Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session P37: Particle Laden Flows: Turbulence Modulation |
Hide Abstracts |
Chair: Toshiyuki Gotoh, Nagoya Institute of Technology Room: 619 |
Monday, November 25, 2019 5:16PM - 5:29PM |
P37.00001: A new timescale for turbulence modulation by particles Izumi Saito, Takeshi Watanabe, Toshiyuki Gotoh A new timescale for turbulence modulation by particles is introduced. This timescale is inversely proportional to the number density and the radius of particles and can be regarded as a counterpart of the phase relaxation time, an important timescale in cloud physics, which characterizes the interaction between turbulence and cloud droplets by condensation-evaporation. Scaling analysis and direct numerical simulations of dilute inertial particles in homogeneous isotropic turbulence suggest that turbulence modulation by particles can be expressed as a function of the mass-loading parameter and the Damkohler number, which is defined as the ratio of the turbulence large-eddy turnover time to the new timescale. [Preview Abstract] |
Monday, November 25, 2019 5:29PM - 5:42PM |
P37.00002: Particle shape and orientation impact on the modulation of isotropic turbulence by Kolmogorov-scale size particles Lennart Schneiders, Konstantin FrÃ¶hlich, Wolfgang SchrÃ¶der The modulation of decaying isotropic turbulence by non-spherical particles of Kolmogorov-scale size is investigated via direct particle-fluid simulations. A Cartesian cut-cell method with dynamic mesh refinement and dynamic load balancing is applied to explicitly resolve the stresses acting on the fluid-particle interfaces. Up to $60\,000$ ellipsoids are fully resolved, requiring $O(10^{10})$ mesh points. The decay rates of the fluid and particle kinetic energy are found to increase with the particle aspect ratio. This is due to the particle-induced dissipation rate and the direct transfer of kinetic energy, both of which can be substantially larger than for spherical particles depending on the particle orientation. The extra dissipation rate resulting from the translational and rotational particle motion is quantified using a recently derived analytical model. This generic expression describes the impact of individual inertial particles on the local energy balance independent of the particle shape and enables to quantify the share of the rotational particle motion in the kinetic energy budget. [Preview Abstract] |
Monday, November 25, 2019 5:42PM - 5:55PM |
P37.00003: Experimental Estimation of Turbulence Modification by Inertial Particles at Moderate $Re_\lambda$ Martin Obligado, Daniel Odens Mora, Alain Cartellier Several experimental and numerical studies have aimed at quantifying the impact of inertial particles on turbulent kinetic energy, and turbulent kinetic energy dissipation ($\varepsilon$) of particle-laden flows. We propose a new experimental method to estimate the carrier-flow dissipation $\varepsilon_p$ in the presence of inertial sub-kolmogorov particles at moderate $Re_\lambda$ (Mora et al. PRF, 2019). Its foundations rely on the unladen flow dissipation calculation using the Rice theorem, and the density of zero crossings $n_s$ of the longitudinal velocity fluctuation coming from a laser doppler anemometry device. We show that, under some mild assumptions, that $\varepsilon_p$ can be deduced from the value of $n_s$. Our experimental results provide strong evidence, regarding the non-negligible effect that dense sub-kolmogorov particles have on the carrier flow energy cascade at $\phi_v=\mathcal{O}(10^{-5})$, and $Re_\lambda \in [200-600]$. Our observations are consistent with previous two-way coupling DNS studies at similar concentrations. Our results may also have an impact on distinct phenomena on particle-laden flows that depend on the coupling of the particles with the flow, such as preferential concentration and settling velocity modifications. [Preview Abstract] |
Monday, November 25, 2019 5:55PM - 6:08PM |
P37.00004: Drag and turbulence modulation by particles and viscoelasticity in channel flow Amir Esteghamatian, Tamer Zaki Direct numerical simulations are performed to examine the effect of neutrally-buoyant particles on turbulence and drag in viscoelastic channel flow. Comparison is drawn between the single-phase conditions and semi-dilute suspensions of particles ($20 \%$ solid volume fraction), at various Weissenberg numbers. Viscoelastic effects are included using the FENE-P model, and an immersed-boundary method that is tailored for simulations of non-Newtonian particle-laden flows is used to impose the rigid-body motion at the surface of the particles. The results highlight a remarkable contrast in drag modulation between the single-phase and particle-laden conditions. Unlike the single-phase cases, the particle-laden flows undergo a drag enhancement with increasing viscoelasticity above a certain Weissenberg number. This effect is due to a drastic increase in polymer stresses near the surfaces of particles. Nonetheless, Reynolds stresses are effectively diminished in the particle-laden viscoelastic cases. In fact, the onset of viscoelastic drag enhancement in the particle-laden flows occurs when the Reynolds stresses are completely eradicated and the higher viscoelasticity results in increased polymer stresses. [Preview Abstract] |
Monday, November 25, 2019 6:08PM - 6:21PM |
P37.00005: Stability of a Lamb-Oseen vortex in two-way coupled particle-laden flows Shaui Shuai, M. Houssem Kasbaoui We investigate the stability of a columnar vortex tube loaded with inertial particles in Eulerian-Lagrangian simulations. The vortex tube is represented as a Lamb-Oseen vortex with a circulation-based Reynolds number equal to $\mathrm{Re}_\Gamma=50$. The particles considered have a small, yet non-zero, circulation Stokes number $\mathrm{St}=0.01$, and are dispersed at a volume fraction $10^{-3}$. We show that when the particle feed-back on the fluid is neglected, the flow is stable to all infinitesimal perturbations. However, when the two-way coupling is taken in account, a centrifugal Rayleigh-Taylor instability may develop leading to the destruction of the vortical structure. [Preview Abstract] |
