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 M03: Flash Oral Presentations: Biological and Low Reynolds Number Flows |
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Chair: Laura Miller, UNC Room: 6c |
Monday, November 25, 2019 3:20PM - 3:21PM |
M03.00001: Long-term low shear of a waxy potato starch paste produces a highly viscous gel by formation of intermolecular double-helices. Fang Fang, Xiao Zhu, Mario Martinez, Osvaldo Campanella, Bruce Hamaker Our group recently reported that waxy potato and corn pure starch amylopectin pastes undergo a shear-thickening behavior at a low shear rate range of 5 to 25 s$^{\mathrm{-1}}$, and that the effect did not occur in waxy rice starch. Here, we show that gelatinized potato amylopectin subjected to prolonged shear at 20 s$^{\mathrm{-1\thinspace }}$for 24 h at 5$^{\mathrm{o}}$C produced a highly viscous gel with 5x more double-helices than without shear. Shear-induced aggregates formed within 20 min. Double-helices melted between 40 to 75$^{\mathrm{o}}$C leading to a total loss of gel elasticity and a steep decrease in G', indicating that the retrogradation process occurred in part among amylopectin molecules (i.e. intermolecularly). Thus, a new phenomenon is reported whereby waxy potato amylopectin with long linear chains forms double-helical aggregated structures in the presence of long-term low shear that dramatically affects material properties. [Preview Abstract] |
Monday, November 25, 2019 3:21PM - 3:22PM |
M03.00002: Numerical and experimental investigation of fluid flow in tapered orifices for needle-free injectors. Yatish Rane, Jeremy Marston Transdermal drug delivery using spring-powered jet injection has been studied for several decades, and is an attractive option for delivery of highly viscous and non-Newtonian fluids. In particular, third-generation vaccines such as DNA-vaccines have shear-thinning behaviour, which dictates the need to study the influence of fluid rheology in jet injection. Here, numerical simulations are performed with steady state flow and turbulence modelling based on the system Reynolds number at the orifice to generate characteristic curves of dimensionless pressure drop (Euler number) versus generalized Reynolds number. The results are experimentally validated for a given geometry over a wide range of Reynolds numbers (10$^{\mathrm{1}}$ - 10$^{\mathrm{4}})$, and we find shear-thinning (Carreau) fluids with high zero-shear viscosities can be injected due to the presence of high shear (\textasciitilde 10$^{\mathrm{6}})$ regions near the orifice. In addition to fluid rheology, the orifice geometry (e.g. conical, multi-tier tapers and sigmoid contraction) is varied to study boundary layer thickness, which also affects jet collimation. Ultimately, our results indicate there may be optimal geometries for creating jets to target specific tissue depths. [Preview Abstract] |
Monday, November 25, 2019 3:22PM - 3:23PM |
M03.00003: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 3:23PM - 3:24PM |
M03.00004: Acoustic Streaming in Confined Liquid Subject to High Intensity Focused Ultrasound (HIFU) Exposure Ghanem Oweis, Hussein Daoud, Rasha Seblany HIFU is an ex-corporeal therapeutic modality for the non-invasive treatment of tumors. A HIFU transducer emits spherically focused ultrasonic energy unto the target tissue deep under the skin, which is consequently absorbed and turned into heat, causing thermal ablation. Non-thermal effects can be present too, including cavitation bubble formation, radiation force, and acoustic streaming. The liquid streaming patterns were elucidated in previous HIFU investigations in an infinite medium. The aim of this study is to probe the effect of fluid confinement size on acoustic streaming. Two cubic water cuvettes of 5 mm, and 20 mm confinements were placed in an acoustic-coupling water bath at the geometric focus of the HIFU transducer (1.6 MHz, $f${\#} 1, 60 mm). A single 30 ms HIFU pulse exposure was used. PIV was implemented to measure the centerline streaming field (radial and axial components) at the end of the acoustic emission (avg. of 100 repeats). Significant differences were found in the flow patterns between the small (5 mm) and large (20 mm) confinements. The streaming velocity levels were also dramatically different. In conclusion, fluid confinement has a very important effect on the streaming flow from HIFU. [Preview Abstract] |
Monday, November 25, 2019 3:24PM - 3:25PM |
M03.00005: Could an implantable sensor both monitor lung flow and generate power? Lucy Fitzgerald, Luis Lopez Ruis, Jianzhong Zhu, John Lach, Daniel Quinn The rise of Smart Health has led to implantable healthcare devices that can diagnose and monitor diseases in real-time. Some diagnoses are based on fluids in the body, like asthma. A key challenge of current implantables is that they are difficult to power and require surgeries to replace batteries. We show that a piezoelectric flow sensor could monitor a fluid flow and simultaneously power itself from that flow. The effectiveness of this sensor/harvester depends on flow properties. It therefore demands advanced models that capture tradeoffs between sensing fidelity and harvesting potential. To develop these models, we built a platform for testing the sensing/harvesting capability of piezocantilevers in airflows modeled after human breathing. We found that oscillating voltage on the piezocantilever can both charge a capacitor and map to the amplitude and frequency of the breath. We explored how well models can predict harvesting and sensing potential based on breath type. These models open up a broad range of applications that we are exploring, including a smart stent that alerts patients to obtrusions or dislodging. How these models scale with flow speed/direction, turbulence intensity, and cantilever size offer design ideas for sensing/harvesting in other bodily channels. [Preview Abstract] |
Monday, November 25, 2019 3:25PM - 3:26PM |
M03.00006: Physics-Informed Deep Neural Nets for Super-Resolution, Denoising, and Velocity-Aliasing Correction of 4D-Flow MRI Roshan D'Souza, Mojtaba Fathi, Isaac Perez-Raya 4D-Flow MRI is a non-invasive method for measuring blood velocities in the human vascular system. It suffers from issues such as low spatio-temporal resolution, acquisition noise, and velocity-aliasing artifacts. Here, we present a novel method based on physics-informed Deep Neural Nets (DNNs) for super-resolution, denoising, and velocity-aliasing correction of 4D-Flow MRI. The inputs are the sparsely-sampled 4D-Flow MRI images and a rough geometry mask. The loss function used to train the physics-informed DNN contains terms for volume-averaged data fidelity and point-wise flow physics. Noise is reduced by using an averaging filter on the input data as well as the DNN predictor. Velocity aliasing is handled by computing data fidelity in the velocity encoding space. The trained DNN can be sampled at any desired resolution to generate noise-free flow images without velocity aliasing. Preliminary tests on CFD-derived 2D synthetic data shows that the method is able to automatically address all the aforementioned issues with normalized-root-mean-squared-error in velocity less than 4.8 percent and direction error less than 0.096 when compared to the reference CFD. [Preview Abstract] |
Monday, November 25, 2019 3:26PM - 3:27PM |
M03.00007: MRI-based modeling of CSF flow in the spinal canal Jenna J Lawrence, Wilfried Coenen, Candido Gutierrez-Montes, Antonio L Sanchez, Carlos Martinez-Bazan, Kevin King, Victor Haughton, Juan C Lasheras The oscillatory flow of cerebrospinal fluid (CSF) in the subarachnoid space of the spinal canal is driven by the intracranial pressure fluctuations associated with cerebral blood flow and by the thoracic pressure fluctuations associated with the respiratory cycle. We have previously derived simplified flow models by exploiting the slenderness of the subarachnoid space and the limited deformation of the dura membrane. Application of these models to a specific human subject requires knowledge of their spinal-canal anatomy and of both their spinal-canal and cranial-cavity compliance. We show how this specific information can be extracted from high-resolution magnetic resonance (MR) imaging of the anatomy, along with MR phase-contrast flow measurements of venous and arterial blood flow at the C2 level and of CSF flow at several transverse sections along the spinal canal. We then show how the resulting subject-specific model can be used to predict steady bulk motion and drug-dispersion rates. [Preview Abstract] |
Monday, November 25, 2019 3:27PM - 3:28PM |
