Magnitude Of Particle Velocity Research Articles

On the interaction between a pulsating bubble and a particle on the rigid wall

Sand-laden cavitation poses significant challenges in high dam hydrodynamics and hydraulic machinery. This study examines the interaction between a pulsating bubble and a rigid spherical particle attached to a wall, aiming to reveal its mechanical mechanisms. Particle motion is strongly influenced by two dimensionless distances: the bubble–wall distance γ and the horizontal bubble–particle distance l, both scaled by the maximum bubble radius. Parameter γ determines the bubble's evolution characteristics and affects the particle's motion. Smaller γ means the particle is mainly influenced by bubble pulsation, while larger γ makes the particle more affected by wall vortices. The effect of l is primarily seen in the particle's velocity magnitude. A larger l causes the particle to move toward the bubble, while a smaller l makes it move away, due to the relative strengths of bubble expansion and contraction. We also identify parameter sets that result in 0 particle velocity and observe unique particle motions during bubble splitting and the formation of oblique jets. This study may further promote the application of underwater cavitation cleaning.

DEM investigation on the dynamic characteristics of wall normal stress and particle flow during silo discharge

Violent fluctuations of wall normal stress and particle velocity during silo discharge have been frequently reported by researchers, yet a detailed particle-scale description of these phenomena is still lacking. In this work, the discharge of granular assembly from a flat-bottomed silo was investigated by performing three-dimensional (3D) Discrete Element Method (DEM) simulations. It is found that arc-shaped rupture surfaces, characterized by the lower solid volume fraction, stronger shear interaction between particles and higher particle rotating velocity, developed continuously in the bottom converging part of flowing zone. And the temporal evolution of particle velocity field in this converging part presented a swinging feature manifested by the alternate appearance of large particle velocity magnitude in the right- and left- side regions. Discrete Fourier transform results showed that the fluctuation of wall normal stress at the transition point contained two dominate frequencies. The lower frequency matched well with the dynamic evolution of the rupture surface joining the transition point, and the higher frequency was nearly the same as the fluctuating frequency of particle vertical velocity. Thus, our DEM simulation results suggested that for the silo discharge considered in this work, the periodic fluctuation of wall normal stress at the transition point was contributed by both the alternating flow pattern mechanism and the free-fall arch mechanism.

Modeling Dense Particle Flow in Multistage and Obstructed Flow Receivers Using High Fidelity Simulations

Particles are a leading contender for next-generation, concentrating solar power technologies, and the design of the particle receiver is critical to minimize the levelized cost of electricity. Falling particle receivers (FPRs) are a viable receiver concept, but many new designs feature complex particle obstructions that include dense discrete phase flows. This creates additional challenges for modeling as particle-to-particle interactions (i.e., collisions) and particle drag become more complex. To improve upon existing modeling strategies, a CFD-DEM simulation capability was created by coupling two independent codes: Sierra/Fuego and LAMMPS. A suitable receiver model was then defined using a traditional continuum-based model for the air and a granular model for the particle curtain. A sensitivity study was executed using this model to determine the relevance of different granular model inputs on important quantities of interest in obstructed flow FPRs: the particle velocity and curtain opacity. The study showed that the granular model inputs had little effect on the particle velocity magnitude and curtain opacity after an obstruction.

CFD Analysis for Valve-Holding Camber Permanent Inhaler Spacer (AerospaAcer) with Different Valves

During the COVID-19 pandemic, data statistics showed that patients with respiratory problems become infected. One of the therapy techniques for the respiratory condition was the use of a metered-dose inhaler and spacer. The objective of this paper is to determine the flow parameters of three types of valves which is duckbill valve, cross slit valve and umbrella valve in inhaler spacer to compare fluid flow between valve Previous researchers chose the duckbill valve to control fluid flow in inhaler spacer. The flow characteristics are unaffected by the materials used in the new disposable inhaler spacers, such as paper and polylactic acid (PLA). Several design valves reduced the skewness below 0.94 by suppressing the fillet and chamfer. ANSYS Workbench Fluent 19.2 is used to calculate flow parameters such as turbulence kinetic energy (TKE), turbulence eddy dissipation (TED), velocity, particle velocity magnitude, streamline, and vector velocity. The setup input data is based on the previous researcher's specified parameters such as viscosity model, drug characteristics (salbutamol and propellant), discrete phase model (DPM) equal to 80, boundary condition model, and SIMPLE technique. For the three types of valves, the nozzle injection used a 0.50-millimetre dimension. The simulation work is cross-checked against the results of prior simulations. Within each iteration, the transient flow employed a time step size of 0.01 for 200 steps. The results show that computational analysis can distinguish between models of varying complexity. The TED, TKE, and velocity graphs showed the approximate value between the model geometries. Overall, the study was successful in achieving the desired velocity magnitude in terms of visual and graph representations of the various valve.

