Particle Tracking Thesis 2018

2D/3D PTV Application and Technique

Particle Tracking Velocimetry Thesis
Abstract: Shallow mixing layers have been the subject of many experimental studies, yet further understanding of the hydrodynamics of shallow flows is important to better predict their effect on the dispersion of pollutants/nutrients, sediment transport, and erosion processes. Understanding the hydrodynamics and the characteristics of shallow flows requires a fully three-dimensional (3D) observation of the flow and its turbulent structures. This thesis is a first attempt to study shallow mixing layers in the near-field of coflowing streams using a Lagrangian reference frame by applying 3D Particle Tracking Velocimetry (3D-PTV). The present study investigates a simplified laboratory model of a river confluence modelled by parallel coflowing streams with different velocities (U1 = 0.45 m/s, U2 = 0.31 m/s) between which a shallow mixing layer develops. A new shallow recirculating glass flume, with dimensions of 9 m x 1.5 m x 0.25 m, (glass walls and bed) was set up for experiments for one turbulent hydraulic condition (mean Re = 24,700), having a water depth of 6.5 cm and a bed slope of zero. 3D-PTV measurements were made from the end of a splitter plate to a distance of 30 cm in the downstream direction using three high speed (600 Hz) and high-resolution (2016x2016 pixels) CCD cameras positioned to record images from below the glass flume bed. Information on the flow field was extracted from the image sequences using OpenPTV. The flow was seeded with rice bran wax microspheres (Florabeads RBW) with a specific gravity ~ 1 at 25°C and natural color, illuminated with halogen lamps. The 3D-PTV system was calibrated using a solid 3D calibration object. The data from 3D-PTV was post-processed to obtain the velocity flow field, which was in turn analyzed to obtain velocity time-series and shallow mixing layer transverse profiles for mean streamwise velocity and turbulent intensity, as well as instantaneous velocity information at different downstream positions.A shallow mixing layer formed from coflowing streams can be divided into two regions in the downstream direction, a near-field zone in which the flow defined by the initial geometry evolves into a mixing layer and a self-similar region in which the mixing layer has developed its characteristic properties. In this first stage of investigation, the first 30 cm of the near-field were studied. In this region, the following flow characteristics were observed. Boundary layers, developing along the splitter plate dividing the parallel channels, result in a wake or velocity deficit at the streams confluence (at the end of the splitter plate). This velocity deficit decreases in magnitude in the downstream distance but has not fully decayed by x=30 cm. The wake has a high turbulent intensity, as it is a shear layer forming due to the velocity gradient between the free streams and the velocity deficit, which decreases as the velocity deficit decreases in magnitude with downstream distance. The wake formed by the splitter plate is reducing, which limits establishment and growth of the mixing layer, causing the width of the shear layer to remain constant over the measurement distance and shifts towards the slower moving stream due to transverse momentum transfer. Lastly, the development of a secondary circulation is possibly appearing by the end of the measurement distance, as in instantaneous flow sections, transverse flow towards the slow stream appears at the surface and towards the fast stream at the bed. Keywords: 3D-particle Tracking Velocimetry (PTV) ; OpenPTV;
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Author: Claudio S. M. Consuegra Martínez
HSFB Thesis Particle Tracking
Abstract A new type of tracer is making its entry in the scenario of wind-tunnel measurements: helium-filled soap bubbles (HFSB). The present work discusses the main fluid-dynamic and optical properties of HFSB to evaluate their use for quantitative measurements in aerodynamic experiments.In the past three decades, particle image velocimetry (PIV) has become a standard measuring technique in experimental fluid mechanics. Advances in both hardware components and software analysis have allowed achieving many milestones in flow diagnostics, mainly time-resolved and instantaneous volumetric measurements. In particular, the extension to the third dimension in space, i.e. tomographic PIV and 3D particle tracking velocimetry (PTV), has been used to provide quantitative visualizations of the coherent structures occurring in various turbulent flows and have provided insight in the spatial organization of the turbulent motions at different scales. The extension of the aforementioned techniques towards industrial practice in wind tunnel testing requires the development of a more efficient approach in terms of scaling and versatility.The present dissertation tackles the upscaling of PIV experiments towards industrial wind tunnels with the use of HFSB as tracing particles. The reasons and motivations behind this choice are addressed in the first chapter and followed by a description of the state-of-the-art of PIV. The second chapter aims at familiarising the reader with the working principles of PIV, which will be later recalled when presenting the advances towards large-scale experiments. Information on the mechanical behaviour of tracer particles and on the underlying physics are discussed in the third chapter, where also the case of HFSB is examined for use during quantitative measurements in the low-speed flow regime. The problem of seeding in wind tunnels is discussed in chapter 4, where a system for the injection of HFSB in a large wind tunnel is presented. Here, the relationship between HFSB production rate and the resulting spatial concentration and dynamic spatial range (DSR) are discussed. Specific experiments that examine the tracing fidelity of sub-millimetre HFSB tracers are presented in chapter 5. The behaviour of HFSB is compared to micro-size droplets, yielding a characteristic response time in the range of 10 μs. The latter milestone opens up to the applicability of HFSB tracers for quantitative velocimetry in wind tunnel flows. In chapter 6, a specific case of interest is presented whereby HFSB tracers are used to measure the flow velocity within steady vortices such as those released at the tip of wings. A dedicated experiment shows that the neutrally or slightly buoyant HFSB return a rather homogeneous spatial concentration within the core of vortices, solving the long-standing issue encountered for small heavy tracers, such as fog droplets, that are systematically ejected from highly vortical regions. An analysis of the light scattering by HFSB was conducted with theoretical and experimental approaches, as described in chapter 7. The light intensity scattered by the HFSB is characterised by two source points: the glare points. The overall scattered light appears to be 104-105 times more intense with respect to the oil-based micro-size droplets. This information is used to retrieve the maximum size of the measurement volume for a given light source.
