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 G30: Experimental Techniques: Velocimetry and Permeability |
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Chair: Zifeng Yang, Wright State University Room: Georgia World Congress Center B402 |
Monday, November 19, 2018 10:35AM - 10:48AM |
G30.00001: Design and Development of a Smartphone-Based Particle Image Velocimetry System Vishesh Kashyap, Sushrut Kumar, Nehal Amit Jajal, Mrudang Mathur, Raj Kumar Singh Our research focuses on developing a smartphone-based Particle Image Velocimetry (PIV) system for use in educational and research purposes. Due to the high cost of components, a number of institutions across the world do not possess a PIV system for flow visualisation. Low-cost, accessible PIV systems are an essential requirement in such cases, which will also enable them to be included as a part of laboratory courseware for students. In our system, developed open-channel flow is visualised around a cylindrical body using smartphone cameras and low-intensity laser diodes. Hydrogen bubbles generated from electrolysis (termed Bubble Image Velocimetry) are used as a seeding medium. OpenPIV, an open-source MATLAB toolbox, is used to track particle motion and obtain flow profiles and velocities accurately, with flow separation and vortex formation being observed. A parametric analysis of smartphone cameras of different specifications is conducted, across varying camera characteristics such as ISO, exposure and frame rate. A base camera specification for PIV is hence determined. A low-cost (under USD 200), accessible yet accurate Particle Image Velocimetry system is so obtained. |
Monday, November 19, 2018 10:48AM - 11:01AM |
G30.00002: Underwater PIV Systems Callum Gray, Radomir Beslac, Christina Hesseling, Joseph Calantoni, Sean Griffin, Edward Braithwaite III, Bradley Lingsch Meaningful oceanographic PIV measurements cannot always be achieved within a conventional laboratory environment with digital cameras and pulsed laser positioned outside a wave flume or wide tank. Studying ship dynamics in a wide tank, for example, requires a PIV system that can be mounted onto a superstructure and towed, submerged alongside the model. A modular system of cylindrical torpedoes for housing cameras singly, in stereo pairs or even multi-camera configurations has been developed along with beam delivery and sheet or volume illumination optics that can be mounted rigidly relative to the cameras. Taking this concept further a stereo PIV system has been developed that can be submerged in the ocean and operated remotely from a distance of 1.5km for periods of days or weeks without being brought to the surface. Details of implementation and results from both systems are presented. |
Monday, November 19, 2018 11:01AM - 11:14AM |
G30.00003: Image automasking for dual-sided stereo PIV measurements of wind-driven waves Matthew Stegmeir, Corey D Markfort An automasking technique for multiphase interface identificantion is presented, along with sample application to Time Resolved PIV measurements of wind-driven wave flow. Measurements are performed on both sides of air-water interface in order to study the coupling between air and fluid motion. High resolution and dynamic range in space and time and accurate interface identification are required to resolve relevant flow scales along a complex and ever-changing interface. Approaches to obtain near-boundary measurement on both sides of interface are discussed, including optimal flow seeding procedures, illumination, data analysis, and interface tracking. Techniques are applied to the IIHR Boundary-Layer Wind-Wave Tunnel. The facility combines a 30m long recirculating water channel with an open-return boundary layer wind tunnel, allowing for the study of boundary layer turbulence interacting with a wind-driven wave field. |
Monday, November 19, 2018 11:14AM - 11:27AM |
G30.00004: Benchmarking particle shadow velocimetry (PSV) with particle image velocimetry (PIV) using higher-order statistics Christine Truong, Jeff Harris Planar PIV and PSV are used to measure the velocity of a fully-developed turbulent pipe flow at the 11.2” diameter glycerin tunnel at Penn State. The turbulent energy spectrum is calculated from both PIV and PSV, and compared. PSV is a type of PIV that uses an in-line backlight to illuminate particles, so shadows are recorded. The shadows are inverted as to appear as an image acquired using PIV. Because the inverted image will typically contain more out-of-focus particles, PSV has a higher noise level than PIV. While previous works by the authors suggest that the ability to estimate velocity based on PSV images should be similar to that of PIV images, more rigorous analysis is needed to examine how noise in PSV affects the measured velocity. To do this, PSV is used to measure velocity in a fully-developed turbulent pipe flow. Turbulence statistics, such as the mean velocity, velocity correlations, and turbulent energy spectrum, are obtained. These measurements are compared to those obtained using PIV at the same facility. It is expected that this will demonstrate the effectiveness of PSV as type of velocimetry akin to PIV, and encourage the use of PSV in the velocimetry world. |
Monday, November 19, 2018 11:27AM - 11:40AM |
G30.00005: Soap Film Patterns Versus Flow Structures: Do they match? Javad Eshraghi, Mark Andrew Stremler, Pavlos Vlachos Flowing soap films are widely used to visualize two-dimensional hydrodynamics. In that regard, interference fringe visualization is one of the most common methods. In this method, soap film fringes appear based on the thickness of each grid point in the flow field, while the thickness itself is a function of the velocity at that point. Contrary to this qualitative visualization, Particle Image Velocimetry (PIV) is applied to obtain a quantitative description of the velocity field and subsequently the flow structures. However, correlation between fringe patterns and underlying flow structures, which is crucial in understanding of complex wakes, has remained unexplored. Here, the challenge is a simultaneous comparison between the identified flow structures and visualized soap film patterns. In this study, we conduct a well-controlled experiment and characterize the flow field behind a stationary cylinder by applying simultaneous PIV measurement and interference fringe visualization in a vertical flowing soap film. This helps us obtain the flow structures from PIV and compare them with visualized fringe patterns. |
