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1
Jayaram, Rohith, Yucheng Jie, Lihao Zhao e Helge I. Andersson. "Dynamics of inertial spheroids in a decaying Taylor–Green vortex flow". Physics of Fluids 35, n. 3 (marzo 2023): 033326. http://dx.doi.org/10.1063/5.0138125.
Abstract (sommario):
Inertial spheroids, prolates and oblates, are studied in a decaying Taylor–Green vortex (TGV) flow, wherein the flow gradually evolves from laminar anisotropic large-scale structures to turbulence-like isotropic Kolmogorov-type vortices. Along with particle clustering and its mechanisms, preferential rotation and alignment of the spheroids with the local fluid vorticity are examined. Particle inertia is classified by a nominal Stokes number [Formula: see text] which to first-order aims to eliminate the shape effect. The clustering varies with time and peaks when the physically relevant flow and particle time scales are of the same order. Low inertial ([Formula: see text]) spheroids are subjected to the centrifuging mechanism, thereby residing in stronger strain-rate regions, while high inertial ([Formula: see text]) spheroids lag the flow evolution and modestly sample strain-rate regions. Contrary to the expectations, however, spheroids reside in high strain-rate regions when the particle and flow time scales are comparable due to the dynamic interactions between the particles and the evolving flow scales. Moderately inertial ([Formula: see text]) prolates preferentially spin and oblates tumble throughout the qualitatively different stages of the TGV flow. These preferential modes of rotation correlate with parallel and perpendicular alignments of prolate and oblate spheroids, respectively, with the local fluid vorticity. However, for high inertial spheroids preferential rotation and alignment are decorrelated due to a memory effect, i.e., inertial particles require longer time to adjust to the local fluid flow. This memory effect is not only due to high particle inertia, as in statistically steady turbulence, but also caused by the continuously evolving TGV flow scales.
2
Sapsis, Themistoklis, e George Haller. "Inertial Particle Dynamics in a Hurricane". Journal of the Atmospheric Sciences 66, n. 8 (1 agosto 2009): 2481–92. http://dx.doi.org/10.1175/2009jas2865.1.
Abstract (sommario):
Abstract The motion of inertial (i.e., finite-size) particles is analyzed in a three-dimensional unsteady simulation of Hurricane Isabel. As established recently, the long-term dynamics of inertial particles in a fluid is governed by a reduced-order inertial equation, obtained as a small perturbation of passive fluid advection on a globally attracting slow manifold in the phase space of particle motions. Use of the inertial equation enables the visualization of three-dimensional inertial Lagrangian coherent structures (ILCS) on the slow manifold. These ILCS govern the asymptotic behavior of finite-size particles within a hurricane. A comparison of the attracting ILCS with conventional Eulerian fields reveals the Lagrangian footprint of the hurricane eyewall and of a large rainband. By contrast, repelling ILCS within the eye region admit a more complex geometry that cannot be compared directly with Eulerian features.
3
Riggs, Peter J. "Inertia and inertial resistance in the Special Theory of Relativity". Canadian Journal of Physics 99, n. 9 (settembre 2021): 795–98. http://dx.doi.org/10.1139/cjp-2021-0087.
Abstract (sommario):
A broader concept of “resistance to acceleration” than used in classical dynamics, called “inertial resistance”, is quantified for both inertial and non-inertial relativistic motion. Special Relativity shows that inertial resistance is more than particle inertia and originates from Minkowski spacetime structure. Current mainstream explanations of inertia do not take inertial resistance into account and are, therefore, incomplete.
4
Li, Gaojin, Gareth H. McKinley e Arezoo M. Ardekani. "Dynamics of particle migration in channel flow of viscoelastic fluids". Journal of Fluid Mechanics 785 (23 novembre 2015): 486–505. http://dx.doi.org/10.1017/jfm.2015.619.
Abstract (sommario):
The migration of a sphere in the pressure-driven channel flow of a viscoelastic fluid is studied numerically. The effects of inertia, elasticity, shear-thinning viscosity, secondary flows and the blockage ratio are considered by conducting fully resolved direct numerical simulations over a wide range of parameters. In a Newtonian fluid in the presence of inertial effects, the particle moves away from the channel centreline. The elastic effects, however, drive the particle towards the channel centreline. The equilibrium position depends on the interplay between the elastic and inertial effects. Particle focusing at the centreline occurs in flows with strong elasticity and weak inertia. Both shear-thinning effects and secondary flows tend to move the particle away from the channel centreline. The effect is more pronounced as inertia and elasticity effects increase. A scaling analysis is used to explain these different effects. Besides the particle migration, particle-induced fluid transport and particle migration during flow start-up are also considered. Inertial effects, shear-thinning behaviour, and secondary flows are all found to enhance the effective fluid transport normal to the flow direction. Due to the oscillation in fluid velocity and strong normal stress differences that develop during flow start-up, the particle has a larger transient migration velocity, which may be potentially used to accelerate the particle focusing.
5
Zhao, Lihao, Niranjan R. Challabotla, Helge I. Andersson e Evan A. Variano. "Mapping spheroid rotation modes in turbulent channel flow: effects of shear, turbulence and particle inertia". Journal of Fluid Mechanics 876 (31 luglio 2019): 19–54. http://dx.doi.org/10.1017/jfm.2019.521.
Abstract (sommario):
The rotational behaviour of non-spherical particles in turbulent channel flow is studied by Lagrangian tracking of spheroidal point particles in a directly simulated flow. The focus is on the complex rotation modes of the spheroidal particles, in which the back reaction on the flow field is ignored. This study is a sequel to the letter by Zhao et al. (Phys. Rev. Lett., vol. 115, 2015, 244501), in which only selected results in the near-wall buffer region and the almost-isotropic channel centre were presented. Now, particle dynamics all across the channel is explored to provide a complete picture of the orientational and rotational behaviour with consideration of the effects of particle aspect ratio ranging from 0.1 to 10 and particle Stokes number from 0 (inertialess) to 30. The rotational dynamics in the innermost part of the logarithmic wall layer is particularly complex and affected not only by modest mean shear, but also by particle inertia and turbulent vorticity. While inertial disks exhibit modest preferential orientation in either the wall-normal or cross-stream direction, inertial rods show neither preferential tumbling nor spinning. Examination of the co-variances between particle orientation, particle rotation and fluid rotation vectors explains the qualitatively different ‘wall mode’ rotation and ‘centre mode’ rotation. Inertialess spheroids transition between the two modes within a narrow zone ($15<z^{+}<35$) in the buffer region. If the spheroids have inertia, the transition zone between the two modes shifts to the inner part of the logarithmic layer, i.e. $z^{+}\geqslant 40$. We ascribe the transition of inertialess spheroids from the ‘wall mode’ to the ‘centre mode’ rotation to the changeover between the time scales associated with mean shear and small-scale turbulence. Inertial spheroids, however, transition between the two rotational modes when the Kolmogorov time scale becomes comparable to the time scale for particle rotation, i.e. the effective Stokes number is of order unity. The aforementioned findings reveal, in addition to the effects of particle shape and alignment, the importance of the characteristic local time scale of fluid flow for the rotation of both tracer and inertial spheroids in turbulent channel flows.
6
Ireland, Peter J., e Lance R. Collins. "Direct numerical simulation of inertial particle entrainment in a shearless mixing layer". Journal of Fluid Mechanics 704 (2 luglio 2012): 301–32. http://dx.doi.org/10.1017/jfm.2012.241.
Abstract (sommario):
AbstractWe present the first computational study of the dynamics of inertial particles in a shearless turbulence mixing layer. We parametrize our direct numerical simulations to isolate the effects of turbulence, Reynolds number, particle inertia, and gravity on the entrainment process. By analysing particle concentrations, particle and fluid velocities, particle size distributions, and higher-order velocity moments, we explore the impact of particle inertia and gravity on the mechanism of turbulent mixing. We neglect thermodynamic processes, including phase changes between the drops and surrounding air, which is equivalent to assuming the air is saturated (i.e. 100 % humidity). Entrainment is found to be governed by the large scales of the flow and is relatively insensitive to the Reynolds number over the range considered. Our results show that both fluid and particle velocities exhibit intermittency and that gravity and turbulent diffusion interact in unexpected ways to dictate particle dynamics. An analysis of the temporal evolution of fluid and particle statistics suggests that particle concentration profiles and velocities are self-similar under certain circumstances. We also observe large fluctuations in particle concentrations resulting from entrainment and introduce a model to estimate the impact these fluctuations have on the radial distribution function, a statistic that is often used to quantify inertial particle clustering. Our study is both a computational counterpart to and an extension of the wind tunnel experiments by Gerashchenko, Good & Warhaft (J. Fluid Mech., vol. 668, 2011, pp. 293–303) and Good, Gerashchenko, & Warhaft (J. Fluid Mech., vol. 694, 2012, pp. 371–398). We find good agreement between these experimental studies and our computational results. We anticipate that a better understanding of the role of gravity and turbulence in inertial particle entrainment will lead to improved cloud evolution predictions.
7
Tsuda, A., J. P. Butler e J. J. Fredberg. "Effects of alveolated duct structure on aerosol kinetics. II. Gravitational sedimentation and inertial impaction". Journal of Applied Physiology 76, n. 6 (1 giugno 1994): 2510–16. http://dx.doi.org/10.1152/jappl.1994.76.6.2510.
