Kinetic Simulations for Analysing the Wall Collision Process of Non-Spherical Particles

2002 ◽  
Author(s):  
M. Sommerfeld
Keyword(s):  
Particle Shape ◽  
Fluid Dynamic ◽  
Impact Angle ◽  
Distribution Functions ◽  
Spherical Particles ◽  
Collision Process ◽  
Wall Collision ◽  
Particle Velocities ◽  
The Impact ◽  
Particle Shapes

In wall-bounded gas-solid flows the wall collision process plays an important role and may be strongly affected by wall roughness and particle shape. The modelling of the particle-wall collision mostly relies on the assumption of spherical particles. To extend such models appropriately for non-spherical particles, two-dimensional kinetic simulations were performed for different particle shapes. This implies, that the particle translational and angular motion is calculated by considering the particle shape, however neglecting fluid dynamic effects. The change of the particle velocities during the impact and rebound process was calculated by solving the impulse equations together with Coulombs law of friction. The simulations were performed for a given initial particle velocity by varying impact angle and initial angular velocity. The results for 2000 particle wall collisions allowed us to derive the distribution functions of the impact parameters required to describe the wall collision process for non-spherical particles correctly. Moreover, other wall collision properties, such as rebound angle and velocity ratios could be determined. Finally also a comparison with measurements was possible.

Study on Rebound Characteristics of Fine Spherical Particles Impacting an AISI 403 Steel With High Velocity

2015 ◽  
Author(s):  
Juan Di ◽  
Shun-sen Wang ◽  
Liu-xi Cai ◽  
Shang-fang Cheng ◽  
Chuang Wu
Keyword(s):  
Particle Size ◽  
High Velocity ◽  
Particle Diameter ◽  
Impact Angle ◽  
Spherical Particles ◽  
Dissipated Energy ◽  
Normal Velocity ◽  
Relative Impact ◽  
Restitution Coefficient ◽  
The Impact

Impingement on blade surface by fine particles with high velocity is commonly seen in steam turbines, gas turbines and compressors, which affect the service life and reliability of the equipment. Study on particles’ rebound characteristics is of great significance to reduce the blade erosion and to control particle trajectory. Based on the nonlinear explicit dynamics analysis software ANSYS/LS-DYNA, the impacts of fine spherical particles with different diameters (20 to 500μm) on a typical martensitic stainless steel (AISI 403) target with high velocity (50 to 250m/s) have been systematically studied. The influences of incident velocities, impact angles, particles sizes on its rebound characteristics, relative impact depth, and relative dissipated energy have been analyzed. Results show that velocity restitution coefficient e decreased with the impact angle β1, the incident velocity V1, and the particle size dp. However, the role of particle size on the velocity restitution coefficient seemed to be far less than that of the other two factors. Both of particle’s tangential and normal velocity coefficient of restitution declined with the increasing impact angle in most cases. However, when the incident velocity V1 = 200m / s and the impact angle β1 > 45°, the tangential velocity restitution coefficient et of 100 μm and 200 μm particles increased with the increase in the impact angle β1. The reason might be that the relative impact depth drel was located a zone ranged from 0.1515 to 0.1677, where the tangential rebound behavior could be enhanced. Most of the variation of the tangential and normal velocity restitution coefficient along β1 decreased with the increase in the particle diameter. However, when V1 = 200m/s and β1 > 15°, the tangential reflected velocity of the larger particles was enhanced gradually. In addition, the values of the relative impact depth drel increased with the increasing impact angle and incident velocity, and it increased with the increasing particle diameter in most cases. The relative dissipated energy of particles steadily increased with the impact angle and incident velocity, respectively. Particle diameter had little effect on energy dissipation in comparison with the impact angle and incident velocity.

The decay of isotropic turbulence carrying non-spherical finite-size particles

2019 ◽  
Vol 875 ◽  
pp. 520-542 ◽  
Author(s):  
Lennart Schneiders ◽  
Konstantin Fröhlich ◽  
Matthias Meinke ◽  
Wolfgang Schröder
Keyword(s):  
Energy Balance ◽  
Kinetic Energy ◽  
Energy Budget ◽  
Particle Motion ◽  
Particle Shape ◽  
Dissipation Rate ◽  
Isotropic Turbulence ◽  
Finite Size ◽  
Spherical Particles ◽  
The Impact

