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A forced ignition probability analysis method using kernel formation analysis with turbulent transport and lagrangian flame particle tracking

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Chinese Journal of Aeronautics 2021年第4期34卷 403-415页

作者： Qing XIE Zhuyin REN Ke WANG Hongjun LIN Shoutang SHANG Wei XIAO School of Aerospace Engineering Tsinghua UniversityBeijing 100084China Institute for Aero Engine Tsinghua UniversityBeijing 100084China Aero Engine Academy of China Beijing 101300China AECC Shenyang Engine Research Institute Shenyang 110000China AECC Hunan Aviation Powerplant Research Institute Zhuzhou 412000China

A forced ignition probability analysis method is developed for turbulent combustion,in which kernel formation is analyzed with local kernel formation criteria,and flame propagation and stabilization are simulated with lagrangian flame particle tracking.For kernel formation,the effect of turbulent scalar transport on flammability is modelled through the incorporation of turbulenceinduced diffusion in a spherically outwardly propagating flame kernel model.The dependence of flammability limits on turbulent intensities is tabulated and serves as the flammability criterion for kernel formation.For lagrangian flame particle tracking,flame particles are tracked in a structured grid with flow fields being interpolated from a Computational Fluid Dynamics(CFD)solution.The particle velocity follows a Langevin model consisting of a linear drift and an isotropic diffusion term.The Karlovitz number is employed for the extinction criterion,which compares chemical and turbulent timescales.The integration of the above two-step analysis approach with non-reacting CFD is achieved through a general interpolation interface suitable for general unstructured CFD grids.The method is demonstrated for a methane/air bluff-body flame,in which flow and fuel/air mixing characteristics are extracted from a non-reacting simulation.Results show that the computed ignition probability map agrees qualitatively with experimental results.A reduction of the ignition probability in the recirculation zone and a high ignition probability on the shear layer of the recirculation zone near the mean stoichiometric surface are well captured.The tools can facilitate optimization of spark placement and offer insights into ignition processes.

关键词： Bluff-body stabilized flame Igniting process Ignition criterion Ignition probability lagrangian particle tracking

Scouring of a granular bed by dam break: Experimental study and numerical simulation by a VOF-LPT coupling

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International Journal of Sediment Research 2023年第3期38卷 432-445页

作者： Quyen Thi Le Nguyen Viet Dung Nguyen Patrice Coorevits EPROAD Research Unit University of Picardie Jules Verne IUT of Aisne Hanoi University of Civil Engineering

The first part of the research reported here consists of an experimental campaign to study the scouring of a granular bed(glass beads, sand) induced by a dam break in an open channel. Two configurations are considered: with and without cylinders. In the second part of this study, the volume of fluid method coupled with the shear stress transport turbulent model and the lagrangian particle tracking method is used to simulate the local scour processes. The four-way coupling is realized by considering the drag force and collisions between particles. Using a vortex map and velocity profiles, the flow dynamics and scour pattern can be studied. The current research also focuses on the profiles of the erodible particle bed and the sediment transport rate to study the effects of a cylinder on local scour. The presence of the cylinder increases the experimental erosion depth by up to 42%. It was found that for relatively close particle diameters(2 and 3 mm), a granular bed with larger porosity(larger diameter) erodes the most.Experimentally and numerically it was found that the center of the granular bed experiences more erosion compared to the channel sides. In the last part of the research, comparisons between the numerical results and the experimental data allowed risk areas to be identified and the roles of porosity,sediment density, and flow dynamics on erosion to be identified.

关键词： Volume of fluid lagrangian particle tracking Scour Granular bed Cylinder Dam break

Developing a lagrangian sediment transport model for open channel flows

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International Journal of Sediment Research 2023年第2期38卷 153-165页

作者： Saman Baharvand Habib Ahmari Poorya Taghvaei Department of Civil Engineering The University of Texas at Arlington Department of Civil Engineering Semnan University

A three-dimensional stochastic lagrangian particle tracking sediment transport model is developed to solve the discrete advection-dispersion equation using a combination of empirical dispersion equations.The performance of three widely-used longitudinal dispersion coefficient equations was examined to select one of them as the primary dispersion equation term in the developed model. Also, a conditional empirical equation was used to consider the effect of vertical dispersion term in top layers near the water surface. The performance of particle tracking model(PTM) to calculate the sediment concentration was evaluated for various sediment classes(very fine sand, fine sand, and medium sand) using available laboratory dataset. Multiple statistical measures were calculated using the Taylor diagram for each dispersion equation. Based on the result, the developed particle tracking model estimated the suspended sediment concentration in a rectangular open channel with a correlation coefficient(R) of 0.96, standard deviation(STD) of 0.262, and root mean square deviation(RMSD) of 0.06 for three different sediment classes proving the acceptable accuracy of the developed model for different range of sediment gradations. In addition, the accuracy of PTM was compared to recently developed models. Comparison between the particle tracking model and the analytical solution of the advection-dispersion equation showed that the developed model predicted the maximum concentration of suspended sediment 6% and9.4% lower than the analytical solution result for 30 and 50 s simulation time in the straight channel,respectively. However, there was a good agreement between the longitudinal and transverse sediment concentration distribution from the model and the analytical solution approach. The result of the sensitivity analysis and validation process showed that the model could be used to simulate sediment transport in open channel flows.