Flow structure and aerodynamic forces of finned cylinders during flow-induced acoustic resonance

This experimental study investigated the impact of self-excitation of acoustic resonance on the fluctuating lift force, flow structure, and aeroacoustic energy transfer of spirally finned cylinders with crimps in cross-flow. Three different finned cylinders with varying fin pitch-to-root diameter ratios (p/Dr) were compared with their equivalent diameter (Deq) bare cylinders. The study found that self-excitation of acoustic resonance occurred at a lower reduced flow velocity for the finned cylinders. During acoustic resonance excitation, finned cylinders with lower p/Dr experienced an abrupt increase in the fluctuating lift force coefficient and acoustic pressure. The decomposition of the fluctuating lift force with respect to the acoustic pressure showed that the earlier onset of resonance and the abrupt increase in the lift force and acoustic pressure were due to the increased susceptibility to flow-induced acoustic resonance. Phase-locked particle image velocimetry (PIV) measurements of the vorticity field supported this finding by showing a well-organized vorticity field in the wake of these finned cylinders. However, the fins and crimps had a significant effect on the distribution of the acoustic particle velocity field compared to the bare cylinder. The presence of the fins and crimps caused the acoustic particle velocity magnitude to be concentrated within the fins and rapidly decline away from the cylinder base. As a result, the acoustic power generated was lower in the case of the finned cylinders. This ultimately resulted in a lower peak acoustic pressure and fluctuating lift force being generated in the case of the crimped spirally finned cylinders.

Computational fluid dynamics and machine learning algorithms analysis of striking particle velocity magnitude, particle diameter, and impact time inside an acinar region of the human lung

Complementing computational fluid dynamics (CFD) simulations with machine learning algorithms is becoming increasingly popular as the combination reduces the computational time of the CFD simulations required for classifying, predicting, or optimizing the impact of geometrical and physical variables of a specific study. The main target of drug delivery studies is indicating the optimum particle diameter for targeting particular locations in the lung to achieve a desired therapeutic effect. In addition, the main goal of molecular dynamics studies is to investigate particle–lung interaction through given particle properties. Therefore, this study combines the two by numerically determining the optimum particle diameter required to obtain an ideal striking velocity magnitude (velocity at the time of striking the alveoli, i.e., deposition by sedimentation/diffusion) and impact time (time from release until deposition) inside an acinar part of the lung. At first, the striking velocity magnitudes and time for impact (two independent properties) of three different particle diameters (0.5, 1.5, and 5 μm) are computed using CFD simulations. Then, machine learning classifiers determine the particle diameter corresponding to these two independent properties. In this study, two cases are compared: A healthy acinus where a surfactant layer covers the inner surface of the alveoli providing low air–liquid surface tension values (10 mN/m), and a diseased acinus where only a water layer covers the surface causing high surface tension values (70 mN/m). In this study, the airflow velocity throughout the breathing cycle corresponds to a person with a respiratory rate of 13 breaths per minute and a volume flow rate of 6 l/min. Accurate machine learning results showed that all three particle diameters attain larger velocities and smaller impact times in a diseased acinus compared to a healthy one. In both cases, the 0.5-μm particles acquire the smallest velocities and longest impact times, while the 1.5-μm particles possess the largest velocities and shortest impact times.