Abstract (sommario):
We studied the effects of alveolated duct structure on deposition processes for particle diameters > or = 1 micron. For such large particles, Brownian motion is insignificant but gravity and inertial forces play an important role. A Lagrangian description of particle dynamics in an alveolated duct flow was developed, and computational analysis was performed over the physiologically relevant range. At low flow rates gravity caused deposition. Gravitational cross-streamline motion depended on the coupled effects of curvature of gas streamlines and duct orientation relative to gravity. The detailed convective flow pattern was an important factor in determining deposition. At higher flow rates, inertial impaction contributed markedly to deposition. The curved nature of streamlines again played a major role on deposition, but duct orientation had little effect. In the medium range of flow rates, both gravitational and inertial forces simultaneously influenced particle motion. Particle inertia, per se, did not cause deposition but substantially suppressed gravitational deposition. The deposition mechanism was complex; contrary to what is often assumed in past analyses, the interaction between gravitational and inertial effects could not be described in a simple additive fashion. We conclude that the structure of the alveolar duct has an important role in gravitational sedimentation and inertial impaction in the lung acinus.
8
Gibert, Mathieu, Haitao Xu e Eberhard Bodenschatz. "Where do small, weakly inertial particles go in a turbulent flow?" Journal of Fluid Mechanics 698 (27 marzo 2012): 160–67. http://dx.doi.org/10.1017/jfm.2012.72.
Abstract (sommario):
AbstractWe report experimental results on the dynamics of heavy particles of the size of the Kolmogorov scale in a fully developed turbulent flow. The mixed Eulerian structure function of two-particle velocity and acceleration difference vectors $\langle {\delta }_{r} \mathbi{v}\boldsymbol{\cdot} {\delta }_{r} {\mathbi{a}}_{\mathbi{p}} \rangle $ was observed to increase significantly with particle inertia for identical flow conditions. We show that this increase is related to a preferential alignment between these dynamical quantities. With increasing particle density the probability for those two vectors to be collinear was observed to grow. We show that these results are consistent with the preferential sampling of strain-dominated regions by inertial particles.
9
Schaaf, Christian, Felix Rühle e Holger Stark. "A flowing pair of particles in inertial microfluidics". Soft Matter 15, n. 9 (2019): 1988–98. http://dx.doi.org/10.1039/c8sm02476f.
Abstract (sommario):
A flowing pair of particles in inertial microfluidics gives important insights into understanding and controlling the collective dynamics of particles like cells or droplets in microfluidic devices. For rigid particles we determine the two-particle lift force profiles, which govern their coupled dynamics.
10
Banerjee, I., M. E. Rosti, T. Kumar, L. Brandt e A. Russom. "Analogue tuning of particle focusing in elasto-inertial flow". Meccanica 56, n. 7 (23 marzo 2021): 1739–49. http://dx.doi.org/10.1007/s11012-021-01329-z.
Abstract (sommario):
AbstractWe report a unique tuneable analogue trend in particle focusing in the laminar and weak viscoelastic regime of elasto-inertial flows. We observe experimentally that particles in circular cross-section microchannels can be tuned to any focusing bandwidths that lie between the “Segre-Silberberg annulus” and the centre of a circular microcapillary. We use direct numerical simulations to investigate this phenomenon and to understand how minute amounts of elasticity affect the focussing of particles at increasing flow rates. An Immersed Boundary Method is used to account for the presence of the particles and a FENE-P model is used to simulate the presence of polymers in a Non-Newtonian fluid. The numerical simulations study the dynamics and stability of finite size particles and are further used to analyse the particle behaviour at Reynolds numbers higher than what is allowed by the experimental setup. In particular, we are able to report the entire migration trajectories of the particles as they reach their final focussing positions and extend our predictions to other geometries such as the square cross section. We believe complex effects originate due to a combination of inertia and elasticity in the weakly viscoelastic regime, where neither inertia nor elasticity are able to mask each other’s effect completely, leading to a number of intermediate focusing positions. The present study provides a fundamental new understanding of particle focusing in weakly elastic and strongly inertial flows, whose findings can be exploited for potentially multiple microfluidics-based biological sorting applications.
11
Lee, C. M., Á. Gylfason, P. Perlekar e F. Toschi. "Inertial particle acceleration in strained turbulence". Journal of Fluid Mechanics 785 (12 novembre 2015): 31–53. http://dx.doi.org/10.1017/jfm.2015.579.
Abstract (sommario):
The dynamics of inertial particles in turbulence is modelled and investigated by means of direct numerical simulation of an axisymmetrically expanding homogeneous turbulent strained flow. This flow can mimic the dynamics of particles close to stagnation points. The influence of mean straining flow is explored by varying the dimensionless strain rate parameter $Sk_{0}/{\it\epsilon}_{0}$ from 0.2 to 20, where $S$ is the mean strain rate, $k_{0}$ and ${\it\epsilon}_{0}$ are the turbulent kinetic energy and energy dissipation rate at the onset of straining. We report results relative to the acceleration variances and probability density functions for both passive and inertial particles. A high mean strain is found to have a significant effect on the acceleration variance both directly by an increase in the frequency of the turbulence and indirectly through the coupling of the fluctuating velocity and the mean flow field. The influence of the strain on the normalized particle acceleration probability distribution functions is more subtle. For the case of a passive particle we can approximate the acceleration variance with the aid of rapid-distortion theory and obtain good agreement with simulation data. For the case of inertial particles we can write a formal expression for the accelerations. The magnitude changes in the inertial particle acceleration variance and the effect on the probability density function are then discussed in a wider context for comparable flows, where the effects of the mean flow geometry and of the anisotropy at small scales are present.
12
ESCAURIAZA, CRISTIAN, e FOTIS SOTIROPOULOS. "Trapping and sedimentation of inertial particles in three-dimensional flows in a cylindrical container with exactly counter-rotating lids". Journal of Fluid Mechanics 641 (19 novembre 2009): 169–93. http://dx.doi.org/10.1017/s0022112009991534.
Abstract (sommario):
Stirring and sedimentation of solid inertial particles in low-Reynolds-number flows has acquired great relevance in multiple environmental, industrial and microfluidic systems, but few detailed numerical studies have focused on chaotically advected experimentally realizable flows. We carry out one-way coupling simulations to study the dynamics of inertial particles in the steady three-dimensional flow in a cylindrical container with exactly counter-rotating lids, which was recently studied by Lackey & Sotiropoulos (Phys. Fluids, vol. 18, 2006, paper no. 053601). We elucidate the rich Lagrangian dynamics of the flow in the vicinity of toroidal invariant regions and show that depending on the Stokes number inertial particles could get trapped for long times in different equilibrium positions inside integrable islands. In the chaotically advected region of the flow the balance between inertia and gravity forces (represented by the settling velocity) can produce a striking fractal sedimentation regime, characterized by a sequence of discrete deposition events of seemingly random number of particles separated by hiatuses of random duration. The resulting staircase-like distribution of the time series of the number of particles in suspension is shown to be a devil's staircase whose fractal dimension is equal to the 0.87 value found in multiple dissipative dynamical systems in nature. Our work sheds new light on the complex mechanisms governing the stirring and deposition of inertial particles and provides new information about the parameters that are relevant in the characterization of particle dynamics in different regions of chaotically advected flows.
13
Haddadi, Hamed, e Dino Di Carlo. "Inertial flow of a dilute suspension over cavities in a microchannel". Journal of Fluid Mechanics 811 (13 dicembre 2016): 436–67. http://dx.doi.org/10.1017/jfm.2016.709.
Abstract (sommario):
Microfluidic experiments and discrete particle simulations using the lattice-Boltzmann method are used to study interactions of finite size hard spheres and vortical flow inside confined cavities in a microchannel. The work focuses on entrapment of particles inside confined cavities and particle dynamics after entrapment. Numerical simulations and imaging of fluorescent tracers demonstrate that spiralling flow generates exchange of fluid mass between the vortical flow and the channel, contrary to the concept of a well-defined separatrix in unconfined cavities. An isolated finite size particle entrapped in the cavity migrates towards a stable orbit, i.e. a limit cycle trajectory. The topology of the limit cycle depends on cavity size, particle diameter and flow inertia, represented by Reynolds number. By studying various factors affecting the acceleration of a particle before entrapment, it is discussed that entrapment is a collective effect of flow morphology and particle dynamics. The effect of hydrodynamic interaction between particles inside the cavity, which results in deviation from the stable limit cycle orbit and depletion of cavities, will also be discussed. It is shown that a wall-confined microcavity entraps particles based on particle size, therefore it provides a platform for microfiltration.
14
Zamansky, R., F. Coletti, M. Massot e A. Mani. "Turbulent thermal convection driven by heated inertial particles". Journal of Fluid Mechanics 809 (10 novembre 2016): 390–437. http://dx.doi.org/10.1017/jfm.2016.630.
Abstract (sommario):
The heating of particles in a dilute suspension, for instance by radiation, chemical reactions or radioactivity, leads to local temperature fluctuations in the fluid due to the non-uniformity of the disperse phase. In the presence of a gravity field, the fluid is set in motion by the resulting buoyancy forces. When the particle density is different than that of the fluid, the fluid motion alters the spatial distribution of the particles and possibly strengthens their concentration inhomogeneities. This in turn causes more intense local heating. Direct numerical simulations in the Boussinesq limit show this feedback loop. Various regimes are identified depending on the particle inertia. For very small particle inertia, the macroscopic behaviour of the system is the result of many thermal plumes that are generated independently of each other. For significant particle inertia, clusters of particles are observed and their dynamics controls the flow. The emergence of very intermittent turbulent fluctuations shows that the flow is influenced by the larger structures (turbulent convection) as well as by the small-scale dynamics that affect particle segregation and thus the flow forcing. Assuming thermal equilibrium between the particles and the fluid (i.e. infinitely fast thermal relaxation of the particle), we investigate the evolution of statistical observables with the change of the main control parameters (namely the particle number density, the particle inertia and the domain size), and propose a scaling argument for these trends. Concerning the energy density in the spectral space, it is observed that the turbulent energy and temperature spectra follow a power law, the exponent of which varies continuously with the Stokes number. Furthermore, the study of the spectra of the temperature and momentum forcing (and thus of the concentration/temperature and velocity/temperature correlations) gives strong support to the proposed feedback loop mechanism. We then discuss the intermittency of the flow, and analyse the effect of relaxing some of the simplifying assumptions, thus assessing the relevance of the original studied configuration.