Direct particle–fluid simulations of heavy spheres and ellipsoids interacting with decaying isotropic turbulence are conducted. This is the rigorous extension of the spherical particle analysis in Schneiders et al. (J. Fluid Mech., vol. 819, 2017, pp. 188–227) to $O(10^{4})$ non-spherical particles. To the best of the authors’ knowledge, this represents the first particle-resolved study on turbulence modulation by non-spherical particles of near-Kolmogorov-scale size. The modulation of the turbulent flow is precisely captured by explicitly resolving the stresses acting on the fluid–particle interfaces. The decay rates of the fluid and particle kinetic energy are found to increase with the particle aspect ratio. This is due to the particle-induced dissipation rate and the direct transfer of kinetic energy, both of which can be substantially larger than for spherical particles depending on the particle orientation. The extra dissipation rate resulting from the translational and rotational particle motion is quantified to detail the impact of the particles on the fluid kinetic energy budget and the influence of the particle shape. It is demonstrated that the previously derived analytical model for the particle-induced dissipation rate of smaller particles is valid for the present cases albeit these involve significant finite-size effects. This generic expression allows us to assess the impact of individual inertial particles on the local energy balance independent of the particle shape and to quantify the share of the rotational particle motion in the kinetic energy budget. To enable the examination of this mechanistic model in particle-resolved simulations, a method is proposed to reconstruct the so-called undisturbed fluid velocity and fluid rotation rate close to a particle. The accuracy and robustness of the scheme are corroborated via a parameter study. The subsequent discussion emphasizes the necessity to account for the orientation-dependent drag and torque in Lagrangian point-particle models, including corrections for finite particle Reynolds numbers, to reproduce the local and global energy balance of the multiphase system.

scholarly journals Non-spherical particle mixing behaviors by spherical inert particles assisted in a fluidized bed

2019 ◽  
Vol 17 (2) ◽  
pp. 509-524 ◽  
Author(s):  
An-Xing Ren ◽  
Tian-Yu Wang ◽  
Tian-Qi Tang ◽  
Yu-Rong He
Keyword(s):  
Fluidized Bed ◽  
Binary Mixtures ◽  
Volume Fraction ◽  
Fluid Dynamic ◽  
Rolling Friction ◽  
Spherical Particles ◽  
Industrial Processes ◽  
Vertical Orientation ◽  
Inert Particles ◽  
Particle Velocities

AbstractFluidized beds are widely used in many industrial fields such as petroleum, chemical and energy. In actual industrial processes, spherical inert particles are typically added to the fluidized bed to promote fluidization of non-spherical particles. Understanding mixing behaviors of binary mixtures in a fluidized bed has specific significance for the design and optimization of related industrial processes. In this study, the computational fluid dynamic–discrete element method with the consideration of rolling friction was applied to evaluate the mixing behaviors of binary mixtures comprising spherocylindrical particles and spherical particles in a fluidized bed. The simulation results indicate that the differences between rotational particle velocities were higher than those of translational particle velocities for spherical and non-spherical particles when well mixed. Moreover, as the volume fraction of the spherocylindrical particles increases, translational and rotational granular temperatures gradually increase. In addition, the addition of the spherical particles makes the spherocylindrical particles preferably distributed in a vertical orientation.

scholarly journals Influence of the particle shape on the impact force of lahar on an obstacle

2021 ◽  
Vol 249 ◽  
pp. 03010
Author(s):  
Rime Chehade ◽  
Bastien Chevalier ◽  
Fabian Dedecker ◽  
Pierre Breul
Keyword(s):  
Particle Shape ◽  
Urban Areas ◽  
Large Scale ◽  
Distinct Element ◽  
Fluid Velocity ◽  
Solid Particles ◽  
Impact Pressure ◽  
Spherical Particles ◽  
Coupling Scheme ◽  
The Impact

Lahars represent natural phenomena that can generate severe damage in densely populated urban areas. The evaluation of pressures generated by these mass flows on constructions (buildings, infrastructure…) is crucial for civil protection and assessment of physical vulnerability. The existing tools to model the spread of flows at large scale in densely populated urban areas remain inaccurate in the estimation of mechanical efforts. A discrete numerical model is developed for evaluating debris flow (DF) impact pressures at the local scale of one structure. The large-sized solid particles are modelled explicitly using Distinct Element Method (DEM) and the fine-grained solid particles are integrated in a fluid phase which generates two effects on the movement of particles, i.e. buoyancy and drag. Fluid velocity field and the fluid free surface are obtained from Computational Fluid Dynamics (CFD) code then imported in the DEM simulation in a one way coupling scheme. In this paper, the influence of particle shape on the impact forces generated on the obstacle is investigated: spherical particles and polygonal rigid blocks (r-blocks) are considered. The shape of the particle influences the contact surface and therefore the impact pressure. With an angular shape and several facets like r-blocks, the impact pressure on an obstacle is more important for a flow with the same characteristics.