M03.00008: In Vitro Assessment of Cycle to Cycle Flow Variability in Intracranial Aneurysms using Radial 4D Flow MRI and Tomographic PIV. Rafael Medero, Katrina Ruedinger, David Rutkowski, Kevin Johnson, Alejando Roldán-Alzate Intracranial aneurysm rupture has been related with aneurysm geometry, and high flow activity. 4D Flow MRI has been shown to be a feasible imaging technique for assessing hemodynamics in different vascular territories. However, one of its limitations is the need to average several cardiac cycles to obtain a complete data set, causing a smoothing of the velocity profiles and errors in areas with non-laminar flow. Additionally, it requires prospective determination of the velocity encoding setting, restricting the range of velocities acquired. Furthermore, the need for reasonable scan times can lead to limits in spatial resolution, which motivates the development of improved MRI sequences such as radial acquisitions. In this study, velocities acquired with radial 4D Flow MRI where compared to tomographic PIV using a patient-specific intracranial aneurysm in-vitro model under pulsatile flow. Velocity data from multiple time points within a group of 10 cardiac cycles acquired with tomo-PIV were compared pixel-to-pixel, and averaged velocity data was compared between methods. Statistically differences were found between velocities measured with tomo-PIV at peak systole and end diastole. However, good agreement was seen when comparing 4D Flow MRI with the average time points. [Preview Abstract] |
Monday, November 25, 2019 3:28PM - 3:29PM |
M03.00009: An experimental study of pulsatile flow over rectangular sidewall cavities Ruihang Zhang, Benjamin Eichholz, Yan Zhang Open cavity flow is a classic benchmark fluid dynamic model that has been extensively studied over the past decades. The existence of the free shear layer causes variations of vortex structures and flow stagnations inside the cavity in different flow regimes. However, how the flow pulsatility affects the vortex dynamics of the cavity flow is still not fully understood. Such question is of critical importance to many biological flow phenomena, such as blood past the brain aneurysms and left atrial appendage blood flows. The goal of this study is to reveal the flow characteristics of two simple rectangular sidewall cavity models under physiologically-relevant pulsatile flow. Cavities with two depth-to-width ratios were studied. Flow waveforms were generated using a programmable pulsatile pump to mimic the heart functions. Phase-locked PIV were conducted to study the cyclic variation of vortex flow structures inside and across the cavity. The velocity and vorticity fields were analyzed and found to significantly vary at different peak Reynolds numbers, Womersley numbers, and pulsatility indices. This study represents a systematic experimental effort towards pulsatile flow over a standard cavity model, which could serve as a benchmark for future computational simulations. [Preview Abstract] |
Monday, November 25, 2019 3:29PM - 3:30PM |
M03.00010: Elucidating Left Ventricular Hemodynamics and Aggregation Zones Using Platelet-focused Lagrangian analysis Venkat Keshav Chivukula, Fanette Chassagne, Jennifer Beckman, Claudius Mahr, Alberto Aliseda Left Ventricular Assist Devices (LVAD) have improved significantly over the last three decades and its use has expanded beyond the original Bridge-to-transplant indication. Thromboembolic complications, however, have not decreased in frequency or severity despite the advances in pump design. We investigate unfavorable hemodynamics in the left ventricle (LV) of a HF patient implanted with an LVAD. High-fidelity computational fluid dynamics are used to quantify thrombogenicity in the LV for several implantation configurations. Platelet Lagrangian tracking characterize the mechanical stimuli along individual trajectories, including residence time and shear stress history. Rigorous statistical analysis reveals recirculation zones inside the LV where platelet aggregation and thrombus formation can occur. PIV in a flow phantom implanted with a real-world LVAD provides validation. Clinically relevant parameters and patient management strategies for intermittent aortic valve opening that encourage the patient's ventricular contraction are assessed to optimize intraventricular flow patterns. Risk stratification is demonstrated to develop strategies that minimize stroke risk and have the potential to improve patient outcomes. [Preview Abstract] |
Monday, November 25, 2019 3:30PM - 3:31PM |
M03.00011: Hemodynamics of the left heart with physiologic and pathologic mitral valve: the chordae tendinae effect Roberto Verzicco, Valentina Meschini, Francesco Viola One of the advantages of computational engineering is the possibility to vary one factor of a system, while leaving all the others unchanged, and to assess its effect. In cardiovascular flows this strategy allows to selectively investigate modifications of the intraventricular hemodynamics produced by myocardial tissue remodeling or pathologies. In this study, we rely on our in-house multi-physics numerical model that dynamically couples electrophysiology, tissue mechanics and hemodynamics in physiological and pathological conditions to carry out direct numerical simulations of the left heart dynamics. Here, we present the effect of loose or broken chordae tendinae of the mitral valve on the ventricular pumping efficiency in terms of cardiac output, valve regurgitation and large scale flow structures. The results are seen to agree with the available clinical data, thus suggesting that this computational tool could be used to predict the effects of a valve sparing procedure and to improve the outcome of a surgical interventions. [Preview Abstract] |
Monday, November 25, 2019 3:31PM - 3:32PM |
M03.00012: Computational Hemodynamics of Prosthetic Aortic Valves with Application to Continuous Monitoring of Valve Function Shantanu Bailoor, Jung-Hee Seo, Hoda Hatoum, Lakshmi Prasad Dasi, Rajat Mittal Transcatheter heart valves suffer from complications such as leaks, thrombosis, endocarditis etc. Of these, sub-clinical or clinical thrombosis, even if resolved by anti-coagulation therapy, impacts the long-term durability of the valve. Technology to help avoid these complications and detect them very early is key towards advancing heart valve therapy. A small number of wireless pressure micro-sensors mounted at strategic locations on the valve frame could enable continuous monitoring and alerting to very early- stages of thrombosis or other complications, as well as to guide anti-coagulation therapy or other clinical management. We employ hemodynamics simulations of transvalvular flow in a canonical model of the aorta with a transcatheter valve and determine optimal sensor configurations for discriminating between healthy leaflets and those exhibiting reduced mobility. By applying machine-learning based techniques to a large cohort of in-silico aorta models, we demonstrate that a small number of in-situ sensors can effectively predict early-stage leaflet abnormalities. [Preview Abstract] |
Monday, November 25, 2019 3:32PM - 3:33PM |
M03.00013: A novel 1D flow model for transient FSI simulation of aortic valve Haoxiang Luo, Ye Chen In contrast with costly 3D flow simulations, simple aortic flow models are much more efficient and have applications in non-invasive clinical flow measurement as well as design optimization of prosthetic valves. Existing simple flow models are typically based on the old Bernoulli principle. In this work, we have developed a novel one-dimensional (1D) unsteady flow model based on the momentum and mass conservation equations, which takes into consideration of both valve movement and pressure loss through the valve. We couple this simplified flow model with a 3D FEM model of the thin-leaflet aortic valve as a 1D/3D hybrid model and perform FSI simulations for the valve of different bending rigidity. The nonuniform pressure distribution on the leaflets is included in the simulation. The full 3D FSI model that simulates the 3D pulsatile flow fully coupled with the same valve is used to assess the performance of the simplified flow model. The results show that the hybrid simulation is able to capture reasonably well the 3D deformation sequence of the leaflets, the valve opening area, and the flow rate, especially in the cases of low bending rigidity. [Preview Abstract] |
Monday, November 25, 2019 3:33PM - 3:34PM |