15
Wang, Lian-Ping, e Martin R. Maxey. "Settling velocity and concentration distribution of heavy particles in homogeneous isotropic turbulence". Journal of Fluid Mechanics 256 (novembre 1993): 27–68. http://dx.doi.org/10.1017/s0022112093002708.
Abstract (sommario):
The average settling velocity in homogeneous turbulence of a small rigid spherical particle, subject to a Stokes drag force, has been shown to differ from that in still fluid owing to a bias from the particle inertia (Maxey 1987). Previous numerical results for particles in a random flow field, where the flow dynamics were not considered, showed an increase in the average settling velocity. Direct numerical simulations of the motion of heavy particles in isotropic homogeneous turbulence have been performed where the flow dynamics are included. These show that a significant increase in the average settling velocity can occur for particles with inertial response time and still-fluid terminal velocity comparable to the Kolmogorov scales of the turbulence. This increase may be as much as 50% of the terminal velocity, which is much larger than was previously found. The concentration field of the heavy particles, obtained from direct numerical simulations, shows the importance of the inertial bias with particles tending to collect in elongated sheets on the peripheries of local vortical structures. This is coupled then to a preferential sweeping of the particles in downward moving fluid. Again the importance of Kolmogorov scaling to these processes is demonstrated. Finally, some consideration is given to larger particles that are subject to a nonlinear drag force where it is found that the nonlinearity reduces the net increase in settling velocity.
16
Zaza, Domenico, e Michele Iovieno. "Influence of Coherent Vortex Rolls on Particle Dynamics in Unstably Stratified Turbulent Channel Flows". Energies 17, n. 11 (3 giugno 2024): 2725. http://dx.doi.org/10.3390/en17112725.
Abstract (sommario):
This work investigates the dynamics of heavy particles dispersed in turbulent channel flows under unstable thermal stratification conditions using point-particle direct numerical simulations (PP-DNS), to quantify the influence of large-scale coherent vortex rolls, arising from the combined effects of shear and buoyancy, on the spatial distribution and preferential sampling behavior of inertial particles. We examined three particle Stokes numbers (St+=0.6,60,120) and two friction Richardson numbers, Riτ=0.272 and Riτ=27.2, which exemplify the regimes below and above the critical condition for vortex roll formation, respectively. The results indicate that the flow reorganization into large-scale longitudinal vortices significantly alters the topological features of small scales in the near-wall region impinged by the thermal plumes, resulting in a prevalence of vorticity-dominated topologies. The interplay between this phenomenon and the tendency of particles to preferentially sample strain-dominated topologies leads to a distinctive asymmetric particle distribution in the near-wall planes. Inertial particles markedly accumulate in the strain-dominated regions where the coherent thermal plumes emerge from the walls, while avoiding the vorticity-dominated impingement zones. This peculiar particle response to the vortex rolls is most pronounced when the particle response time matches the characteristic timescale of the large-scale coherent motions in the cross-stream planes.
17
Ray, Baidurja, e Lance R. Collins. "Investigation of sub-Kolmogorov inertial particle pair dynamics in turbulence using novel satellite particle simulations". Journal of Fluid Mechanics 720 (27 febbraio 2013): 192–211. http://dx.doi.org/10.1017/jfm.2013.24.
Abstract (sommario):
AbstractClustering (or preferential concentration) of weakly inertial particles suspended in a homogeneous isotropic turbulent flow is driven primarily by the smallest eddies at the so-called Kolmogorov scale. In particle-laden large-eddy simulations (LES), these small scales are not resolved by the grid and hence their effect on both the resolved flow scales and the particle motion have to be modelled. In order to predict clustering in a particle-laden LES, it is crucial that the subgrid model for the particles captures the mechanism by which the subgrid scales affect the particle motion (Ray & Collins, J. Fluid Mech., vol. 680, 2011, pp. 488–510). In this paper, we describe novel satellite particle simulations (SPS), in which we study the clustering and relative velocity statistics of inertial particles at separation distances well below the Kolmogorov length scale. SPS is designed to isolate pairwise interactions of particles, and is therefore well suited for developing two-particle models. We show that the power-law dependence of the radial distribution function (RDF), a statistical measure of clustering, is predicted by the SPS in excellent agreement with direct numerical simulations (DNS) for Stokes numbers up to 3, implying that no explicit information from the inertial range is required to accurately describe particle clustering. This result further explains our successful prediction of the RDF power using the drift-diffusion model of Chun et al. (J. Fluid Mech., vol. 536, 2005, pp. 219–251) for $\mathit{St}\leq 0. 4$. We also consider the second-order longitudinal relative velocity structure function for the particles; we show that the SPS is able to capture its power-law exponent for $\mathit{St}\leq 0. 5$ and attribute the disagreement at larger $\mathit{St}$ to the effect of the larger scales of motion not captured by the SPS. Further, the SPS is able to capture the ‘caustic activation’ of the structure function at zero separation and predict the critical $\mathit{St}$ and rate of activation in agreement with the DNS (Salazar & Collins, J. Fluid. Mech., vol. 696, 2012, pp. 45–66). We show comparisons between filtered DNS and equivalently filtered SPS, and the findings are similar to the unfiltered case. Overall, SPS is an efficient and accurate computational tool for investigating particle pair dynamics at small separations, as well as an interesting platform for developing LES subgrid models designed to accurately reproduce particle clustering.
18
Patel, Kuntal, e Holger Stark. "A pair of particles in inertial microfluidics: effect of shape, softness, and position". Soft Matter 17, n. 18 (2021): 4804–17. http://dx.doi.org/10.1039/d1sm00276g.
19
VOLK, R., E. CALZAVARINI, E. LÉVÊQUE e J. F. PINTON. "Dynamics of inertial particles in a turbulent von Kármán flow". Journal of Fluid Mechanics 668 (26 gennaio 2011): 223–35. http://dx.doi.org/10.1017/s0022112010005690.
Abstract (sommario):
We study the dynamics of neutrally buoyant particles with diameters varying in the range [1, 45] in Kolmogorov scale units (η) and Reynolds numbers based on Taylor scale (Reλ) between 590 and 1050. One component of the particle velocity is measured using an extended laser Doppler velocimetry at the centre of a von Kármán flow, and acceleration is derived by differentiation. We find that the particle acceleration variance decreases with increasing diameter with scaling close to (D/η)−2/3, in agreement with previous observations, and with a hint for an intermittent correction as suggested by arguments based on scaling of pressure spatial increments. The characteristic time of acceleration autocorrelation increases more strongly than previously reported in other experiments, and possibly varying linearly with D/η. Further analysis shows that the probability density functions of the acceleration have smaller wings for larger particles; their flatness decreases as well, as expected from the behaviour of pressure increments in turbulence when intermittency corrections are taken into account. We contrast our measurements with previous observations in wind-tunnel turbulent flows and numerical simulations.
20
Haller, George. "Solving the inertial particle equation with memory". Journal of Fluid Mechanics 874 (3 luglio 2019): 1–4. http://dx.doi.org/10.1017/jfm.2019.378.
Abstract (sommario):
The dynamics of spherical particles in a fluid flow is governed by the well-accepted Maxey–Riley equation. This equation of motion simply represents Newton’s second law, equating the rate of change of the linear momentum with all forces acting on the particle. One of these forces, the Basset–Boussinesq memory term, however, is notoriously difficult to handle, which prompts most studies to ignore this term despite ample numerical and experimental evidence of its significance. This practice may well change now due to a clever reformulation of the particle equation of motion by Prasath, Vasan & Govindarajan (J. Fluid Mech., vol. 868, 2019, pp. 428–460), who convert the Maxey–Riley equation into a one-dimensional heat equation with non-trivial boundary conditions. Remarkably, this reformulation confirms earlier estimates on particle asymptotics, yields previously unknown analytic solutions and leads to an efficient numerical scheme for more complex flow fields.
21
Saha, Suvash C., Isabella Francis e Tanya Nassir. "Computational Inertial Microfluidics: Optimal Design for Particle Separation". Fluids 7, n. 9 (16 settembre 2022): 308. http://dx.doi.org/10.3390/fluids7090308.
Abstract (sommario):
Following the emergence of many blood transfusion-associated diseases, novel passive cell separation technologies, such as microfluidic devices, are increasingly designed and optimized to separate red blood cells (RBCs) and white blood cells (WBCs) from whole blood. These systems allow for the rapid diagnosis of diseases without relying on complicated and expensive hematology instruments such as flow microscopes, coagulation analyzers, and cytometers. The inertia effect and the impact of intrinsic hydrodynamic forces, the Dean drag force (FD), and the inertial lift force (FL) on the migration of particles within curved and complex confined channels have been explored theoretically, computationally, and experimentally. This study aimed to optimize the dimensions of a microfluidic channel for fast particle propagation and separation. Several spiral geometries with different cross-sections were tested using computational fluid dynamics (CFD) to separate two particle types representing RBCs and WBCs. The chosen three geometries consist of a single inlet, two outlets, and three spiral turns, each having a different cross-sectional height (120, 135, and 150 µm). Particle separation was successfully achieved in the 135 µm-height microchannel, while other microchannels demonstrated mixed particle types at the outlets.
