Three-dimensional Particle Image Research Articles

Influence of sweep angle on leading edge vortex dynamics of a fully passive oscillating-plate hydrokinetic turbine prototype

The present work assesses the use of spanwise flow in enhancing the performance of the fully passive oscillating-plate hydrokinetic turbine prototype by relating the dynamics of the leading edge vortex (LEV) to the power extraction performance. Two-dimensional (2D) planar and three-dimensional (3D) tomographic particle image velocimetry were employed to obtain quantitative flow structure of oscillating-plates undergoing heave and pitch motion in uniform inflow at Reynolds number of 21 000. A plate with a 6° sweep angle and an unswept plate (control case) were considered in the present study. Dynamics of the LEV were investigated using the patterns of the phase-averaged vorticity during the oscillation cycle. The 3D vector fields provided insights into the spanwise variation of the vortical structure and the rate of deformation of the vortex, which was determined by calculating the deformation terms in the vorticity transport equations which are related to the stability of the vortex. The results show evidence of a delay in the shedding of the LEV and an increase in its stability in the case of the swept plate, compared to the control case, which in turn benefit the power extraction performance at high inflow velocities.

Second order and transverse flow visualization through three-dimensional particle image velocimetry in millimetric ducts

Despite recent advances in 3D particle image velocimetry (PIV), challenges remain in measuring small-scale 3D flows, in particular flows with large dynamic range. This study presents a scanning 3D-PIV system tailored for oscillatory flows, capable of resolving transverse flows less than a percent of the axial flow amplitude. The system was applied to visualize transverse flows in millimetric straight, toroidal, and twisted ducts. Two PIV analysis techniques, stroboscopic and semi-Lagrangian PIV, enable the quantification of net motion as well as time-resolved axial and transverse velocities. The experimental results closely align with computational fluid dynamics (CFD) simulations performed in a digitized representation of the experimental model. The proposed method allows the examination of periodic flows in systems down to microscopic scale and is particularly well-suited for applications that cannot be scaled up due to their complex, multi-physics nature.

Advancement in computational simulation and validation of congenital heart disease: a review

The improvement in congenital heart disease (CHD) treatment and management has increased the life expectancy in infants. However, the long-term efficacy is difficult to assess and thus, computational modelling has been applied for evaluating this. Here, we provide an overview of the applications of computational modelling in CHD based on three categories; CHD involving large blood vessels only, heart chambers only, and CHD that occurs at multiple heart structures. We highlight the advancement of computational simulation of CHD that uses multiscale and multiphysics modelling to ensure a complete representation of the heart and circulation. We provide a brief future direction of computational modelling of CHD such as to include growth and remodelling, detailed conduction system, and occurrence of myocardial infarction. We also proposed validation technique using advanced three-dimensional (3D) printing and particle image velocimetry (PIV) technologies to improve the model accuracy.

Three-dimensional particle image velocimetry experimental study of transient motion characteristics of different scale vortices in gasoline engine

The paper adopted three-dimensional (3D) Particle Image Velocimetry (PIV) combined with high-speed measurement technology to study the transient motion characteristics of tumble flow induced by small and medium-sized vortices on an optical gasoline engine. Meanwhile, the Proper Orthogonal Decomposition (POD) method was introduced to analyze the evolution of transient vortices, revealing the three-dimensional motion principle of vortices with different spatial scales within the cylinder. The results showed that increasing the engine speed can cause boosted in-plane and out-of-plane velocity, especially for the in-plane velocity. However, the average velocity in the plane was higher than that out of the plane with the difference generally within an order of magnitude. The strong intake jet was the main reason for bringing turbulent kinetic energy in the cylinder. The average kinetic energy and turbulent kinetic energy in the cylinder are both significantly improved at high engine speed. From the results of this experiment, it was revealed that there exists isotropic turbulent pulsation characteristics. Overall, the corresponding flow characteristics of different decomposed modes were different. The first mode section had the lowest average velocity ratio, while the other two had the highest. Due to the dissipation of large vortices into small vortices or the shear action between flow layers, new vortices were generated, leading to the intermittent phenomenon of the motion path of the vortex cluster in the target plane. The average vortex size and velocity circularity corresponding to two varied engine speeds presented a downward trend. The average vortex size was smaller at high engine speed, while the vortex intensity was higher. In addition, increasing the engine speed would decrease the vortex scale but increase the vortex strength. This work provided new fundamental insights into analyzing the characteristics of micro-scaled vortices in turbulent flow, as well as the organization of intake in the gasoline engine.

