Bulletin of the American Physical Society
74th Annual Meeting of the APS Division of Fluid Dynamics
Volume 66, Number 17
Sunday–Tuesday, November 21–23, 2021; Phoenix Convention Center, Phoenix, Arizona
Session H20: Experimental Techniques: Quantitative Flow Visualization and Data Analysis I |
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Chair: Michael Benson, West Point Academy Room: North 221 AB |
Monday, November 22, 2021 8:00AM - 8:13AM |
H20.00001: Physics-informed compressed sensing: reconstruction of magnetic resonance velocimetry signals as an inverse Navier-Stokes problem Alexandros Kontogiannis, Matthew P Juniper Magnetic resonance velocimetry (MRV) can measure all three components of a time varying velocity field but as the spatial resolution is increased the measurements become increasingly noisy. To acquire velocity images of acceptable signal-to-noise ratio, repeated scans are required, leading to long acquisition times. We present an algorithm that is capable of reconstructing magnetic resonance velocimetry signals from a single scan, by formulating a Bayesian inverse Navier--Stokes problem for the unknown velocity field. In this way we can infer the most likely boundaries of the flow, the boundary conditions, the viscosity, and the reconstructed velocity field, and estimate the uncertainty in the prediction. Our physics-based approach does not only provide a way to reconstruct the MRV signal, but it can furthermore infer hidden flow quantities such as the pressure and the wall shear stress, which are otherwise difficult to measure. |
Monday, November 22, 2021 8:13AM - 8:26AM |
H20.00002: The 2021 MRV Challenge: Introduction and Stanford-USMA Results Christopher Elkins, Andrew J Banko, Michael J Benson, David B Helmer, John K Eaton This presentation is part of the 2021 Magnetic Resonance Velocimetry (MRV) Challenge which was created to test the accuracy of phase averaged, three-dimensional, three component (4D3C) MRV measurements in periodic flows across multiple MR system platforms and flow labs around the world. The results from the combined team of researchers from Stanford University and the United States Military Academy (USMA) are presented. Experiments were performed on a square cross-section water channel containing a periodic array of rectangular buildings and an injection site in the floor behind one building at a channel Reynolds number of 15,000. The injector was pulsed periodically to produce a transient, highly three-dimensional (3D) flow. 4D3C velocity measurements were obtained using a 3T GE whole body scanner and reconstructed to 20 phases across the injection cycle. Additional scan conditions are outlined, as well as an overview of the experimental techniques and equipment used. Detailed results are presented for the flow behavior during several phases of the injection cycle at multiple locations, particularly focusing on complex fluid dynamic behaviors that are highly three-dimensional in nature. Agreement with the results from the other international participants suggest an increased capacity to leverage MRI measurements for flows that are periodic in nature or that may be approximated using repeatable transients. |
Monday, November 22, 2021 8:26AM - 8:39AM |
H20.00003: 2021 MRV Challenge: Seoul National University Results Wontae Hwang, Kyuho Han This work is a contribution to the 2021 Magnetic Resonance Velocimetry (MRV) Challenge, and describes the results of Seoul National University. Experiments were conducted on a square cross-section water channel, which had an array of rectangular blocks that represent buildings, and an injection hole in the floor behind the first building. It should be noted that this apparatus was transferred between multiple research groups worldwide to provide a common platform to compare results. The Reynolds number of the main channel flow is 15,000, and a pulsatile jet is ejected into the main flow, producing a highly transient 3D flow structure. Phase-locked 3D velocity measurements were acquired by a 3T Siemens MRI scanner, and reconstructed using 22 phases across the jet injection cycle. Detailed results of the complex 3D flow interaction between the transient jet, main flow, and buildings are presented throughout the injection cycle at various locations. Implications in regards to mixing with transient jet plumes will be discussed. |
Monday, November 22, 2021 8:39AM - 8:52AM |
