Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session D30: Experimental Techniques: Micro and Nano Scale |
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Chair: Minami Yoda, Georgia Institute of Technology Room: Georgia World Congress Center B402 |
Sunday, November 18, 2018 2:30PM - 2:43PM |
D30.00001: Non-invasive micro-rheology of a single bacterium-scale filament of extracellular polymeric substances using oscillating flow Andrew White, Maryam Jalali, Jian Sheng While extracellular polymeric substances (EPS) account for up to 90% of biofilm mass, their material properties are difficult to measure due in part to their spatial heterogeneity within biofilms and delicate structure that is easily disrupted by invasive rheological techniques. Here we present a non-invasive micro-rheological technique to measure material properties of a single filament of EPS with sparsely attached bacteria in an oscillating flow. A bacterial suspension flows through a microfluidic channel containing a single pinned submillimeter oil droplet on which bacteria attach and secrete EPS. The EPS extrudes into a long filament (or streamer) with thickness approximately equal to one bacterium. Using high speed microscopy, single bacteria trapped in the filament are tracked to determine the filament deformation. Concurrently, freely suspended bacteria are used as flow tracers to perform PIV-assisted PTV to measure highly resolved velocity fields and determine viscous stresses and pressures experienced by the filament as the flow oscillates. Stress-strain relationships are developed with the tell-tale hysteresis of viscoelastic materials. Deformation at both oscillation and mean flow time scales is observed. |
Sunday, November 18, 2018 2:43PM - 2:56PM |
D30.00002: Digital Inline Holographic PTV using Regularized Inverse Volume Reconstruction Jiarong Hong, Kevin Mallery We demonstrate an improved algorithm for digital inline holographic PTV (DIH-PTV) measurements. We utilize an inverse problem formulation whereby the 3D optical field best explaining the recorded hologram is iteratively reconstructed utilizing the sparsity and spatial smoothness of the volume to regularize the solution. The reconstruction is substantially noise-free with dramatically improved axial resolution and increased maximum tracer particle concentration relative to prior DIH-PTV approaches. The use of sparsity regularization enables a sparse data representation which reduces memory requirements and enables processing very large holographic images (5k x 5k) while simplifying the identification and tracking of individual particles. Using synthetic data, we show a 3x improvement in localization accuracy and a similar reduction in the RMS velocity fluctuation in addition to a threefold increase in the allowable tracer concentration. We further present experimental demonstration cases measuring nanofiber dynamics, swimming behaviors of algae, and turbulent channel flow. |
Sunday, November 18, 2018 2:56PM - 3:09PM |
D30.00003: Multi-dimensional confocal laser scanning microscopy image correlation for nanoparticle flow velocimetry Brian H Jun, Matthew N Giarra, Pavlos P Vlachos We present a new multi-dimensional confocal laser scanning microscopy (CLSM) image correlation for nanoparticle flow velocimetry that is robust to sources of decorrelating errors. Random and bias errors from nanoparticle flow measurements exacerbate with increased dimensionality in CLSM images, rendering measurements unusable. Our new algorithm tackles these measurement limitations in two-fold. First, we model and correct for the bias errors introduced by the effects of the volumetric laser scanning image acquisition. Second, we developed a new spectral filter using a phase quality masking technique that optimizes its size for the spectral content of CLSM images, without requiring a priori knowledge of displacement fields or flow tracer properties. We validated our algorithm using synthetic images and experimentally obtained 2D and 3D CLSM images of nanoparticle flow through a micro-channel. We show that our technique significantly outperforms the standard cross correlation (SCC) in reducing both the random and bias errors and accelerated the convergence of ensemble correlation velocity measurements from CLSM images. |
Sunday, November 18, 2018 3:09PM - 3:22PM |
D30.00004: Abstract Withdrawn
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Sunday, November 18, 2018 3:22PM - 3:35PM |
D30.00005: Particle Image Diffusimetry (PID) Adib Ahmadzadegan, Arezoo M Ardekani, Pavlos Vlachos We will be presenting a visualization-based technique utilizing µPIV to determine the diffusion coefficient of micro/nanoparticles. The location of the Cross-correlation peak of two or more consecutive images in PIV and µPIV shows the information about the most probable displacement of a flow field. It has been shown that the diffusion coefficient of tracer particles can also be found from the spread of the cross-correlation plane with some limiting assumptions. we will demonstrate a new generalized probability-based method to quantify the diffusion coefficient while eliminating previous limiting assumptions. We will compare our results with the existing method and show validation of our technique using both synthetic images and experimental data sets. |
Sunday, November 18, 2018 3:35PM - 3:48PM |
D30.00006: An evaluation of volumetric velocimetry (3D-3C) techniques for use in microscale flows using a stereo microscope Douglas R. Neal, Lutz Fiedler, Dirk Michaelis, Bernhard Wieneke Measuring volumetric velocity (3D-3C) in micro-PIV remains a challenge. Volumetric techniques have matured for measuring the velocities in non-microscale flows (tomographic PIV, Shake-the-Box: 3D particle tracking), but usually four or more cameras are used. This study examines whether the same volumetric techniques can be adapted to a standard stereo-microscope (using only two cameras). This would allow for volumetric measurements to be carried out using any existing stereo micro-PIV system. However, in contrast to stereo micro-PIV, the complete depth of the measurement volume needs to be in focus, and this has to be considered when adjusting magnification and aperture of the microscope. The flow in a micro-channel (channel height 100 μm) with a backward facing step (step height 50 μm) is investigated with two high-repetition rate cameras and a corresponding laser. “Two-camera” tomographic PIV and Shake-the-Box are used to get instantaneous and average flow fields. It is found that the thickness of the channel (in voxels) is too small to allow the detection of the parabolic flow profile in the out of plane direction with tomographic PIV. However, using Shake-the-Box and PTV-based binning, the velocity profile can be resolved and the average pressure field can be calculated. |
