Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session L21: Quantitative Flow Visualization I: PIV, PTV, PLIF |
Hide Abstracts |
Chair: Michael Benson, Oak Ridge National Laboratory Room: 147A |
Monday, November 20, 2023 8:00AM - 8:13AM |
L21.00001: Wakes of Three Cylinders in a Falling Soap Film: Linking Lagrangian Coherent Structures from PIV to Interferograms Abhishek Singh, Pranjal Anand, Javad Eshraghi, Brett A. Meyers, Sayantan Bhattacharya, Pavlos P. Vlachos The falling soap film tunnel offers an inexpensive and convenient experimental solution for studying cross-sectional flows at low Reynolds numbers. Interferometry and Particle Image Velocimetry (PIV) are the primary measurement techniques for analyzing such flows. Interferometry visualizes vortical patterns through the variation in the film thickness, while PIV enables both flow visualization and quantification using particles seeded in the soap film. Existing works compare PIV measurements with interferometry either visually from the Eulerian properties like velocity and vorticity or by quantitatively extracting local vortical features such as the vortex center from these fields. This however does not compare how a vortex stretches downstream and how the surrounding fluid gets entrained. Thus, we aim to establish a connection between the instantaneous Lagrangian Coherent Structures (LCS) from the PIV measurements and interferograms. A flow of Re = 280 across nine configurations of three cylinders forming a triangle is considered, by varying height and base w.r.t. cylinder size. The LCS is calculated from the Finite Time Lyapunov Exponents (FTLE). Noise effects in the PIV results can alter the particle trajectory and corrupt the FTLE field, particularly in regions of slow flow. To address this, we explore a noise reduction technique based on principal orthogonal decomposition. This approach aims to enhance the quality of the FTLE field, thereby enabling a more accurate comparison. |
Monday, November 20, 2023 8:13AM - 8:26AM |
L21.00002: Dual-PIV with Exact Dynamic Mode Decomposition: an experimental method to investigate the spatio-temporal dynamics with a high spatial resolution of high-speed turbulent shear flows. Alexis Duddridge, Julio Soria, Vishal Chaugule, Callum Atkinson High-speed turbulent shear flows are prevalent in many industrial and air transport applications. Despite these flows' chaotic and fluctuating nature, it is still possible to identify large-scale coherent structures, which are often the consequence of shear layer instabilities, that help understand and control their dynamics. Quantitative experimental techniques are employed to study the actual physics of these flows and identify patterns. One commonly used technique is particle image velocimetry (PIV), which estimates the velocity vector field in the measured flow region. To ensure accurate measurements, high spatial resolution is required to enable important aspects of turbulent shear flows such as turbulence statistics, velocity gradients, and vorticity, as well as flow topologies to be assessed and studied. However, due to current limitations in camera sensor technology, time-unresolved measurements are only possible at a high spatial resolution. These methods do not provide information about the frequencies and corresponding growth or decay rates of flow oscillations, thus limiting insight into the temporal dynamics of high-speed turbulent shear flows. A dual-PIV system combined with exact dynamic mode decomposition (EDMD) is presented that enables the extraction of turbulent shear flow dynamics. This approach enables high-resolution spatial and temporal measurements, overcoming the limitations of traditional time-resolved low-spatial resolution or standard time-unresolved high-spatial resolution PIV systems. By applying this experimental approach and utilizing EDMD on the acquired high spatial resolution dual-PIV dataset, it is possible to extract frequencies of interest, as well as their corresponding spatial modes, providing insight into the dominant turbulent shear flow dynamics. Results of the application of the dual-PIV system combined with EDMD to high-speed turbulent jet flows will be presented as a pertinent application example. |
Monday, November 20, 2023 8:26AM - 8:39AM |