H20.00004: 2021 MRV Challenge: Hanyang University Results Don-Gwan An, Simon Song This presentation is part of the 2021 Magnetic Resonance Velocimetry (MRV) Challenge and represents the results from a combined team of researchers from Hanyang University. Experiments were performed on a square cross-section water channel containing a periodic array of rectangular buildings and an injection site in the floor behind one building at a channel Reynolds number of 15,000. The injector was pulsed periodically to produce a transient, highly three-dimensional (3D) flow. Phase-averaged, 3D three-component velocity measurements were obtained using a 3T Philips scanner and reconstructed to 20 phases across the injection cycle. Additional scan conditions are outlined, as well as an overview of the experimental techniques and equipment used. Detailed results are presented for the flow behavior during several phases of the injection cycle at multiple locations, particularly focusing on complex fluid dynamic behaviors that are highly three-dimensional in nature. The apparatus was also transferred between various research labs worldwide to benchmark transient MRI measurement techniques across independent groups. The results suggest an increased capacity to leverage MRI measurements for flows that are periodic in nature or have repeatable transients. |
Monday, November 22, 2021 8:52AM - 9:05AM |
H20.00005: Three-dimensional velocity measurements in pulsatile flows via Magnetic Resonance Velocimetry, 2021 MRV Challenge Laura Villafane, Tuhin Bandopadhyay, Sina Tafti, Brad P Sutton This presentation is part of the 2021 Magnetic Resonance Velocimetry (MRV) Challenge and represents the results from experiments performed at the Beckman Institute within the University of Illinois at Urbana-Champaign. Experiments were performed on a square cross-section water channel containing a periodic array of rectangular buildings and an injection site in the floor behind one building at a channel Reynolds number of 15,000. The injector was pulsed periodically to produce a transient, highly three-dimensional (3D) flow. Phase-averaged, 3D three-component velocity measurements were obtained using a 3T Siemens scanner with 30 temporal phases across the injection cycle. Additional scan conditions are outlined, as well as an overview of the experimental techniques and equipment used. Detailed results are presented for the flow behavior during several phases of the injection cycle at multiple locations, particularly focusing on complex fluid dynamic behaviors that are highly three-dimensional in nature. The apparatus was also transferred between various research labs worldwide to benchmark transient MRI measurement techniques across independent groups. The results suggest an increased capacity to leverage MRI measurements for flows that are periodic in nature or have repeatable transients. |
Monday, November 22, 2021 9:05AM - 9:18AM |
H20.00006: 2021 MRV Challenge: Results and Comparisons Michael J Benson, Christopher Elkins, Andrew J Banko, Sven Grundmann, Simon Song, Wontae Hwang, Laura Villafane, John K Eaton, David B Helmer This presentation is part of the 2021 Magnetic Resonance Velocimetry (MRV) Challenge and represents the combined results from all the participants of the challenge. The objective of this challenge is to benchmark equipment and imaging sequences for obtaining three-dimensional, phase-locked measurements of a flow with periodic unsteadiness. Four research groups have made measurements in the same apparatus comprising a square cross section water channel apparatus with a periodic array of cuboids representing buildings, motivated by applications of turbulent transport in urban areas. The apparatus that was transferred between the research labs includes detailed flow conditioning to ensure that variations in supply and exit plumbing will limit disruptions to the test section flow. The test was conducted at a Reynolds Number of 15,000 based on the channel hydraulic diameter, and the geometry includes an injector located in the floor of the channel in a building wake which is pulsed between on and off conditions. The pulsatile nature of the flow lends itself to transient measurements through the injection cycle and ensures strongly three-dimensional flow fields in each set of measurements. This presentation will focus on the results from each team, which will be compared at the injection location and through the downstream building array using velocity field contour plots, iso-surfaces, and quantities derived from the mean velocity components. Similarities and differences will be presented which can provide insight into the opportunities that state of the art MRV provides to researchers. |
Monday, November 22, 2021 9:18AM - 9:31AM |
