKC) for the case of breaking of shoaling waves. Monochromatic wave trains were generated in a large wave flume and allowed to shoal and break naturally on an artificial inclination changeable shore, thus allowing inspection of a range of slopes. Instantaneous horizontal Lagrangian water surface velocity was measured by particle tracking velocimetry and compared to the instantaneous propagation speed of the crest on a verge of breaking, the latter calculated using time series produced by resistance-type wave gauges staged along the flume. The inception of a breaker was found to occur when the monotonically increasing horizontal water velocity on the crest, during the process of steepening, approached that of the slowing steep crest, thus confirming the LKC for shoaling conditions. In addition, an objective method of breaking detection was developed utilizing the phase–time method and wavelet analysis by recognizing a specific pattern in the instantaneous local frequency fluctuations. The two main expected contributions of this study are the formation of an applicable criterion for breaking occurrences in shoaling waves and development of a wave breaking detection method independent of human decision. Incorporation of the suggested criterion into existing waves prediction models can be a significant contribution to maritime projects efficiency, whereas the breakers detection method will be useful for conducting further experimental research on waves breaking both in laboratory installations and in the highly unstable environment of an open sea.
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Levenstein, Mark A., Daniel J. Gysbers, Kristen L. Marhaver, Sameh Kattom, Lucas Tichy, Zachary Quinlan, Haley M. Tholen i in. "Millimeter-scale topography facilitates coral larval settlement in wave-driven oscillatory flow". PLOS ONE 17, nr 9 (12.09.2022): e0274088. http://dx.doi.org/10.1371/journal.pone.0274088.
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Larval settlement in wave-dominated, nearshore environments is the most critical life stage for a vast array of marine invertebrates, yet it is poorly understood and virtually impossible to observe in situ. Using a custom-built flume tank that mimics the oscillatory fluid flow over a shallow coral reef, we isolated the effect of millimeter-scale benthic topography and showed that it increases the settlement of slow-swimming coral larvae by an order of magnitude relative to flat substrates. Particle tracking velocimetry of flow fields revealed that millimeter-scale ridges introduced regions of flow recirculation that redirected larvae toward the substrate surface and decreased the local fluid speed, effectively increasing the window of time for larvae to settle. Regions of recirculation were quantified using the Q-criterion method of vortex identification and correlated with the settlement locations of larvae for the first time. In agreement with experiments, computational fluid dynamics modeling and agent-based larval simulations also showed significantly higher settlement onto ridged substrates. Additionally, in contrast to previous reports on the effect of micro-scale substrate topography, we found that these topographies did not produce key hydrodynamic features linked to increased settlement. These findings highlight how physics-based substrate design can create new opportunities to increase larval recruitment for ecosystem restoration.
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Lin, Chang, Ming-Jer Kao, James Yang, Juan-Ming Yuan i Shih-Chun Hsieh. "Effects of Nonlinearity on Velocity, Acceleration and Pressure Gradient in Free-Stream Zone of Solitary Wave over Horizontal Bed—An Experimental Study". Water 14, nr 22 (9.11.2022): 3609. http://dx.doi.org/10.3390/w14223609.