22
Haugen, Jeffery, Jesse Ziebarth, Eugene C. Eckstein, Mohamed Laradji e Yongmei Wang. "Hydrodynamic and transport behavior of solid nanoparticles simulated with dissipative particle dynamics". Advances in Natural Sciences: Nanoscience and Nanotechnology 14, n. 2 (15 maggio 2023): 025006. http://dx.doi.org/10.1088/2043-6262/acc01e.
Abstract (sommario):
Abstract Inertial migration of micro- and nanoparticles flowing through microchannels is commonly used for particle separation, sorting, and focusing on many lab-on-a-chip devices. Computer simulations of inertial migration of nanoparticles by mesoscale simulation methods, such as Dissipative Particle Dynamics (DPD) would be helpful to future experimental development of these lab-on-a-chip devices. However, the conventional DPD approach has a low Schmidt number and its ability to model inertial migration is questioned. In this work, we examine the ability of DPD simulations to investigate the inertial migration of rigid nanoparticles flowing through a slit channel. By varying the exponent and cutoff distance in the weight function of the random and dissipative forces, DPD models with Schmidt number varying between 1 and 370 were examined. We show that solvent penetration into nanoparticles and solvent-induced attraction between nanoparticles can be controlled by choosing appropriate interaction coefficients of the DPD conservative force and that these properties are not influenced by the Schmidt number of the DPD model. On the other hand, hydrodynamic properties and transport behaviour of rigid nanoparticles are influenced by the Schmidt number. With the conventional DPD model, nanoparticles tend to be evenly distributed across the channel and do not remain in steady-state positions during flow. At high Schmidt numbers, the particles migrate to long-lasting steady-state positions located between the channel center and walls, in agreement with known experimental observations. We conclude that to properly simulate inertial migration, modifications to the conventional DPD model that yield a high Schmidt number are required.
23
Olsen, Kristian Stølevik, e Hartmut Löwen. "Dynamics of inertial particles under velocity resetting". Journal of Statistical Mechanics: Theory and Experiment 2024, n. 3 (27 marzo 2024): 033210. http://dx.doi.org/10.1088/1742-5468/ad319a.
Abstract (sommario):
Abstract We investigate stochastic resetting in coupled systems involving two degrees of freedom, where only one variable is reset. The resetting variable, which we think of as hidden, indirectly affects the remaining observable variable via correlations. We derive the Fourier–Laplace transforms of the observable variable’s propagator and provide a recursive relation for all the moments, facilitating a comprehensive examination of the process. We apply this framework to inertial transport processes where we observe the particle position while the velocity is hidden and is being reset at a constant rate. We show that velocity resetting results in a linearly growing spatial mean squared displacement at later times, independently of reset-free dynamics, due to resetting-induced tempering of velocity correlations. General expressions for the effective diffusion and drift coefficients are derived as a function of the resetting rate. A non-trivial dependence on the rate may appear due to multiple timescales and crossovers in the reset-free dynamics. An extension that incorporates refractory periods after each reset is considered, where post-resetting pauses can lead to anomalous diffusive behavior. Our results are of relevance to a wide range of systems, such as inertial transport where the mechanical momentum is lost in collisions with the environment or the behavior of living organisms where stop-and-go locomotion with inertia is ubiquitous. Numerical simulations for underdamped Brownian motion and the random acceleration process confirm our findings.
24
Krafcik, Andrej, Peter Babinec, Oliver Strbak e Ivan Frollo. "A Theoretical Analysis of Magnetic Particle Alignment in External Magnetic Fields Affected by Viscosity and Brownian Motion". Applied Sciences 11, n. 20 (15 ottobre 2021): 9651. http://dx.doi.org/10.3390/app11209651.
Abstract (sommario):
The interaction of an external magnetic field with magnetic objects affects their response and is a fundamental property for many biomedical applications, including magnetic resonance and particle imaging, electromagnetic hyperthermia, and magnetic targeting and separation. Magnetic alignment and relaxation are widely studied in the context of these applications. In this study, we theoretically investigate the alignment dynamics of a rotational magnetic particle as an inverse process to Brownian relaxation. The selected external magnetic flux density ranges from 5μT to 5T. We found that the viscous torque for arbitrary rotating particles with a history term due to the inertia and friction of the surrounding ambient water has a significant effect in strong magnetic fields (range 1–5T). In this range, oscillatory behavior due to the inertial torque of the particle also occurs, and the stochastic Brownian torque diminishes. In contrast, for weak fields (range 5–50μT), the history term of the viscous torque and the inertial torque can be neglected, and the stochastic Brownian torque induced by random collisions of the surrounding fluid molecules becomes dominant. These results contribute to a better understanding of the molecular mechanisms of magnetic particle alignment in external magnetic fields and have important implications in a variety of biomedical applications.
25
Cardall, Christian. "Minkowski and Galilei/Newton Fluid Dynamics: A Geometric 3 + 1 Spacetime Perspective". Fluids 4, n. 1 (26 dicembre 2018): 1. http://dx.doi.org/10.3390/fluids4010001.
Abstract (sommario):
A kinetic theory of classical particles serves as a unified basis for developing a geometric 3 + 1 spacetime perspective on fluid dynamics capable of embracing both Minkowski and Galilei/Newton spacetimes. Parallel treatment of these cases on as common a footing as possible reveals that the particle four-momentum is better regarded as comprising momentum and inertia rather than momentum and energy; and, consequently, that the object now known as the stress-energy or energy-momentum tensor is more properly understood as a stress-inertia or inertia-momentum tensor. In dealing with both fiducial and comoving frames as fluid dynamics requires, tensor decompositions in terms of the four-velocities of observers associated with these frames render use of coordinate-free geometric notation not only fully viable, but conceptually simplifying. A particle number four-vector, three-momentum (1, 1) tensor, and kinetic energy four-vector characterize a simple fluid and satisfy balance equations involving spacetime divergences on both Minkowski and Galilei/Newton spacetimes. Reduced to a fully 3 + 1 form, these equations yield the familiar conservative formulations of special relativistic and non-relativistic fluid dynamics as partial differential equations in inertial coordinates, and in geometric form will provide a useful conceptual bridge to arbitrary-Lagrange–Euler and general relativistic formulations.
26
Hiranuma, Naruki, Ottmar Möhler, Gourihar Kulkarni, Martin Schnaiter, Steffen Vogt, Paul Vochezer, Emma Järvinen et al. "Development and characterization of an ice-selecting pumped counterflow virtual impactor (IS-PCVI) to study ice crystal residuals". Atmospheric Measurement Techniques 9, n. 8 (18 agosto 2016): 3817–36. http://dx.doi.org/10.5194/amt-9-3817-2016.
Abstract (sommario):
Abstract. Separation of particles that play a role in cloud activation and ice nucleation from interstitial aerosols has become necessary to further understand aerosol-cloud interactions. The pumped counterflow virtual impactor (PCVI), which uses a vacuum pump to accelerate the particles and increase their momentum, provides an accessible option for dynamic and inertial separation of cloud elements. However, the use of a traditional PCVI to extract large cloud hydrometeors is difficult mainly due to its small cut-size diameters (< 5 µm). Here, for the first time we describe a development of an ice-selecting PCVI (IS-PCVI) to separate ice in controlled mixed-phase cloud system based on the particle inertia with the cut-off diameter ≥ 10 µm. We also present its laboratory application demonstrating the use of the impactor under a wide range of temperature and humidity conditions. The computational fluid dynamics simulations were initially carried out to guide the design of the IS-PCVI. After fabrication, a series of validation laboratory experiments were performed coupled with the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) expansion cloud simulation chamber. In the AIDA chamber, test aerosol particles were exposed to the ice supersaturation conditions (i.e., RHice > 100 %), where a mixture of droplets and ice crystals was formed during the expansion experiment. In parallel, the flow conditions of the IS-PCVI were actively controlled, such that it separated ice crystals from a mixture of ice crystals and cloud droplets, which were of diameter ≥ 10 µm. These large ice crystals were passed through the heated evaporation section to remove the water content. Afterwards, the residuals were characterized with a suite of online and offline instruments downstream of the IS-PCVI. These results were used to assess the optimized operating parameters of the device in terms of (1) the critical cut-size diameter, (2) the transmission efficiency and (3) the counterflow-to-input flow ratio. Particle losses were characterized by comparing the residual number concentration to the rejected interstitial particle number concentration. Overall results suggest that the IS-PCVI enables inertial separation of particles with a volume-equivalent particle size in the range of ~ 10–30 µm in diameter with small inadvertent intrusion (~ 5 %) of unwanted particles.
27
Zhu, Zeen, Pavlos Kollias e Fan Yang. "Particle inertial effects on radar Doppler spectra simulation". Atmospheric Measurement Techniques 16, n. 15 (10 agosto 2023): 3727–37. http://dx.doi.org/10.5194/amt-16-3727-2023.