Sunday, November 18, 2018 3:48PM - 4:01PM |
D30.00007: Multi-parametric defocusing particle tracking velocimetry (PTV) for micro-fluidic channels Tianqi Guo, Arezoo M Ardekani, Pavlos Vlachos A 3D particle model based on defocusing effect is proposed for 3-dimensional 3-component particle tracking velocimetry measurements in microfluidic systems. The model parameters describing the particle behavior are used directly as tracking features in the multi-parametric PTV. Micro-fluidic channels are mounted on a nano-positioning piezo stage which sweeps periodically in the out-of-plane direction, and a high-speed camera is synchronized to take two-dimensional microscopy images. Particles identification from the intensity volume is achieved by a combination of a 3D Hessian filter and a dynamic thresholding segmentation. Estimation of the measurement uncertainties over a large dynamic range is performed by artificial images based on direct numerical simulations of flow through porous media, and shows improvement over other PTV methods. A proof-of-concept experiment is performed by measuring the steady-state flow through a refractive-index-matched randomly packed glass bead channel. This experimental method doesn’t require calibration since the out-of-plane position of each image is recorded from the piezo stage position feedback, and thus eliminates any uncertainties associated with the calibration required by other PTV methods for micro-fluidics. |
Sunday, November 18, 2018 4:01PM - 4:14PM |
D30.00008: Digital Frensel Reflection Holography for 3D high resolution near-wall flow measurement Santosh Kumar Sankar, Jiarong Hong Fundamental study of wall-bounded turbulence requires measurement techniques that capture 3D near-wall flow at high spatial resolution. The typical resolution offered by commercial 3D PIV techniques is ~1 mm, insufficient to capture fine flow structures near the wall. Conventional Digital Inline Holography (DIH) can achieve substantially higher resolution but requires local injection of tracers upstream of the measurement region to minimize noise introduced through cross interference. This increases system complexity and can lead to temporally variable seeding, limiting the usage of DIH in large-scale facilities or over surfaces with complex geometries. Here, we demonstrate a new 3D holographic method that works with bulk flow seeding at a concentration ~1000 times that of conventional DIH, by capturing the interference between the backscattered light from particles (signal wave) and the reflection at the liquid-solid interface at the wall (reference wave). The technique is calibrated with brightfield imaging, and specific metrics relating measurement resolution with particle concentration are presented. Finally, we implement the approach to resolve near-wall flows in a flow channel, extracting the 3D flow field at ~50 μm resolution. |
Sunday, November 18, 2018 4:14PM - 4:27PM |
D30.00009: Micro-Particle Tracking Velocimetry in the impingement zone formed by a micro-droplet train Anoop B Kanjirakat, Reza Sadr, Jorge Alvarado, Taolue Zhang, Jayveera Muthusamy The flow field in the impingement zone of a single droplet train is studied experimentally. The near-wall velocities are measured at different heights from the impingement wall utilizing a Micro-Particle Tracking Velocimetry (μ-PTV) technique. The flow experiments are conducted using a dielectric cooling fluid (HFE 7100) seeded with fluorescent particles. Measurements are performed using double–exposed single-frame images at low frequency as required by the existence of high magnitude quasi-steady velocities in the impingement zone. The methodology with an algorithm to estimate the radial velocities at different heights is described. The observations from the micro-droplet experiments are then compared with a micro-jet stream case where the flow is at a steady state to establish the performance of the measurement technique. A μ-PTV technique is found to be appropriate for the study of this kind of flow field, as it requires a low fluorescent particle seeding loading, which will not interfere with the droplet generation, manage the unstable impingement point from one image to the next, and the quasi-steady nature of the flow. |
Sunday, November 18, 2018 4:27PM - 4:40PM |
D30.00010: High Resolution Boundary Layer Measurements on a Wing-Fuselage Model David Jeon, Christian Willert, Damian G Hirsch, Morteza Gharib A persistent problem in boundary layer experiments has been the inability to experimentally measure close enough to the wall the resolve the near wall region. This can be because a physical probe, like a hot wire anemometer, is larger than the near wall scales or because an optical probe, like laser Doppler velocimetry, lacks the resolution to get close enough to the wall. A variation on particle image velocimetry (PIV), has been developed by one of us (Willert), where a long-range micro PIV setup is used to resolve down to sub-layer scales in a turbulent boundary layer. This type of micro PIV setup was used on a semi-span wing-fuselage model to measure the boundary layer on the fuselage ahead of the wing at Reθ up to 2700, where the sub-layer could be characterized down to y+≈1. Since this is a PIV based technique, the measurement includes not just the mean profile, but also the variance and co-variance terms. The extension of the profile into the sub-layer means that the wall shear stress can be directly checked against the Clauser method. This talk will include an overview of the technique and challenges of implementing it in this setting, as well as preliminary results from wind tunnel testing. |
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