Numerical estimations of lunar regolith trajectories and damage potential due to rocket plumes

This study presents a numerical investigation of rocket plumes carrying regolith particles in the context of the lunar environment (gravity and vacuum conditions). We investigated two lander masses with a single rocket hovering at 5 different low altitudes perpendicular to a flat surface. For the regolith, we considered 9 particle sizes, with diameters from 1μm to 1 cm. The initial condition of all particles was a null velocity at 0.3m above the ground. The particles started at 19 different radial positions from the centerline of the rocket jet, 1m to 10 m. We used a DSMC method to solve the rocket plume cases, considering the combustion product molecules from the propellant N2O4+Aerozine 50. Steady-state plume flow solutions are one-way coupled with discrete particles, considering drag and weight forces. The results showed that particle angle is nearly constant for small (dp<100μm) particles varying with initial radial position and lander altitude. Particle velocity is related to particle diameter as a power-law function and a Gaussian function of the initial particle position. Lander altitude and mass modulate the magnitude of particle velocity. Using the numerical solution data, we derived a numerical correlation for particle velocity that provides insight to avoid regolith abrasive blasting into the lunar lander, surrounding structures, and orbital satellites.

Response Surface Methodology (RSM) Approach for Optimizing the Actuator Nozzle Design of Pressurized Metered-Dose Inhaler (pMDI)

Recently, a remarkable scientific interest in the inhalation therapy for respiratory disease was spiked attributed to the growing prevalence of asthma, chronic obstructive pulmonary disease (COPD), and coronavirus disease 2019 (COVID-19) pandemic. A pressurized metered-dose inhaler (pMDI) is the best option by providing fast and efficient symptomatic relief within the lung. However, the rapid development of new inhalation devices could be critical in this competitive environment, and optimizing the inhalation devices could be costly and time-consuming. Therefore, the computational fluid dynamic (CFD) approach was used to shorten the development time. In this study, response surface methodology (RSM) in ANSYS version 19.2 was introduced to discover the optimal design for the actuator nozzle to increase the performance of pMDI. Three (3) parameters (orifice diameter, length, and actuator angle) were optimized, and the best design was selected according to the analysis of particle tracking. The analysis of spray plume was also conducted and compared to analyze the spray plume characteristic produced by three designs. The result showed that RSM generated three (3) models for the new design of the actuator nozzle (Design A, Design B, and Design C). Among three (3) designs, actuator nozzle design C showed the highest injection particle number (232457) and the only one that produced maximum particles velocity magnitude in the acceptable ranges (35.67m/s). All three designs showed a similar pattern as maximum particle velocity magnitude decreased along the axial length until they match the air velocity (0.03-0.04 m/s). Furthermore, the spray plume length, angle, and width were observed to increase linearly with the decreasing maximum particle velocity magnitude. Thus, this study suggested that design C might have the potential as a new actuator nozzle to develop future pMDI to relieve the respiratory condition.

Clusters and coherent voids in particle-laden wake flow

Inertial point particles suspended in a two-dimensional unsteady circular cylinder flow at Re=100 are studied by one-way coupled three-dimensional numerical simulations. The striking clustering pattern in the near-wake is strongly correlated with the periodically shed Kármán vortex cells. The particles are expelled from the vortex cores due to the centrifugal mechanism and coherent voids encompassing the local Kármán cells are therefore observed. The particle clustering at the upstream side of each void hole form a smooth edge, where the particle velocity magnitude is consistently lower than at the downstream edge of the voids. The trajectories of these particles originate from the side of the cylinder where the sign of vorticity is opposite to that of the vortex encompassed by the corresponding void hole. The particles are seen to decelerate along a substantial part of their trajectories. Particle inertia is parameterized by means of a Stokes number Sk and smooth edges around the void holes still exist when Sk is increased, although their formation is delayed due to larger inertia. Increasing inertia contributes to a decoupling of the particle acceleration from the slip velocity, which almost coincided at Sk=1.