M03.00014: Venous valve dynamic behavior and function: a computational investigation Matthew Ballard, Parker Elliott To fulfill their role of returning blood from the body back to the heart, veins often need pumping beyond that provided by the heart. This is especially true where blood must be raised vertically a significant distance against gravity, such as from the deep veins of the legs. Thus, many veins contain a series of ``venous valves'' which open and close with pressure fluctuations to allow flow only in the direction back toward the heart. These valves enable veins to act as a series of ``miniature hearts'' that provide the requisite pumping effect. Under certain conditions including flow stasis associated with sitting still, long airplane flights and surgery, venous valves can become blocked through thrombus formation (deep vein thrombosis, or DVT), causing insufficient blood flow. Thrombi can even break free and become lodged in the lungs as a deadly pulmonary embolism (PE). We use a three-dimensional, fully coupled fluid-solid model based on the lattice-Boltzmann and lattice spring models to investigate the behavior of a viscous fluid and venous valves in a section of vein. We study the dynamics of venous valves and assess the effect of valve morphology on fluid transport. Further, we study flow in the valve region with a focus on understanding its effect on development of disease. This work increases our understanding of venous valve behavior and the resulting flow conditions, with possible applications in evaluating patient risk for DVT and in designing prosthetic venous valves. [Preview Abstract] |
Monday, November 25, 2019 3:34PM - 3:35PM |
M03.00015: Can you hear better if you're lopsided? Tympanal asymmetry may enhance hearing in a parasitoid fly Max Mikel-Stites, Paul Marek, Anne Staples \textit{Ormia ochracea} is a parasitoid fly endemic to the Americas. Gravid females respond phonotactically to calls of their male \textit{Gryllidae} cricket hosts. Astonishingly, \textit{Ormia} can locate their hosts with an azimuthal precision of 2$^{\circ}$ -- equal to that of humans, in spite of their small size, which should prohibit this level of precision because of fundamental constraints imposed by the physics of sound propagation (Mason \textit{et al., Nature}, 2001). Miles \textit{et al}. demonstrated that \textit{Ormia} is capable of resolving nanosecond time differences due to a direct mechanical coupling of the fly’s tympanal membranes (Miles \textit{et al., J Acoust Soc Am}, 1995). This mechanical coupling increases the interaural time delay (ITD) between the tympana, thus enhancing the fly’s sound localization precision. Here, we introduce an asymmetry in tympanal area into the mathematical model provided by Miles \textit{et al}. and demonstrate that an asymmetry of less than 10\% between the left and right tympanal areas can more than double the ITD. We further present initial measurements of 44 \textit{Ormia} tympana that demonstrate an average asymmetry in tympanal area of approximately 5\%. [Preview Abstract] |
Monday, November 25, 2019 3:35PM - 3:36PM |
M03.00016: Thumbs up! Bird's thumb induces leading-edge vortex during slow gliding flight Thomas Linehan, Kamran Mohseni The alula, or bird's thumb, consists of a small set of feathers stationed near the bird's wrist that protract from the wing during slow flight to enhance lift. The recent discovery of leading-edge vortices (LEVs) on the thin hand-wings of some birds suggest that the alula may play a role in LEV formation. Using stereoscopic-digital particle image velocimetry we measured the flow over a model wing with and without protracted alulae in a wind tunnel and made volumetric reconstructions of the three-dimensional vortex flow. We found that the alula induces and stabilizes a robust conical leading-edge vortex (LEV) that sweeps across the outer wing and smoothly merges with the tip vortex. LEV formation is the result of the alula scraping spanwise vorticity from the leading-edge shear layer and inducing its roll-up. The subsequent stabilization of the LEV is the result of root-to-tip spanwise flow in the LEV core of magnitude greater than 80\% of the freestream value. In essence, the protracted alula, mimicking a canted flap, is a clever way of inducing and stabilizing a LEV on a steadily translating wing inclined to the flow at high angles. These results grant new insights into the intelligent design of the modern bird wing and has important implications for aircraft flight control. [Preview Abstract] |
Monday, November 25, 2019 3:36PM - 3:37PM |
M03.00017: Wake Dynamics of Bat Flapping Vaibhav Joshi, Rajeev Jaiman Natural selection has evolved the geometry as well as mechanical properties of wings of a bat to achieve better flight performance, maneuverability and agility. The highly anisotropic and deformable membranes of the flapping wing and complex kinematics make their study more imperative for bio-inspired aerodynamic applications such as micro-air vehicles (MAVs). The current study is a first step towards understanding such complex flapping dynamics using a flexible multibody fluid-structure interaction framework. We aim to study the effect of the flexibility or compliance of the wing on the vortex dynamics and flight performance during hovering of the bat. We find that for the same power input to the flapping wing, the flexible compliant wing has better flight performance compared to its rigid counterpart. Moreover, the vortex structures generated supply more vorticity to the vortex ring patterns in the flexible wing leading to its large amplitude of deformation and unsteady lift coefficient. [Preview Abstract] |
Monday, November 25, 2019 3:37PM - 3:38PM |
M03.00018: Hydrodynamic thrust generation by honeybee (\textit{Apis mellifera}) Chris Roh, Morteza Gharib In our previous studies, we reported honeybee's locomotion at the air-water interface. Their ventrally wetted wings beat at high frequency (30-220 Hz), which propel them forward. Honeybee's locomotion on a water surface uses added mass as the dominant hydrodynamic force. Disregarding other forces, an added mass force associated with idealized sinusoidal wing kinematics is modeled. The resulting body movement shows good agreement with the experimentally measured body motion. Furthermore, body kinematics predicted based on the experimentally measured flow field under the mechanical model wing also shows similar locomotive pattern. [Preview Abstract] |
Monday, November 25, 2019 3:38PM - 3:39PM |
M03.00019: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 3:39PM - 3:40PM |
M03.00020: Bioinspired Passively Actuated Microflap Surface for Improving Airfoil Performance Sean Devey, Chris Jarmon, Amy Lang, Paul Hubner Flow separation acts to limit the efficiency of aerodynamic systems. A novel dynamic surface is proposed as a mechanism to limit flow separation. This surface is derived from the flank skin of the shortfin mako shark, which has been proven effective at limiting flow separation in adverse pressure gradient flows. An array of passively actuatable ``microflaps'' mimics the geometry and flexibility of mako flank denticles. It is hypothesized that these microflaps will respond to local reversing flows to passively enforce a selective flow direction and increase mixing within the boundary layer to limit flow separation. This surface has been produced with additive manufacturing and incorporated into the upper surface of a NACA 0012 airfoil. Low speed wind tunnel testing (Re \textasciitilde 2e5) of this airfoil is in progress. An increase in maximum lift and delay of stall is expected due to limiting of flow separation by the microflap array. [Preview Abstract] |
Monday, November 25, 2019 3:40PM - 3:41PM |
M03.00021: Fluid dynamics of nutrient exchange through the branched arrays of sea fans and jellyfish oral arms Laura Miller Numerous small organisms that swim, fly, smell, or feed in flows at the mesoscale, where inertial and viscous forces are balanced, rely on branched, bristled and hairy structures. Such mesoscale structures can augment particle capture and nutrient exchange by moving in a manner to transition from acting as solid surfaces to leaky/porous rakes at Reynolds numbers close to one. Although mesoscale flows have been studied in many organisms, the fluid dynamic mechanisms underlying the leaky rake to solid plate transition remain unclear. A detailed understanding of how this leaky-to-solid transition affects chemical exchange and particle capture in mesoscale filtering, where advective and diffusive transport rates are nearly balanced, also remains unavailable. In this presentation, flow visualization and computational fluid dynamics will be used to quantify the fundamental fluid dynamics of biological filtering arrays in this regime. Two types of marine invertebrates will be examined for understanding mesoscale biological filters: 1) upside-down jellyfish that use bell pulsations to filter particles within 3D bristled oral arms, and 2) sea fans that are branched into approximately 2D sheets. [Preview Abstract] |
Monday, November 25, 2019 3:41PM - 3:42PM |
