Image-preprocessing method for near-wall particle image velocimetry (PIV) image interrogation with very large in-plane displacement

International Nuclear Information System (INIS)

Zhu, Yiding; Yuan, Huijing; Zhang, Chuanhong; Lee, Cunbiao

2013-01-01

Accurate particle image velocimetry (PIV) measurements very near the wall are still a great challenge. The problem is compounded by the very large in-plane displacement on PIV images commonly encountered in measurements in hypersonic boundary layers. An improved image-preprocessing method is presented in this paper which expands the traditional window deformation iterative multigrid scheme to PIV images with very large displacement. Before the interrogation, stationary artificial particles of uniform size are added homogeneously in the wall region. The mean squares of the intensities of signals in the flow and in the wall region are postulated to be equal when half the initial interrogation window overlaps the wall region. The initial estimation near the wall is then smoothed by data from both sides of the shear layer to reduce the large random uncertainties. Interrogations in the following iterative steps then converge to the correct results to provide accurate predictions for particle tracking velocimetries. Significant improvement is seen in Monte Carlo simulations and experimental tests. The algorithm successfully extracted the small flow structures of the second-mode wave in the hypersonic boundary layer from PIV images with low signal-noise-ratios when the traditional method was not successful. (paper)

Comparison of Tomo-PIV Versus Dual Plane PIV on a Synthetic Jet Flow

Science.gov (United States)

Wernet, Mark P.

2017-01-01

Particle Imaging Velocimetry (PIV) is a planar velocity measurement technique that has found widespread use across a wide class of engineering disciplines. Tomographic PIV (tomoPIV) is an extension of the traditional PIV technique whereby the velocity across a volume of fluid is measured. TomoPIV provides additional fluid mechanical properties of the flow due to the adjacent planes of velocity information that are extracted. Dual Plane PIV is another approach for providing cross-plane flow field properties. Dual Plane PIV and tomoPIV provide all of the same flow properties, albeit through very different routes with significantly different levels of effort, hence a comparison of their application and performance would prove beneficial in a well-known, highly three dimensional flow field. A synthetic jet flow which has a wide range of flow field features including high velocity gradients and regions of high vorticity was used as a rigorous test bed to determine the capabilities limitations of the Dual Plane PIV and tomoPIV techniques. The results show that compressing 3D particle field information down to a limited number of views does not permit the accurate reconstruction of the flow field. The traditional thin sheet techniques are the best approach for accurate flow field measurements.

Visualizing the transient electroosmotic flow and measuring the zeta potential of microchannels with a micro-PIV technique.

Science.gov (United States)

Yan, Deguang; Nguyen, Nam-Trung; Yang, Chun; Huang, Xiaoyang

2006-01-14

We have demonstrated a transient micro particle image velocimetry (micro-PIV) technique to measure the temporal development of electroosmotic flow in microchannels. Synchronization of different trigger signals for the laser, the CCD camera, and the high-voltage switch makes this measurement possible with a conventional micro-PIV setup. Using the transient micro-PIV technique, we have further proposed a method on the basis of inertial decoupling between the particle electrophoretic motion and the fluid electroosmotic flow to determine the electrophoretic component in the particle velocity and the zeta potential of the channel wall. It is shown that using the measured zeta potentials, the theoretical predictions agree well with the transient response of the electroosmotic velocities measured in this work.

The application of μPIV technique in the study of magnetic flows in a micro-channel

International Nuclear Information System (INIS)

Nguyen, N.T.; Wu, Z.G.; Huang, X.Y.; Wen, C.-Y..

2005-01-01

In this preliminary experimental study, micro-scale particle image velocimetry (μPIV) was adopted for the first time to get the quantitative information of magnetic flows in a micro-channel. The μPIV consists of an inverted florescent microscope, a Q-switch Nd:YAG laser and a CCD camera. The florescent liquid with particles of 3 μm diameter was blended homogeneously with the prepared magnetic fluid. A permanent magnet approached and left one end of the micro-channel. The response of the magnetic fluid was recorded with the μPIV simultaneously. The flow features validate the feasibility of using μPIV technique in the study of magnetic flows in a micro-channel. μPIV provides a promising experimental tool for visualization and quantitative measurement of magnetic micro-flows

Two-phase PIV of bubbly flows: status and trends

NARCIS (Netherlands)

Deen, N.G.; Westerweel, Jerry; Delnoij, E.

