Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session J36: Particle-Turbulence Interactions II |
Hide Abstracts |
Chair: Martin Erinin, Princeton University; Amirfarhang Mehdizadeh, University of Missouri-Kansas City Room: 244 |
Sunday, November 20, 2022 4:35PM - 4:48PM |
J36.00001: The origin of particle streaks in high-Re turbulent boundary layers Tim Berk, Filippo Coletti Recent changes in climate have led to more extreme wind events, drier soils, and exposed lake beds. Across the Western United States, this has caused increasing amounts of dust in cities such as Phoenix and Salt Lake City. The majority of this dust is not transported in large-scale dust storms, but rather in continuous small-scale dust events. Dust transport in these events is driven by fluctuations rather than bulk transport. One fluctuating feature are the streak-like structures the dust forms above the ground. In order to better predict transport rates, in-depth understanding of the origins and dynamics of these streaks is necessary. Here we perform two-phase measurements of microscopic inertial particles in high-Re turbulent boundary layers. Particles are injected in the boundary layer in the one-way coupled regime. Flow field measurements (PIV) and tracking of inertial particles (PTV) are performed simultaneously. This enables comparison of particle streaks to underlying streaks in the flow. This shows how particle streaks are created and how the flow structures that they sample influence their dynamics. |
Sunday, November 20, 2022 4:48PM - 5:01PM |
J36.00002: Direct Numerical Simulations of Small Particles in Wall-Bounded Turbulence Ryan Kelly, David Goldstein, Robert A Handler, Saikishan Suryanarayanan Wall-bounded turbulence is characterized by hairpin-like structures near the wall. These structures are known to increase skin friction drag, so one method of drag reduction is to disrupt these structures using, for example, polymer additives or microbubbles. The current study seeks to find out how very small particles (on the order of the Kolmogorov scale) which release polymer behave near these structures to determine if there is an optimal particle one can design to target them. We have performed direct numerical simulations of various particles in a turbulent channel flow to better understand their clustering properties. The flow is simulated using a pseudo-spectral solver, and the particles are modeled as massless point particles using modified Maxey-Riley equations. The flow is driven by a constant pressure gradient with no gravity in order to figure out if certain particles are preferentially drawn to hairpin vortices found in turbulent wall-bounded flows. Hairpin vortex locations—identified by the λ-2 criterion—are correlated with particle locations to show the capturing capabilities by these structures. |
Sunday, November 20, 2022 5:01PM - 5:14PM Not Participating |
J36.00003: The effects of particle stokes number on particle dynamics in a linear cascade Cairen J Miranda, John Palmore Gas turbine engines are highly susceptible to damage caused by particles as they enter the engine and impact the compressor blades. Analyzing particle trajectories within a compressor is important to prevent damage to the components. A simpler solution to extracting data from experimental turbomachinery is to create a linear cascade of airfoils to analyze the flow physics. This study uses different turbulence modeling techniques to predict the particle trajectories in a linear cascade. RANS turbulence models and LES turbulence models are used to determine a quantitative analysis of particle trajectories, impact locations and erosion. The Stokes Number (St) is used to characterize the importance of particle size. Smaller St particles act as tracers and follow the flow streamlines while the large St particles are more ballistic in nature. St≈1 are light enough to be affected by the flow, but also large enough that it does not act as a tracer. Particles with different St are tested to observe the dependence of particle diameter on the impact locations, the erosion occurring, as well as the energy lost on impact. Particles are tested with the coefficient of restitution set to 0 and 1 to mimic particle sticking to and rebound off compressor blades, respectively. |
Sunday, November 20, 2022 5:14PM - 5:27PM |
J36.00004: On the Closure of Diffusion Current in the PDF Kinetic Equation for the Separations and Relative Velocities of High-Inertia Particle Pairs Sarma L Rani, Rohit Dhariwal Relative motion of inertial, monodisperse particle pairs in stationary isotropic turbulence is investigated by evolving the Langevin stochastic differential equations governing pair relative velocities and separations in the limit of Stokes number $\gg 1$. The stochastic force in the Langevin equations is evaluated from the relative-velocity-space diffusivity that is equal to $1/\tau_v^2$ multiplied by the time integral of the Eulerian two-time correlation of fluid velocity differences seen by particle pairs that are nearly stationary ($\tau_v$ is the particle viscous relaxation time). The Eulerian two-time correlation of fluid velocity differences is computed using direct numerical simulation (DNS) of isotropic turbulence seeded with fixed particles. Since numerical forcing of energy-containing eddies is employed to achieve stationarity in DNS, the impact of forcing scheme on the two-time correlation is quantified as a function of separation $r$ and Taylor micro-scale Reynolds number $Re_\lambda$. As the DNS-computed correlation is needed to compute the stochastic force in Langevin simulations (LS), a key objective is to quantify the effects of forcing scheme on the LS predictions of pair relative motion. |