L21.00003: FluidNeRF: A machine learning framework for 3D flow field reconstructions Brian S Thurow, Dustin Kelly A new machine learning framework for 3D flow field reconstructions, termed here as FluidNeRF, is presented. FluidNeRF is based on the concept of Neural Radiance Fields (NeRF), whereby a volume is represented using a deep neural network and trained via image projections. FluidNeRF is an inherently modular framework that seamlessly allows for data assimilation, fusion, and compression. The methodology is demonstrated here using image projections of a passive scalar field generated from a DNS simulation of a turbulent jet. 3D flow field reconstructions are compared with reconstructions obtained with an adaptive simultaneous algebraic reconstruction technique (ASART) algorithm. The influence of hyperparameters and experimental arrangement (e.g. number of cameras) on the 3D reconstruction quality are presented. FluidNeRF is shown to produce comparable or better reconstruction quality than ASART with orders of magnitude reduction in computer memory requirements. Incorporation of temporal information and physical priors via additional loss functions will be introduced. Preliminary experimental results will be demonstrated using a vortex ring facility |
Monday, November 20, 2023 8:39AM - 8:52AM |
L21.00004: A Novel Inverse Imaging Approach to Brightfield Micro-PIV Evan J Williams, John Murray-Bruce, David W Murphy Brightfield micro-PIV, which uses a collimated light source aligned with the optical axis of the imaging camera to illuminate particles throughout a seeded volume, is commonly employed to study various micro-flows. In micro-PIV, a microscope objective provides a narrow depth-of-view, isolating in-focus particles and defining the plane of velocity measurements. Particle image morphology depends on its position with respect to the focal plane, with particles blurring outside of this plane. Out-of-focus particles can be eliminated via image processing (e.g. intensity thresholding), but precise differentiation of in- and out-of-focus particles is difficult, resulting in lost information and degraded vector fields. Here we present a novel approach to processing brightfield micro-PIV images based on inverse imaging. This approach implements a computational algorithm to extract in-focus particles and suppress noise in PIV images by solving the sparsity-regularized inverse problem that arises when a Gaussian function is used to model each particle’s intensity morphology. We show application of this approach using measurements of the flow generated by a tiny, free-flying insect and demonstrate enhanced image quality and vector field quality. |
Monday, November 20, 2023 8:52AM - 9:05AM |
L21.00005: Reconstructing complex flows from inertial Lagrangian particle tracks Ke Zhou, Samuel J Grauer Particle tracking velocimetry (PTV) is widely used to reconstruct 4D flow states from Lagrangian particle trajectories, a.k.a. "tracks", assuming that particles faithfully follow the flow. However, particles can lag the flow or travel ballistically due to rapid acceleration, large temperature gradients, strong body forces, etc., complicating the interpretation of PTV data. We report a novel method to simultaneously reconstruct unsteady flow states and individual particle properties (e.g., size, density, effective response time, …) from inertial tracks. To do this, we use a neural-implicit particle transport model to predict PTV tracks as a function of estimated flow states and particle properties. The flow states and tracks are parameterized by physics-informed neural networks (or similar). Optimizing an objective loss comprising a PTV data loss, Navier–Stokes residuals, and particle transport residuals yields tracks that match the data, physically-plausible flow states, and estimates of the unknown particle properties. We demonstrate this approach using synthetic tracks of inertial particles carried by laminar and turbulent flows. To the best of our knowledge, we report the first unsteady flow reconstructions from inertial tracks as well as implicit PTV-based particle sizing. |
Monday, November 20, 2023 9:05AM - 9:18AM |
L21.00006: Odor landscape dynamics in low-Reynolds number, low-Schmidt number plumes Lars Larson, Aaron C True, John P Crimaldi Terrestrial olfaction occurs in relatively low-Re, low-Sc odor landscapes (plumes). Coupled flow and odor cues are particularly relevant for insects sampling these plumes during olfactory navigation, which is fundamental to predator-prey dynamics, mate location, habitat selection, and foraging. In this study, we experimentally measured the spatiotemporal evolution of both fluid velocity and odor concentration in low-Re, low-Sc plumes generated in fractal grid turbulence using stereo particle image velocimetry (sPIV) and planar laser-induced fluorescence (PLIF). Acetone vapor serves as an odor simulant and is released isokinetically 10 cm downstream of a square fractal grid. Fluorescence is excited by four ultra-violet pulsed lasers (266 nm, 90 mJ/pulse) and imaged at up to 40 Hz with 350 micron spatial resolution over a 30 cm FOV. A separate pulsed green laser (532 nm, 200 mJ/pulse) and two additional sCMOS cameras capture sPIV data over the same FOV with comparable vector resolution at up to 30 Hz. Here, we present turbulent velocity and scalar statistics measured separately in stationary plumes, while future work will combine this infrastructure to make simultaneous sPIV and PLIF measurements of odor landscapes in the low-Re, low-Sc regime relevant to olfactory navigation. |