M03.00022: CFD Time Machine: Using CFD to Understand the History of Long Extinct Swimmers Nicholas Hebdon, Kathleen Ritterbush, YunJi Choi Ammonoids are a group of cephalopods that were found in oceans worldwide for nearly 300 million years. These organisms once swam freely in the ocean and were as abundant as fish are today but went extinct 65 million years ago in the same extinction that killed the dinosaurs. In this study, we use Computational Fluid Dynamics model (Ansys V18.0) to study the locomotion of these now extinct animals. The fossil record shows that ammonoids underwent numerous periods of evolutionary boom and bust. During these cycles, ammonoids with a planispiral shell type often show clear shifts in their shell morphology, strongly emphasizing traits such as lowered cross-sectional area or increased coiling exposure. However, because there are no modern members of the group and there is no soft tissue preservation, it has been difficult for researchers to understand the implications of these shifts on their swimming pattern. We used CFD to study the hydrodynamic impacts of their morphological transformation, in terms of drag and lift. Incremental changes in shell shape across three common shape characters were studied: Shell inflation (total shell width), Whorl Expansion (the rate at which coil diameter increases, and Umbilical Exposure (the ratio of exposed coiling to total diameter). Our results show that drag and lift are sensitive not only to the particular parameter being changed but also that they are non-uniformly sensitive to the direction (increasing or decreasing) and magnitude of how that parameter is being changed. [Preview Abstract] |
Monday, November 25, 2019 3:42PM - 3:43PM |
M03.00023: Effect of viscosity on Lingulodinium Polyedrum micro swimmer motility and properties Lourdes Mónica Bravo Anaya, Hugues Bodiguel, Frédéric Pignon, Marvin Brun-Cosme-Bruny, Philippe Peyla, Salima Rafai \textit{Lingulodinium Polyedrum} (LP) microalgae is a marine protist, belonging to the dynoflagellata gender that emits bright blue light flashes once submitted to a shear stress. It carries an equatorial flagellum and a longitudinal one, allowing the swimming. In this work, we studied the effect of viscosity on LP microswimmer motility and bioluminescence properties through rheological measurements and a bright field microscopy imaging. The microalgae velocity dependency on the viscosity of the medium was measured in the presence of different concentrations of selected polymers. Xanthan was selected due to its shear-thinning behavior and a hydrolyzed polyacrylamide was also chosen due to its Newtonian behavior at concentrations lower than C*. These polymers were found to be biocompatible and stable in seawater and in presence of LP. The swimming velocity of LP microswimmer was found to be inversely proportional to the suspension viscosity for both polymers, suggesting that the force needed to stop the swimming LP cell remains constant. Finally, it was observed that the applied shear rate necessary for LP microalgae to emit bioluminescence decreases while increasing the suspension viscosity. [Preview Abstract] |
Monday, November 25, 2019 3:43PM - 3:44PM |
M03.00024: Reversal of Flagellar Wave Propagation Is Controlled by Proximal to Distal Asymmetry in Molecular Motor Dynamics Feng Ling, Yi Man, Eva Kanso The `9+2' axoneme of the motile cilium/flagellum is an important cellular structure that is highly-conserved among eukaryotic cells. Asymmetries of dynein motors along the flagellum have been identified in a number of organisms, and they have been specifically linked to the reversal in the direction of flagellar wave propagation in certain trypanosomes. Trypanosomes are a class of single-celled parasites that are known to switch their flagellar beating between tip-to-base and base-to-tip waveforms. In this talk, we analyze cilia oscillations and direction of wave propagation in the context of a known geometric feedback model. We introduce proximal to distal asymmetry in the molecular motor dynamics, consistent with recent experiments on trypanosomes. We show that the experimentally-observed reversal of wave propagation is only achievable when sliding-control feedback is dominant. We conclude by commenting on the implications of these results to flagellar waveforms in other organisms, and the feasibility of a universal geometric feedback mechanism for explaining the diverse waveforms in cilia oscillations. [Preview Abstract] |
Monday, November 25, 2019 3:44PM - 3:45PM |
M03.00025: Cilia-driven mixing and transport in complex geometries Hanliang Guo, Hai Zhu, Shravan Veerapaneni Cilia and flagella are self-actuated microtubule-based structures that are present on many cell surfaces, ranging from the outer surface of single-cell organisms to the internal epithelial surfaces in larger animals. A novel and exciting research direction in {\em in vitro} cell cultures is the development of engineered tissues in microfluidic chips, so called `organs-on-chips'. A fast and reliable numerical method that simulates the coupled hydrodynamics of cilia and the constituent particles in the fluid such as rigid particles, drops or cells would be useful to not only understand several disease and developmental pathologies due to ciliary dysfunction but also to design microfluidic chips with ciliated cultures for some targeted functionality, e.g., maximizing fluid transport or particle mixing. Here we propose a hybrid numerical scheme that employs the boundary integral method for handling the channel and particle boundaries and the method of regularized Stokeslets for handling the cilia. The algorithm is efficient, easy to implement and scales linearly with the problem size. We provide several examples demonstrating the effects of complex geometries on cilia-generated fluid mixing as well as the cilia-particle hydrodynamics. [Preview Abstract] |
Monday, November 25, 2019 3:45PM - 3:46PM |
M03.00026: Cryptographic analysis of chaotic fluid flows William Gilpin In computer science, hash functions are elementary operators that convert arbitrary-length inputs into finite-length outputs. We describe a direct analogy between these functions and the motion of particles advected by fluid flows, and we show that, when the governing flow is chaotic, hydrodynamic hash functions exhibit statistical properties typically associated with hash functions used for digital cryptography. These include non-invertibility, sensitivity to initial input, and avoidance of collisions, in which two similar inputs produce the same output. We show that this analogy originates from the tendency of certain chaotic flows to braid together particle trajectories across space in time in an irreducible manner, and we describe how techniques used to probe the properties of digital hash functions may be used to characterize the properties of flows when only limited observational data is available. Our findings have potential applications as microfluidic proof-of-work systems, as well as for characterizing large-scale transport by ocean flows and biological microswimmers. [Preview Abstract] |
Monday, November 25, 2019 3:46PM - 3:47PM |
M03.00027: Development of a Microfluidic Device to Sort Sperm based on Rheotaxis Effect Afrouz Ataei, Andy W.C. Lau, Waseem Asghar The first step of in-vitro fertilization is to sort out the motile sperm from the non-motile ones. Currently, centrifugation based sperm swim-up and density gradient separation are common methods to sort sperm. However, these methods reduce sperm quality during the repetitive centrifugation steps and isolate sperm with high DNA fragmentation. In this work, we construct a microfluidic device based on the observation that motile sperm can swim against the flow within a specific range of flow rates. This sperm sorting device consists of two chambers, separated by a filter. After 45 minutes the sorted motile sperm are collected from the top retrieval chamber and is placed on a glass slide for visual inspection and data collection. We find that 1) the most motile and functional sperm pass selectively through the micropores against the flow, 2) the optimum flow rate gives the highest concentration of motile sperm, the lowest DNA fragmentation and higher percentage of morphologically normal sperm compared to stock sample. Taken together, our device provide an efficient way to sort sperm without centrifugation [Preview Abstract] |
Monday, November 25, 2019 3:47PM - 3:48PM |