A New Methodology for Erosion Prediction Using Eulerian-Eulerian CFD Models

2015 ◽  
Author(s):  
Gianandrea V. Messa ◽  
Irene Ingrosso ◽  
Stefano Malavasi
Keyword(s):  
Fluid Dynamic ◽  
Fluid Phase ◽  
Impact Angle ◽  
Solid Particles ◽  
Dynamic Parameters ◽  
Gas Industry ◽  
Erosion Prediction ◽  
Cfd Models ◽  
Erosion Models ◽  
The Impact

The erosion of a surface caused by the impact of solid particles dragged by a fluid is a serious concern in the oil&gas industry. At present, the erosion prediction is performed using algebraic erosion models which express the volume of eroded material per impact as a function of the mass of the abrasive particles as well as of fluid dynamic parameters (such as the impact velocity and the impact angle of the eroding particle) and properties of the materials involved in the process. The fluid dynamic parameters are, in turn, evaluated using Eulerian-Lagrangian CFD models which interpret the fluid phase as a continuous mean and follow the trajectories of all the particles. However, the huge computational burden makes it difficult, or even precludes, to adopt this approach in many flows of engineering interest. An innovative methodology is proposed for estimating the parameters required as input by the erosion models using computationally cheaper Eulerian-Eulerian CFD models which solve for the average properties of the ensamble of particles. The good results obtained when predicting the erosion caused the by impingement of an abrasive jet against a surface make the application of this methodology to more complex flows very promising.

On the dependency of jumps on particle shape in bedload transport of monodisperse non-spherical particles

2021 ◽  
Author(s):  
Ramandeep Jain ◽  
Ricardo Rebel ◽  
Jochen Fröhlich
Keyword(s):  
Particle Shape ◽  
Dynamic Time Warping ◽  
Industrial Applications ◽  
Bedload Transport ◽  
Spherical Particles ◽  
Time Warping ◽  
Present Contribution ◽  
Moving Particle ◽  
Dynamic Time ◽  
Particle Shapes

<p><span><span>Accurate prediction of sediment transport is highly desirable because of its </span><span>key</span><span> importance in many environmental and industrial applications. One way to approach this is to measure the length and height of the jump of a moving particle. This led to many studies dealing with the quantification of a particle jump. Nevertheless, few experiments have been performed to understand the effect of particle shape on its jump. A dataset of jumps of different</span><span>ly</span><span> shaped particles has been generated </span><span>by the authors</span><span> from direct numerical simulations of bedload transport in a turbulent open channel flow. A total of four simulations were performed with a large number of mobile single shaped, mono-disperse particles. Four ellipsoidal shapes were used in these simulations, i.e. oblate, prolate, sphere, and a generally shaped ellipsoid. In the present contribution, statistical properties of the jump trajector</span><span>ies</span><span> such as ejection and landing angles, flight length, height, and time, etc. </span><span>w</span><span>ill be reported</span><span>. </span><span>M</span><span>ean jump trajectories for different particle shapes were calculated using </span><span>the </span><span>Dynamic-Time-Warping algorithm. The analysis provides a quantification of the different behavior of the particles under the present conditions. For example, it is observed that oblate particles travel a maximum distance in a jump, while spherical particles take small jumps but more often. </span></span></p>

Erosion of a Silicon Carbide Whisker Reinforced Silicon Nitride

1986 ◽  
Vol 78 ◽  
Author(s):  
C. T. Morrison ◽  
J. L. Routbort ◽  
R. O. Scatitergood
Keyword(s):  
Matrix Material ◽  
Weight Percent ◽  
Impact Angle ◽  
High Fiber ◽  
Erosion Processes ◽  
Base Materials ◽  
Base Matrix ◽  
Sic Whiskers ◽  
Particle Velocities ◽  
The Impact

ABSTRACTThe steady-state solid particle erosion behavior of hot-pressed Si3N4 reinforced with 0, 10, and 20 weight percent SiC whiskers has been investigated at room temperature using angular alumina particles (63 to 270 μm diameter) as the erodent. The impact angle was varied from 30 to 90 ° and particle velocities were varied from 80 to 140 m/s. These materials were found to be very erosion resistant. However, there was little effect of the SiC whisker reinforcement on either the absolute erosion rate or on the velocity or particle-size exponents for the rates.The lack of a fiber reinforcement effect occurs even though the fiber additions provide an increase in the fracture toughness at high fiber contents. Results on differently processed Si3Na4 .base materials showed that microstructural variations due to processing history have very significant influence on the erosion resistance of the base (matrix) material. The results substantiate the idea that microstructure plays an important, but not fully understood role in the erosion processes for brittle materials.

