Inertial Particles Research Articles

Effect of Shape and Size on the Transport of Floating Particles on the Free Surface in a Natural Stream

AbstractUnderstanding how floating particles are transported by streaming waters is crucial in predicting the transport of plastic pollution, which is dramatically abundant in rivers, lakes, and oceans. Using particle tracking velocimetry, we investigate the motion of floating particles of different shape and size on the turbulent free surface of a field‐scale meandering stream. We consider two different locations, where the role of surface waves on transport is deemed negligible. Millimeter‐sized spheres are used as tracers to characterize the surface flow. These are compared with centimeter‐sized discs and rods, approximating typical‐sized pieces of floating litter. The larger particles exhibit similar mean and fluctuating velocities as the tracers but filter out the extreme turbulent accelerations. Consequently, their motion is more time‐correlated and their spreading rate is larger. This behavior is also confirmed by complementary laboratory measurements in an open channel flow. The rotation of the rods, affected by a range of turbulent scales, reduces the correlation time scale of their translational motion, and leads to a slower dispersion compared to the discs, despite the rods' length being larger than the discs' diameter. Taken together, these results indicate that the motion of finite‐sized objects floating on the surface of weakly wavy turbulent waters is consistent with the behavior of inertial particles in three‐dimensional turbulence. These results can be valuable when constructing predictive models of floating plastics.

Oblique collisions of three wet spheres

Oblique collisions of three solid spheres coated with thin viscous layers are simulated, both to elucidate the interesting physics of the collision outcomes and to lay the groundwork for a new approach to modeling flows of many wet particles. Included in the analysis are fluid viscous and capillary forces, as well as solid contact and friction forces. A novel approach is developed based on a rotating polar coordinate system for each particle pair in near contact, including the possibility that a given particle is in simultaneous contact with both other particles. As the Stokes number (a dimensionless ratio of particle inertia and viscous forces) is increased, the collision outcome progresses from full agglomeration (all three particles sticking together due to viscous and capillary forces) to partial agglomeration (two particles sticking together while the third one separates) to full separation (all three particles separating post-collision). The results are also sensitive to various physical and geometrical properties, such as the ratio of fluid film thickness to particle diameter, the coefficient of friction, and the collision angles.

Lnertia Weight-free Particle Swarm Optimization in Optimal Control Design for Vehicle Active Suspension Systems

Vehicle active suspension systems play an important role in ride comfort and driving safety. This study considers the problem of an efficient control scheme design for vehicle active suspension systems. The active suspension systems aim to get more comfortable riding and good handling for random road disturbances. The purpose of this work is to reduce the driver’s entire body acceleration and thereby improve ride comfort. The inertial weight-free particle swarm optimization (PSO) method is utilized to obtain weighting matrices of the optimal control namely linear quadratic regulator (LQR) for the active suspension systems. The designed state-feedback controller is applied to the quarter-car suspension system under different road profiles. Simulation results of the inertia weight-free PSO-tuned LQR are compared with the results of the classical-tuned controller and standard PSO-tuned LQR controller to show the effectiveness.

Role of translational noise on current reversals of active particles on ratchet

In this study, we explore using Langevin dynamics simulations, the role of thermal fluctuations on the rectification of non-interacting inertial active (self-propelled) particles in a rocking ratchet setup in the absence and in the presence of the external time periodic drive. The system is first studied in the absence of the external drive. It is found that the average velocity is always positive and a peaked function of the translational noise, indicating that the asymmetry effects dominate at intermediate values of the strength of the thermal noise. In the second part of this work, we study the effect of the external drive on the dynamics of the system by exploring a phase diagram in the parameter space of translational noise and driving frequency for two different strengths of rotational diffusion. For a given constant amplitude of the active force and amplitude of external drive less than the maximum force due to the potential, the average velocity magnitude as well as the direction (+ {hat{x}}/- {hat{x}}) is found to depend on the rotational diffusion, frequency of the external drive and the strength of the translational noise. We discover certain critical parameters in the phase space at which current reversals happen. It is found that when the average particle energy is lower than the potential energy of the barrier, symmetry breaking dominates and the currents are in the ‘easy’ direction of the ratchet. On the other hand, when the energy available per particle crosses the potential energy of the barrier, the competition between inertial effects and diffusion effects decides the direction of currents. We explain our findings by constructing phase difference datum, velocity probability distribution, and current probability analyses. Our results provide a novel method for controlling the direction of transport of inertial active particles.