Intersonic shear crack propagation using peridynamic theory

Dynamic crack propagation of mode-II cracks is simulated using bond-based Peridynamic Theory (PD) implemented in finite element analysis software ABAQUS. The specimen is a bonded homogeneous Homalite plate with a pre-notch that is subjected to impact shear loading simulating the experiments of Rosakis et al. (1999). The PD bonds at the bonding interface are utilized with a scalar critical stretch value that corresponds to mode-II fracture toughness of the interface. The crack initiation and propagation are naturally captured in the bond-based PD simulations by modifying the original prototype microelastic brittle law formulation introduced by Silling and Askari (2005). Impact loading is introduced at the specimen as a pulse speed field boundary condition. Using bond-based PD, sub-Rayleigh and intersonic regimes of crack growth are obtained as a function of fracture toughness ( $$G_{II}$$ ) and impact speed ( $$V_i$$ ) values. The intersonic crack growth is discerned from the sub-Rayleigh crack growth by the existence of shear Mach waves in the particle velocity magnitude contours. For critical values of $$G_{II}$$ and $$V_i$$ , a crack growing at a speed just below the Rayleigh wave speed is observed to transition to an intersonic speed with a Burridge-Andrews mechanism. The sustained intersonic crack tip speed is found to be between $$1.57c_S$$ ( $$c_S$$ is the shear wave speed) and $$c_D$$ ( $$c_D$$ is the dilatational wave speed). For a reduced impact pulse duration, an intersonic crack is found to approach the theoretical value of $$\sqrt{2}c_S$$ , which, however is not maintained. The results are in qualitative agreement with the experiments of Rosakis et al. (1999) and previous simulations in the literature.

Investigate Flow Characteristics of Metered-Dose Inhaler (MDI) Disposable Inhaler Spacer (AeroCup) for COVID-19 Patient by using Computational Fluid Dynamic (CFD)

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory coronavirus-2 syndrome (SARS-CoV-2) were first reported by officials in Wuhan City, China, in December 2019. COVID-19 patients have a symptom of respiratory pneumonia diseases which have difficulties in breathing normally. Previously, the nebulizer machine commonly used to treat respiratory pneumonia diseases. However, the usage for this machine was not suggested during this COVID-19 period because the virus will be spread off easily. To overcome these shortcomings, the uses of Metered-Dose Inhaler (MDI) with MDI disposable inhaler spacer is preferable. Besides, it had been known that the used of MDI disposable inhaler spacer helps to increase the uptaking of the drug into the lung. Besides that, the high demand for the MDI Disposable Inhaler Spacer in the hospital, causing a shortage of supply in Malaysia. Thus, this study aims to produce a new design of this spacer to full fill the market need. This new design of MDI Disposable Inhaler Spacer (AeroCup) was designed by using Solid Work 2018. Then, the parameters for flow characteristic such as particle velocity magnitude, velocity, Eddy viscosity, turbulence Eddy dissipation and turbulence kinetic energy (TKE) was successfully characterized and compared with commercial design A using ANSYS Fluent Version 19.2. The result showed that new design (AeroCup) had the desired characteristic, which was almost similar to commercial design A. This study can provide a piece of information to produce the low-cost metered-dose inhaler (MDI) disposable inhaler spacer to enlighten the burden shouldered by front liners, especially during the pandemic and also can scale-up the economic viability.

Velocity estimation of micro-particles driven by cavitation bubble collapses through controlled erosion experiments

The high-energy phenomenon of particle acceleration driven by cavitation bubble collapses has garnered research interests over the past few decades. Potential applications range from cavitation-induced drug delivery, chemical synthesis, sonochemistry to micro-machining operations. However, the acceleration mechanisms and the velocities attained by particles remain in huge contention. A novel particle velocity estimation model based on experimental mass loss input is put forward in this paper. Micro-abrasive particles, of 5 µm to 50 µm average diameter, were exposed to intense ultrasonic irradiation of 20 kHz in a deionized water medium for 10 min. The accelerated particles were captured by target specimens placed at 0.5 mm from the ultrasonic horn surface in a controlled experiment. Through the quantification of specimen mass loss, the average particle impact velocity could be estimated by a reverse solid particle erosion model. Results show that the magnitude of particle velocity is in the range of 8–40 m/s and is dependent on both particle size and ultrasonic amplitude. The results also suggest that micro-jet is the likely particle acceleration mechanism in the presence of a solid wall boundary from a microscopic perspective.