2002-01-01

Particle Image Velocimetry (PIV) is a measurement technique that has received a lot of attention for this purpose in the last decade. PIV is an optical and thus non-intrusive measurement technique that gives instantaneous 2D velocity data for a whole plane in a 3D flow field. In this paper we will

Digital PIV Measurements in the Diffuser of a High Speed Centrifugal Compressor

Science.gov (United States)

Wernet, Mark P.

1998-01-01

Particle Imaging Velocimetry (PIV) is a powerful measurement technique which can be used as an alternative or complementary approach to Laser Doppler Velocimetry (LDV) in a wide range of research applications. PIV data are measured simultaneously at multiple points in space, which enables the investigation of the non-stationary spatial structures typically encountered in turbomachinery. Obtaining ample optical access, sufficiently high seed particle concentrations and accurate synchronization of image acquisition relative to impeller position are the most formidable tasks in the successful implementation of PIV in turbomachinery. Preliminary results from the successful application of the standard 2-D digital PIV technique in the diffuser of a high speed centrifugal compressor are presented. Instantaneous flow. measurements were also obtained during compressor surge.

Application of particle imaging velocimetry in windtunnels

International Nuclear Information System (INIS)

Kompenhans, J.; Reichmuth, J.

1987-01-01

Recently the instantaneous and nonintrusive measurement of the flow velocity in a large area of the flow field (two-dimensional plane) became possible by means of particle imaging velocimetry (PIV). Up to now PIV has mainly been used for model experiments at low flow velocities in order to test and to improve the measuring technique. The present aim is the application of PIV in large wind tunnels at high flow velocities. 7 references

Ghost Particle Velocimetry implementation in millimeters devices and comparison with μPIV

Science.gov (United States)

Riccomi, Marco; Alberini, Federico; Brunazzi, Elisabetta; Vigolo, Daniele

2016-11-01

Micro/milli-fluidic devices are becoming an important reference for several disciplines and are quickly increasing their applications in scientific, as well as industrial, environment. As a consequence, the development of techniques able to analyse these kinds of systems is required to allow their progress. Here we show the implementation of the Ghost Particle Velocimetry (GPV) for the flow velocity field investigation in milli-fluidic devices. This innovative technique has been recently introduced, and has been already proven to be useful in describing rapid phenomenon at a small scale. In this work, the GPV has been used to characterize the trapping of light suspended material in a branching junction. Experiments have been performed to identify the flow velocity field close to a millimeters scale T-junction, at different Reynolds numbers. Particularly interesting are the complex structures, such as vortices and recirculation zones, induced by the vortex breakdown phenomenon. The results obtained have been deeply validated and compared with the well-established μPIV, highlighting the differences in terms of qualitative and quantitative parameters. A performance comparison has been designed to underline the strengths and weaknesses of the two experimental techniques.

Particle image velocimetry new developments and recent applications

CERN Document Server

Willert, Christian E

2008-01-01

Particle Image Velocimetry (PIV) is a non-intrusive optical measurement technique which allows capturing several thousand velocity vectors within large flow fields instantaneously. Today, the PIV technique has spread widely and differentiated into many distinct applications, from micro flows over combustion to supersonic flows for both industrial needs and research. Over the past decade the measurement technique and the hard- and software have been improved continuously so that PIV has become a reliable and accurate method for "real life" investigations. Nevertheless there is still an ongoing process of improvements and extensions of the PIV technique towards 3D, time resolution, higher accuracy, measurements under harsh conditions and micro- and macroscales. This book gives a synopsis of the main results achieved during the EC-funded network PivNet 2 as well as a survey of the state-of-the-art of scientific research using PIV techniques in different fields of application.

Use of complementary PIV and LDV techniques to study industrial complex flows

International Nuclear Information System (INIS)

Cahen, C.; Benard, J.; Barcoula, M.; Hofmann, F.