M03.00028: Bending of charged bilayer membranes Hammad Faizi, Cody Reeves, Petia Vlahovska Cells and internal cellular organelles are enveloped by membranes composed primarily of lipid bilayers. The bilayer bending rigidity (resistance to changes in curvature) plays a crucial role in cell deformations. We explore the effect of transmembrane potential on the bending rigidity. We experimentally analyze the dependence of bending rigidity on bilayer charge out of equilibrium due to charge accumulated near the membrane surfaces by an applied electric field. We measure the membrane bending modulus with three different techniques using the same giant unilamellar vesicle: equilibrium shape fluctuations, electrodeformation based on a frequency sweep, and shape fluctuations in the presence of uniform AC field [Preview Abstract] |
Monday, November 25, 2019 3:48PM - 3:49PM |
M03.00029: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 3:49PM - 3:50PM |
M03.00030: A Study of Flow Separation in Microfluidic Channels Mrudhula Baskaran, Jesse Ault, Clarence Rowley, Howard Stone Flow separation is detrimental in aerodynamics and the paradigm for studying this concept is the flow over a cylinder. Prior works have studied this problem extensively in macroscale setups. However, no work has studied it in microscale systems. This work aims to study the flow over a cylinder and laminar flow separation in microfluidic devices. Such channels were fabricated using lithography and the flow was imaged and analyzed using particle image velocimetry. The experimental results were verified through numerical simulations. Data show the onset of similar flow regimes in microchannels as those observed in macroscale experiments, such as detached flow, separation bubble/recirculation zone formation and growth, and van Karman vortex street formation. However, these occur at larger Reynolds numbers in the confined microchannels because the free shear layer formed during flow separation is slowed down by the presence of walls. The effect of the walls is also studied in numerical simulations of the system, which are done for confined geometries mimicking microchannels, as well as the 2D flow over a cylinder case in the absence of walls. Overall, this work contributes to the understanding of laminar flow separation and has important applications in topics such as physiology. [Preview Abstract] |
Monday, November 25, 2019 3:50PM - 3:51PM |
M03.00031: Fast prediction of inertial lift on particles in rectangular microchannels Guoqing Hu, Jinghong Su Inertial migration has been extensively used for manipulation and separation of engineered particles and bioparticles in microfluidic platforms. Inertial lift stems from the asymmetry of pressure and viscous stresses on the particle surface in a Poiseuille flow with finite Reynolds numbers. To design inertial microfluidic devices for particle manipulation, researchers need to predict the focusing positions of the targeted particles under various operating conditions, mainly by estimating the lift forces acting on the particles. Direct numerical simulations provide direct and realistic images of the particle migration, but they could become dramatically burdensome for the complex microchannels encountered in the practical devices. Here we use three-dimensional direct numerical simulations to calculate about 8,000 cases to determine the inertial lift distribution under different operating conditions. Based on these simulation data, we build a database of inertial lifts over a wide range of parameters. The interpolation is performed to apply the database to obtain the inertial lift within the parameter space, by specifying Reynolds number, particle blockage ratio, and channel aspect ratio. We then implement the interpolated lift in the Lagrangian tracking method to predict the particle trajectories in two typical microchannels for the inertial microfluidic applications, yielding good agreement with the experiments. [Preview Abstract] |
Monday, November 25, 2019 3:51PM - 3:52PM |
M03.00032: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 3:52PM - 3:53PM |
M03.00033: Numerical analysis of the pattern formation of chemotactic bacteria based on a kinetic transport model Shugo Yasuda Pattern formation of chemotactic bacteria is investigated numerically and theoretically based on a Boltzmann-like kinetic transport equation for chemotactic bacteria, say a kinetic chemotaxis model. In the theoretical part, we discover a novel instability mechanism, i.e., stiff-response-induced instability [B. Perthame\&S. Yasuda, Nonlinearity \textbf{31} (2018) 4065], where the uniform state of the bacterial population becomes unstable when the stiffness of the chemotactic response of bacteria is sufficiently large. Furthermore, the unstable modes are always bounded as is observed in Turing instability, so that the pattern formation occurs. A Monte Carlo method is also developed based on the kinetic chemotaxis model [S. Yasuda, J. Comput. Phys. \textbf{330} (2017) 1022] and the MC method is applied to the pattern formation problems of chemotactic bacteria in one- and two-dimensional spaces. The MC results illustrate the pattern formation mechanism of chemotactic bacteria induced by the stiff chemotactic response. [Preview Abstract] |
Monday, November 25, 2019 3:53PM - 3:54PM |
M03.00034: 3D vesicle microcirculation Dhwanit Agarwal, George Biros We study numerically the problem of equilibrium shapes of three-dimensional vesicles in confined axisymmetric Poiseuille flow. We explore a range of the following relevant dimensionless parameters: 1) reduced volume ($\nu$), defined as the ratio of volume of vesicle to the sphere of same area as vesicle, 2) viscosity contrast, $\lambda$, defined as the ratio of viscosities of internal and external fluids, 3) confinement ratio ($C_{n}$), defined as the ratio of vesicle diameter over channel width, 4) capillary number ($C_{a}$), measuring flow strength over membrane bending rigidity. We present a phase diagram of equilibrium shapes of vesicles, both with and without viscosity contrast. Our study reveals that slipper shape is the preferred equilibrium shape in low confinement ($C_{n} < 0.5$) while a transition to parachute shape takes place as $C_{a}$ is increased. For high confinement ($C_{n} >= 0.5$), the force exerted by the confining walls dominates, causing the vesicle to mostly take axisymmetric shapes. Outward migration tendency due to higher viscosity contrast causes the shape transitions to occur at higher $C_{a}$ when $\lambda=5$ compared to the case when $\lambda = 1$, resulting in a phase diagram shifted towards higher $C_{a}$. [Preview Abstract] |
Monday, November 25, 2019 3:54PM - 3:55PM |
M03.00035: Design and validation of a microfluidic pillar device to study hemostasis under flow Hari Hara Sudhan Lakshmanan, Adity Pore, Rachel Thompson, Jeevan Maddala, Patrick Jurney, Joseph Shatzel, Siva Vanapalli, Owen McCarty Hemostasis is an active process between plasma and blood cells, resulting in thrombin generation, platelet activation and fibrin formation to generate a hemostatic plug that staunches blood loss following vessel injury. The events that support hemostasis (outside the blood vessel) versus thrombosis (inside the blood vessel) are distinct in part due to the rheology of blood flow that differentially distributes blood constituents inside and outside blood vessels. We created an in vitro `bleeding chip' to study the spatial dynamics and cell biology of hemostasis under shear flow. The bleeding chip consists of two orthogonal channels, with series of 3 pillars spaced 10 microns apart at the intersection of the channels acts as a model of endothelial cell barrier function between the intravascular and extravascular space. The bleeding channel is coated with extracellular matrix proteins. We found that platelets aggregate at or behind the pillars as a function of shear rate. Activation of the coagulation cascade staunched blood flow in the bleeding channel while blocking platelet function or coagulation prevented formation of a hemostatic plug. Based on the percolation theory of fluid dynamics, we will discuss the impact of platelet interactions during hemostasis. [Preview Abstract] |
Monday, November 25, 2019 3:55PM - 3:56PM |
M03.00036: Interfacial-shear induces protein amyloid fibrils Hannah Middlestead, Nicholas Debono, Aditya Raghunandan, Amir Hirsa The formation of amyloid fibril plaques and the accumulation of such material in vivo is the hallmark of many disorders including Alzheimer’s and type-II diabetes. Fibril formation can be induced by several factors including changes to pH and temperature conditions. However, the role of the dominant and most varying physiological factors of fluid flow and shear at hydrophobic interfaces in amyloidogenesis remain poorly understood. Proteins adsorbed at the air/liquid interface are also subjected to significant hydrodynamic stresses during bioprocessing and drug delivery, which leads to unwarranted denaturation/aggregation and loss in efficacy. We report on the kinetics of fibril formation in human recombinant insulin solutions sheared in a knife-edge surface viscometer using fixed time-point ThT fluorescence and native-protein absorbance assays across a wide range of concentrations and rotation rates. We identify differences in the morphology of the fibril structures formed at the air/liquid interface and in the bulk at different stages of pre-fibrils and fibril growth. This is key to elucidating the aggregation pathway and toxicity of shear-induced denaturation and protein fibril formation. [Preview Abstract] |