Experimental investigation of particle dynamics in particle-laden turbulent boundary layer

In a horizontal wind tunnel, experiments were performed on both particle-free and particle-laden flows at the same incoming velocity. Glass micro-spheres were carried by air along the turbulent boundary layer at a high Reynolds number (Reτ=3200). The Stokes numbers of the solid particles considered were O(10) and O(102). Under a similar volume fraction, Φv=O(10−5), the velocity and spatial distribution of solid inertial particles were investigated using simultaneous particle image/tracking velocimetry measurements and time-resolved particle imaging. This allowed for the exploration of particle dynamics and their corresponding spatial structure in the particle-laden turbulent boundary layer. The results showed that particle–wall (P-W) interaction occurs in both types of particle-laden flows. However, the particle Stokes number directly affects the intensity of the P-W interaction, significantly altering the behavior and spatial organization of particles. The results from the Voronoi tessellation technique confirmed that preferential clustering still happens for the small particle case. In particular, the premultiplied spectra for the particle concentration showed that the temporal pattern of particle clustering presents a similar time-scale to very large-scale motion (around 22δ, where δ is the boundary layer thickness) in the near-wall region.

Stochastic resetting-induced reentrance phenomena of inertial Brownian particle in the rough periodic potential

Stochastic resetting-induced reentrance phenomena of inertial Brownian particle in the rough periodic potential

An experimental study on the settling velocity of inertial particles in different homogeneous isotropic turbulent flows

We propose an experimental study on the gravitational settling velocity of dense, sub-Kolmogorov inertial particles under different background turbulent flows. We report phase Doppler particle analyser measurements in a low-speed wind tunnel uniformly seeded with micrometre scale water droplets. Turbulence is generated with three different grids (two consisting of different active-grid protocols while the third is a regular static grid), allowing us to cover a very wide range of turbulence conditions in terms of Taylor-scale-based Reynolds numbers ( $Re_\lambda \in [30\unicode{x2013}520]$ ), Rouse numbers ( $Ro \in [0\unicode{x2013}5]$ ) and volume fractions ( $\phi _v \in [0.5\times 10^{-5}\unicode{x2013}2.0\times 10^{-5}]$ ). We find, in agreement with previous works, that enhancement of the settling velocity occurs at low Rouse number, while hindering of the settling occurs at higher Rouse number for decreasing turbulence energy levels. The wide range of flow parameters explored allowed us to observe that enhancement decreases significantly with the Taylor–Reynolds number and is significantly affected by the volume fraction $\phi _v$ . We also studied the effect of large-scale forcing on settling velocity modification. The possibility of changing the inflow conditions by using different grids allowed us to test cases with fixed $Re_\lambda$ and turbulent intensity but with different integral length scale. Finally, we assess the existence of secondary flows in the wind tunnel and their role on particle settling. This is achieved by characterising the settling velocity at two different positions, the centreline and close to the wall, with the same streamwise coordinate.

Optimized inversion method for thermal parameters of concrete dam under the insulated condition

It is crucial to study how thermal characteristics of concrete dam change over time, especially in cold regions, in order to guarantee long-term safety of the engineering projects. In this manuscript, an inverse analysis method by coupling the numerical simulation model and dam safety monitoring data, is proposed to solve the problem that true thermal parameters of the whole structure cannot be obtained by laboratory experiments or field tests of single points. Moreover, a numerical equivalence method of the dam and its insulation layer is introduced, in order to overcome the problem that the thickness of the insulation layer is much smaller than that of the concrete dam, resulting in low accuracy of the simulation model. Thirdly, the particle swarm optimization is introduced, in order to solve the ill-posed problems occurring during the solution process of multi-parameter inverse analysis. Considering the problem that the original particle swarm algorithm is easy to fall into local optimum and stuck edge, this study improves particles velocity and inertia weights. Benchmark function tests are applied to show the performance compared to several typical optimized algorithms. Numerical simulation and engineering verification are used to demonstrate the rationality and feasibility of the proposed method. The cases show that the residual box diagram of two typical measuring points calculated by inversion value is smaller than the median line and mean point calculated by design value. Moreover, the change law of the temperature field of the finite element calculation using the inversion values is closer to the actual measured value than that of the design value. The results indicate that the multi-parameter inverse method is feasible in insulated dam engineering. In addition, the result of the improved PSO optimization converges faster and has a higher fitness value than that of the original algorithm. It suggests that the improved PSO algorithm for thermal parameters inversion has fitting accuracy and rationality for insulated concrete dams in cold regions.