1996-06-01

Cracks detected in some nuclear vessels led to design a scale mockup in order to understand the origin of this problem and where experimental results and computation could be compared. Two methods, LDV (Laser Doppler Velocimetry) and PIV (Particle Image Velocimetry), were used to measure the velocity field. It appeared that the two methods were complementary: LDV was dedicated to measure precisely the velocity and the turbulent energy fields, PIV was used to capture flow patterns as the location of stagnation point. If LDV is a local pointwise measurement, classical PIV is intrinsically A 2D image measurement. Consequently, a detailed analysis is done of the 3D effects upon the 2D measurements. The methodology of this analysis is presented. The results have demonstrated the capability of the code to predict such a complex flow even though some discrepancies were found. PIV needs some improvements especially in terms of an higher capacity of processing large set of data a methodology to compute the actual measurement accuracy. (authors). 4 refs., 12 figs

Multiple Δt strategy for particle image velocimetry (PIV) error correction, applied to a hot propulsive jet

Science.gov (United States)

Nogueira, J.; Lecuona, A.; Nauri, S.; Legrand, M.; Rodríguez, P. A.

2009-07-01

PIV (particle image velocimetry) is a measurement technique with growing application to the study of complex flows with relevance to industry. This work is focused on the assessment of some significant PIV measurement errors. In particular, procedures are proposed for estimating, and sometimes correcting, errors coming from the sensor geometry and performance, namely peak-locking and contemporary CCD camera read-out errors. Although the procedures are of general application to PIV, they are applied to a particular real case, giving an example of the methodology steps and the improvement in results that can be obtained. This real case corresponds to an ensemble of hot high-speed coaxial jets, representative of the civil transport aircraft propulsion system using turbofan engines. Errors of ~0.1 pixels displacements have been assessed. This means 10% of the measured magnitude at many points. These results allow the uncertainty interval associated with the measurement to be provided and, under some circumstances, the correction of some of the bias components of the errors. The detection of conditions where the peak-locking error has a period of 2 pixels instead of the classical 1 pixel has been made possible using these procedures. In addition to the increased worth of the measurement, the uncertainty assessment is of interest for the validation of CFD codes.

Simultaneous measurement of a fluid flow and the fluid's free surface using PIV

International Nuclear Information System (INIS)

Philip, O.G.; Hassan, Y.A.; Okamoto, K.

1995-01-01

The objective of this investigation is to study the interaction between a fluid flow and its free surface with an improved application of the flow measurement technique, particle image velocimetry (PIV). In this study, improvements in the data acquisition and tracking method of the PIV technique were developed

Implementation of a Particle Image Velocimetry (PIV) system. An example application of PIV to wake-flows behind objects

International Nuclear Information System (INIS)

Tokuhiro, A.; Hishida, K.; Ohki, Y.

1996-10-01

In the present work an introduction to PIV is given by way of an example. The selected flow configuration is that of wake-flow behind a bubble and its solid equivalent. By solid equivalent we mean a solid model with approximately the equivalent bubble breadth and volume. This two-component, two-phase flow aptly demonstrates the applicability of PIV to spatio-temporal flows. Use was additionally made of an Infrared Shadow Technique (IST) in order to capture the unlit image (shadow) of the bubble or solid within the flow field. By triggering both the laser and infrared light sources with the CCD camera, the shape of the object as well as the flow field was simultaneously recorded. Besides the 2D vector field, calculations of the vorticity, Reynolds stress and turbulent kinetic energy (tke) distributions were made. The results indicate that for counter-current flow (U avg ∼0.245m/s) of water in a square channel (100mm) with a single air bubble of roughly 10mm diameter (Re Db ∼10 4 ) one could conclude the following: 1) PIV can detect differences in the wake flow field behind a bubble and that behind an equivalently sized solid, 2) the wake flow field behind the bubble is spatio-temporal due to the oscillation of the bubble, 3) as the bubble tries to minimize the energy-loss associated with its inherent motion it does so by distributing the hydrodynamic tke uniformly in the wake-field whereas in the case of the solid, the energy is distributed in a confined region in the near-wake. The order of magnitude of the tke is however similar which strongly suggests leads us to believe that the energy dissipation mechanisms are different in the two cases. We also made a limited comparison of velocity data obtained via DPIV and ultrasound Doppler velocimetry. (J.P.N.)

