Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session L16: Experimental Techniques: Laser Based Diagnostics |
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Chair: Nathaniel Bristow, University of Minnesota; Michele Guala, University of Minnesota Room: 143 |
Monday, November 21, 2022 8:00AM - 8:13AM |
L16.00001: GAIA: Grand-scale Atmospheric Imaging Apparatus – bringing together drones, holography, computer vision, PIV/PTV and LiDAR Nathaniel Bristow, Peter W Hartford, Jiaqi Li, Nikolas Pardoe, Matteo Puccioni, Coleman F Moss, Michele Guala, Giacomo Valerio Iungo, Jiarong Hong Atmospheric flows, through their transport of airborne particles, affect many geophysical, biological, and engineering processes associated with climate, meteorology, agriculture, and geomorphology. The GAIA project (Grand-scale Atmospheric Imaging Apparatus) aims to develop advanced instruments that can provide detailed characterization of these processes in the field. Here we offer an overview of the scope of this project and the methodologies being employed, wherein we leverage image-based diagnostics, across a range of measurement scales, and integrate them with state-of-the-art UAS and computer vision technologies. Specifically, we employ digital inline holography (DIH) to measure the properties (size, morphology, compositions, etc.) of particles of different types (e.g., snow, soot, pollen), multi-view 3D tracking to measure detailed particle movements driven by flows, as well as optical flow, PTV, PIV, and scanning Doppler wind LiDAR for simultaneous characterization of atmospheric flow ranging from centimeter to kilometer scales. A key goal of this project is to deploy such imaging apparatus primarily as a drone-based system, which raises a host of challenges while also opening new opportunities to obtain field data previously inaccessible. |
Monday, November 21, 2022 8:13AM - 8:26AM |
L16.00002: UAV-based digital inline holography for real-time, autonomous aerosol diagnostics Peter W Hartford, Nathaniel Bristow, Nikolas Pardoe, Jiarong Hong Understanding the dispersion of aerosols from wildfire can improve our ability to model air quality and radiative forcing for various environmental applications. Currently, due to measurement challenges, there is a lack of field data of how these aerosols disperse in the atmosphere, which depends strongly on their properties (e.g., concentration, morphology, and composition) that may vary temporally and spatially over a large domain. In this work, we develop an autonomous drone system integrated with lensless digital inline holography (DIH) to measure the properties of such aerosols generated from wildfires. Combining machine learning object detection with vision-based flow diagnostics, our drone can autonomously identify a smoke plume, fly toward it, and then trace along the motion of the smoke plume, while measuring local aerosols with the DIH sensor. This tool can enable detailed in situ characterization of wildfire smoke aerosols during emission and dispersion downwind in a manner that yields real-time data for air quality and climate science. Furthermore, the capabilities of this system may be extended to applications for other airborne PM diagnostics, such as dust, pollen transport, etc. This research is part of the GAIA (Grand-scale Atmospheric Imaging Apparatus) project. |
Monday, November 21, 2022 8:26AM - 8:39AM |
L16.00003: MTV for instantaneous wall shear stress measurements in turbulent flows Charles Fort, Philippe M Bardet Measurements of the instantaneous wall shear stress (WSS) in turbulent flows are particularly challenging at high Reynolds numbers due to the small spatial and temporal scales involved. Among the existing non-intrusive optical diagnostics, molecular tagging velocimetry (MTV) gives continuous velocity profiles and is hence well suited to measure velocity gradients. The traditional limitations of spatio-temporal resolution of MTV techniques in liquids are overcome by a novel photobleaching approach of an inexpensive dye with Talbot-effect structured illumination using a pair of common pulsed neodymium-doped lasers (355 and 527 nm). The system is made compact and modular by using motorized optical mounts and small-pixel low-noise cameras. With those improvements, MTV reaches unprecedented spatio-temporal resolutions and becomes a very flexible scheme to study a broad range of liquid flows. Here, it is demonstrated in a turbulent channel flow with viscous length scales on the order of 10 µm. Special attention is paid to the tails of the probability density function of the fluctuating WSS. |
Monday, November 21, 2022 8:39AM - 8:52AM |
L16.00004: Computational and physical modeling of pollution dispersion in a rural area Yucheng He, Sanika Nishandar, Marko Princevac, Rufus Edwards Use of open fires for cooking in rural Mexico is known to cause poor indoor air quality. However, contributions to local ambient pollution caused by these emissions are poorly quantified due to the lack of pollution monitoring stations in rural areas. Air quality models Quick Urban & Industrial Complex (QUIC) and AERMOD were deployed to simulate the dispersion of stove emissions in a Mexican village. A Planar Laser Induced Fluorescence (PLIF) was used for visualization and quantification of dispersed PM2.5 concentration around modeled buildings in a water tank. The physical experiment is conducted for validation of the QUIC simulation results, and the comparison demonstrates good qualitative agreements. Based on experiments and simulations, we intend to scale the essential features of flows from simplified morphology to complex flows in real village configurations. Pollutants trapped in the building wakes tend to infiltrate back into houses and consequently impair indoor air quality. Factors that determine pollution distribution in the wake of buildings such as the meteorological condition, emission rate, and configuration of buildings are evaluated in the study as well. We discuss the experimental setup, laboratory results, and comparable modeling results in the presentation. |
Monday, November 21, 2022 8:52AM - 9:05AM |