Monday, November 25, 2019 3:56PM - 3:57PM |
M03.00037: CFD Simulation to Characterise Variation In-Duct Germicidal UV System Performance Catherine Noakes, Azael Cortes Capetillo, P. Andrew Sleigh Germidical UV lamps applied in ventilation ducts can inactivate microorganisms in air and on system surfaces; the approach is advocated for infection control and to tackle excess energy consumption associated with contaminated cooling coil surfaces. Here we use CFD simulation to explore the influence of UV system design and flow parameters on the effectiveness of the system against airborne pathogens. Simulations are carried out in ANSYS Fluent, with a discrete ordinates model to model the UV lamp irradiation. Lagrangian particle tracking models are used to determine cumulative UV dose within the duct, with a coupled survival model to simulate microorganism inactivation. A parametric study considers single and multi-lamp configurations at velocities between 0.5 and 4 m/s and duct reflectivity of 0\% and 15\%. CFD modelled microbial inactivation compares well to experimental data for three microorganisms, however simulations reveal the variation in dose distribution that is not apparent experimentally. Single lamp systems show a higher mean dose and inactivation when located parallel to the duct, but a greater distribution of dose compared to particle residence time. Multi-lamp systems show similar mean dose, but variation in the distribution with lamp location. [Preview Abstract] |
Monday, November 25, 2019 3:57PM - 3:58PM |
M03.00038: Contact line motion from molecular dynamics, the diffuse interface model and the sharp interface model. U. Lacis, P. Johansson, T. Fullana, S. Zaleski, S. Bagheri, B. Hess, G. Amberg In the context of the sharp interface model Huh and Scriven wrote “not even Herakles could sink a solid if the physical model were entirely valid”. The resolution of this paradox has occupied a large number of investigators, however a popular fix is to assume a Navier boundary condition for the tangential fluid velocity on the solid surface, which introduces a slip length $\lambda$. Nevertheless realistic molecular models show no slip of the first water layer on the SiO2 substrate. Alternate models of the contact line motion involve a dissipative relaxation of the order parameter at the boundary. This relaxation towards contact angle equilibrium involves a contact line friction $\mu_f$. We thus compare interface shapes obtained from a phase-field diffusive-interface model with the results of molecular dynamics (MD) simulation using the GROMACS code. The setup is a simple Couette flow between two plates, with a vapor droplet sheared in the middle of the domain. Another com parison is performed between MD and the sharp-interface model with a slip length and a Generalized Navier Boundary Condition. The sharp interface model is implemented using a VOF method. The role of diffusion across the interface, which is possible in the diffuse interface model, is given particular attention. [Preview Abstract] |
Monday, November 25, 2019 3:58PM - 3:59PM |
M03.00039: Charged nanoporous graphene membrane for enhancing reverse osmosis water desalination performance. Chinh Nguyen, Ali Beskok Positively and negatively charged single-layer nanoporous graphene membranes are investigated for applications in water desalination using molecular dynamics (MD) simulations. Pressure-driven flows are induced by moving specular reflection boundaries with a constant speed. Simulations are performed for hydraulic pore diameter membrane as large as 14.40 {\AA} with four different electric charges distributed on the pore edges. Salt rejection efficiencies and the resulting pressure drops are compared with the obtained base-line case of 9.9 {\AA} diameter uncharged nanoporous graphene membrane, which exhibits 100{\%} salt rejection with 35.02 MPa pressure drop at the same flow rate. For the positively charged membranes, $q=$ 9e shows 100{\%} and 98{\%} rejection for Na$^{\mathrm{+}}$ and Cl$^{\mathrm{-}}$ ions respectively, with 35{\%} lower pressure drop than the reference. For the negatively charged membranes, optimum rejection efficiencies of 94{\%} and 93{\%} are obtained for Na$^{\mathrm{+}}$ and Cl$^{\mathrm{-}}$ ions with $q=$ -6e, which requires 60.6{\%} less pressure drop than the reference. The results indicate the high potential of using charged nanoporous in reverse osmosis (RO) desalination systems with significantly enhanced performance. [Preview Abstract] |
Monday, November 25, 2019 3:59PM - 4:00PM |
M03.00040: A 2D Lattice Boltzmann Model for Hydrodynamics of Emulsions laden with Ellipsoidal particles Subhabrata Das, Kevin Connington We study the dynamics of randomly placed two-dimensional elliptical particles at droplet interfaces in a gravity-driven draining emulsion system consisting of a Newtonian fluid using 2D Lattice Boltzmann Model with long-range repulsive and frustrated short range attractive interactions. Both fluid-particle and particle-particle interactions along with the orientation of the particles need to be accounted for because the mutual competition between these phenomena coupled with tumbling effect govern the key features of elliptical particle-laden flows. As the denser liquid phase drains out, the dense to sparse emulsion transition is observed with droplet deformation, coalescence and eventual collapse with the emulsion start breaking at the top of the cell. However, this transition and droplet coalescence process is drastically reduced in presence of ellipsoids of varied hydrophobicity leading to formation of particle layers arresting coalescence with reduction of tumbling effects in the arrested state. The effects are changed when the affinity of the particles to each of the phases and the aspect ratio of the particles are varied. [Preview Abstract] |
Monday, November 25, 2019 4:00PM - 4:01PM |
M03.00041: Confinement effects on natural gas within carbon nanotubes Alexsandro Kirch, Teresa Lanna, Naiyer Razmara, Julio Meneghini, Caetano Miranda The current membrane technology for gas separation displays a low flow rate and/or low selectivity. Improvements in the separation technologies are desirable for natural gas usage as a fuel supply under carbon restrains. Advances in the membrane functionality may be favored by the development of nanotechnology. Notably with the emergence of the nanostructured carbon-based materials could lead to significant phase separation devices due to their fast mass flow and regular pore size. However, the separation process depends on fine-tuned properties of the pore structure which nowadays could be benefited by atomistic level research studies using molecular dynamics simulations (MD). In particular, the understanding of the fluid’s basic properties in confined geometries and interfaces plays a central role in the separation process optimization. In this work, we investigated the structure and transport of natural gas within carbon nanotubes in the light of fully atomistic MD simulations. Firstly, molecular models of natural gas are explored and confinement and interface effects on gas selectivity were analyzed with decreasing nanotube diameter. Finally, we could evaluate the underlying molecular mechanisms which could lead to the phase separation and influencing nanoflows. [Preview Abstract] |
Monday, November 25, 2019 4:01PM - 4:02PM |
M03.00042: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 4:02PM - 4:03PM |