Monday, November 20, 2023 9:18AM - 9:31AM |
L21.00007: Time-resolved WMS tomography with velocimetry for high-enthalpy flows Joseph P. Molnar, Samuel J Grauer, Jacob J France, Bradley A Ochs, Jeffrey M Donbar Experimental characterization of high-enthalpy flows entails a host of instrumentation and signal processing challenges due to facility vibrations, limited optical access, elevated temperatures, high data rates, interference from condensation and particulate matter, and more. Instantaneous velocity, pressure, and temperature fields are needed to calculate performance metrics like mass capture, localize shocks, and resolve flow instabilities. Multi-beam wavelength modulation spectroscopy (WMS) can measure these quantities at a high repetition rate, is robust to harsh environments, and requires minimal optical access for 2D sensing. Existing algorithms for WMS tomography presume constant flow properties along each beam over a scan, which is often violated, e.g., during unstart in a high-speed inlet. This talk presents a neural-implicit WMS tomography, which yields velocity, pressure, and temperature fields that are continuous in (x,y,t) and processed at the photodiode acquisition rate. This approach can potentially resolve dynamics that are faster than the scan rate. Physics-based priors may be included to promote piecewise spatial and temporal smoothness and constant stagnation properties, when appropriate. The method is demonstrated through a representative phantom study. |
Monday, November 20, 2023 9:31AM - 9:44AM |
L21.00008: Application of stereomicroscope in volumetric micro-PIV Reza Babakhani Galangashi, Sayantan Bhattacharya, Brett A. Meyers, Pavlos P Vlachos Flow visualization offers valuable and accurate insights into flow characteristics. Doing tomographic volumetric measurements in micro-scale flows is challenging due to physical constraints to fit multiple cameras in a small field of view and ensuring that the entire depth of the measurement volume remains in focus. In this study, a novel stereo-microscope system with a high degree of overlap at high magnification between the two cameras is introduced, and its practical application for internal flow measurement within a microchannel is demonstrated. Therefore, the challenge of using two cameras which reduces volumetric reconstruction accuracy due to the underdetermination of the inverse problem of 3D reconstruction from fewer camera projections, is mitigated. We performed physical experiments to measure volumetric velocity within a phantom with an inner diameter of 3 mm. A validation step is performed by comparing experimental and theoretical velocity profiles. By validating the measured velocity profiles against established theoretical models, the reliability of the results and performance of the system is ensured. Any discrepancies between the measured and theoretical profiles are carefully analyzed and addressed to further refine and improve the measurement process. |
Monday, November 20, 2023 9:44AM - 9:57AM |
L21.00009: Experimentation and Validation of UAS Mounted Wind Sensors for Microscale Wind Mapping Braydon S Revard, Jamey D Jacob UAS technologies are becoming more widely utilized in civil and commercial |
Monday, November 20, 2023 9:57AM - 10:10AM |
L21.00010: 3-D printed luminescent sensor for heat transfer study in a micro-channel flow Hirotaka Sakaue, Daiki Kurihara, Mitsugu Hasegawa, Oscar Pontiff, Chih-Yung Huang The heat transfer in a microchannel has been paid great attention for various fluid-science applications, such as in an electronic component and a biochip. Due to the limitations in experimental data collection, the understanding of the microscale heat-transfer process is very challenging. Currently, only conventional CFD can provide information, but experimental validation is needed. There may exist a unique fluid-scientific phenomenon, but parametric experimental study is essential to extract such kind of scientific evidence. The research goal of the present topic is two folds. One is to develop a luminescent-imaging technique to capture detailed temperature information in a microchannel within the region of interest. The other is to create a model explaining the heat transfer in a microchannel. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700