Monday, November 25, 2019 6:21PM - 6:34PM |
P37.00006: Modulation of coherent structures by inertial particles in a turbulent channel flow Himanshu Dave, Mohamed Kasbaoui In this study, we explore how skin friction drag can be reduced by carefully modulating the near-wall coherent structures using inertial point particles. The particles in this study have a diameter $d_p^+=0.2$ in wall units and are smaller than the smallest turbulent eddies. Owing to the preferential concentration mechanism, these particles are able to modulate the coherent structures as they get expelled from the vortical regions and gather in the extensional regions of the flow. In doing so, these particles may remove momentum from the energetic core of hairpin vortices while damping fluctuations in the sweep and ejection regions. This mechanism is investigated in Euler-Lagrangian simulations of a two-way coupled turbulent channel flow at a friction Reynolds number $Re_\tau=180$. The particles are inertial, with a Stokes number $St^+=1$, and present at a semi-dilute concentration, i.e., such that the average volume fraction is low ($\langle \phi\rangle=2.23\; 10^{-4}$) but the mass loading is significant ($M=0.1$). We explore how particles distribute in the near-wall region, and how they modulate the turbulent structures in the fluid. [Preview Abstract] |
Monday, November 25, 2019 6:34PM - 6:47PM |
P37.00007: Influence of sand particle on the wake of circular cylinder Guohua Wang We conducted two-phase flow around a circular cylinder experiment in wind tunnel and measured air and sand particle velocities synchronously in the sand-laden flow by Particle Image Velocimetry (PIV) technique. The influence of moving sand particle (with an average diameter of \textasciitilde 159um) on the wake of the circular cylinder was investigated. The results show that the wake of the circular cylinder inclines downward in the sand-laden flow, and the inclination angle increases with the increase of sand concentration. Under the influence of sand particles, the defect of mean streamwise velocity in the wake decreases with the increase of particle volume fraction. The settling particles cause the air in the wake flow downwards where the mean vertical velocity is no longer equal to 0. The streamwise and vertical turbulence intensities in the wake are weakened, in which the streamwise turbulence intensity in the wake gradually changes from a bimodal to an unimodal distribution with the increase of particle volume fraction. [Preview Abstract] |
Monday, November 25, 2019 6:47PM - 7:00PM |
P37.00008: Scale-by-scale measurements of turbulence modification by heavy particles in homogeneous turbulence Roumaissa Hassaini, Filippo Coletti There is substantial evidence that, even at moderate concentrations, particles can significantly alter the turbulent fluctuations, but it is still debated under which conditions these will be excited or inhibited. The issue is complicated by the multiplicity of the influencing parameters, the scarcity of systematic experimental studies, and the difficulty in measuring fluid velocity in a particle-laden flow. We target this question using a facility featuring hundreds of individually controlled jets, in which homogeneous air turbulence with negligible shear and mean flow is generated and laden with microscopic solid particles. We vary the volume fraction by two orders of magnitude and use high-speed laser imaging at multiple resolutions. We combine particle tracking velocimetry (PTV) and particle image velocimetry (PIV) to simultaneously measure the position and trajectory of particles as well as the fluid velocity down to the Kolmogorov scales. We demonstrate the impact of the particles on the turbulent kinetic energy, dissipation rate, and energy spectrum, to an increasing extent with increasing volume fraction. In the considered range of parameters, gravitational settling is found to be a deciding factor as for whether turbulence is increased or reduced at different scales. [Preview Abstract] |
Monday, November 25, 2019 7:00PM - 7:13PM |
P37.00009: Turbulence collapses at a threshold particle loading in a dilute particle-gas suspension Viswanathan Kumaran, Pradeep Muramalla, Ankit Tyagi, Partha Goswami In order to examine the turbulence attenuation mechanism in a dilute particle-gas suspension, Direct Numerical Simulations (DNS) of a particle-gas suspension are carried out at a Reynolds number of about 3300 based on the average gas velocity and channel width. The particle Reynolds number based on the particle diameter and the flow velocity is about 42 and the Stokes number is in the range $9.5-377$. The particle volume fraction is in the range $0-3 \times 10^{-3}$, and the particle mass loading is in the range $0-12$. As the volume fraction is increased, a discontinuous reduction in the turbulent velocity fluctuations is observed at a critical volume fraction when the volume fraction is increased by $10^{-4}$. There is a reduction, by one order of magnitude, in the mean square fluctuating velocities in all directions, in the Reynolds stress and the turbulent energy production rate. Turbulence attenuation is due to a disruption of the turbulence production mechanism, and not due to the increased dissipation due to the particles. The turbulence collapse phenomenon is universal and is observed for different particle Reynolds numbers and for different models for the drag and lift force models, though the critical volume fraction depends on drag law and force model. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2020 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700