Extension of PIV for measuring granular temperature field in dense fluidized beds.

NARCIS (Netherlands)

Dijkhuizen, W.; Bokkers, G.A.; Deen, N.G.; van Sint Annaland, M.; Kuipers, J.A.M.

2007-01-01

In this work a particle image velocimetry (PIV) technique has been extended to enable the simultaneous measurement of the instantaneous velocity and granular temperature fields. The PIV algorithm has been specifically optimized for dense granular systems and has been thoroughly tested with

Application of stereoscopic particle image velocimetry to studies of transport in a dusty (complex) plasma

International Nuclear Information System (INIS)

Thomas, Edward Jr.; Williams, Jeremiah D.; Silver, Jennifer

2004-01-01

Over the past 5 years, two-dimensional particle image velocimetry (PIV) techniques [E. Thomas, Jr., Phys. Plasmas 6, 2672 (1999)] have been used to obtain detailed measurements of microparticle transport in dusty plasmas. This Letter reports on an extension of these techniques to a three-dimensional velocity vector measurement approach using stereoscopic PIV. Initial measurements using the stereoscopic PIV diagnostic are presented

Multiple Δt strategy for particle image velocimetry (PIV) error correction, applied to a hot propulsive jet

International Nuclear Information System (INIS)

Nogueira, J; Lecuona, A; Nauri, S; Legrand, M; Rodríguez, P A

2009-01-01

PIV (particle image velocimetry) is a measurement technique with growing application to the study of complex flows with relevance to industry. This work is focused on the assessment of some significant PIV measurement errors. In particular, procedures are proposed for estimating, and sometimes correcting, errors coming from the sensor geometry and performance, namely peak-locking and contemporary CCD camera read-out errors. Although the procedures are of general application to PIV, they are applied to a particular real case, giving an example of the methodology steps and the improvement in results that can be obtained. This real case corresponds to an ensemble of hot high-speed coaxial jets, representative of the civil transport aircraft propulsion system using turbofan engines. Errors of ∼0.1 pixels displacements have been assessed. This means 10% of the measured magnitude at many points. These results allow the uncertainty interval associated with the measurement to be provided and, under some circumstances, the correction of some of the bias components of the errors. The detection of conditions where the peak-locking error has a period of 2 pixels instead of the classical 1 pixel has been made possible using these procedures. In addition to the increased worth of the measurement, the uncertainty assessment is of interest for the validation of CFD codes

Simultaneous PIV and pulsed shadow technique in slug flow: a solution for optical problems

Energy Technology Data Exchange (ETDEWEB)

Nogueira, S. [Karman Institute for Fluid Dynamics, Chaussee de Waterloo 72, B-1640, Rhode Saint Genese (Belgium); Centro de Estudos de Fenomenos de Transporte, Departamento de Eng. Quimica, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465, Porto (Portugal); Sousa, R.G.; Pinto, A.M.F.R.; Campos, J.B.L.M. [Centro de Estudos de Fenomenos de Transporte, Departamento de Eng. Quimica, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465, Porto (Portugal); Riethmuller, M.L. [Karman Institute for Fluid Dynamics, Chaussee de Waterloo 72, B-1640, Rhode Saint Genese (Belgium)

2003-12-01

A recent technique of simultaneous particle image velocimetry (PIV) and pulsed shadow technique (PST) measurements, using only one black and white CCD camera, is successfully applied to the study of slug flow. The experimental facility and the operating principle are described. The technique is applied to study the liquid flow pattern around individual Taylor bubbles rising in an aqueous solution of glycerol with a dynamic viscosity of 113 x 10{sup -3} Pa s. With this technique the optical perturbations found in PIV measurements at the bubble interface are completely solved in the nose and in annular liquid film regions as well as in the rear of the bubble for cases in which the bottom is flat. However, for Taylor bubbles with concave oblate bottoms, some optical distortions appear and are discussed. The measurements achieved a spatial resolution of 0.0022 tube diameters. The results reported show high precision and are in agreement with theoretical and experimental published data. (orig.)