Keywords: helium-filled soap bubbles (HFSB); air-flow seeding; large-scale Particle Image Velocimetry (PIV); Tomo-PIV; 3D- Particle Tracking Velocimetry (PTV)
Thesis PDF link: repository.tudelft.nlThesis Author: Caridi, Giuseppe Carlo Alp
Particle Tracking Velocimetry: A Review Thesis
Abstract: Particle tracking velocimetry (PTV) and particle image velocimetry (PIV) are methodologies that allow for volumetric velocity measurements within a fluid flow by imaging the motion of suspended micron-size particles. The only difference between the techniques is that PTV tracks the motion of individual particles, while PIV measures the mean displacement of groups of particles. PIV is more commonly used that PTV, and thus the techniques are robust and have been reviewed extensively. PTV, however, offers the advantages of increased spatial resolution and decreased computational cost. The focus of this review is to present the work that has been done to improve PTV. The review begins with an overview of the equipment required for a PTV experiment. Then, data processing algorithms are discussed for identifying particle images, mapping images to physical space, and tracking particles through time. Finally, post-processing techniques, which are used for calculating vorticity and pressure fields, are presented.
Keywords: PTV, review of recent particle tracking techniques
Thesis PDF link: digital.lib.washington.eduThesis Author: Pecora, Charles
Particle Tracking Simulation Thesis
Abstract: Visualization methods of fluid data are crucial for studying flows and turbulence, and one of the most common methods of simulation is particle tracking velocimetry (PTV). In this project, the visualization of flow is studied using PTV simulation of an Oseen vortex. For statistically fitting the fluid data, two main methods were used: regressive fitting and spline fitting. Final fits of data were done using Kriging, which is a sophisticated regression method, and thin plate spline fitting. Then, comparisons of the two methods were drawn using statistical methods. Kriging yielded lower mean squared error overall, but thin plate spline fitting method takes smoothness of fit into account.In presenting this thesis in partial fulfillment of the requirements for a masters degree at the University of Washington, I agree that the Library shall make its copies freely available for inspection. I further agree that extensive copying of this thesis is allowable only for scholarly purposes, consistent with the “fair use” as prescribed in the U.S. Copyright Law. Any other reproduction for any purposes or by any means shall not be allowed without my written permission.
Keywords: PTV; Surface fitting method; Particle Tracking Simulation
Thesis PDF link:
Thesis Author: Isabelle Lee
N-pulse Particle Tracking Velocimetry Accelerometry Thesis
Abstract: Over the past three decades, particle image velocimetry (PIV) has been continuously growing to become an informative and robust experimental tool for fluid mechanics research. Compared to the early stage of PIV development, the dynamic range of PIV has been improved by about an order of magnitude (Adrian, 2005; Westerweel et al., 2013). Further improvement requires a breakthrough innovation, which constitutes the main motivation of this dissertation. N -pulse particle image velocimetry-accelerometry (N -pulse PIVA, where N ≥ 3) is a promising technique to this regard. It employs bursts of N pulses to gain advantages in both spatial and temporal resolution. The performance improvement by N -pulse PIVA is studied using particle tracking (i.e. N -pulse PTVA), and it is shown that an enhancement of at least another order of magnitude is achievable. Furthermore, the capability of N -pulse PIVA to measure unsteady acceleration and force is demonstrated in the context of an oscillating cylinder interacting with surrounding fluid. The cylinder motion, the fluid velocity and acceleration, and the fluid force exerted on the cylinder are successfully measured. On the other hand, a key issue of multi-camera registration for the implementation of N -pulse PIVA is addressed with an accuracy of 0.001 pixel. Subsequently, two applications of N-pulse PTVA to complex flows and turbulence are presented. A novel 8-pulse PTVA analysis was developed and validated to accurately resolve particle unsteady drag in post-shock flows. It is found that the particle drag is substantially elevated from the standard drag due to flow unsteadiness, and a new drag correlation incorporating particle Reynolds number and unsteadiness is desired upon removal of the uncertainty arising from non-uniform particle size. Next, the estimation of turbulence statistics utilizes the ensemble average of 4-pulse PTV data within a small domain of an optimally determined size. The estimation of mean velocity, mean velocity gradient and isotropic dissipation rate are presented and discussed by means of synthetic turbulence, as well as a tomographic measurement of turbulent boundary layer. The results indicate the superior capability of the N -pulse PTV based method to extract high-spatial-resolution high-accuracy turbulence statistics.