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For solitary waves on a horizontal bed, the study deals experimentally with the high ratio of wave height (H0) to still water depth (h0) that amplifies the wave nonlinearity. The value of H0/h0 tested in a wave flume ranges from 0.050 to 0.550, indicating the shift from a quasi-linear solitary wave to a highly nonlinear one. A high-speed particle image velocimetry (HSPIV) and a flow visualization technique of particle-trajectory tracking method are utilized to measure velocity fields and identify near-bed flow structures. The unsteady free-stream velocities with equal magnitude take place in a free-stream zone, FSZ). The FSZ underlies the internal flow zone, over which the external free surface of solitary wave exists and is situated beyond the boundary layer. The spatio-temporal variation of free-stream velocity, moving in phase with the free surface elevation, characterizes the pattern of pressure gradient in the FSZ and thus dominates the behavior of boundary layer flow. Accordingly, nonlinear effects on the time series as well as the maximum values of horizontal velocity, particle acceleration, and pressure gradient in the FSZs of solitary waves are presented. Before, at, and after the wave crest’s intersection with a given measurement location, favorable, zero, and adverse pressure gradients occur in the FSZ, respectively. For H0/h0 = 0.179, 0.363, and 0.550, the values of the dimensionless maximum free-stream velocity are about 3.10, 5.32, and 6.20 times that (= 0.0473) for H0/h0 = 0.050; and the corresponding values of the dimensionless maximum adverse pressure gradient are about 5.74, 14.54 and 19.84 times that (= 0.0061) for H0/h0 = 0.050. This evidence highlights the nonlinear effect on the kinematic and hydrodynamic features of solitary waves. Finally, the effect of nonlinearity on the relationship between the dimensionless time for the maximum adverse pressure gradient in the FSZ and that for the incipient flow reversal in the bottom boundary layer is explored for the first time. It is found that the incipient flow reversal takes place immediately after the maximum adverse pressure gradient, together with a decrease in the dimensionless time for flow reversal if H0/h0 increases. The fact accentuates the nonlinear effect on the incipient flow reversal right above the bed.
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LIBERZON, DAN, i LEV SHEMER. "Experimental study of the initial stages of wind waves' spatial evolution". Journal of Fluid Mechanics 681 (24.06.2011): 462–98. http://dx.doi.org/10.1017/jfm.2011.208.
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Despite a significant progress and numerous publications over the last few decades a comprehensive understanding of the process of waves' excitation by wind still has not been achieved. The main goal of the present work was to provide as comprehensive as possible set of experimental data that can be quantitatively compared with theoretical models. Measurements at various air flow rates and at numerous fetches were carried out in a small scale, closed-loop, 5 m long wind wave flume. Mean airflow velocity and fluctuations of the static pressure were measured at 38 vertical locations above the mean water surface simultaneously with determination of instantaneous water surface elevations by wave gauges. Instantaneous fluctuations of two velocity components were recorded for all vertical locations at a single fetch. The water surface drift velocity was determined by the particle tracking velocimetry (PTV) method. Evaluation of spatial growth rates of waves at various frequencies was performed using wave gauge records at various fetches. Phase relations between various signals were established by cross-spectral analysis. Waves' celerities and pressure fluctuation phase lags relative to the surface elevation were determined. Pressure values at the water surface were determined by extrapolating the measured vertical profile of pressure fluctuations to the mean water level and used to calculate the form drag and consequently the energy transfer rates from wind to waves. Directly obtained spatial growth rates were compared with those obtained from energy transfer calculations, as well as with previously available data.
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Modak, Abhijit, Karthik Puduppakkam, Chitralkumar Naik i Ellen Meeks. "Simulation of Particle Synthesis by Premixed Laminar Stagnation Flames". MRS Proceedings 1506 (2013). http://dx.doi.org/10.1557/opl.2013.1049.
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ABSTRACTA sectional method for determining particle size distributions has been implemented within the particle tracking module included with CHEMKIN-PRO. The module is available for use with many types of reactor models, ranging from 0-D batch reactors to laminar flame simulations. Coupled with the Burner-stabilized Stagnation Flame (BSSF) Model, the sectional model offers a high-fidelity, robust, and efficient computational framework for simulating flame synthesis of particles in a laminar, premixed stagnation flame environment. The CHEMKIN-PRO coupling allows inclusion of detailed gas-phase chemistry that determines key particle-formation precursors, along with physical processes such as nucleation and coagulation of particles. These capabilities are demonstrated for two flame-particle systems of practical importance, viz. nanocrystalline titania synthesis and soot formation. The results are compared with experimental data obtained at the University of Southern California (USC) flame facility. Computed particle size distributions show good agreement with experimental data. Simulations have led to exploration of the parameter space for particle production and particle-size influences.