Pair dispersion of inertial particles crossing stably stratified turbulent/non-turbulent interfaces

In the present work we study the pair dispersion of inertial particles crossing two-layer stably stratified turbulent/non-turbulent interfaces (STNTI) of finite thickness. The goal is to investigate two-particle dispersion, a problem of great importance in a wide range of applications, within very complex flows. STNTI flows are in fact constituted not only by non-homogeneous turbulence and density stratification, but also by effects generated by their interaction, such as internal waves. The problem is addressed numerically, two direct numerical simulations (DNS) of STNTI flow are performed: moderate intensity turbulence, Reλ=35,44 is produced in the DNSs using a convective forcing (heat source at the domain boundary) in one case, and a forcing that mimics a vertically oscillating grid, through an immersed boundary method, in the other. We tracked inertial particles, with one-way coupling approach, using a modified Basset-Boussinesq-Oseen equation which includes a stratification-induced term FS. We first analyze particle pairs settling from the turbulent region toward the STNTI and then pairs moving in the opposite direction from the non-turbulent layer. In general results for all pair tested present a t2-scaling law for small times. Pairs crossing the STNTI from the non-turbulent region show a peculiar dispersion behavior: approaching the internal waves layer, pairs tend to reduce the dispersion rate and then they present a fast growing separation regime (tα, α≥6) possibly induced by non-local effects. Different particle densities, which affect inertia, the initial pair separation and the effect of stratification on the dispersion, by means of FS, are tested as well. Results confirm the importance of the first two parameters for the pair evolution. The stratification force, which has been not taken into account so far, plays as well an important role, which may lead to discrepancies in pair dispersion larger than the role FS has in the equation of motion itself.

Numerical Investigation on Separation Efficiency of a Novel Hybrid Engine Air-Particle Separator

This paper proposes a novel design for a hybrid engine air-particle separator filter (HEAPS) that combines the vortex tube separator (VTS) with the inertial particle separator (IPS) to enhance separation efficiency. Helicopters often operate in harsh environments, such as deserts, and landing on unprepared runways poses a severe risk to turboshaft engines due to the ingestion of dust and sand. This can result in significant damage to the engine's rotating components, impacting its life, reliability, and performance. To protect the engine from erosion and damage, an engine air particle separator system (EAPS) is installed in the engine inlet. In this study, a comparative numerical simulation was conducted between the hybrid filter and the VTS using the commercial software ANSYS Fluent. The Reynolds-averaged Navier–Stokes equations (RANS) were used to simulate incompressible turbulent flow, and the trajectory of particles was tracked using the Discrete Phase Model (DPM). Particle trajectories and separation efficiency were analyzed for different particle sizes, inlet velocities, and bypass mass flow ratios between the scavenge channel and the core engine channel. The results show that the hybrid design provides excellent separation efficiency, with a recovery efficiency of over 97%.