Abstract (sommario):
Abstract. Radar Doppler spectra observations provide a wealth of information about cloud and precipitation microphysics and dynamics. The interpretation of these measurements depends on our ability to simulate these observations accurately using a forward model. The effect of small-scale turbulence on the radar Doppler spectra shape has been traditionally treated by implementing the convolution process on the hydrometeor reflectivity spectrum and environmental turbulence. This approach assumes that all the particles in the radar sampling volume respond the same to turbulent-scale velocity fluctuations and neglects the particle inertial effect. Here, we investigate the inertial effects of liquid-phase particles on the forward modeled radar Doppler spectra. A physics-based simulation (PBS) is developed to demonstrate that big droplets, with large inertia, are unable to follow the rapid change of the velocity field in a turbulent environment. These findings are incorporated into a new radar Doppler spectra simulator. Comparison between the traditional and newly formulated radar Doppler spectra simulators indicates that the conventional simulator leads to an unrealistic broadening of the spectrum, especially in a strong turbulent environment. This study provides clear evidence to illustrate the droplet inertial effect on radar Doppler spectrum and develops a physics-based simulator framework to accurately emulate the Doppler spectrum for a given droplet size distribution (DSD) in a turbulence field. The proposed simulator has various potential applications for the cloud and precipitation studies, and it provides a valuable tool to decode the cloud microphysical and dynamical properties from Doppler radar observation.
28
Brandt, Luca, e Filippo Coletti. "Particle-Laden Turbulence: Progress and Perspectives". Annual Review of Fluid Mechanics 54, n. 1 (5 gennaio 2022): 159–89. http://dx.doi.org/10.1146/annurev-fluid-030121-021103.
Abstract (sommario):
This review is motivated by the fast progress in our understanding of the physics of particle-laden turbulence in the last decade, partly due to the tremendous advances of measurement and simulation capabilities. The focus is on spherical particles in homogeneous and canonical wall-bounded flows. The analysis of recent data indicates that conclusions drawn in zero gravity should not be extrapolated outside of this condition, and that the particle response time alone cannot completely define the dynamics of finite-size particles. Several breakthroughs have been reported, mostly separately, on the dynamics and turbulence modifications of small inertial particles in dilute conditions and of large weakly buoyant spheres. Measurements at higher concentrations, simulations fully resolving smaller particles, and theoretical tools accounting for both phases are needed to bridge this gap and allow for the exploration of the fluid dynamics of suspensions, from laminar rheology and granular media to particulate turbulence.
29
Ireland, Peter J., Andrew D. Bragg e Lance R. Collins. "The effect of Reynolds number on inertial particle dynamics in isotropic turbulence. Part 1. Simulations without gravitational effects". Journal of Fluid Mechanics 796 (11 maggio 2016): 617–58. http://dx.doi.org/10.1017/jfm.2016.238.
Abstract (sommario):
In this study, we analyse the statistics of both individual inertial particles and inertial particle pairs in direct numerical simulations of homogeneous isotropic turbulence in the absence of gravity. The effect of the Taylor microscale Reynolds number, $R_{{\it\lambda}}$, on the particle statistics is examined over the largest range to date (from $R_{{\it\lambda}}=88$ to 597), at small, intermediate and large Kolmogorov-scale Stokes numbers $St$. We first explore the effect of preferential sampling on the single-particle statistics and find that low-$St$ inertial particles are ejected from both vortex tubes and vortex sheets (the latter becoming increasingly prevalent at higher Reynolds numbers) and preferentially accumulate in regions of irrotational dissipation. We use this understanding of preferential sampling to provide a physical explanation for many of the trends in the particle velocity gradients, kinetic energies and accelerations at low $St$, which are well represented by the model of Chun et al. (J. Fluid Mech., vol. 536, 2005, pp. 219–251). As $St$ increases, inertial filtering effects become more important, causing the particle kinetic energies and accelerations to decrease. The effect of inertial filtering on the particle kinetic energies and accelerations diminishes with increasing Reynolds number and is well captured by the models of Abrahamson (Chem. Engng Sci., vol. 30, 1975, pp. 1371–1379) and Zaichik & Alipchenkov (Intl J. Multiphase Flow, vol. 34 (9), 2008, pp. 865–868), respectively. We then consider particle-pair statistics, and focus our attention on the relative velocities and radial distribution functions (RDFs) of the particles, with the aim of understanding the underlying physical mechanisms contributing to particle collisions. The relative velocity statistics indicate that preferential sampling effects are important for $St\lesssim 0.1$ and that path-history/non-local effects become increasingly important for $St\gtrsim 0.2$. While higher-order relative velocity statistics are influenced by the increased intermittency of the turbulence at high Reynolds numbers, the lower-order relative velocity statistics are only weakly sensitive to changes in Reynolds number at low $St$. The Reynolds-number trends in these quantities at intermediate and large $St$ are explained based on the influence of the available flow scales on the path-history and inertial filtering effects. We find that the RDFs peak near $St$ of order unity, that they exhibit power-law scaling for low and intermediate $St$ and that they are largely independent of Reynolds number for low and intermediate $St$. We use the model of Zaichik & Alipchenkov (New J. Phys., vol. 11, 2009, 103018) to explain the physical mechanisms responsible for these trends, and find that this model is able to capture the quantitative behaviour of the RDFs extremely well when direct numerical simulation data for the structure functions are specified, in agreement with Bragg & Collins (New J. Phys., vol. 16, 2014a, 055013). We also observe that at large $St$, changes in the RDF are related to changes in the scaling exponents of the relative velocity variances. The particle collision kernel closely matches that computed by Rosa et al. (New J. Phys., vol. 15, 2013, 045032) and is found to be largely insensitive to the flow Reynolds number. This suggests that relatively low-Reynolds-number simulations may be able to capture much of the relevant physics of droplet collisions and growth in the adiabatic cores of atmospheric clouds.
30
Li, Xiang-Yu, e Lars Mattsson. "Coagulation of inertial particles in supersonic turbulence". Astronomy & Astrophysics 648 (aprile 2021): A52. http://dx.doi.org/10.1051/0004-6361/202040068.
Abstract (sommario):
Coagulation driven by supersonic turbulence is primarily an astrophysical problem because coagulation processes on Earth are normally associated with incompressible fluid flows at low Mach numbers, while dust aggregation in the interstellar medium for instance is an example of the opposite regime. We study coagulation of inertial particles in compressible turbulence using high-resolution direct and shock-capturing numerical simulations with a wide range of Mach numbers from nearly incompressible to moderately supersonic. The particle dynamics is simulated by representative particles and the effects on the size distribution and coagulation rate due to increasing Mach number is explored. We show that the time evolution of particle size distribution mainly depends on the compressibility (Mach number). We find that the average coagulation kernel ⟨Cij⟩ scales linearly with the average Mach number ℳrms multiplied by the combined size of the colliding particles, that is, 〈Cij〉∼〈(ai+aj)3〉 ℳrmsτη−1, which is qualitatively consistent with expectations from analytical estimates. A quantitative correction 〈Cij〉∼〈(ai+aj)3〉(vp,rms/cs)τη−1 is proposed and can serve as a benchmark for future studies. We argue that the coagulation rate ⟨Rc⟩ is also enhanced by compressibility-induced compaction of particles.
31
Kawaguchi, Misa, Tomohiro Fukui e Koji Morinishi. "Contribution of Particle–Wall Distance and Rotational Motion of a Single Confined Elliptical Particle to the Effective Viscosity in Pressure-Driven Plane Poiseuille Flows". Applied Sciences 11, n. 15 (22 luglio 2021): 6727. http://dx.doi.org/10.3390/app11156727.
Abstract (sommario):
Rheological properties of the suspension flow, especially effective viscosity, partly depend on spatial arrangement and motion of suspended particles. It is important to consider effective viscosity from the microscopic point of view. For elliptical particles, the equilibrium position of inertial migration in confined state is unclear, and there are few studies on the relationship between dynamics of suspended particles and induced local effective viscosity distribution. Contribution of a single circular or elliptical particle flowing between parallel plates to the effective viscosity was studied, focusing on the particle–wall distance and particle rotational motion using the two-dimensional regularized lattice Boltzmann method and virtual flux method. As a result, confinement effects of the elliptical particle on the equilibrium position of inertial migration were summarized using three definitions of confinement. In addition, the effects of particle shape (aspect ratio and confinement) on the effective viscosity were assessed focusing on the particle–wall distance. The contribution of particle shape to the effective viscosity was found to be enhanced when the particle flowed near the wall. Focusing on the spatial and temporal variation of relative viscosity evaluated from wall shear stress, it was found that the spatial variation of the local relative viscosity was larger than temporal variation regardless of the aspect ratio and particle–wall distance.
32
Vié, Aymeric, François Doisneau e Marc Massot. "On the Anisotropic Gaussian Velocity Closure for Inertial-Particle Laden Flows". Communications in Computational Physics 17, n. 1 (28 novembre 2014): 1–46. http://dx.doi.org/10.4208/cicp.021213.140514a.
Abstract (sommario):
AbstractThe accurate simulation of disperse two-phase flows, where a discrete particulate condensed phase is transported by a carrier gas, is crucial for many applications; Eulerian approaches are well suited for high performance computations of such flows. However when the particles from the disperse phase have a significant inertia compared to the time scales of the flow, particle trajectory crossing (PTC) occurs i.e. the particle velocity distribution at a given location can become multi-valued. To properly account for such a phenomenon many Eulerian moment methods have been recently proposed in the literature. The resulting models hardly comply with a full set of desired criteria involving: 1- ability to reproduce the physics of PTC, at least for a given range of particle inertia, 2- well-posedness of the resulting set of PDEs on the chosen moments as well as guaranteed realizability, 3- capability of the model to be associated with a high order realizable numerical scheme for the accurate resolution of particle segregation in turbulent flows. The purpose of the present contribution is to introduce a multi-variate Anisotropic Gaussian closure for such particulate flows, in the spirit of the closure that has been suggested for out-of-equilibrium gas dynamics and which satisfies the three criteria. The novelty of the contribution is three-fold. First we derive the related moment system of conservation laws with source terms, and justify the use of such a model in the context of high Knudsen numbers, where collision operators play no role. We exhibit the main features and advantages in terms of mathematical structure and realizability. Then a second order accurate and realizable MUSCL/HLL scheme is proposed and validated. Finally the behavior of the method for the description of PTC is thoroughly investigated and its ability to account accurately for inertial particulate flow dynamics in typical configurations is assessed.