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"Particle tracking in a pre-mixed flame". Physics World 4, nr 1 (styczeń 1991): 25. http://dx.doi.org/10.1088/2058-7058/4/1/24.
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Zirwes, Thorsten, Feichi Zhang, Yiqing Wang, Peter Habisreuther, Jordan A. Denev, Zheng Chen, Henning Bockhorn i Dimosthenis Trimis. "In-situ flame particle tracking based on barycentric coordinates for studying local flame dynamics in pulsating Bunsen flames". Proceedings of the Combustion Institute, wrzesień 2020. http://dx.doi.org/10.1016/j.proci.2020.07.033.
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Versailles, Philippe, Antoine Durocher, Gilles Bourque i Jeffrey M. Bergthorson. "Measurements of the reactivity of premixed, stagnation, methane-air flames at gas turbine relevant pressures". Journal of Engineering for Gas Turbines and Power 141, nr 1 (17.10.2018). http://dx.doi.org/10.1115/1.4041125.
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The adiabatic, unstrained, laminar flame speed, SL, is a fundamental combustion property, and a premier target for the development and validation of thermochemical mechanisms. It is one of the leading parameters determining the turbulent flame speed, the flame position in burners and combustors, and the occurrence of transient phenomena, such as flashback and blowout. At pressures relevant to gas turbine engines, SL is generally extracted from the continuous expansion of a spherical reaction front in a combustion bomb. However, independent measurements obtained in different types of apparatuses are required to fully constrain thermochemical mechanisms. Here, a jet-wall, stagnation burner designed for operation at gas turbine relevant conditions is presented, and used to assess the reactivity of premixed, lean-to-rich, methane–air flames at pressures up to 16 atm. One-dimensional (1D) profiles of axial velocity are obtained on the centerline axis of the burner using particle tracking velocimetry, and compared to quasi-1D flame simulations performed with a selection of thermochemical mechanisms available in the literature. Significant discrepancies are observed between the numerical and experimental data, and among the predictions of the mechanisms. This motivates further chemical modeling efforts, and implies that designers in industry must carefully select the mechanisms employed for the development of gas turbine combustors.
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XIE, Qing, Zhuyin REN, Ke WANG, Hongjun LIN, Shoutang SHANG i Wei XIAO. "A forced ignition probability analysis method using kernel formation analysis with turbulent transport and Lagrangian flame particle tracking". Chinese Journal of Aeronautics, wrzesień 2020. http://dx.doi.org/10.1016/j.cja.2020.08.023.
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Cassel, Mathieu, Jérôme Lavé, Alain Recking, Jean-René Malavoi i Hervé Piégay. "Bedload transport in rivers, size matters but so does shape". Scientific Reports 11, nr 1 (12.01.2021). http://dx.doi.org/10.1038/s41598-020-79930-7.
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AbstractBedload transport modelling in rivers takes into account the size and density of pebbles to estimate particle mobility, but does not formally consider particle shape. To address this issue and to compare the relative roles of the density and shape of particles, we performed original sediment transport experiments in an annular flume using molded artificial pebbles equipped with a radio frequency identification tracking system. The particles were designed with four distinct shapes and four different densities while having the same volume, and their speeds and distances traveled under constant hydraulic conditions were analyzed. The results show that particle shape has more influence than particle density on the resting time between particle displacement and the mean traveling distance. For all densities investigated, the particle shape systematically induced differences in travel distance that were strongly correlated (R2 = 0.94) with the Sneed and Folks shape index. Such shape influences, although often mentioned, are here quantified for the first time, demonstrating why and how they can be included in bedload transport models.
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Jiang, Xiao, i Tat Leung Chan. "Lagrangian particle tracking with new weighted fraction Monte Carlo method for studying the soot particle size distributions in premixed flames". International Journal of Numerical Methods for Heat & Fluid Flow ahead-of-print, ahead-of-print (2.09.2021). http://dx.doi.org/10.1108/hff-04-2021-0247.