Mechanisms of drag reduction by semidilute inertial particles in turbulent channel flow

Mechanisms of drag reduction by semidilute inertial particles in turbulent channel flow

Transport of inertial ellipsoidal particles in turbulent flow over rough walls

Transport of inertial ellipsoidal particles in turbulent flow over rough walls

Particle dynamics in compressible turbulent vertical channel flows

In this work, we carry out direct numerical simulations of particle suspensions in the compressible turbulent vertical channel (TVC) flows with Mach number Ma = 1.5 and particle Stokes number St = 1–100. The compressibility effect is considered in the particle dynamic model for the first time in the study of compressible particle-laden wall turbulence. We find that in both incompressible and compressible flow, gravity weakens the wall-normal and spanwise fluctuations of particle velocities as the Stokes number increases. However, compared to the incompressible flow case, the compressible effect amplifies the mean velocity, fluctuations of velocity, and slip velocity of particle in the streamwise direction. The wall-normal and spanwise fluctuations of particle velocities are augmented by the compressible effect in the channel core region. Moreover, in the core region, the effect of fluid compressibility on the wall-normal and spanwise fluctuations of particle velocities attenuates as the Stokes number increases, indicating a competition between the compressible effect and the particle inertia effect. We, furthermore, conduct the quadrant analysis of the local fluctuation velocities of fluid at particle positions and observe preferential distributions in the second and the fourth quadrants at y+ = 12.5–13.5. For compressible TVC flows, the pattern of probability distributions is more elongated, and the percentage is slightly higher in the second and fourth quadrants than that of incompressible flows. This observation implies that more particles locate in the ejection and sweep events in compressible flows than that in incompressible flows, which is anticipated to influence the particle wall-normal transport.

Characteristics of clustered particle relative velocity in homogeneous and isotropic turbulence

Particle collisions are mainly governed by the preferential concentration of inertia particles and the formation of fold caustics. By fold caustics, we mean that relative velocity does not go smoothly to zero when the particle separations decrease due to inertia. Despite the importance of the second-order relative velocity structure function, there has been relatively little experimental research on the formation of caustics due to the high accuracy requirements for the particle relative velocity measurements. In the dissipation range, an obvious departure between the second-order structure function of particles normalized by the square of the Kolmogorov velocity and the Kolmogorov turbulent scaling of r2 was observed for all four experimental conditions. In the inertial range, the second-order structure function normalized by the square of the Kolmogorov velocity was consistent with the scale form of r2/3 in all cases. The conditional second-order relative velocity structure function of particles in clusters differs from that of the arithmetically averaged particle statistics in both the dissipation range and the inertial subrange. In the dissipation range, caustics are present for all categories of particles. In the inertial range, the scaling of the second-order velocity structure function is almost identical for all categorized particle types.

Inverted Sedimentation of Active Particles in Unbiased ac Fields.

Gaining control over the motion of active particles is crucial for applications ranging from targeted cargo delivery to nanomedicine. While much progress has been made recently to control active motion based on external forces, flows, or gradients in concentration or light intensity, which all have a well-defined direction or bias, little is known about how to steer active particles in situations where no permanent bias can be realized. Here, we show that ac fields with a vanishing time average provide an alternative route to steering active particles. We exemplify this route for inertial active particles in a gravitational field, observing that a substantial fraction of them persistently travels in the upward direction upon switching on the ac field, resulting in an inverted sedimentation profile at the top wall of a confining container. Our results offer a generic control principle that could be used in the future to steer active motion, direct collective behaviors, and purify mixtures.

Velocity and acceleration statistics of heavy spheroidal particles in turbulence

Non-spherical particles transported by turbulent flow have a rich dynamics that combines their translational and rotational motions. Here, the focus is on small, heavy, inertial particles with a spheroidal shape fully prescribed by their aspect ratio. Such particles undergo an anisotropic, orientation-dependent viscous drag with the carrier fluid flow whose associated torque is given by the Jeffery equations. Direct numerical simulations of homogeneous, isotropic turbulence are performed to study systematically how the translational motion of such spheroidal particles depends on their shape and size. It is found that the Lagrangian statistics of both velocity and acceleration can be described in terms of an effective Stokes number obtained as an isotropic average over angles of the particle's orientation. Corrections to the translational motion of particles due to their non-sphericity and rotation can hence be recast as an effective radius obtained from such a mean.