Optimum Design of Nozzle Geometry of Dry Ice Blasting Using CFD for the Reduction of Noise Emission

Dry ice blasting has been used in the modern cleaning industry. However, the primary disadvantage of dry ice blasting is high noise exposure. At a high blasting pressure, the process reaches a harmful noise level of up to 130 dBA. The situation significantly impairs to a human being when the noise emission occurs in an inaudible frequency area. Present safety measures are only based on administrative control by encapsulating the entire system with sound insulation. The main objective of this project is to study the optimum nozzle configuration on the effect of dry ice blasting particle velocity and acoustic noise emission. Different nozzle geometry were simulated several times until optimization is achievable. Three-dimension models are designed using CATIA V5. Then the models are simulated with Ansys Fluent V18.2. The numerical studies have been carried out using density based, standard k- e turbulence and Acoustic Broadband Noise Sources model. Six (6) different nozzle configuration namely divergent length, the angle of particle inlet, convergent diameter, expansion ratio, gas inlet diameter and length ratio are analyzed in term of particle velocity magnitude and acoustic power level. The result shows that the optimum nozzle configuration for divergent length, the angle of particle inlet, convergent diameter, expansion ratio, gas inlet diameter and length ratio are 230 mm, 30 mm, 35 mm, 1.00, 6 mm and 0.80 respectively. This configuration provides minimum lowest acoustic noise emission and maximum particle velocity magnitude.

A primer on vector hydrophones

Vector hydrophones are used by the military to track submarines, and, more recently, by scientists attempting to measure the influence of particle velocity on the behaviour of fish. Despite being in use for decades, vector hydrophones remain poorly understood by both communities. The problem is particularly acute for those aiming to measure particle velocity because vector hydrophones do not measure particle velocity directly; rather they measure pressure difference, the force that creates particle velocity. Topics covered will be the two types of vector hydrophone and why only one works well at low frequencies, the importance of knowing the phase of the directional channels relative to each other and to the pressure hydrophone, how bearings are determined, calibration of vector hydrophones and near-field effects, the magnitude of particle velocity for typical sound pressure levels, why bigger is better for mechanical noise, why neutral buoyancy is unnecessary and undesirable, and best practice for mounting.

Simulation of Gas Solid Flow in Quasi Two Dimensional Fluidized Bed by Immersed Boundary Method

Gas solid two phase flow occurs in multiple fields of industry. Therefore, a study researching the phenomena of this type of systems is highly adequate. In the present work subsonic, compressible flow equation in conservative Euler form is solved numerically on PC by a two step finite difference method, which is validated by the analytical solution of Sod’s shock tube problem. Fluid solid interaction is described by Immersed Boundary Method, where body force is calculated by direct forcing algorithm. Two dimensional simulation of a single solid circle shaped particle motion in the gas flow is calculated and compared to the trajectory of a particle recorded by a high speed camera measurement system in a laboratory scale quasi two dimensional fluidized bed. Image processing algorithms are implemented to track the motion of a chosen single. Comparison of experimental measurement and simulation resulted in the same magnitude of particle velocities. The possible reasons of differences and opportunities of improving the results are discussed in the study. The results are promising, and the presented preliminary simulator can be a useful tool in supporting industrial design and operation after further developments.

Investigating mixing and segregation using discrete element modelling (DEM) in the Freeman FT4 rheometer

Mixing and segregation in a Freeman FT4 powder rheometer, using binary mixtures with varied particle size ratio and volume fraction, were studied using the Discrete Element Method (DEM). As the blade moves within the particle bed, size induced segregations can occur via a sifting mechanism. A larger particle size ratio and/or a larger volume fraction of large particles lead to a quicker segregation process. A higher particle velocity magnitude can promote the segregation process and the rate for the segregation index increases in the radial direction: from the centre towards the outer layer. In the current DEM simulations, it is shown that the change in flow energy associated with segregation and mixing depends on the choice of frictional input parameters. FT4 is proposed as a potential tool to compare and rank the segregation tendency for particulate materials with distinct differences in flow energy of each component. This is achieved by measuring the flow energy gradient after a number of test cycles for mixing powders with different flow properties. Employing the FT4 dynamic powder characterisation can be advantageous to establish blending performances in an industrial context.