Sunday, November 20, 2022 5:27PM - 5:40PM |
J36.00005: Simultaneous measurements of fiber-turbulence coupling past a backward-facing step Claudia Esposito, Francisco Alves Pereira Anisotropic particles suspended in turbulent flow may show preferential concentration and alignment. In turn, their orientation and motion prompt forces and torques that alter the morphology and intensity of the turbulence. To explore the impact of particles' inertia and concentration on such particles-turbulence interplay, we studied the case of fiber-inseminated flow past a backward-facing step, whose produced turbulence in the unladen case is a classical paradigm for turbulent flows. Experiments have been conducted in a channel with Reynolds numbers ranging between 10000 and 16000. Low and high Stokes number cases are compared using two sets of fibers with different lengths and diameters. Tests were repeated for fibers' volume fraction from 10-6 to 10-4. For each dataset, simultaneous Digital Holography (DH) and PIV measurements could resolve the 3D fibers orientation dynamics and tumbling and characterize the flow field. Special attention is given to implementing DH and understanding its limits when increasing the fibers' concentration. Finally, we performed the modal analysis of the PIV images. By correlating the most energetic particle and flow structures for the different cases, we obtained a more thorough picture of how fibers modulate the turbulent flow morphology. |
Sunday, November 20, 2022 5:40PM - 5:53PM |
J36.00006: Experimental Investigation of Turbulent Effect on Settling Velocity of Inertial Particles Seungjun Baek, Yong Sung Park Experiments were conducted to investigate the effect of turbulence on the settling velocity increase. First, the settling velocity of particles and the ambient turbulence in the open-channel flow were measured. Second, to identify the influence of advection caused by mean vertical velocity on the settling velocity, experiments using Vertical Recirculating Tube (VeRT) were conducted. In both experiments, the velocity of inertial particles was measured using PTV methods, and turbulence was measured using PIV and LDA. For the last experiment, the settling behavior of inertial particles in turbulent flow was numerically simulated based on the equation of motion for a particle in a fluid flow. The experimental results showed that the settling velocity of particles was faster in turbulent flow than in stagnant water, consistent with the previous studies, and its increase rate depends on the Stokes number, St, which is the ratio of particle relaxation time, τp, to Kolmogorov time scale, τk. These results may help understand the settling behavior of particles in a natural flow and improve the performance of existing particle tracking models, in which the vertical displacement of a particle was predicted based on the settling velocity in stagnant water. |
Sunday, November 20, 2022 5:53PM - 6:06PM |
J36.00007: Settling velocity of inertial particles in turbulent flows with different characteristics Amelie Ferran, Martin Obligado, Alberto Aliseda Inertial particles are ubiquitous in both environmental and industrial flows. This study focuses on sub-Kolmogorov inertial particles advected in a turbulent air flow. Phase Doppler Particle Analyzer measurements of inertial droplets were taken in homogeneous isotropic turbulence with a wide range of Taylor microscale Reynolds numbers and integral length scales. The study explores a wide range of flow Reynolds number, Rouse number and volume fractions. Three types of isotropic and homogeneous turbulence were tested by means of a passive grid and an active grid used in two different configurations. The settling velocity of the inertial particles were also investigated in a turbulent/ non-turbulent interface. The use of different grid allows us to create turbulent flow with similar Reynolds number and turbulent intensity but significantly different integral length scale. |
Sunday, November 20, 2022 6:06PM - 6:19PM |
J36.00008: Influence of inertial particles on the evolution of scalar flow fields in a high-Sc turbulent jet Krishna kompally, Gokul Pathikonda Experiments of a particle-laden turbulent axisymmetric jet were performed in water to understand the influence of inertial particles on the concentration fields in a high Schmidt number, Sc, mixing environment. Experimental measurements were made using particle-image velocimetry (PIV) and high-resolution planar-LIF (pLIF) to obtain velocity and mixture fraction fields of a passive scalar. Highly inertial Tungsten Carbide Microspheres (SG = 9.5) of nominal diameter of 200μm dispersed in water were injected with a mass loading in the range of 1-5%. The presence of particles causes two-way coupled interactions between the two phases i.e., additional momentum flux from the inertial particles to the flow field at small scales. Changes to the macroscopic jet behavior due to the presence of particles, and statistical descriptions of the particle distribution, slip velocity and particle-Reynolds number, Rep are presented for jet Reynolds numbers, Rej up to 10000 in the self-similar regime. Conditional fields of turbulent kinetic energy and the scalar variance in the neighborhood of particles are discussed to highlight the influence of particle-induced local perturbations on the scalar dissipation. |
Sunday, November 20, 2022 6:19PM - 6:32PM |