Particle dispersion over side-by-side square cylinders: Proximity interference effects

This paper investigates the dispersion of tiny inertial particles in the two-dimensional laminar wake from a pair of square cylinders placed side-by-side to each other. The flow Reynolds number (defined based on the cylinder size h and uniform inflow velocity Uc) in our study is fixed at 75. The wake pattern resulting from the interaction between vortices shed from individual cylinders depends on the cross-stream spacing between the cylinders, i.e. spacing ratio s/h. We examine the effect of varying the cross-stream spacing between the cylinders on the body impaction and dispersion of particles in the wake flow over a range of their responses. Three different spacing ratios, s/h = 0.3, 2, and 4 are considered. We find that the impaction efficiency of Stokes number St = 0.1 particles is not sensitive to the spacing ratio. However, the impaction efficiency of St = 1 and 10 particles is dependent on the spacing ratio and increases with the latter. We illustrate how the distribution and clustering of representative inertial particles (i.e., with Stokes number unity) evolve over a vortex shedding cycle uniquely due to the wake flow in each spacing ratio configuration and explain the physical mechanism of particle clustering using backward tracking. The non-uniform clustering of particles with different responses to the wake flow in each spacing ratio configuration is analyzed using the Voronoï diagrams. The spacing ratio effects on the dispersion of particles are quantified in terms of mean statistical quantities such as mean local concentration, clustering intensity, and velocity statistics. The local concentration of St = 1 and 10 particles at streamwise positions away from cylinders is significantly influenced by the wake flow behavior governed by the choice of the spacing ratio. Further, the combined effect of gravity and hydrodynamic drag forces on the impaction and clustering behavior of particles is reported, where the Froude number Fr=0.32. In all the cases, particles exhibit ballistic behavior, showing a significantly reduced tendency to form clusters and a drastic increase in the impaction efficiency.

Preliminary Study on the Damping Effect of a Rotational Inertia Particle Damper Considering the Explosion Response of Continuous Concrete Bridges

Preliminary Study on the Damping Effect of a Rotational Inertia Particle Damper Considering the Explosion Response of Continuous Concrete Bridges

A Novel Parameter Estimation Method for PMSM by Using Chaotic Particle Swarm Optimization With Dynamic Self-Optimization

In this study, a novel parameter estimation method for permanent magnet synchronous motor (PMSM) of chaotic particle swarm optimization with dynamic self-optimization (DSCPSO) is proposed, where the voltage source inverter (VSI) nonlinearity is estimated simultaneously with the parameters to achieve real-time compensation of VSI nonlinearity. In DSCPSO, the tent chaos theory is introduced into the updating of particle swarm algorithm (PSO) populations, inertia weights and learning factors to enhance its ability to explore potentially better regions. Moreover, a memory tempering annealing (MTA) strategy is employed to guarantee particle pluralistic learning, which combines the superior robustness of the simulated annealing algorithm (SA) while enhancing population diversity. Furthermore, to achieve a reasonable tradeoff between exploration and exploitation, a dynamic lens imaging opposition-based learning (DLIOBL) and domain optimization strategy based on evolutionary information is designed, i.e., DLIOBL in the pre-evolutionary stage guarantees the depth of the exploration learning, while the domain optimization strategy is performed in the post-evolutionary stage accelerates the exploitation operation and avoids the problem of slow convergence in the late stages of PSO. The proposed method is applied to the parameter estimation of PMSM and the experimental results show that, the proposed method can track the VSI nonlinearity and variable parameter better than the conventional method under different working conditions.

Dust transport law and deposition characteristic in coal workers' respiratory tract based on CFD simulations

During the coal mining process, the particle produced enters the worker's body with breathing and likely leads to lung diseases such as pneumoconiosis. In this paper, an idealized model of the human respiratory tract is established, and the gas flow field is simulated using CFD for both steady and unsteady human respiration, followed by analysis of the trajectory and deposition of particle. Results show that during steady state breathing, airflow produces complex changes in the larynx, particles are mainly deposited in the pharynx, and the main deposition factors are impact and particle inertia. In non-steady respiration, the fraction of particles deposited in the inhalation phase is much greater than in the exhalation phase. Exhaling immediately after inhaling in a dusty room and holding the breath after inhaling when using inhaled drug therapy. This paper has positive implications for the study of the pathogenesis and treatment of lung diseases.