M03.00043: Effect of Volume Fraction on Droplet Break-up in an Emulsion flowing through a Microfluidic Constriction Alison Bick, Sindy K. Y. Tang We report the effect of droplet volume fraction on the break-up of droplets within an emulsion flowing as a two-dimensional monolayer through a tapered microchannel into a constriction. A concentrated emulsion was injected into the channel, and an additional continuous phase was injected on-chip to dilute the emulsion to achieve different effective volume fractions. At a fixed flow rate, the break-up fraction decreases significantly when the droplet volume fraction $\varphi $ decreases below \textasciitilde 0.50. This result is consistent with our previous report that droplet break-up arises primarily from droplet-droplet interactions. Furthermore, an optimal location for the introduction of the additional continuous phase to dilute the emulsion was identified as approximately equal to one to two droplet diameters upstream of the constriction. Away from this optimal location, the dilution of the emulsion is ineffective. Assuming a tolerance of a maximum break-up fraction of 0.1, diluting the emulsion 2.1 times from $\varphi =$0.85 to $\varphi =$0.40 increases the throughput by \textasciitilde 1.3 times. Consequently, although a higher emulsion volume fraction packs more drops per unit volume, the propensity of the drops to undergo break-up limits the throughput of the process if droplet integrity and assay accuracy are to be maintained. [Preview Abstract] |
Monday, November 25, 2019 4:03PM - 4:04PM |
M03.00044: Fine-scale dynamics of bubble induced turbulence with and without breakup and coalescence Immanuvel Paul, Bruno Fraga, Michael Dodd, Chris Lai We study bubble induced turbulence (BIT) through a swarm of air bubbles rising in a vertical column. We consider two types of bubbles: one without and another with breakup and coalescence. The immersed boundary method is used to model the bubbles without breakup and coalescence while the volume of fluid is utilized for the other case. The void fraction of air bubbles is 0.5$\%$ at the start in both the simulations. We focus on the quasi-steady stage of the temporal evolution of the BIT. For this stage, we also note the -3 slope in the energy spectrum as reported in the experiments. We further explore the fine-scale turbulence dynamics by studying the evolution equation of the velocity gradient tensor (VGT) in Q-R space. We observe an entirely different conditional mean trajectories (CMT) of R and Q in both the BIT simulations. Here, the trajectories no longer spiral towards the origin as in the case of the homogeneous isotropic turbulence. Rather, the CMTs evolve to a particular line on the right branch of D=0 line leading to divergence in finite time. This is accompanied with the larger magnitude of the pressure Hessian term compared with all other terms in the VGT evolution equation. [Preview Abstract] |
Monday, November 25, 2019 4:04PM - 4:05PM |
M03.00045: Secondary flows and bubbly drag reduction on heterogeneously rough surfaces in Taylor--Couette turbulence Pim Bullee, Dennis Bakhuis, Rodrigo Ezeta, Sander Huisman, Chao Sun, Rob Lammertink, Detlef Lohse We investigate turbulent flow at Reynolds numbers (Re) ranging from $0.5 \times 10^{6}$ till $1.8 \times 10^{6}$ over surfaces that are composed of rough and smooth patches. Our main interest is in how the structure of the flow is influenced by this alternating rough and smooth surface, and how this changes the position of air bubbles in the flow. For this we use the Taylor--Couette geometry, which allows for accurate drag and flow measurements, as well as flow visualisations through its transparant outer cylinder. The inner cylinder wall is covered with sandpaper, leaving room between bands to form a constant pattern in axial direction. This results in a strong secondary flow pattern of radially outward flow on the rough patches and radially inward flow on the smooth patches. Surprisingly, air bubbles do not follow this secondary flow, but rather accumulate on top of the rough wall sections in the flow. Here, locally, the drag is largest and so the drag reducing effect of the bubbles is felt strongest. Therefore, a larger maximum value of bubbly drag reduction is found for the alternating rough and smooth inner cylinder walls compared to the completely rough and completely smooth inner cylinder walls. [Preview Abstract] |
Monday, November 25, 2019 4:05PM - 4:06PM |
M03.00046: Investigation of Cavitation Regimes Using Large Eddy Simulations Mrugank Bhatt, Krishnan Mahesh Cavitation occurs over different regimes, ranging from inception to massive regions of vapor. We use LES to examine the different regimes of cavitation for i) partial cavitation over a wedge and ii) cavitation over a marine propeller. Cavitation over a wedge is simulated at Re = 200,000 and b=2.47, 1.89 and 1.78 demonstrating respectively the incipient, the transitory and the periodic regimes. Cavitation over a five bladed marine propeller (P4381) is studied at Re = 894,000 and = and 0.6showing respectively the wetted and thrust breakdown conditions. The performance of a homogeneous mixture approach is assessed for capturing wetted conditions over a propeller and small scale vapor regions in the incipient cavitation over a wedge. Also the large regions of vapor resulting in the transitory and the periodic regimes over a wedge and thrust breakdown conditions over a propeller are studied. The flow field obtained using LES in each regime is discussed. [Preview Abstract] |
Monday, November 25, 2019 4:06PM - 4:07PM |
M03.00047: Dynamics of gas bubbles and slugs in 2-dimensional porous media Petr Denissenko, Rufat Abiev, Sam Tucker Harvey, Evgeny Rebrov A 3d-printed 2-dimensional channel is used to study 2-phase flow in a bench-scale trickle-bed reactor. As the maximum size of a spherical bubble is limited by the pore size, slugs with complex shapes form when bubbles merge. The slugs do not move constantly but perform intermittent manoeuvres. Break-up, coalescence, and propagation dynamics of the slugs are studied in relation to their length. The balance between pressure, viscosity, and surface tension terms is considered to predict slug propagation dynamics. Interaction between slugs is considered. Results are interpreted in the context of the gas hold-up and the flow quality in relation to mass transfer between gas phase and liquid phase. [Preview Abstract] |
Monday, November 25, 2019 4:07PM - 4:08PM |
M03.00048: Application-Specific Microfluidic Networks Faiz K. Mohammad, Vedula Murali, Raghunathan Rengaswamy Microfluidic devices have applications in various fields. This paper reports a simple approach for designing application-specific microfluidic networks with low effort and time. Here, we also demonstrate how this approach can be utilized to find networks that can perform logic computations based on droplets’ motion inside the network. We applied our approach to find networks that can control the motion of drops for logical computations, i.e., AND (.) gate where a drop will emerge from an arm only if drops enter the network simultaneously and OR (+) where a drop will emerge from an arm, whenever drops enter the network. Finding a device which can do AND (.), OR (+) logic computations might be easy (has been demonstrated) and can be achieved by trial and error. However, for more complex logical operations, trial and error approaches will be time consuming and unreliable. However, the proposed approach can handle these problems quite easily. This approach can also work with multiple drops entering from different source positions into the network to be used in more complex logical operations. We will describe computationally identified device designs for such logic computations in this work. [Preview Abstract] |
Monday, November 25, 2019 4:08PM - 4:09PM |
M03.00049: Acoustic droplet vaporization on hydrophobic and hydrophilic solid surfaces Seho Kwon, Gihun Son Acoustic-driven vaporization of volatile droplets, such as dodecafluoropentane (DDFP) droplets with a lower boiling temperature of 29°C, receives attention as a promising means for medical diagnostic and therapeutic applications. The acoustic droplet vaporization (ADV) process on hydrophobic and hydrophilic surfaces is experimentally investigated using a microscope and high-speed camera system with temporal and spatial resolutions of 150,000 frames/s and 5 pixels/um, respectively. A water-repellent agent is coated on a slide glass for a hydrophobic surface whereas an anti-fogging agent for a hydrophilic surface. The DDFP droplet has a contact angle of 105 degree on the hydrophobic surface and 45 degree on the hydrophilic surface. Ultrasound with a center frequency of 5 MHz was applied to DDFP droplets immersed in liquid water. The present ADV experiments show that the droplet vaporization rate is higher on the hydrophilic surface than on the hydrophobic surface. The droplet-bubble compound is always attached on the hydrophobic surface during the ADV process, but the compound grown on the hydrophilic surface slides off while leaving a small droplet portion. The effect of ambient water temperature on the droplet and bubble motion was quantified. [Preview Abstract] |
Monday, November 25, 2019 4:09PM - 4:10PM |