Trajectory shaping guidance law design using constraint-combining multiplier

2021 ◽  
pp. 095441002098637
Author(s):  
Min-Guk Seo ◽  
Chang-Hun Lee ◽  
Tae-Hun Kim
Keyword(s):  
Design Method ◽  
Impact Angle ◽  
State Variables ◽  
Flight Trajectory ◽  
Potential Significance ◽  
Guidance Law ◽  
Terminal Constraints ◽  
The Impact ◽  
Guidance Laws ◽  
Impact Angle Constraint

A new design method for trajectory shaping guidance laws with the impact angle constraint is proposed in this study. The basic idea is that the multiplier introduced to combine the equations for the terminal constraints is used to shape a flight trajectory as desired. To this end, the general form of impact angle control guidance (IACG) is first derived as a function of an arbitrary constraint-combining multiplier using the optimal control. We reveal that the constraint-combining multiplier satisfying the kinematics can be expressed as a function of state variables. From this result, the constraint-combining multiplier to achieve a desired trajectory can be obtained. Accordingly, when the desired trajectory is designed to satisfy the terminal constraints, the proposed method directly can provide a closed form of IACG laws that can achieve the desired trajectory. The potential significance of the proposed result is that various trajectory shaping IACG laws that can cope with various guidance goals can be readily determined compared to existing approaches. In this study, several examples are shown to validate the proposed method. The results also indicate that previous IACG laws belong to the subset of the proposed result. Finally, the characteristics of the proposed guidance laws are analyzed through numerical simulations.

scholarly journals The effect of heat treatment and impact angle on the erosion behavior of nickel-tungsten carbide cold spray coating using response surface methodology

2021 ◽  
Author(s):  
Marios Kazasidis ◽  
Elisa Verna ◽  
Shuo Yin ◽  
Rocco Lupoi
Keyword(s):  
Heat Treatment ◽  
Response Surface Methodology ◽  
Mass Loss ◽  
Tungsten Carbide ◽  
Response Surface ◽  
Spray Coating ◽  
Impact Angle ◽  
Control Factors ◽  
Heat Treated ◽  
The Impact

AbstractThis study elucidates the performance of cold-sprayed tungsten carbide-nickel coating against solid particle impingement erosion using alumina (corundum) particles. After the coating fabrication, part of the specimens followed two different annealing heat treatment cycles with peak temperatures of 600 °C and 800 °C. The coatings were examined in terms of microstructure in the as-sprayed (AS) and the two heat-treated conditions (HT1, HT2). Subsequently, the erosion tests were carried out using design of experiments with two control factors and two replicate measurements in each case. The effect of the heat treatment on the mass loss of the coatings was investigated at the three levels (AS, HT1, HT2), as well as the impact angle of the erodents (30°, 60°, 90°). Finally, the response surface methodology (RSM) was applied to analyze and optimize the results, building the mathematical models that relate the significant variables and their interactions to the output response (mass loss) for each coating condition. The obtained results demonstrated that erosion minimization was achieved when the coating was heat treated at 600 °C and the angle was 90°.

scholarly journals High-energy operator product expansion at sub-eikonal level

2021 ◽  
Vol 2021 (6) ◽  
Author(s):  
Giovanni Antonio Chirilli
Keyword(s):  
Operator Product Expansion ◽  
Evolution Equations ◽  
Energy Operator ◽  
High Energy ◽  
Structure Functions ◽  
Distribution Functions ◽  
Impact Factors ◽  
Operator Product ◽  
The Impact ◽  
New Distribution

Abstract The high energy Operator Product Expansion for the product of two electromagnetic currents is extended to the sub-eikonal level in a rigorous way. I calculate the impact factors for polarized and unpolarized structure functions, define new distribution functions, and derive the evolution equations for unpolarized and polarized structure functions in the flavor singlet and non-singlet case.

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