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Purpose The purpose of this paper is to study the soot formation and evolution by using this newly developed Lagrangian particle tracking with weighted fraction Monte Carlo (LPT-WFMC) method. Design/methodology/approach The weighted soot particles are used in this MC framework and is tracked using Lagrangian approach. A detailed soot model based on the LPT-WFMC method is used to study the soot formation and evolution in ethylene laminar premixed flames. Findings The LPT-WFMC method is validated by both experimental and numerical results of the direct simulation Monte Carlo (DSMC) and Multi-Monte Carlo (MMC) methods. Compared with DSMC and MMC methods, the stochastic error analysis shows this new LPT-WFMC method could further extend the particle size distributions (PSDs) and improve the accuracy for predicting soot PSDs at larger particle size regime. Originality/value Compared with conventional weighted particle schemes, the weight distributions in LPT-WFMC method are adjustable by adopting different fraction functions. As a result, the number of numerical soot particles in each size interval could be also adjustable. The stochastic error of PSDs in larger particle size regime can also be minimized by increasing the number of numerical soot particles at larger size interval.
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Ragessi, I. Matias, Carlos Marcelo García, Santiago Marquez Damian, Leticia Tarrab, Antoine Patalano i Andres Rodriguez. "Detailed experimental and numerical analysis of hydrodynamics in the outflow measurement channel of a sewage treatment plant". Journal of Hydroinformatics, 15.06.2022. http://dx.doi.org/10.2166/hydro.2022.168.
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Abstract The ‘Bajo Grande’ Wastewater Treatment Plant has a design capacity of 2.78 m3/s, and discharges into the Suquia River (Córdoba, Argentina). The river has an average flow rate of 10 m3/s, with lower values during the summer. Currently, the treatment plant does not have an accurate discharge-measurement system prior to the discharge into the river, which makes it difficult to evaluate the dosing of the disinfection treatment. The outflow rate is measured in a straight flume. However, at the inlet section of the flume, a 180° sharp bend induces a complex turbulent flow with instabilities and low-frequency velocity fluctuations which are not appropriate for flow quantification. In this type of flow, most of the in situ flow discharge-measurement systems have great uncertainty. Therefore, in situ flow measurements with an Acoustic Doppler Current Profiler, Large-Scale Particle-Tracking Velocimetry techniques and a prototype-scale Detached Eddy Simulation model were combined to obtain a detailed characterization of the turbulent flow. The results provide flow rates, fields of mean flow velocity, temporal evolution, and characteristic parameters of the turbulence. This allowed a better understanding of the effects of turbulence and flow instabilities. The results provide a basis to validate numerical models used in the hydraulics design of contact chambers to improve the disinfection process.
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Sanjou, Michio, i Yuji Sugihara. "Experimental study on characteristics of turbulence and sediment transport produced by wind-induced water waves". Physics of Fluids, 2.02.2023. http://dx.doi.org/10.1063/5.0138538.
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Many researchers and engineers have shown great interest in mass transfer processes produced by wind-induced waves. Such waves contribute significantly to the transfer of environmental materials such as marine debris and sediment, and the turbulence occurring beneath the waves further complicates wave-induced mass transport. The phase cycle of wave motion is generally considered to be a key determinant of mean flow and turbulence. In aqueous environmental engineering, this relationship is a crucial one to investigate, since turbulence is also related to mass transport. To address this question, we measured the time-series of instantaneous velocity vectors by particle image velocimetry (PIV) in a laboratory flume to reveal the turbulence structure induced by wave motion. In a wavelet analysis free of specific assumptions, we were able to decompose the instantaneous velocity data into mean current, wave motion, and turbulence components. This analysis allowed for the objective evaluation of the shear stresses related to wave energy and turbulence energy production. <p>Furthermore, we found significant phase characteristics of energy transfer among mean-velocity, wave, and turbulence components. In order to examine the diffusion and convection properties induced by wind-waves, we also conducted tracking analysis of imaginary sediment markers. Our results support the conclusion that mass transfer induced by wind-waves impacts the entire range of water depths, at least in relatively shallow aqueous environments.