Three-dimensional particle image velocimetry measurement through three-dimensional U-Net neural network

This paper proposes a light field (LF) three-dimensional (3D) particle image velocimetry (PIV) method based on a digital refocused algorithm and 3D U-Net neural network for 3D three-component (3D-3C) velocity measurement. A digital refocused algorithm is used to generate a stack of LF-refocused images of tracer particles for establishing the 3D U-Net. The 3D U-Net is then used for the 3D particle field reconstruction. Based on a pair of 3D particle fields, the 3D-3C velocity field is obtained through a 3D cross correlation algorithm. Numerical simulations and experiments are conducted to analyze the accuracy and efficiency of the proposed method. The simulation results show that the elongation along the depth direction and the efficiency of the 3D particle field reconstruction are improved by the 3D U-Net. The 3D U-Net also provides a better correlation coefficient. The experimental results show that the reconstruction time of the proposed method is ∼220 s which is 10 times faster than the LF tomographic PIV. This further demonstrates that the proposed method improves the reconstruction efficiency without affecting the accuracy of velocity measurement.

Effect of turbulent coherent motion on the onset of particle transport using synchronized 3D PIV and PTV

A series of laboratory experiments was conducted to understand the role of unsteady coherent motions of turbulent flow in the onset of particle motion. Turbulent eddies having coherent structures constantly interact with sediment particles within the bottom boundary layer. Therefore, a 3D turbulent flow field and grain trajectories were obtained by the simultaneous operation of three-dimensional (3D) particle image velocimetry and particle tracking velocimetry. Characteristics of the grain motions were investigated with the various particles in the various flow conditions. Based on the Stokes number of sediments, the spectral density of flow field revealed that turbulent eddies in the production subrange initiate grain motion. The proper orthogonal decomposition extracted the flow fields in the production subrange and the quadrant analysis was used to define dominant turbulent event initiating particle motions in the different flow conditions. The events of outward interaction and sweep initiated particle motion under low-velocity conditions, whereas those of sweep and ejection frequently occurred at the onset of particle motion under high-velocity conditions. Based on the results of the quadrant analysis, we proposed a transition curve that determines the dominant turbulent event depending on the flow condition on the conventional Shields diagram

Analysis of the information overlap between the PIV and [formula omitted] chemiluminescence signals in turbulent flames using a sparse sensing framework

The purpose of this study is to quantify the information overlap between the OH* chemiluminescence signal and the three-dimensional Particle Image Velocimetry (PIV) signal for a set of bluff-body stabilized, swirling and non-swirling turbulent methane/air flames issued from the Cambridge/Sandia Stratified Swirl Burner. The time-resolved velocity data was collected using high-speed stereoscopic PIV operated at 3 kHz. This sampling rate was sufficiently high to enable accurate tracking of the large-scale spatial and temporal features of the flow. To investigate flame-flow interactions, high-speed (8 kHz) OH* chemiluminescence imaging was applied on the same set of flames. The two datasets are first independently analyzed using multi-scale Proper Orthogonal Decomposition (mPOD) for the purpose of detecting the relevant flow and heat release rate structures. The resulting modes are qualitatively compared to assess if it is possible to identify the same flow structures from the two datasets. Finally, the information overlap is quantified by predicting the velocity field from the chemiluminescence signal using a sparse sensing framework. Sparse sensing is a mathematical technique that leverages the low-dimensional representation of a physical phenomenon to predict the entire state of the system using few measurements. The results show that the velocity and chemiluminescence mPOD modes display broadly similar features, from which is possible to retrieve the same flow instabilities in the corresponding frequency range. Moreover, the prediction of the velocity field obtained using chemiluminescence as input of the sparse sensing model achieves a good level of accuracy, pointing to an important degree of information overlap between the two signals.