L16.00005: Comparison of CN in the Boundary Layer of Ablating Graphite in High-Temperature Air and Nitrogen Flows using PLIF John S Murray, Greyson Kale, Noel T Clemens Planar laser-induced fluorescence (PLIF) is used to study the distribution and temperature of the cyano radical (CN) present in the reacting boundary layer of ablating graphite. The graphite ablation is induced in the high-temperature plume of the 50 kW inductively-coupled plasma (ICP) torch at The University of Texas at Austin under two flow compositions: ablation induced by a high-temperature air flow, and induced by a high-temperature nitrogen flow. The different flow compositions will offer insight into the production of CN due to surface nitridation versus gas-phase reaction mechanisms. Optical emission spectroscopy (OES) will also be taken in order to compare the two experimental methods. |
Monday, November 21, 2022 9:05AM - 9:18AM |
L16.00006: Optimization of deep learning model for monitoring heterogeneous airborne PM concentrations using digital holographic microscopy Jihwan Kim, Kyler J Howard, Youngdo Kim, Sang Joon Lee Airborne particulate matter (PM) is a global health concern and PMs with diameters less than 2.5 µm can permeate the lungs, causing illnesses. Current PM monitoring methods have limitations of being bulky, expensive, and require specialization. Hand-held devices are still costly while not measuring overly high/low concentrations accurately. Therefore, there is a need to make a compact and handy device that quickly and accurately measures PM concentrations. This study employs a novel digital in-line holographic microscopy setup with a smartphone to capture holographic images of PM signals. The speckle signals of heterogeneous PM2.5 and PM10 recorded by a smartphone can be separated by 2D Gaussian filtering and used to optimize a deep learning network. The network consists of a deep autoencoder to regression layers which were trained on preprocessed speckle signals of homogeneous PM2.5 captured by the smartphone. Using the high-pass filter on speckle signals of homogeneous PMs to extract 2.5 µm PM signals, the model was optimized and applied to predict heterogenous PM concentrations. Prediction results based on the optimized model can be utilized to both validate the method of separating PM2.5 from heterogeneous PM signals and to measure heterogenous PM concentrations in real-time. |
Monday, November 21, 2022 9:18AM - 9:31AM |
L16.00007: A Molecular Tagging Velocimetry Based Plenoptic Microscope for Measuring Wall Shear Stress Peter D Huck, Charles Fort, Philippe M Bardet In this contribution, we describe measurements using a plenoptic microscope that permit acquisition of the near-wall velocity field in an axi-symmetric stagnation jet using a single camera sensor. Three-dimensional, two-velocity component (3D-2C) measurements are acquired using Molecular Tagging Velocimetry, a spectroscopic technique relying on seeded molecular tracers to probe the local velocity field. Standard reconstruction algorithms based on geometrical optics are compared against advanced deconvolution algorithms that take diffraction into account. Convincing improvements in reconstructed probe resolution are obtained using the latter reconstruction. Plenoptic imaging is compared with a scanning confocal microscope which serves as a ground truth measurement, and good agreement is achieved in the near wall velocity profile. The flow facility was designed for a low friction Reynolds number, but with an adjustable viscous length scale comparable with higher Reynolds number flows. As such, it provides a proving ground for the instrument before deployment in higher Reynolds number flows of interest. Our instrument proves capable of resolving viscous length scales on the order of 30 micrometers, which may be improved by up to a factor of four increasing the numerical aperture of the microscope objective. |
Monday, November 21, 2022 9:31AM - 9:44AM |
L16.00008: Molecular Tagging Velocimetry of high-speed flow around a modified NACA airfoil Mir Muhammad Tareq, Roberto Capanna, Charles Fort, Mark Yamakaitis, Philippe M Bardet Molecular tagging velocimetry (MTV) is deployed for the first time in a high-speed anechoic wind tunnel over a modified NACA 0019-94 airfoil. A two-laser system is used to 'write' a continuous line of tracers in the flow and subsequently 'read' them as they are advected downstream. The laser beams are launched from within the airfoil using motorized optical mounts and a sCMOS camera, equipped with an image intensifier, located below the facility floor directly images continuous velocity profiles at the wall. The technique relies on the availability of water vapor content in air. An excimer laser at 193 nm performs the 'write' step by photo-dissociating water vapor molecules from the ambient air, producing OH radicals. Those tracers are then 'read' through laser-induced fluorescence by a tunable dye laser at 281.905 nm. The 'write'/'read' time interval is optimized between 30 μs to 160 μs for the three different speeds studied: 10, 20 and 30 m/s. |
Monday, November 21, 2022 9:44AM - 9:57AM |
L16.00009: Ultrasound for probing the microstructure in sheared dense suspensions of red blood cells Marie Poulain-Zarcos, Simon Mendez, Wassim El Nemer, Laurence Bergougnoux, Emilie Franceschini This study proposes to probe the anisotropic microstructure of sheared dense red blood cells (RBC) suspensions by ultrasonic scattering technique. The principle consists in measuring the structure factor, which is linked to the Fourier transform of the pair correlation function. Recent ultrasonic experiments on sheared hard-spheres suspensions [Lombard et al, J. Acoust. Soc. Am., 2020] demonstrated that the angular-dependent structure factor can detect the main angular position of regions depleted in particle pairs. We conduct here ultrasonic experiments on suspensions of disaggregated RBC sheared in a Couette flow device for several RBC volume fractions and shear rates. The measured angular-dependent structure factors are similar to those obtained for sheared hard-spheres suspensions and suggest the presence of regions depleted in cell pairs. This is corroborated by 3D numerical simulations of sheared RBC suspensions. This new ultrasonic tool will pave the way to a better understanding of the relationship between the rheology and microstructure of opaque RBC suspensions. |
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