33
Ireland, Peter J., Andrew D. Bragg e Lance R. Collins. "The effect of Reynolds number on inertial particle dynamics in isotropic turbulence. Part 2. Simulations with gravitational effects". Journal of Fluid Mechanics 796 (11 maggio 2016): 659–711. http://dx.doi.org/10.1017/jfm.2016.227.
Abstract (sommario):
In Part 1 of this study (Ireland et al., J. Fluid Mech., vol. 796, 2016, pp. 617–658), we analysed the motion of inertial particles in isotropic turbulence in the absence of gravity using direct numerical simulation (DNS). Here, in Part 2, we introduce gravity and study its effect on single-particle and particle-pair dynamics over a wide range of flow Reynolds numbers, Froude numbers and particle Stokes numbers. The overall goal of this study is to explore the mechanisms affecting particle collisions, and to thereby improve our understanding of droplet interactions in atmospheric clouds. We find that the dynamics of heavy particles falling under gravity can be artificially influenced by the finite domain size and the periodic boundary conditions, and we therefore perform our simulations on larger domains to reduce these effects. We first study single-particle statistics that influence the relative positions and velocities of inertial particles. We see that gravity causes particles to sample the flow more uniformly and reduces the time particles can spend interacting with the underlying turbulence. We also find that gravity tends to increase inertial particle accelerations, and we introduce a model to explain that effect. We then analyse the particle relative velocities and radial distribution functions (RDFs), which are generally seen to be independent of Reynolds number for low and moderate Kolmogorov-scale Stokes numbers $St$. We see that gravity causes particle relative velocities to decrease by reducing the degree of preferential sampling and the importance of path-history interactions, and that the relative velocities have higher scaling exponents with gravity. We observe that gravity has a non-trivial effect on clustering, acting to decrease clustering at low $St$ and to increase clustering at high $St$. By considering the effect of gravity on the clustering mechanisms described in the theory of Zaichik & Alipchenkov (New J. Phys., vol. 11, 2009, 103018), we provide an explanation for this non-trivial effect of gravity. We also show that when the effects of gravity are accounted for in the theory of Zaichik & Alipchenkov (2009), the results compare favourably with DNS. The relative velocities and RDFs exhibit considerable anisotropy at small separations, and this anisotropy is quantified using spherical harmonic functions. We use the relative velocities and the RDFs to compute the particle collision kernels, and find that the collision kernel remains as it was for the case without gravity, namely nearly independent of Reynolds number for low and moderate $St$. We conclude by discussing practical implications of the results for the cloud physics and turbulence communities and by suggesting possible avenues for future research.
34
Harding, Brendan, Yvonne M. Stokes e Andrea L. Bertozzi. "Effect of inertial lift on a spherical particle suspended in flow through a curved duct". Journal of Fluid Mechanics 875 (18 luglio 2019): 1–43. http://dx.doi.org/10.1017/jfm.2019.323.
Abstract (sommario):
We develop a model of the forces on a spherical particle suspended in flow through a curved duct under the assumption that the particle Reynolds number is small. This extends an asymptotic model of inertial lift force previously developed to study inertial migration in straight ducts. Of particular interest is the existence and location of stable equilibria within the cross-sectional plane towards which particles migrate. The Navier–Stokes equations determine the hydrodynamic forces acting on a particle. A leading-order model of the forces within the cross-sectional plane is obtained through the use of a rotating coordinate system and a perturbation expansion in the particle Reynolds number of the disturbance flow. We predict the behaviour of neutrally buoyant particles at low flow rates and examine the variation in focusing position with respect to particle size and bend radius, independent of the flow rate. In this regime, the lateral focusing position of particles approximately collapses with respect to a dimensionless parameter dependent on three length scales: specifically, the particle radius, duct height and duct bend radius. Additionally, a trapezoidal-shaped cross-section is considered in order to demonstrate how changes in the cross-section design influence the dynamics of particles.
35
Dabade, Vivekanand, Navaneeth K. Marath e Ganesh Subramanian. "The effect of inertia on the orientation dynamics of anisotropic particles in simple shear flow". Journal of Fluid Mechanics 791 (24 febbraio 2016): 631–703. http://dx.doi.org/10.1017/jfm.2016.14.
Abstract (sommario):
It is well known that, under inertialess conditions, the orientation vector of a torque-free neutrally buoyant spheroid in an ambient simple shear flow rotates along so-called Jeffery orbits, a one-parameter family of closed orbits on the unit sphere centred around the direction of the ambient vorticity (Jeffery, Proc. R. Soc. Lond. A, vol. 102, 1922, pp. 161–179). We characterize analytically the irreversible drift in the orientation of such torque-free spheroidal particles of an arbitrary aspect ratio, across Jeffery orbits, that arises due to weak inertial effects. The analysis is valid in the limit $Re,St\ll 1$, where $Re=(\dot{{\it\gamma}}L^{2}{\it\rho}_{f})/{\it\mu}$ and $St=(\dot{{\it\gamma}}L^{2}{\it\rho}_{p})/{\it\mu}$ are the Reynolds and Stokes numbers, which, respectively, measure the importance of fluid inertial forces and particle inertia in relation to viscous forces at the particle scale. Here, $L$ is the semimajor axis of the spheroid, ${\it\rho}_{p}$ and ${\it\rho}_{f}$ are the particle and fluid densities, $\dot{{\it\gamma}}$ is the ambient shear rate, and ${\it\mu}$ is the suspending fluid viscosity. A reciprocal theorem formulation is used to obtain the contributions to the drift due to particle and fluid inertia, the latter in terms of a volume integral over the entire fluid domain. The resulting drifts in orientation at $O(Re)$ and $O(St)$ are evaluated, as a function of the particle aspect ratio, for both prolate and oblate spheroids using a vector spheroidal harmonics formalism. It is found that particle inertia, at $O(St)$, causes a prolate spheroid to drift towards an eventual tumbling motion in the flow–gradient plane. Oblate spheroids, on account of the $O(St)$ drift, move in the opposite direction, approaching a steady spinning motion about the ambient vorticity axis. The period of rotation in the spinning mode must remain unaltered to all orders in $St$. For the tumbling mode, the period remains unaltered at $O(St)$. At $O(St^{2})$, however, particle inertia speeds up the rotation of prolate spheroids. The $O(Re)$ drift due to fluid inertia drives a prolate spheroid towards a tumbling motion in the flow–gradient plane for all initial orientations and for all aspect ratios. Interestingly, for oblate spheroids, there is a bifurcation in the orientation dynamics at a critical aspect ratio of approximately 0.14. Oblate spheroids with aspect ratios greater than this critical value drift in a direction opposite to that for prolate spheroids, and eventually approach a spinning motion about the ambient vorticity axis starting from any initial orientation. For smaller aspect ratios, a pair of non-trivial repelling orbits emerge from the flow–gradient plane, and divide the unit sphere into distinct basins of orientations that asymptote to the tumbling and spinning modes. With further decrease in the aspect ratio, these repellers move away from the flow–gradient plane, eventually coalescing onto an arc of the great circle in which the gradient–vorticity plane intersects the unit sphere, in the limit of a vanishing aspect ratio. Thus, sufficiently thin oblate spheroids, similar to prolate spheroids, drift towards an eventual tumbling motion irrespective of their initial orientation. The drifts at $O(St)$ and at $O(Re)$ are combined to obtain the drift for a neutrally buoyant spheroid. The particle inertia contribution remains much smaller than the fluid inertia contribution for most aspect ratios and density ratios of order unity. As a result, the critical aspect ratio for the bifurcation in the orientation dynamics of neutrally buoyant oblate spheroids changes only slightly from its value based only on fluid inertia. The existence of Jeffery orbits implies a rheological indeterminacy, and the dependence of the suspension shear viscosity on initial conditions. For prolate spheroids and oblate spheroids of aspect ratio greater than 0.14, inclusion of inertia resolves the indeterminacy. Remarkably, the existence of the above bifurcation implies that, for a dilute suspension of oblate spheroids with aspect ratios smaller than 0.14, weak stochastic fluctuations (residual Brownian motion being analysed here as an example) play a crucial role in obtaining a shear viscosity independent of the initial orientation distribution. The inclusion of Brownian motion leads to a new smaller critical aspect ratio of approximately 0.013. For sufficiently large $Re\,Pe_{r}$, the peak in the steady-state orientation distribution shifts rapidly from the spinning- to the tumbling-mode location as the spheroid aspect ratio decreases below this critical value; here, $Pe_{r}=\dot{{\it\gamma}}/D_{r}$, with $D_{r}$ being the Brownian rotary diffusivity, so that $Re\,Pe_{r}$ measures the relative importance of inertial drift and Brownian rotary diffusion. The shear viscosity, plotted as a function of $Re\,Pe_{r}$, exhibits a sharp transition from a shear-thickening to a shear-thinning behaviour, as the oblate spheroid aspect ratio decreases below 0.013. Our results are compared in detail to earlier analytical work for limiting cases involving either nearly spherical particles or slender fibres with weak inertia, and to the results of recent numerical simulations at larger values of $Re$ and $St$.