Revisiting RANS turbulence modelling used in built-environment CFD simulations

The strong commitment of European Union (EU) to energy efficiency and the increasing energy prices will put pressure on the building sector to find solutions that are simultaneously very low-level or nearly zero energy-consuming, efficient, thermally comfortable and disease free. In the pursuit of such solutions, Computational Fluid Dynamics (CFD) has been used, with great success, in predicting and optimizing built-environment flows. Nonetheless, it is known that the choice of the turbulence model and the way in which it treats the near wall region, influences the quality of the yielded results. A set of experimental three-dimensional particle image velocimetry (3D PIV) data is used to assess the predictive ability of six turbulence models, commonly used in built-environment simulations, together with two new variants of the turbulence model k−ε−v‾2−f. The phenomena variables, inside a 1:30 lab-scale room, with an emulated occupant were computed for two different ventilation strategies, displacement and mixing. Only the k-ε RNG VisEff and the original ‘code-friendly’ variant of the k−ε−v‾2−f (LKM) coherently described the two simulated flows. Furthermore, it was not unequivocal that obeying the dimensionless wall distance (Y+) less than 1 rule, for the first grid node, guaranteed the enhancement of the computed results. The integration of the Standard Wall Functions (SWF) with the k−ε−v‾2−f (LKM) turbulence model proved to yield more accurate and less grid-dependent results than the stand-alone k−ε−v‾2−f (LKM) model, showing, simultaneously, a predictive ability similar to that of the k-ε RNG VisEff model, despite the lower computational complexity of the latter.

Development of Small-Rabbit-Scale Three-Dimensional Magnetic Particle Imaging System With Amplitude-Modulation-Based Reconstruction

Magnetic particle imaging (MPI) is an emerging noninvasive molecular imaging method that can image the concentration and position of superparamagnetic iron oxide nanoparticles. Its applications in the biomedical field are increasing rapidly. However, the scalability of MPI is the major barrier to its clinical use at the moment. For a large bore size of MPI, it is important to achieve a high magnetic gradient for high image resolution with a large field-of-view (FOV) while allowing fast scanning and high sensitivity. In this article, we present a small-rabbit-scale three-dimensional (3-D) amplitude modulation (AM) MPI system with a bore size of 90 mm and a high magnetic gradient of up to 4 T/m/μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . The AM MPI with a soft core can allow a large FOV and good resolution while minimizing the peripheral nerve stimulation constraint and hardware requirements. This new design guideline and optimum design parameters of 3-D AM MPI for scalability were suggested and verified by simulation and experimental studies to allow fast scanning with high resolution and high sensitivity while avoiding vibration and heating issues.

Three-dimensional color particle image velocimetry based on a cross-correlation and optical flow method

Rainbow particle image velocimetry (PIV) can restore the three-dimensional velocity field of particles with a single camera; however, it requires a relatively long time to complete the reconstruction. This paper proposes a hybrid algorithm that combines the fast Fourier transform (FFT) based co-correlation algorithm and the Horn–Schunck (HS) optical flow pyramid iterative algorithm to increase the reconstruction speed. The Rankine vortex simulation experiment was performed, in which the particle velocity field was reconstructed using the proposed algorithm and the rainbow PIV method. The average endpoint error and average angular error of the proposed algorithm were roughly the same as those of the rainbow PIV algorithm; nevertheless, the reconstruction time was 20% shorter. Furthermore, the effect of velocity magnitude and particle density on the reconstruction results was analyzed. In the end, the performance of the proposed algorithm was verified using real experimental single-vortex and double-vortex datasets, from which a similar particle velocity field was obtained compared with the rainbow PIV algorithm. The results show that the reconstruction speed of the proposed hybrid algorithm is approximately 25% faster than that of the rainbow PIV algorithm.