J36.00009: Measurement of snow settling dynamics using 3D particle tracking velocimetry Jiaqi Li, Nathaniel Bristow, Peter W Hartford, Michele Guala, Jiarong Hong Understanding the dynamics of snow settling is important for improving our ability to predict ground snow accumulation, snow water equivalent, and surface thermal properties in a number of applications. Following our previous work using planar particle tracking velocimetry (PTV) to quantify snow settling dynamics in atmospheric surface layer (Nemes et al. JFM, 2017; Li et al., JFM, 2021), we present a further investigation of the problem with large-scale field 3D PTV system composed of four WiFi-synchronized cameras using drone-based calibration approach. The field deployment was conducted on April 17th, 2022 at the field research station to capture 3D snow settling motions in a sampling volume of 4 m x 4 m x 6 m with 6.4 mm and 200 Hz spatial and temporal resolution, respectively. Our study provides a detailed geometric characterization of snow settling trajectories and reveals the highly variable and meandering trajectories of snow particles even under a low level of turbulence. The acceleration of individual snowflake yields a strong correlation with the curvature of particle trajectory and its statistics shows a strong anisotropic behavior under the influence of turbulence and snow particle morphology. Our Voronoi analysis shows evidence of 3D clustering of snow particles. |
Sunday, November 20, 2022 6:32PM - 6:45PM |
J36.00010: A novel LES modeling approach for turbulence modulation in particle-laden flows without particles Naveen Rohilla, PARTHA S GOSWAMI In the present work, first, we have performed direct numerical simulations to capture the fluid phase in the Eulerian framework, and the particles are tracked with the Lagrangian approach. The simulations are performed for bulk Reynolds numbers for 3300 and 5600 for a vertical channel flow. The intensity of fluid fluctuations decreases steadily up to a volume fraction, after which a sudden collapse in the fluid fluctuations is observed. An increase in the anisotropy across the fluid fluctuations is observed with an increase in particle volume loading. The local isotropy of small scales and large scales is analyzed across the channel width. It is observed that local isotropy decreases in the near-wall and channel center region with mass loading, which affects the Kolmogorov constant. The Kolmogorov constant is explored via compensated spectra and second-order velocity structure function for particle-laden cases. It is found that the Kolmogorov constant decreases in the near-wall and channel center region, which depicts the particle feedback effect on the fluid phase. From the assumption of local equilibrium, the eddy viscosity in the Smagorinsky model includes the Kolmogorov constant via Smagorinksy coefficient. A decrease in the Kolmogorov constant results in an increase in the Smagorinksy coefficient. Thus, the simulations are performed with the Smagorinksy model with an increase in the Smagorinsky coefficient to predict the turbulence attenuation without considering the particle phase. The simulations capture the decrease in Reynolds stress, wall-normal and spanwise fluctuations, and the sudden collapse in fluid fluctuations similar to the particle-laden cases. Therefore, the present work demonstrates that a priori knowledge of the variation of eddy viscosity may predict the fluid phase dynamics without considering the particle phase simultaneously. |
Sunday, November 20, 2022 6:45PM - 6:58PM |
J36.00011: Preferential transport of swimmers in heterogeneous two-dimensional turbulent flow Xinyu Si, Lei Fang We investigate the performance of active swimmers in a strongly heterogeneous two-dimensional weakly turbulent flow. The flow is heterogeneous in Reynolds number along one direction. Using a hybrid experimental-numerical model, we demonstrate that there are three regimes of preferential transport for rod-like swimmers as the swimmers' intrinsic speed increases. Using Lagrangian statistics along swimmers' trajectories, we reveal that the three regimes are due to the relative strengths of three different effects: the intrinsic speed of the swimmers, the re-orientation ability of the shear layer at the interface of two flow regions, and the attracting Lagrangian Coherent Structures (LCSs) of the flow field. Our results elucidate the mechanism of preferential transport for swimmers in heterogeneous flow. We hope to raise researchers' attention to the dynamics of swimmers in strongly heterogeneous flow environments. |
Sunday, November 20, 2022 6:58PM - 7:11PM |
J36.00012: Lagrangian Stochastic SGS Model Applied to LES of Evolving Firebrand Transports Iago Dal-Ri dos Santos, Neda Yaghoobian The transport and deposition of smoldering particles, known as firebrands, is an important fire spread mechanism in wildland fires. These particles can be transported by the wind over large distances and can ignite secondary fires upon landing. The transport of firebrands by the wind is a complex, multiscale process, which is largely controlled by interactions between the firebrand particles and the atmospheric wind flow. Such complexities require the use of Large Eddy Simulation (LES) models to account for the temporal evolution of turbulence over large scales of space and time. However, filtering of subgrid-scale (SGS) turbulence in LES hinders the accuracy of particle transport models. In this work, we employ a SGS stochastic model into an LES framework and develop a model to account for and investigate the effects of small-scale (~ O(particles)) turbulence on the transport of mass- and size-changing firebrand particles. This approach will improve the accuracy of firebrand behavior modeling and spot fire prediction. |
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. |
© 2024 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
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700