36
Petersen, Alec J., Lucia Baker e Filippo Coletti. "Experimental study of inertial particles clustering and settling in homogeneous turbulence". Journal of Fluid Mechanics 864 (14 febbraio 2019): 925–70. http://dx.doi.org/10.1017/jfm.2019.31.
Abstract (sommario):
We study experimentally the spatial distribution, settling and interaction of sub-Kolmogorov inertial particles with homogeneous turbulence. Utilizing a zero-mean-flow air turbulence chamber, we drop size-selected solid particles and study their dynamics with particle imaging and tracking velocimetry at multiple resolutions. The carrier flow is simultaneously measured by particle image velocimetry of suspended tracers, allowing the characterization of the interplay between both the dispersed and continuous phases. The turbulence Reynolds number based on the Taylor microscale ranges from $Re_{\unicode[STIX]{x1D706}}\approx 200{-}500$, while the particle Stokes number based on the Kolmogorov scale varies between $St_{\unicode[STIX]{x1D702}}=O(1)$ and $O(10)$. Clustering is confirmed to be most intense for $St_{\unicode[STIX]{x1D702}}\approx 1$, but it extends over larger scales for heavier particles. Individual clusters form a hierarchy of self-similar, fractal-like objects, preferentially aligned with gravity and with sizes that can reach the integral scale of the turbulence. Remarkably, the settling velocity of $St_{\unicode[STIX]{x1D702}}\approx 1$ particles can be several times larger than the still-air terminal velocity, and the clusters can fall even faster. This is caused by downward fluid fluctuations preferentially sweeping the particles, and we propose that this mechanism is influenced by both large and small scales of the turbulence. The particle–fluid slip velocities show large variance, and both the instantaneous particle Reynolds number and drag coefficient can greatly differ from their nominal values. Finally, for sufficient loadings, the particles generally augment the small-scale fluid velocity fluctuations, which however may account for a limited fraction of the turbulent kinetic energy.
37
Pedrol, Eric, Jaume Massons, Francesc Díaz e Magdalena Aguiló. "Two-Way Coupling Fluid-Structure Interaction (FSI) Approach to Inertial Focusing Dynamics under Dean Flow Patterns in Asymmetric Serpentines". Fluids 3, n. 3 (31 agosto 2018): 62. http://dx.doi.org/10.3390/fluids3030062.
Abstract (sommario):
The dynamics of a spherical particle in an asymmetric serpentine is studied by finite element method (FEM) simulations in a physically unconstrained system. The two-way coupled time dependent solutions illustrate the path of the particle along a curve where a secondary flow (Dean flow) has developed. The simulated conditions were adjusted to match those of an experiment for which particles were focused under inertial focusing conditions in a microfluidic device. The obtained rotational modes inferred the influence of the local flow around the particle. We propose a new approach to find the decoupled secondary flow contribution employing a quasi-Stokes flow.
38
Ha, Kyung, Brendan Harding, Andrea L. Bertozzi e Yvonne M. Stokes. "Dynamics of Small Particle Inertial Migration in Curved Square Ducts". SIAM Journal on Applied Dynamical Systems 21, n. 1 (marzo 2022): 714–34. http://dx.doi.org/10.1137/21m1430935.
39
Obligado, M., C. Baudet, Y. Gagne e M. Bourgoin. "Constrained dynamics of an inertial particle in a turbulent flow". Journal of Physics: Conference Series 318, n. 5 (22 dicembre 2011): 052016. http://dx.doi.org/10.1088/1742-6596/318/5/052016.
40
Sardina, G., P. Schlatter, F. Picano, C. M. Casciola, L. Brandt e D. S. Henningson. "Self-similar transport of inertial particles in a turbulent boundary layer". Journal of Fluid Mechanics 706 (13 luglio 2012): 584–96. http://dx.doi.org/10.1017/jfm.2012.290.
Abstract (sommario):
AbstractResults are presented from a direct numerical simulation of a particle-laden spatially developing turbulent boundary layer up to ${\mathit{Re}}_{\theta } = 2500$. The peculiar feature of a boundary-layer flow seeded with heavy particles is the variation of the local dimensionless parameters defining the fluid–particle interactions along the streamwise direction. Two different Stokes numbers can be defined, one using inner flow units and the other with outer units. Since these two Stokes numbers exhibit different decay rates in the streamwise direction, we find a decoupled particle dynamics between the inner and the outer region of the boundary layer. Preferential near-wall particle accumulation is similar to that observed in turbulent channel flow, while different behaviour characterizes the outer region. Here the concentration and the streamwise velocity profiles are found to be self-similar and to depend only on the local value of the outer Stokes number and the rescaled wall-normal distance. These new results are powerful in view of engineering and environmental applications and corresponding flow modelling.
41
Laín, Santiago, Daniel Ortíz, Jesús Antonio Ramirez e Carlos Alberto Duque. "Analysis and Discussion of Two-Way Coupling Effects in Particle-Laden Turbulent Channel Flow". Ingeniería e Investigación 43, n. 1 (1 novembre 2022): e87275. http://dx.doi.org/10.15446/ing.investig.87275.
Abstract (sommario):
This paper studies the turbulence modification caused by the presence of solid particles in fully developed channel flow by means of the point particle Direct Numerical Simulations (DNS) approach. Inertial particles much smaller than the smallest vortical flow structures are considered, maintaining a volume fraction of the order , where inter-particle collisions are rare and have nearly no influence on flow development. To avoid concurrent effects that could mask the analysis of fluid turbulence interaction, gravity is not included in the study, and particle-smooth wall collisions are modelled as ideal reflections. The alteration of fluid turbulence dynamics by the particles is illustrated and discussed, providing an overview of the fluid-particle interaction phenomena occurring at both microscopic and macroscopic flow levels. Finally, the relation of such phenomena with drag-reducing effects by particles is demonstrated.
42
Yu, Liming, Na Li, Jun Long, Xiaogang Liu e Qiliang Yang. "The mechanism of emitter clogging analyzed by CFD–DEM simulation and PTV experiment". Advances in Mechanical Engineering 10, n. 1 (gennaio 2018): 168781401774302. http://dx.doi.org/10.1177/1687814017743025.
Abstract (sommario):
Small but complicated labyrinth channel emitters are easily clogged. In this study, computational fluid dynamics–discrete element method coupling approach was employed to investigate the mechanism of emitter clogging caused by particles in size of 65, 100, and 150 µm. Computational fluid dynamics used Navier–Stokes equation to analyze flow characteristics of continuous phase. Discrete element method used Newton’s laws of motion to measure single particle motion and group distribution of disperse phase. Particle tracking velocimetry was also utilized to follow the trajectories and velocity of single particle. Our results indicated that the smaller the particle size, the less the total force. Tiny sands were mainly influenced by drag forces. The amplitude between tooth tips was small. Particles moved basically in the main stream with fast velocity and short travel distance, thereby having good following performance. It took shorter time to reach micro-dynamic balance. Meanwhile, the amount of sediments in the labyrinth channel was less. Particles in size of 150 µm were mainly affected by inertial forces. They can easily enter vortex areas. Sands staying longer than 0.1 s in the labyrinth channel accounted for 37.9% of total number. Sand groups were mainly distributed at the inlet of labyrinth channel. The more sands trapped in vortex areas, the easier it was to precipitate and cause emitter clogging.
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Gangadhar, Anirudh, e Siva A. Vanapalli. "Inertial focusing of particles and cells in the microfluidic labyrinth device: Role of sharp turns". Biomicrofluidics 16, n. 4 (luglio 2022): 044114. http://dx.doi.org/10.1063/5.0101582.
Abstract (sommario):
Inertial, size-based focusing was investigated in the microfluidic labyrinth device consisting of several U-shaped turns along with circular loops. Turns are associated with tight curvature and, therefore, induce strong Dean forces for separating particles; however, systematic studies exploring this possibility do not exist. We characterized the focusing dynamics of different-sized rigid particles, cancer cells, and white blood cells over a range of fluid Reynolds numbers [Formula: see text]. Streak widths of the focused particle streams at all the turns showed intermittent fluctuations that were substantial for smaller particles and at higher [Formula: see text]. In contrast, cell streaks were less prone to fluctuations. Computational fluid dynamics simulations revealed the existence of strong turn-induced Dean vortices, which help explain the intermittent fluctuations seen in particle focusing. Next, we developed a measure of pairwise separability to evaluate the quality of separation between focused streams of two different particle sizes. Using this, we assessed the impact of a single sharp turn on separation. In general, the separability was found to vary significantly as particles traversed the tight-curvature U-turn. Comparing the separability at the entry and exit sections, we found that turns either improved or reduced separation between different-sized particles depending on [Formula: see text]. Finally, we evaluated the separability at the downstream expansion section to quantify the performance of the labyrinth device in terms of achieving size-based enrichment of particles and cells. Overall, our results show that turns are better for cell focusing and separation given that they are more immune to curvature-driven fluctuations in comparison to rigid particles.
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Xiang, Nan, Zhiguo Shi, Wenlai Tang, Di Huang, Xinjie Zhang e Zhonghua Ni. "Improved understanding of particle migration modes in spiral inertial microfluidic devices". RSC Advances 5, n. 94 (2015): 77264–73. http://dx.doi.org/10.1039/c5ra13292d.
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Angilella, Jean-Régis, Rafael D. Vilela e Adilson E. Motter. "Inertial particle trapping in an open vortical flow". Journal of Fluid Mechanics 744 (11 marzo 2014): 183–216. http://dx.doi.org/10.1017/jfm.2014.38.