Experimental Study of Flow Hydrodynamics Around Circular Cylinder Arrangements Using Particle Image Velocimetry

AbstractThis study investigates the turbulent flow properties experimentally in the vicinity of two side-by-side circular cylinders, along with the influence of the third cylinder of the same dimension placed in the upstream and successively in the downstream forming an equilateral triangle. Three-dimensional stereoscopic particle image velocimetry (PIV) was employed to collect the instantaneous velocity data around the arrangements. The study highlights the prime parameters of turbulence such as the mean velocities, Reynolds stresses, turbulent kinetic energy (TKE), quadrant analysis, and Q-criteria for vortices, which are responsible for the development of various problems such as scour-hole around the cylindrical pier arrangements, disturbance around industrial and marine structures. The spectral analysis was performed to examine the energy distributions, vortex-shedding frequencies with corresponding Strouhal numbers. Dominant vorticity locations were identified from the contours of Q-criteria. The magnitude of turbulence characteristics was reduced by 15–20% (turbulence intensity reduced by 20% and TKE by 15%) when the third cylinder was placed the upstream of side-by-side cylinder group. Streamlines are also studied to visualize the flow patterns for a better understanding of physics in the presence of the third cylinder. The maximum energy of vortices obtained from the spectrum analysis showed that the vortices generated were less when the third cylinder is placed upstream.

Experimental analysis of the effect of dynamic induction control on a wind turbine wake

Abstract. Dynamic induction control (DIC) has proven to be an effective method of increasing the power output for a wind farm in both simulation studies and wind tunnel experiments. By pitching the blades of a wind turbine periodically, the recovery of the low-velocity wake is accelerated, thereby increasing the energy available to downstream turbines. The wake itself of a turbine operating with DIC has not yet been studied experimentally. This paper presents a wind tunnel experiment where the wake of a wind turbine under periodic excitation is investigated. Using three-dimensional particle image velocimetry, the velocity field behind the turbine was reconstructed. Analysis of the velocity fields indicated that the available power in the wake increases when using DIC. This increase was partially due to a lower average thrust force experienced by the turbine with DIC. However, a large difference was seen between measurement results and actuator disk theory, indicating enhanced recovery of the wake is contributing to the increased energy. Instantaneous measurements visualizing the development of blade tip vortices also showed how the location of vortex breakdown, which is directly related to re-energizing the wake, shifts over time with DIC. We believe this shifting location is contributing to the enhanced wake recovery of DIC, providing more energy to downstream wind turbines.

Characteristics of a Single Sensor Fiber-Coupled Three-Dimensional Particle Image Velocimetry for Reacting Flow-Fields

Abstract Tomographic particle image velocimetry (Tomo-PIV) has become a standard tool for capturing a three-dimensional (3D) velocity fields in nonreacting flows. However, the diagnostic approach can become costly and challenging to implement when extended to applications which require high-speed cameras. This limitation has led to the use of fiber wound bundles to allow for multiple views to be captured on a single camera sensor. Additionally, employing this diagnostic approach on reacting flow-fields becomes more complex as the introduction of the flame causes additional luminosity and optical distortion which impacts the particle field reconstruction. This work seeks to validate and determine the limitations when utilizing a single sensor fiber-coupled approach for capturing Tomo-PIV data on a reacting flow-field. A premixed propane (C3H8) and air Bunsen burner flame is utilized to examine if the single sensor approach can meet the parameters for acceptable reconstruction based on previous research. The resulting velocity fields are then compared to a traditional PIV measurement to assess the deviation of the single sensor approach from a standard velocimetry measurement approach. It is demonstrated that there is strong agreement between the velocity and vorticity for the average flow-fields; however, when comparing the Reynolds shear stresses, a significant deviation is revealed. The deviation is attributed to strong velocity fluctuations occurring within the instantaneous Tomo-PIV data, which creates a significant divergence between the measurement techniques on an instantaneous basis. This demonstrates that while the approach can obtain reliable velocity and vorticity statistics, there are significant limitations in calculating second-order turbulence statistics. Thus, revealing that there is a tradeoff between the ability to extract the full velocity gradient tensor and the extent of the turbulence-related analysis which can be reliably performed.