关键词： Sediment transport lagrangian particle tracking Stochastic approach Advection–dispersion Random walk

Tracer advection in a pair of adjacent side-wall cavities, and in a rectangular channel containing two groynes in series

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Journal of Hydrodynamics 2018年第4期30卷 564-572页

作者： Mohammad Mahdi Jalali Alistair G.L.Borthwick Institute for Energy Systems School of Engineering The University of Edinburgh

A model is presented of particle advection near groynes in an open channel. Open channel hydrodynamics is modelled using the shallow water equations, obtained as the depth-averaged form of Reynolds-averaged continuity and Navier-Stokes momentum equations. A lagrangian particle-tracking model is used to predict trajectories of tracer particles advected by the flow field, with bilinear interpolation representing the continuous flow field. The particle-tracking model is verified for chaotic advection in an alternating flow field of a pair of blinking vortices. The combined shallow flow and lagrangian particle-tracking model is applied to the simulation of tracer advection in flow past a pair of side-wall cavities separated by a groyne, and in an open rectangular channel containing a pair of parallel groynes oriented normal to the channel wall. The study is potentially useful in understanding mixing processes in shallow flow fields near hydraulic structures in wide rivers.

关键词： Shallow water equations lagrangian particle tracking chaotic advection blinking vortices side-wall cavities groynes

Modelling ignition probability with pairwise mixing-reaction model for flame particle tracking

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Chinese Journal of Aeronautics 2021年第5期34卷 523-534页

作者： Qing XIE Zhuyin REN Ke WANG School of Aerospace Engineering Tsinghua UniversityBeijing 100084China Institute for Aero Engine Tsinghua UniversityBeijing 100084China Aero Engine Academy of China Beijing 101300China

Reduced order models for ignition analysis can offer insights into ignition processes and facilitate the combustor optimization.In this study,a Pairwise Mixing-Reaction(PMR)model is formulated to model the interaction between the flame particle and the surrounding cell mixture during lagrangian flame particle tracking.Specifically,the model accounts for the two-way coupling of mass and energy between the flame particle and the surrounding shell layer by modelling the corresponding turbulent mixing,chemical reaction and evaporation process if present.The state of a flame particle,e.g.,burnt,hot gas or extinguished,is determined based on particle temperature.This model can properly describe the ignition process with a spark kernel being initiated in a nonflammable region,which is of practical importance in certain turbine engines and has not been rigorously accounted for by the existing models based on the estimation of local Karlovitz number.The model is integrated into an ignition probability analysis platform and is demonstrated for a methane/air bluff-body flame with the flow and fuel/air mixing characteristics being extracted from a non-reacting simulation.The results show that for the spark location being at the extreme fuellean outer shear layer of the recirculation zone,PMR can yield ignition events with a significant number of active flame particles.The mechanisms for the survival of the initial flame particles and the entrainment of the survived flame particles into the recirculation zone are analyzed.The results also show that the ignition probability map from PMR agrees well with the experimental observation:a high ignition probability in the shear layer of the recirculation zone near the mean stoichiometric surface,and low ignition probabilities inside the recirculation zone and the top stagnation region of the recirculation zone.The parametric study shows that the predicted shape of the ignition progress factor and ignition probability is in general insensitive to the model parameters and the model is

关键词： Bluff-body stabilized flame Igniting process Ignition probability lagrangian particle tracking Pairwise mixing-reaction

Numerical Simulation of Water Exchange Characteristics of the Jiaozhou Bay Based on A Three-Dimensional lagrangian Model

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China Ocean Engineering 2009年第2期23卷 277-290页

作者：王翠张学庆孙英兰 College of Environmental Science and Engineering Ocean University of China

Based on theory of three-dimensional hydrodynamics, an Euler-lagrangian particle model is established to study the transport and water exchange capability in the Jiaozhou Bay. The three-dimensional hydrodynamic model, driven by tide and wind, is used to study the effects of wetting and drying of estuarine intertidal flats by the dry-wet grid technology based on the Estuarine, Coastal and Ocean Model （ECOM）. The particle model includes the advection and the diffusion processes, of which the advection process is simulated with a certain method, and the diffusion process is simulated with the random walk method. The effect of the intertidal zone, the turbulent diffusion and the timescales of the water exchange are also discussed. The results show that a moving boundary model can simulate the transport process of the particle in the intertidal zone, where the particles are transported for a longer distance than that of the stationary result. Simulations with and without the turbulent random walk show that the effect of turbulent diffusion is very effective at spreading particles throughout the estuary and speeding up the particle movement. The spatial distribution of residence time is given to quantify the water exchange capability that has very important ramifications to water quality. The effect of wind on the water exchange is also examined and the southeasterly wind in summer tends to block the water exchange near the northeast coast, while the northerly wind in winter speeds up the transport process. These results indicate that the lagrangian particle model is applicable and has a large potential to help understanding the water exchange capability in estuaries, which can also be useful to simulate the transport process of contaminant.

关键词： water exchange residence time numerical simulation turbulent diffusion lagrangian particle tracking Jiaozhou Bay