A consistent approach for the treatment of Fermi acceleration in time-dependent billiards

The standard description of Fermi acceleration, developing in a class of time-dependent billiards, is given in terms of a diffusion process taking place in momentum space. Within this framework, the evolution of the probability density function (PDF) of the magnitude of particle velocities as a function of the number of collisions n is determined by the Fokker-Planck equation (FPE). In the literature, the FPE is constructed by identifying the transport coefficients with the ensemble averages of the change of the magnitude of particle velocity and its square in the course of one collision. Although this treatment leads to the correct solution after a sufficiently large number of collisions have been reached, the transient part of the evolution of the PDF is not described. Moreover, in the case of the Fermi-Ulam model (FUM), if a standard simplification is employed, the solution of the FPE is even inconsistent with the values of the transport coefficients used for its derivation. The goal of our work is to provide a self-consistent methodology for the treatment of Fermi acceleration in time-dependent billiards. The proposed approach obviates any assumptions for the continuity of the random process and the existence of the limits formally defining the transport coefficients of the FPE. Specifically, we suggest, instead of the calculation of ensemble averages, the derivation of the one-step transition probability function and the use of the Chapman-Kolmogorov forward equation. This approach is generic and can be applied to any time-dependent billiard for the treatment of Fermi-acceleration. As a first step, we apply this methodology to the FUM, being the archetype of time-dependent billiards to exhibit Fermi acceleration.

Development of a visiometric process analyzer for real-time monitoring of bottom spray fluid-bed coating

Particle recirculation within the partition column is a major source of process variability in the bottom spray fluid-bed coating process. However, its locality and complex nature make it hidden from the operator. The aim of this study was to take snapshots of the process by employing a visiometric process analyzer based on high-speed imaging and ensemble correlation particle image velocimetry (PIV) to quantify particle recirculation. High-speed images of particles within the partition column of a bottom spray fluid-bed coater were captured and studied by morphological image processing and ensemble correlation PIV. Particle displacement probability density function (PDF) obtained from ensemble correlation PIV was consistent with validation experiments using an image tracking method. Particle displacement PDF was further resolved into particle velocity magnitude and particle velocity orientation histograms, which gave information about particle recirculation probability, thus quantifying the main source of process variability. Deeper insights into particle coating process were obtained and better control of coat uniformity can thus be achieved with use of the proposed visiometric process analyzer. The concept of visiometric process analyzers was proposed and their potential applications in pharmaceutical processes were further discussed. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:346–356, 2010

Kinematics of solid particles in a turbulent protoplanetary disc

We perform numerical simulations of solid particle motion in a shearing box model of a protoplanetary disc. The accretion flow is turbulent due to the action of the magnetorotational instability. Aerodynamic drag on the particles is modelled using the Epstein law with the gas velocity interpolated to the particle position. The effect of the magnetohydrodynamic turbulence on particle velocity dispersions is quantified for solids of different stopping times ts, or equivalently, different sizes. The anisotropy of the turbulence is reflected upon the dispersions of the particle velocity components, with the radial component larger than both the azimuthal and vertical components for particles larger than � 10 cm (assuming minimum-mass solar nebula conditions at 5 AU). The dispersion of the particle velocity magnitude, as well as that of the radial and azimuthal components, as functions of stopping time, agree with previous analytical results for isotropic turbulence. The relative speed between pairs of particles with the same value of ts decays faster with decreasing separation than in the case of solids with different stopping time. Correlations in the particle number density introduce a non-uniform spatial distribution of solids in the 10 to 100 cm size range. Any clump of particles is disrupted by the turbulence in less than one tenth of an orbital period, and the maximally concentrated clumps are stable against self-gravitational collapse.

Measurement of sound power and absorption in reverberation chambers using energy density

Reverberation chamber measurements typically rely upon spatially averaged squared pressure for the calculation of sound absorption, sound power, and other acoustic values. While a reverberation chamber can provide an approximately diffuse sound field, variations in sound pressure consistently produce uncertainty in measurement results. This paper explores the benefits of using total energy density or squared particle velocity magnitude (kinetic energy density) instead of squared pressure (potential energy density) for sound absorption and sound power measurements. The approaches are based on methods outlined in current ISO standards. The standards require a sufficient number of source-receiver locations to obtain suitable measurement results. The total and kinetic energy densities exhibit greater spatial uniformity at most frequencies than potential energy density, thus requiring fewer source-receiver positions to produce effective results. Because the total energy density is typically the most uniform of the three quantities at low frequencies, its use could also impact the usable low-frequency ranges of reverberation chambers. In order to employ total and kinetic energy densities for sound absorption measurements, relevant energy-based impulse responses were developed as part of the work for the assessment of sound field decays.