RESEARCH ON THE INFLUENCE OF FREE SURFACE ON THE FLOW CHARACTERISTICS OF SUBMARINE WAKE

The flow characteristics around the submarine will affect the maneuverability of the submarine, especially when the submarine is near the water surface, the existence of the free surface will increase the complexity of the wake field of the submarine. In order to explore the influence mechanism of free surface on the flow characteristics of submarine wake when the submarine near the free surface, the research on the flow characteristics of submarine wake is carried out with the help of large-scale underwater three-dimensional particle image velocimetry technology. Firstly, the accuracy of the test method in this study is verified by the standard model experiment of DTMB in USA; Then, the wake field of the submarine is measured by the model test, and the axial velocity and pulsating velocity of the propeller disk under different submergence depths and different speeds are obtained. At the same time, the wave and the velocity field of the longitudinal section which can not be measured by the model test are supplemented by numerical simulation, and the influence mechanism of the free surface on the flow characteristics of the wake field is expounded from the wave point of view. The results show that: When the submarine near the water surface, with the increase of Fr, the upper isopleth of the axial velocity at the propeller disk tends to be flattened; and compared with the 4D submergence depths, the local maximum value of pulsating velocity appears in the 1.5D submergence depths, and the structure of pulsating velocity moves down as a whole. When the free surface exists, the velocity of flow field between the hull and the free surface increases obviously, especially in the area of the propeller disk. With the increase of Fr, the height of the free surface of the propeller disk decreases gradually, which leads to a larger fluid velocity and the squeeze phenomenon of wake field on propeller disk.

Holographic 3D Particle Imaging With Model-Based Deep Network

Gabor holography is an amazingly simple and effective approach for three-dimensional (3D) imaging. However, it suffers from a DC term, twin-image entanglement, and defocus noise. The conventional approach for solving this problem is either using an off-axis setup, or compressive holography. The former sacrifices simplicity, and the latter is computationally demanding and time-consuming. To cope with this problem, we propose a model-based holographic network (MB-HoloNet) for three-dimensional particle imaging. The free-space point spread function (PSF), which is essential for hologram reconstruction, is used as a prior in the MB-HoloNet. All parameters are learned in an end-to-end fashion. The physical prior makes the network efficient and stable for both localization and 3D particle size reconstructions.

Free fall of homogeneous and heterogeneous cones

The late stage of the freefall of homogeneous and heterogeneous cones and the induced flow are studied using three-dimensional particle tracking velocimetry and three-dimensional particle image velocimetry. Results showed four distinct patterns modulated by the degree of heterogeneity and specific gravity. They included straight fall, sinusoidal-like trajectories, inclined translations with large rotations, and tumbling followed by an irregular motion.

3D-PIV Measurement for EHD Flow of Spiked Tubular Electrode Corona Discharge in Wide Electrostatic Precipitator