M03.00050: Closed loop control of the acoustic energy shielding by cavitation bubble clouds Kazuki Maeda, Adam Maxwell A closed loop control system is developed to regulate the transmission of ultrasound burst into a solid obstacle that is shielded by a layer of cavitation bubble clouds. The study is motivated by interest in improving the efficacy of kidney stone comminution during a recently proposed ultrasound-based lithtoripsy. In the system, pulses of ultrasound with a frequency of $O$(100) kHz and an amplitude of $O$(1) MPa are focused on a stone model from a multi-element array transducer with a pulse-repetition-frequency (PRF) of $O$(10) Hz. The far-field, bubble-scattered acoustic waves are concurrently measured at the transducer arrays. With a high PRF, the layer of bubbles is excited on the proximal side of the stone and scatters a large portion of the incoming acoustic energy. A data-driven, reduced-order model is used to estimate the portion of the energy transmitted into the stone from the acoustic measurement in real-time. Based on the offset of the estimation from a set point, a proportional-integral controller modulates the PRF to control cavitation. The controller showed favorable performance during $O$(100) s of continuous insonification. Lastly, the system is used to identify the optimal set point that maximizes the effective rate of energy transmission into the stone. [Preview Abstract] |
Monday, November 25, 2019 4:10PM - 4:11PM |
M03.00051: Ensemble-based Data Assimilation Methods for Viscoelastic Material Rheometry during Bubble Collapse Jean-Sebastien Spratt, Mauro Rodriguez, Kevin Schmidmayer, Tim Colonius We examine ensemble-based data assimilation methods for viscoelastic material rheometry, where observation of the radius versus time of a collapsing spherical cavitation bubble is used, together with a physical model for the bubble dynamics, to infer the surrounding material's mechanical properties. Such ensemble-based stochastic methods are attractive for this type of problem, as they fully capture the nonlinear dynamics while keeping computational costs low given the large number of state variables. The ensemble Kalman filter (EnKF), iterative ensemble Kalman smoother (IEnKS), and a hybrid ensemble-based 4D-Var (En4D-Var) method are compared. These are first validated against simulated data with known parameters, and then applied to experimental measurements in water and Polyacrylamide gel (Estrada et. al. 2018, J Mech Phys Solids 112). We show that the IEnKS and En4D-Var improve on the results of the EnKF as expected for this problem, and outperform existing viscoelastic material characterization methods by achieving comparable or better estimation with reduced computational cost. Each method demonstrates particular advantages, the IEnKS being less expensive and better suited for higher frequency data, and the En4D-Var more robust for sparse data sets spanning longer time. [Preview Abstract] |
Monday, November 25, 2019 4:11PM - 4:12PM |
M03.00052: Selective Viscous Withdrawal: Entrainment of Micro-jets and Micro-drops Zehao Pan, Janine Nunes, Niki Abbasi, Howard Stone The study of microscale drop or jet generation has catalyzed the invention of numerous biomedical and industrial technologies. Existing shear-based technologies require active control of both the continuous and the dispersed phases, therefore limiting their capacity for large scale parallelization. A selective viscous withdrawal system is comprised of a nozzle immersed in one fluid near a fluid-fluid interface, where the application of a withdrawal flow can cause the entrainment of the second fluid into the nozzle forming jets or droplets. Since no active or independent flow rate control of the two fluids is needed, this system promises greater capacity for scale up of droplet or jet production. Here, we experimentally study the formation of jets and droplets in a selective viscous withdrawal system, and perform a scaling analysis of the jet and drop sizes with respect to key operation parameters including the flow rate, nozzle-interface distance, nozzle diameter, viscosity, and interfacial tension. Our work lays the groundwork for further application-driven explorations. [Preview Abstract] |
Monday, November 25, 2019 4:12PM - 4:13PM |
M03.00053: Touch Down of a Sphere in Viscoelastic Media shaun fedrick, Theodore Brzinski, Paulo Arratia Many fluids of practical interest contain polymers and show non-Newtonian behavior such as shear-thinning viscosity and elasticity. Lubrication forces in such fluids depend on conformation changes of polymer molecules and at sufficiently high strain-rates can become nonlinear. Here, we experimentally investigate the (lubrication) forces that arise as a sphere approaches the solid surface as a function of fluid elasticity. We use an Instron with a sphere-and-rod attachment to directly measure the forces experienced by a sphere that approaches a smooth surface in fluids with different levels of elasticity. [Preview Abstract] |
Monday, November 25, 2019 4:13PM - 4:14PM |
M03.00054: Prediction of Rheological Behaviour of Unentangled Polymer Solutions in Steady Shear Flows Using a Blob-theory Based Constitutive Model Prabhakar Ranganathan Understanding the effects of polymer concentration and flow-induced stretching on hydrodynamic interaction between segments of polymer molecules is the key to accurately predicting the dynamical behavior of unentangled polymer solutions. Conventional wisdom avers that a polymer solution is dilute when its concentration $c$ is less the concentration $c^\ast$ at which isotropic polymer coils begin to overlap and interpenetrate. This picture is simplistic. Inter-chain interaction becomes increasingly important as chains stretch in flow. In semi-dilute unentangled solutions, on the other hand, concentration-dependence is strong at equilibrium, but inter-chain interactions weaken as chains stretch during flow. Thus, dilute solutions self-concentrate, while semi-dilute solutions self-dilute! A constitutive model based on blob concepts is used to examine the concentration dependence of shear-thinning-thickening-thinning in steady shear flows. It is shown that qualitative nonlinear rheological behaviour in strong flows is surprisingly sensitive to the friction coefficient of the Kuhn segment. [Preview Abstract] |
Monday, November 25, 2019 4:14PM - 4:15PM |
M03.00055: Rheological properties of encaustic painting Jorge Arroyave, Sandra Zetina, Roberto Zenit Encaustic is a painting technique characterized by the use of wax as the main binding media. In addition to wax and pigments, some resins and solvents are used to create the painting media. Since the material is semi-solid at ambient conditions, the painting is often conducted with the aid of heated pallets and torches. As a result, mastering this technique is extremely challenging. In this work we investigate how the composition of the encaustic affects its rheological properties focusing on the effect of pigment color and concentration. We prepare encaustic paints following Diego Rivera's, used for his first large-scale mural which was painted with this technique. In addition to determining the viscosity, using a rheometer, we also conducted ‘controlled painting’ experiments: a device was designed and built to apply a drop of paint to heated surface at different shear rates. We found that all the paints were shear-thinning with small viscoelastic effects; surprisingly, the viscosity of the paints was significantly affected by the pigment color despite the fact that its proportion in the paints was always small (less than 10\%). The size of the traces was found to scale with the shear Reynolds number. A discussion on the implications of these results for artists is presented. [Preview Abstract] |
Monday, November 25, 2019 4:15PM - 4:16PM |
M03.00056: A Mesh Refinement framework for the Lattice Green's Function method Ke Yu, Benedikt Dorschner, Marcus Lee, Tim Colonius We report on progress in developing the lattice Green’s function (LGF) technique for solving viscous, incompressible flows on unbounded domains. This method exploits the regularity of the finite-volume scheme on a formally unbounded Cartesian mesh to yield robust (conservative, stable) and computationally efficient solutions. It is spatially adaptive, but of fixed resolution. Here we develop an adaptive mesh refinement strategy compatible with the LGF algorithm. The solution to the pressure Poisson equation is approximated using the LGF technique on a composite mesh where different regions can have different resolutions. This is further combined with an integrating factor technique for the viscous term and an appropriate Runge-Kutta scheme for the resulting differential-algebraic equations. The algorithm is verified and validated with numerical simulations of vortex rings. [Preview Abstract] |
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