Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session D8: Particle-Laden Flows II: Experimental Studies |
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Chair: Franklin Shaffer, Albany Research Center Room: 330 |
Sunday, November 24, 2013 2:15PM - 2:28PM |
D8.00001: DNS of Oscillatory Boundary Layer Over a Closely Packed Layer of Sediment Particles Chaitanya D. Ghodke, Joseph Skitka, Sourabh V. Apte Fully resolved direct numerical simulations are performed using fictitious domain approach (Apte et al., JCP 2009) to investigate oscillatory turbulent flow over a rough wall corresponding to the experimental work of Keiller \& Sleath (JFM 1976) and representative of a sediment layer in coastal environments. Four particle Reynolds numbers in the range, $Re = 660-2780$ are studied for a fixed sphere size and results are compared against available experimental data. Flow is characterized in terms of coherent vortex structures, Reynolds stress variation, turbulent cross-correlations and PDF distributions. Reynolds stress is negative during the first half of the cycle as ejection and sweep events prevail and is positive during the second half where outward/inward interactions of motion are dominant. The net lift coefficient remains positive over the cycle with a period which is half of that of the forcing function and is well correlated with phase averaged velocity square ($U^2$). The pressure contribution towards the net lift force is found to be more dominant over the viscous contribution. Also the PDF distributions of velocity fluctuations show non-Gaussian behavior. These detailed findings are useful in improving the criterion for predicting sediment incipient motion. [Preview Abstract] |
Sunday, November 24, 2013 2:28PM - 2:41PM |
D8.00002: 4-Frame Particle Tracking Based on PIV to Study Inertial Particle Relative Motion in Isotropic Turbulence Lujie Cao, Zhongwang Dou, Zachary Pecenak, Fan Yang, Zach Liang, Hui Meng The statistics of particle pair relative velocity is a critical parameter in particle collision models. Experimental measurements are required to quantify the dependence of inertial particle relative velocity on turbulence and particle parameters. Our aim is to develop a technique that can directly measure the dynamics of inertial particles relative velocity statistics, in high Re number, lab- generated isotropic turbulence. The technique is based on 4-frame particle tracking using two sets of regular PIV systems, each recording a pair of correlated particle images, with additional synchronization controlling the temporal relationship between two PIV sets. To ensure spatial correlation between coordinates in images, we (1) use perpendicularly polarized laser illumination to label particle scattering with corresponding PIV recording, (2) make the two illumination laser sheets overlap at the test field, (3) arrange two PIV cameras orthogonally after a polarizing beam splitter to record the particle field. This allows us to capture 4 consecutive frames of particle images with a certain spatial shift. PTV algorithm is applied to further extract particle trajectories, from which we directly measure particle position and absolute velocity and further deduce particle relative velocity. [Preview Abstract] |
Sunday, November 24, 2013 2:41PM - 2:54PM |
D8.00003: Simultaneous measurements of velocity gradients and rod rotation in 3D turbulence Stefan Kramel, Rui Ni, Greg Voth, Nicholas Ouellette When anisotropic particles are advected in a fluid flow, they rotate in response to the velocity gradient tensor. In 3D turbulent flows, it has previously not been possible to experimentally measure both the motion of anisotropic particles and the velocity gradients simultaneously. We have built a scanning particle tracking velocimetry system in which we illuminate a narrow slab of the volume of interest and scan the illuminated slab through the entire volume, taking sequential images with four high speed cameras. Compared to full volume illumination, this technique enables us to greatly increase the particle concentration because it removes many stereo-matching ambiguities, resulting in a high spatial resolution of the fluid velocity. The trade-off is that the temporal resolution is decreased. We image a low concentration of rods in addition to a high concentration of tracer particles in order to allow extraction of the velocity gradient tensor at the positions of the rods. Rods are found to preferentially align with the direction of the vorticity vector and the intermediate strain-rate eigenvector. [Preview Abstract] |
Sunday, November 24, 2013 2:54PM - 3:07PM |
D8.00004: ABSTRACT WITHDRAWN |
Sunday, November 24, 2013 3:07PM - 3:20PM |
D8.00005: Interfacial deflection and jetting of a paramagnetic particle-laden fluid Ian Griffiths, Scott Tsai, Zhenzhen Li, Pilnam Kim, Howard Stone Arsenic removal from contaminated water is a formidable challenge in the water-purification industry. A promising technique to remove such contaminants utilizes magnetic separation, whereby arsenic adsorbs onto magnetic nanoparticles that are dispersed in the contaminated water. These magnetically tagged clusters are then collected safely using a magnetic field gradient that pulls the aggregates to the liquid--air interface, which induces an interfacial deflection before transitioning into a jet of magnetic material. We present experiments that are motivated by the applications of collecting aggregates of magnetic material, in which colloidal magnetic particles are first mixed with water, then collected at a liquid-air interface by an applied magnetic field from a permanent magnet. We derive a mathematical model that predicts the interfacial deflection and ejection of magnetic material, and compare the results with the experimental observations. The model is reduced by exploiting the small interfacial deflection for low magnetic fields and is used to make predictions that are more difficult to glean from the experimental observations alone. We draw conclusions on the model's ability to offer a route to design optimization for water purification strategies. [Preview Abstract] |