Keywords: PTVA; PIV; N-pulse particle image velocimetry accelerometry; N-pulse PTVA
Thesis PDF link: repository.asu.eduThesis Author: Liuyang Ding
Particle Tracking Velocimetry Thesis
Abstract: Narrow depth-of-field (DOF) comes as a price when tight lateral focusing is re- quired for applications such as high precision manufacturing and three-dimensional (3D) velocimetry. The thesis addresses the challenges in these fields by using an acoustically-driven ultrafast varifocal lens. The first part of this thesis presents the improvement in eciency of material processing by using an ultrafast varifocal lens. High-throughput laser materials processing demands precise control of the laser beam position to achieve optimal eciency, but existing methods can be both time-consuming and cost-prohibitive. Here, we demonstrate a new high-throughput material processing technique based on rapidly scanning the laser focal point along the optical axis using the ultrafast variable focal length lens. Our results show that this scanning method enables higher processing rate over a range of defo- cus distances, and that the e↵ect becomes more significant as the laser energy is increased. This method holds great potential for improving material processing eciency in traditional systems, and also opens the door to applying laser process- ing to pieces with uneven topography that have traditionally been dicult to process.The second part of the thesis presents a novel idea for high-speed 3D imaging system by using the ultrafast varifocal lens. This 3D imaging system provides a means of high-speed 3D particle tracking velocimetry. This contribution is critical because the ability to understand and visualize complex flow structures in micro-fluidic and biological systems relies heavily on the resolving power of 3D particle velocimetry techniques. The simple technique in this thesis is capable of acquiring volumetric particle information with the potential for microsecond time resolution. By utilizing a fast varifocal lens in a modified wide-field microscope, we capture both volumetric and planar information with microsecond time resolution. As a proof of concept, this technique is demonstrated by tracking particle motions in the complex, 3D flow in a high Reynolds number laminar flow at a branching arrow-shaped junction.
Keywords: 3D particle tracking velocimetry; laser material processing; PTV; TAG lens; ultrafast varifocal lenses
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Thesis Author: Ting-Hsuan Chen
Particle Tracking Velocimetry to Thermal Counterflow and Towed-Grid Turbulence in Helium II
Abstract: The superfluid phase of helium-4, known as He~II, is predominantly used to cool low-temperature devices. It transfers heat by a unique thermally driven counterflow of its two constituents, a classical normal fluid and an inviscid superfluid devoid of entropy. It also has potential use for economical reproduction and study of high Reynolds number turbulent flow due to the extremely small kinematic viscosity and classical characteristics exhibited by mechanically driven flow. A number of diagnostic techniques have been applied in attempts to better understand the complex behavior of this fluid, but one of the most useful, flow visualization, remains challenging because of complex interactions between foreign tracer particles and the normal fluid, superfluid, and a tangle of quantized vortices that represents turbulence in the superfluid. An apparatus has been developed that enables application of flow visualization using particle tracking velocimetry (PTV) in conjunction with second sound attenuation, a mature technique for measuring quantized vortex line density, to both thermal counterflow and mechanically-driven towed-grid turbulence in He~II. A thermal counterflow data set covering a wide heat flux range and a number of different fluid temperatures has been analyzed using a new separation scheme for differentiating particles presumably entrained by the normal fluid ("G2") from those trapped on quantized vortices ("G1"). The results show that for lower heat flux, G2 particles move at the normal fluid velocity vn, but for higher heat flux all particles move at roughly vn/2 ("G3"). Probability density functions (PDFs) for G1 particle velocity vp are Gaussian curves with tails proportional to |vp|⁻³, which arise from observation of particles trapped on reconnecting vortices. A probable link between G1 velocity fluctuations and fluctuations of the local vortex line velocity has been established and used to provide the first experimental estimation of c₂, a parameter related to energy dissipation in He~II. Good agreement between the length of observed G2 tracks and a simple model for the mean free path of a particle traveling through the vortex tangle suggests that flow visualization may be an alternative to second sound attenuation for measurement of vortex line density in steady-state counterflow. Preliminary PTV and second sound data in decaying He~II towed-grid turbulence shows agreement with theoretical predictions, and enables reliable estimation of an effective kinematic viscosity and calculation of longitudinal and transverse structure functions, from which information about the energy spectrum evolution and intermittency enhancement can be obtained.
Keywords: PTV; Towed-Grid Turbulence
Thesis PDF link:
Thesis Author: Mastracci, Brian