Monday, November 19, 2018 11:40AM - 11:53AM |
G30.00006: Flow velocimetry based on dye visualization image of tubing flow using optical flow method Zifeng Yang, Pranay S Pawar, Hongjie Zhao In the present study, a flow visualization experiment was carried out to mimic the transmission-based X-ray imaging process. The flow visualization experiment was performed in a water tubing flow with a tube of internal diameter of 0.375 inch. A pulsating pump connected to a reservoir provides a pulsed flow with the output phase ratio of 36/64, a rate of 50 Hz, and a stroke volume of 15 CC. Red dye was used as the flow tracer. The dye was introduced through a thin tubing connected to a powered dye injector with a constant flow rate of 20 ml/min. A constant light source was placed behind the tube to provide the necessary illumination. Transmission images of the tubing flow were captured using a high-speed camera with a frame rate of 2000 FPS. Optical flow method was adopted to recover the flow field as it provides a high-resolution velocity estimation of the flow. Continuous flow patterns within 2 sec were visualized and quantified based on the transmission image of the mixing flow. The recovered flow velocity map was quantitatively compared to the Particle Image Velocimetry measurement results with the same flow condition. Although different time intervals were used to obtain the best accuracy for each technique, the overall agreement is excellent. |
Monday, November 19, 2018 11:53AM - 12:06PM |
G30.00007: Performance characteristics of a wavelet-based optical flow method for velocimetry from tracer particle images Bryan E Schmidt, Jeffrey A Sutton We present a wavelet-based optical flow (WOF-X) method designed for velocimetry from experimental image pairs of tracer particles. The accuracy of the method is assessed and compared to conventional correlation-based PIV using synthetic tracer particle images that are transported by a simulated two-dimensional flow field. The performance of both methods is evaluated for different values of inter-frame particle displacement and particle seeding density. Optimal values for these parameters are found for both methods, and it is observed that the optical flow method out-performs correlation-based PIV in terms of accuracy and spatial resolution; that is, WOF-X produces a dense estimate of the velocity field (i.e. one velocity vector per pixel). The dynamic range is computed for both methods and the sensitivity to out-of-plane displacement of tracer particles also is assessed. |
Monday, November 19, 2018 12:06PM - 12:19PM |
G30.00008: Molecular tagging velocimetry for shocked particle interactions John Charonko, Ankur Deep Bordoloi, Katherine P Prestridge Knowledge of the unsteady particle kinematics behind a shock wave is important for the understanding of many flows in extreme environments, such as supernovae and the distribution of blast debris in explosions. However, recent measurements of shock-accelerated particles indicate that drag coefficients are an order of magnitude larger than existing models would predict (Bordoloi et al. 2017). This discrepancy cannot be explained by current theory, and simulations in such regimes are extremely challenging. This leaves a need for experimental measurements of the flow around the accelerating particles to explain the unknown unsteady effects. We are developing a velocity diagnostic to measure the flow field behind a shock, targeting simultaneous measurement of the particles’ motion and the carrier phase gas velocity. Techniques like particle image velocimetry are limited by the response time of tracer particles. We overcome this difficulty by using acetone-based molecular tagging velocimetry, with the goal being to implement it simultaneously with a particle tracking system. In this presentation, we will demonstrate the accuracy of our method on simple laminar and turbulent flows, and show our progress toward its implementation on shocked particle flows. |
Monday, November 19, 2018 12:19PM - 12:32PM |
G30.00009: Measuring particle collision rates Reece Kearney, Gregory P Bewley Collisions between particles in turbulent flow are important in a variety of natural and industrial processes, including rainfall and combustion. A great deal of work has been done to predict and simulate the interactions between particles, though no one has yet measured collision rates with well-understood uncertainties in such settings. We introduce a new computer algorithm to track particles and measure particle collision rates. We characterize the uncertainty of the method by testing it on synthetic data and then use the new method to measure collision rates of real water droplets in a simple benchtop experiment. In this experiment, we vary the diameters of the droplets between 10 and 300 microns and observe collisions varying the impact parameter between 0 and 1 and the Weber number from 0.1 to 20. |
Monday, November 19, 2018 12:32PM - 12:45PM |
G30.00010: A novel method to measure 3D permeability of highly porous materials Christoph Efstathiou, Anika Todt, Mitul Luhar Characterization of the complete three-dimensional (3D) permeability of porous materials is important for a range of industrial applications, from the manufacturing of composites to the extraction of oil and gas. Previous studies have developed methods to estimate the 1D or 2D permeabilities of samples, but there are few methods that can completely characterize the permeability matrix that appears in the 3D generalization of the Darcy-Forchheimer relation. To address this need, we have developed a constant-flow 3D permeameter that simultaneously measures the pressure drop across confined porous samples in all three directions (c.f., the more traditional constant-head or falling-head 1D systems). Pressure gradient measurements are translated into estimates for permeability using the Darcy-Forchheimer relation. We have also designed and 3D-printed a range of anisotropic porous lattices with pore sizes ranging from 0.6 mm to 2.0 mm and porosities >80% to test this new system. The measured permeabilities show good agreement with predictions from numerical simulations. |
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