H20.00007: Microscopic molecular tagging velocimetry within PWR bundles for wall shear stress measurements Charles Fort, Roberto Capanna, Philippe M Bardet Wall shear stress and near wall velocity profile strongly affect the thermal and hydraulic performances of nuclear fuel assemblies. There exist very few datasets that have attempted to measure the wall shear stress directly. The Reynolds number in most reactor make the numerical measurement with direct simulations out of reach for any high-performance computers, still today. In this work we implement microscopic Molecular Tagging Velocimetry (μ-MTV) for direct measurement of wall shear stress and near wall velocity profile around fuel bundle rods in a geometry typical of pressurized water reactors (PWR). MTV is a non-intrusive time-of-flight technique that relies on fluorescent molecules as tracers. One key benefit of MTV is the ability to write lines or patterns within the fluid (without need for solid particles).To obtain high resolution and accurate data, the laser light and the images need to be delivered and collected locally with custom optics, optical fibers and borsescopic imaging. In the paper a demonstration design with typical data available from this technique will be illustrated with the goal of proving the capabilities of this technique. |
Monday, November 22, 2021 9:31AM - 9:44AM |
H20.00008: High-spatio-temporal resolution molecular tagging velocimetry by photobleaching of rhodamine 6G Philippe M Bardet, Charles Fort Molecular tagging velocimetry (MTV) is a non-intrusive optical diagnostic well suited to measure velocity gradients. However, in liquids, the technique has suffered from limited temporal and spatial resolutions and the need for specialized lasers. Here, rhodamine 6G dye is the molecular tracer in a two-laser write/read configuration. A frequency-tripled, pulsed, Nd:YAG laser photobleaches the dye efficiently. The read signal is a laser-induced fluorescence of the untagged dye by a green (frequency-doubled Nd:YLF) laser, leading to images of a dark pattern against a bright background. The write process is prompt (order of nanoseconds) enabling very short read times; it is also permanent. Additionally, very fine patterns (tens of micrometers) are generated by Talbot-effect structured illumination. With those improvements, MTV by photobleaching 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 spatial resolution of 25 micrometer and repetition rate of 10 kHz. |
Monday, November 22, 2021 9:44AM - 9:57AM |
H20.00009: A MTV Based Plenoptic Microscope to Measure Small-Scale Velocity Gradients Peter D Huck, Charles Fort, Philippe M Bardet Determination of small-scale velocity gradients and frictional drag in near-wall regions is fundamental for understanding overall resistance in ships moving at low to moderate speed. We present a novel measurement technique based on Molecular Tagging Velocimetry (MTV), used to determine the two wall-parallel velocity components in three dimensions (3D-2C) within the viscous sublayer of a turbulent channel flow using a single plenoptic camera. The Talbot Effect Structured Illumination (TESI) method creates an array of small diameter (30 um) beamlets extending in the wall-normal direction with 300 um) periodicity. The pattern is photobleached in rhodamine 6G dye with a frequency-tripled Nd:YAG laser (355 nm); the write pulse. A frequency-doubled Nd:YLF laser (527 nm) excites the remaining fluorescent dye (the read pulse). The laser induced fluorescent signal permits visualizing the initial pattern and its deformation by local flow structures. A plenoptic microscope (3x) resolves the wall-parallel velocity components in the wall-normal direction, giving the velocity gradient. Due to the continuous nature of the photobleached signal, the resolution of the velocity gradient is as good as the 3D reconstruction algorithm. Novel algorithms tailored to TESI-MTV are presented which improve the resolution of a non-opaque object. |
Monday, November 22, 2021 9:57AM - 10:10AM |
H20.00010: Experimentally Validated Image Simulations of Tracer Particles for Laboratory-Scale X-Ray PIV Jason Parker, Simo A Makiharju We evaluate two simulation methods for prediction of X-ray PIV (XPIV) system performance: Beer-Lambert (BL) ray tracing and Monte Carlo N-Particle (MCNP) photon tracking. These simulation tools enable the design and methodical improvement of XPIV experiments and tracer particles. Simulated and experimental data of hollow, silver-coated, glass sphere tracer particles (AGSF-33) are compared. We also compare two tracer particles. As predicted by the simulations, the AGSF-33 particles are visible with a signal-to-noise ratio greater than unity in 100ms exposure time images, demonstrating their potential as XPIV and XPTV tracers. Although BL simulations neglect scattering detections, among other simplifications, the BL approach provides a first-order estimate of the system behavior and is computationally cheap. BL enables exploration of a vast parameter space for system design. MCNP simulations, on the other hand, more accurately predict experimental images. For most applications, however, the order of magnitude greater computational expense of MCNP may not be justified by the improved performance compared to BL. Additionally, we present data showing the localizability of 10 micrometer-scale, neutrally buoyant tracer particles along with preliminary in-lab XPIV measurements. |
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