Sunday, November 24, 2013 3:20PM - 3:33PM |
D8.00006: An experimental investigation of the settling and resuspension of gravity-driven, mono- and bi-disperse slurries Gilberto Urdaneta, Matt Hin, Kaiwen Huang, Shreyas Kumar, Aliki Mavromoustaki, Jeffrey Wong, Sungyon Lee, Andrea Bertozzi We investigate the dynamics of gravity-driven mono- and bidisperse suspensions consisting of silicone oil and negatively buoyant particles of different densities experimentally. The well-mixed slurry mixtures spread down an inclined plane, exhibiting distinct flow patterns arising from competition of gravitational sedimentation and varying shear forces. We confirm the results of previous studies where, an initially well-mixed flow evolves towards either a ``settled'' regime in which the particles settle to the substrate, or a ``ridged'' regime in which the particles aggregate at the front of the flow. Our results show that the addition of a second particle species induces or prevents the setting of particles due to the mismatch in particle densities. We show that the latter depends strongly on the relative amount of heavy to light particles used. We compare our experimental results to spreading relations as applied to particle-free, thin-fluid films. Further, we investigate the evolution of particle concentrations in each of the two regimes by using fluorescent particle beads and compare our results to existing theoretical models. [Preview Abstract] |
Sunday, November 24, 2013 3:33PM - 3:46PM |
D8.00007: Particle-turbulence interaction of suspended load by forced jet impinging jet on a mobile sediment bed Rahul Mulinti, Kyle Corfman, Ken Kiger Particle suspension and transport induced by a forced impinging jet on a sediment layer has been investigated experimentally using two-phase particle image velocimetry (PIV). Glass spheres of two size classes, 45-63 micrometers and 120-180 micrometers have been used, with focus on transport characteristics during both the early development time (when the bed is relatively flat and smooth just following the passage of starting transients) and at late times (when a significant erosion bedforms are present in the form of annular wave-like patterns). Preferential mobilization and suspension has been observed at the crests of these waves and deposition due to entrainment of particles by the secondary, counter-rotating vortex formed by boundary layer separation near the surface. The effect of turbulent coupling between the particle and fluid momentum, as based on a point-particle drag law valid for dilute concentrations of particles has also been studied. The effect of the changing sediment bed profile on sediment erosion rates has also been examined briefly. [Preview Abstract] |
Sunday, November 24, 2013 3:46PM - 3:59PM |
D8.00008: Laboratory Study of Homogeneous and Isotropic Turbulence at High Reynolds Number Zachary Pecenak, Zhongwang Dou, Fan Yang, Lujie Cao, Zach Liang, Hui Meng To study particle dynamics modified by isotropic turbulence at high Reynolds numbers and provide experimental data for DNS validation, we have developed a soccer-ball-shaped truncated icosahedron turbulence chamber with 20 adjoining hexagon surfaces, 12 pentagon surfaces and twenty symettrically displaced fans, which form an enclosed chamber of 1m diameter. We use Particle Image Velocimetry (PIV) technique to characterize the base turbulent flow, using different PIV set ups to capture various characteristic scales of turbulence. Results show that the stationary isotropic turbulence field is a spherical domain with diameter of 40 mm with quasi-zero mean velocities. The maximum rms velocity is $\sim$1.5 m/s, corresponding to a Taylor microscale Re of 450. We extract from the PIV velocity field the whole set of turbulent flow parameters including: turbulent kinetic energy, turbulent intensity, kinetic energy dissipation rate, large eddy length and time scales, the Kolmogorov length, time and velocity scales, Taylor microscale and Re, which are critical to the study of inter-particle statistics modified by turbulence. [Preview Abstract] |
Sunday, November 24, 2013 3:59PM - 4:12PM |
D8.00009: Bead resuspension and saltation in a turbulent channel flow Rene van Hout Resuspension and saltation of near neutrally buoyant, polystyrene beads in a turbulent boundary layer was studied using TR-PIV and PTV in a horizontal, water channel facility (Re $=$ 7353). Near wall coherent structures were visualized using spatial distributions of vorticity and swirling strength in combination with instantaneous u$_{1}$u$_{2}$ correlations and u$_{1}$. Two case studies, (i) on resuspension and (ii) on saltation showed that lift-off coincided with vortex core passage creating an ejection-sweep cycle. In all cases, beads left the wall when immersed in near-wall ejections and exposed to positive shear. A high shear induced lift force coincided with bead lift-off while the Magnus force and translation induced lift were negligible. The wall-normal component of the drag force mostly opposed lift-off. The difference between resuspension and saltation was governed by the type of coherent structures the beads encountered when lifted out of the viscous sublayer. Resuspension occurred when beads were carried upwards by a combination of a strong, spatially coherent upstream fast moving flow structure and a downstream ejection. On the other hand, saltation was accompanied by similar albeit weaker and spatially less coherent near-wall turbulence structures. [Preview Abstract] |
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