Abstract (sommario):
AbstractRecent numerical results on advection dynamics have shown that particles denser than the fluid can remain trapped indefinitely in a bounded region of an open fluid flow. Here, we investigate this counterintuitive phenomenon both numerically and analytically to establish the conditions under which the underlying particle-trapping attractors can form. We focus on a two-dimensional open flow composed of a pair of vortices and its specular image, which is a system we represent as a vortex pair plus a wall along the symmetry line. Considering particles that are much denser than the fluid, referred to as heavy particles, we show that two attractors form in the neighbourhood of the vortex pair provided that the particle Stokes number is smaller than a critical value of order unity. In the absence of the wall, the attractors are fixed points in the frame rotating with the vortex pair, and the boundaries of their basins of attraction are smooth. When the wall is present, the point attractors describe counter-rotating ellipses in this frame, with a period equal to half the period of one isolated vortex pair. The basin boundaries remain smooth if the distance from the vortex pair to the wall is large. However, these boundaries are shown to become fractal if the distance to the wall is smaller than a critical distance that scales with the inverse square root of the Stokes number. This transformation is related to the breakdown of a separatrix that gives rise to a heteroclinic tangle close to the vortices, which we describe using a Melnikov function. For an even smaller distance to the wall, we demonstrate that a second separatrix breaks down and a new heteroclinic tangle forms farther away from the vortices, at the boundary between the open and closed streamlines. Particles released in the open part of the flow can approach the attractors and be trapped permanently provided that they cross the two separatrices, which can occur under the effect of flow unsteadiness. Furthermore, the trapping of heavy particles from the open flow is shown to be robust to the presence of viscosity, noise and gravity. Navier–Stokes simulations for large flow Reynolds numbers show that viscosity does not destroy the attracting points until vortex merging takes place, while simulation of thermal noise shows that particle trapping persists for extended periods provided that the Péclet number is large. The presence of a gravitational field does not alter the permanent trapping by the attracting points if the settling velocities are not too large. For larger settling velocities, however, gravity can also give rise to a limit-cycle attractor next to the external separatrix and to a new form of trapping from the open flow that is not mediated by a heteroclinic tangle.
46
Cui, Zhiwen, Huancong Liu, Jingran Qiu e Lihao Zhao. "Effect of slip-induced fluid inertial torque on the angular dynamics of spheroids in a linear shear flow". Physics of Fluids 36, n. 3 (1 marzo 2024). http://dx.doi.org/10.1063/5.0197006.
Abstract (sommario):
The angular dynamics of tiny spheroidal particles in shear flows have been widely investigated, but most of the studies mainly focus on the effect of strong shear, while the combined effect of both shear and slip velocity at the center of the particle has been less considered. Actually, the fluid inertial torque induced by the slip velocity between particle and fluid plays a significant role in spheroid angular dynamics. However, it is difficult to investigate these dynamics theoretically until the analytical expression of the fluid inertial torque at a small Reynolds number was derived by Dabade et al. [J. Fluid Mech. 778, 133–188 (2015)]. In this study, the effect of the fluid inertial torque on the particle rotations is considered in a linear shear flow with a small streamwise slip velocity at the center of the particle. We find that as the fluid inertial torque dominates, the prolate spheroids tend to logroll while oblate ones have a tendency to tumble or align to a direction with a relative angle to the streamwise direction. These results are opposite to the earlier results in the absence of the fluid inertial torque. Different ultimate rotation modes of spheroids are dependent on the relative importance between the fluid inertial torque and the particle inertia, as well as the initial orientations. This reflects a non-trivial effect of fluid inertial torque on the angular dynamics of inertial spheroidal particles.
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Sprenger, Alexander R., Lorenzo Caprini, Hartmut Lowen e René Wittmann. "Dynamics of active particles with translational and rotational inertia". Journal of Physics: Condensed Matter, 14 aprile 2023. http://dx.doi.org/10.1088/1361-648x/accd36.
Abstract (sommario):
Abstract Inertial effects affecting both the translational and rotational dynamics are inherent to a broad range of active systems at the macroscopic scale. Thus, there is a pivotal need for proper models in the framework of active matter to correctly reproduce experimental results, hopefully achieving theoretical insights. For this purpose, we propose an inertial version of the active Ornstein-Uhlenbeck particle (AOUP) model accounting for particle mass (translational inertia) as well as its moment of inertia (rotational inertia) and derive the full expression for its steady-state properties. The inertial AOUP dynamics introduced in this paper is designed to capture the basic features of the well-established inertial active Brownian particle (ABP) model, i.e., the persistence time of the active motion and the long-time diffusion coefficient. For a small or moderate rotational inertia, these two models predict similar dynamics at all timescales and, in general, our inertial AOUP model consistently yields the same trend upon changing the moment of inertia for various dynamical correlation functions.
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Magnani, Marta, Stefano Musacchio e Guido Boffetta. "Inertial effects in dusty Rayleigh–Taylor turbulence". Journal of Fluid Mechanics 926 (7 settembre 2021). http://dx.doi.org/10.1017/jfm.2021.713.
Abstract (sommario):
We investigate the dynamics of a dilute suspension of small, heavy particles superposed on a reservoir of still, pure fluid. The study is performed by means of numerical simulations of the Saffman model for a dilute particle suspension (Saffman, J. Fluid Mech., vol. 13, issue 1, 1962, pp. 120–128). In the presence of gravity forces, the interface between the two phases is unstable and evolves in a turbulent mixing layer which broadens in time. In the case of negligible particle inertia, the particle-laden phase behaves as a denser fluid, and the dynamics of the system recovers to that of the incompressible Rayleigh–Taylor set-up. Conversely, particles with large inertia affect the evolution of turbulent flow, delaying the development of turbulent mixing and breaking the up–down symmetry within the mixing layer. The inertial dynamics also leads to particle clustering, characterised by regions with higher particle density than the initial uniform density, and by the increase of the local Atwood number.
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Chen, Dongming, Wenjun Yuan e Xiangdong Han. "Dynamics and dispersion of inertial particles in circular cylinder wake flows: A two-way coupled Eulerian–Lagrangian approach". Modern Physics Letters B, 30 novembre 2023. http://dx.doi.org/10.1142/s0217984924501239.
Abstract (sommario):
In this paper, the motion of inertial particles in three-dimensional (3D) unsteady cylindrical wake flow is investigated by a two-way coupled Eulerian–Lagrangian approach. At different flow Reynolds numbers (Re), the corresponding striking dynamic property and dispersion mechanism of four particle classes have been studied, with inertia parameterized by means of Stokes number (Sk). It is found that inertial particles with lower Stokes number are expelled from vortex cores, and coherent voids encompass the local Kármán vortex cells. As Stokes number increases, a low velocity particle channel could be formed, which almost coincides with the results in the literature. Moreover, with the increase of Reynolds number, numerous irregular coherent voids are observed in the cylinder wake, and the high-speed particles follow the fluid flow closely when they are contained in the vortices. Although the centrifugal force of Kármán vortex cells significantly affects the dynamics of inertial particles, the fluid flow modulation is believed to be responsible for the distinctive particle dispersion patterns in the vortex streets. For particles with medium inertia, the two-way coupled modulation weakens the centrifugal effect of vortex structures on the particles. This trend declines with the increase of Reynolds number, and vanishes with light particles, while both two-way coupled modulation and the centrifugal effect of vortex structures are almost equally effective with heavy particles. The investigations contribute to a better understanding of the particle-laden flows in practical applications, which will benefit the optimized design of certain machinery and equipment for the industry.
50
Cui, Zhiwen, Jingran Qiu, Xinyu Jiang e Lihao Zhao. "Effect of fluid inertial torque on the rotational and orientational dynamics of tiny spheroidal particles in turbulent channel flow". Journal of Fluid Mechanics 977 (14 dicembre 2023). http://dx.doi.org/10.1017/jfm.2023.942.
Abstract (sommario):
Rotation and orientation of non-spherical particles in a fluid flow depend on the hydrodynamic torque they experience. However, little is known about the effect of the fluid inertial torque on the dynamics of tiny inertial spheroids in turbulent channel flows, as only Jeffery torque has been considered in previous studies by point-particle direct numerical simulations. In this study, we investigate the rotation and orientation of tiny spheroids with both fluid inertial torque and Jeffery torque in a turbulent channel flow. By comparing with the case in the absence of fluid inertial torque, we find that the rotational and orientational dynamics of spheroids is significantly affected by the fluid inertial torque when the Stokes number, which is non-dimensionalized by fluid viscous time scale, is larger than the critical value $St_c\approx 2$ , indicating that the fluid inertial torque is non-negligible for most particle cases considered in earlier studies. In contrast to the earlier findings considering only Jeffery torque (Challabotla et al., J. Fluid Mech., vol. 776, 2015, p. R2), we find that prolate (oblate) spheroids with a large Stokes number tend to tumble (spin) in the streamwise–wall-normal plane in a thinner region near the wall due to the presence of the fluid inertial torque. Approaching the channel centre, the flow shear gradually vanishes, but the velocity difference between local fluid and particles is still pronounced and increasing as particle inertia grows. As a result, in the core region, fluid inertial torque is dominant and drives the particles to align with its broad side normal to the streamwise direction rather than a random orientation observed in earlier studies without fluid inertial torque. Meanwhile, the presence of fluid inertial torque enhances the tumbling rates of spheroids in the core region. In addition, the effect of fluid inertial force on the dynamics of spheroids is also examined in this study, but the results indicate the effect of fluid inertial force is weak. Our findings imply the importance of fluid inertial torque in modelling the dynamics of inertial non-spherical particles in turbulent channel flows.