Abstract The electrohydrodynamic (EHD) flow induced by a corona discharge has an important influence on the movement and collection of fine particles in an electrostatic precipitator. In this paper, three-dimensional particle image velocimetry (3D-PIV) is used to investigate the impact of different primary flow velocities and applied voltage on diffusion and transport of the spiked tubular electrode corona discharge EHD flow in a wide type electrostatic precipitator. In order to measure the flow characteristics of different positions of a spiked tubular electrode, the PIV measurements are carried out in several cross-sectional planes along the ESP duct. From 2D flow streamlines, in plane 1 (where the tip of the spike is oriented in the direction of primary flow), the velocity of the counter-clockwise vortex caused by the EHD flow near the plate decreases as the primary flow velocity increases. However, in plane 3 (where the tip direction is opposite to the primary flow), two vortices rotate adversely, and the flow velocity of the clockwise vortex near the plate increases as the primary flow velocity increases. Flow velocity increasing near the plate makes the particles deposited on the plate more easily to be re-entrained. It can be found in the three-dimensional analysis of the flow field that there are mainly “ascending vortex” and downward tip jet in the three observation planes. There is a discrepancy (in terms of distribution region and the magnitude of velocity) between the three-dimensional characteristics of these vortices and tip jets in the different cross-sectional planes.

A novel three-dimensional magnetic particle imaging system based on the frequency mixing for the point-of-care diagnostics

The magnetic particle imaging (MPI) is a technology that can image the concentrations of the superparamagnetic iron oxide nanoparticles (SPIONs) which can be used in biomedical diagnostics and therapeutics as non-radioactive tracers. We proposed a point-of-care testing MPI system (PoCT-MPI) that can be used for preclinical use for imaging small rodents (mice) injected with SPIONs not only in laboratories, but also at emergency sites far from laboratories. In particular, we applied a frequency mixing magnetic detection method to the PoCT-MPI, and proposed a hybrid field free line generator to reduce the power consumption, size and weight of the system. The PoCT-MPI is 20 times 33 times 45,{hbox{cm}}^3 in size and weighs less than 100 kg. It can image a three-dimensional distribution of SPIONs injected into a biosample with less than 120 Wh of power consumption. Its detection limit is 0.13,upmu {hbox{L}}, 10 mg/mL, 1.3,upmu {hbox{g}} (Fe).

Stereo three-dimensional particle image velocimetry measurement and aerodynamic force analysis of non-spinning soccer balls

A knuckle shot, resulting from non-spinning kicking, is an essential technique in soccer. The irregular flight path of the knuckle shot is caused by the aerodynamic force from the three-dimensional twin vortices generated in the wake behind the ball. However, the detailed behavior of the twin vortices and relation between the jet flow and the acting forces on the balls is still not understood. In addition, a more thorough understanding of the effect of ball panels on the formation of twin vortices and jet flow is important to develop balls with high controllability. To study the effect of the ball panel shape on the flight path, stereo three-dimensional particle image velocimetry wake flow measurements and synchronized force measurements were performed on various soccer balls. It was confirmed that the aerodynamic force on the ball is produced by the jet flow generated by the vortices in the wake flow. The directions of the force followed the changes of the jet flow, and the magnitude of the force was strongly associated with the flow rate of the jet. Moreover, the shape of the ball panels, especially the groove volume, determines the critical Reynolds number and the fluttering of the balls.

Three-dimensionality of shallow island wakes

Island wakes are thought to play a significant role in the vertical and cross-shelf mixing processes in strong tidally forced coastal regions. This paper describes a comprehensive laboratory study of shallow water wakes behind islands of circular cross section forced by a sinusoidal tidal flow. The wake structure and vertical circulation are determined through novel three-dimensional particle imaging velocimetry measurements. Four archetypal wake forms (symmetric, asymmetric, unsteady bubble, and vortex shedding) are observed. Through examination of the vertical structure of each of these wake forms, we demonstrate the dependence of vertical transport in island wakes on three key parameters: (1) the tidal excursion relative to the island size, (2) the bottom boundary layer thickness relative to the flow depth and (3) the aspect ratio of the island size to the flow depth. The importance of secondary vortices in island upwelling is highlighted by local peaks in vertical velocity that exceed 40% of the peak external tidal velocity. This study fundamentally changes the view of island wake upwelling from a weak ‘tea cup’-like recirculation process to one where primary and secondary flow structures vigorously stir the water column over the full depth. This has fundamental implications for the fate of passive biological tracers and the time scales that determine productivity in topographically-complex continental shelf regions.