Multi-frame pyramid correlation for time-resolved PIV

NARCIS (Netherlands)

Sciacchitano, A.; Scarano, F.; Wieneke, B.

2012-01-01

A novel technique is introduced to increase the precision and robustness of time-resolved particle image velocimetry (TR-PIV) measurements. The innovative element of the technique is the linear combination of the correlation signal computed at different separation time intervals. The domain of the

A Novel Plasma-Based Fluid for Particle Image Velocimetry (PIV): In-Vitro Feasibility Study of Flow Diverter Effects in Aneurysm Model.

Science.gov (United States)

Clauser, Johanna; Knieps, Marius S; Büsen, Martin; Ding, Andreas; Schmitz-Rode, Thomas; Steinseifer, Ulrich; Arens, Jutta; Cattaneo, Giorgio

2018-02-27

Particle image velocimetry (PIV) is a commonly used method for in vitro investigation of fluid dynamics in biomedical devices, such as flow diverters for intracranial aneurysm treatment. Since it is limited to transparent blood substituting fluids like water-glycerol mixture, the influence of coagulation and platelet aggregation is neglected. We aimed at the development and the application of a modified platelet rich plasma as a new PIV fluid with blood-like rheological and coagulation properties. In standardized intracranial aneurysm silicone models, the effect of this new PIV plasma on the fluid dynamics before and after flow diverter implantation was evaluated and compared with water-glycerol measurements. The flow diverting effect was strongly dependent on the used fluid, with considerably lower velocities achieved using PIV plasma, despite the same starting viscosity of both fluids. Moreover, triggering coagulation of PIV plasma allowed for intra-aneurysmal clot formation. We presented the first in vitro PIV investigation using a non-Newtonian, clottable PIV plasma, demonstrating a mismatch to a standard PIV fluid and allowing for thrombus formation.

Evaluation of StereoPIV Measurement of Droplet Velocity in an Effervescent Spray

Directory of Open Access Journals (Sweden)

Sina Ghaemi

2010-06-01

Full Text Available Particle image velocimetry (PIV is a well known technique for measuring the instantaneous velocity field of flows. However, error may be introduced when measuring the velocity field of sprays using this technique when the spray droplets are used as the seed particles. In this study, the effect of droplet number density, droplet velocity profile, and droplet size distribution of a spray produced by an effervescent atomizer on velocity measurement using a StereoPIV has been investigated. A shadowgraph-particle tracking velocimetry (S-PTV system provided measurement of droplet size and velocity for comparison. This investigation demonstrated that the StereoPIV under-estimates velocity at near-field dense spray region where measurement accuracy is limited by multi-scattering of the laser sheet. In the dilute far-field region of the spray, StereoPIV measurement is mostly in agreement with velocity of the droplet size-class which is close to the mean diameter based on droplet number frequency times droplet cross sectional area.

High Dynamic Velocity Range Particle Image Velocimetry Using Multiple Pulse Separation Imaging

Directory of Open Access Journals (Sweden)

Tadhg S. O’Donovan

2010-12-01

Full Text Available The dynamic velocity range of particle image velocimetry (PIV is determined by the maximum and minimum resolvable particle displacement. Various techniques have extended the dynamic range, however flows with a wide velocity range (e.g., impinging jets still challenge PIV algorithms. A new technique is presented to increase the dynamic velocity range by over an order of magnitude. The multiple pulse separation (MPS technique (i records series of double-frame exposures with different pulse separations, (ii processes the fields using conventional multi-grid algorithms, and (iii yields a composite velocity field with a locally optimized pulse separation. A robust criterion determines the local optimum pulse separation, accounting for correlation strength and measurement uncertainty. Validation experiments are performed in an impinging jet flow, using laser-Doppler velocimetry as reference measurement. The precision of mean flow and turbulence quantities is significantly improved compared to conventional PIV, due to the increase in dynamic range. In a wide range of applications, MPS PIV is a robust approach to increase the dynamic velocity range without restricting the vector evaluation methods.

High dynamic velocity range particle image velocimetry using multiple pulse separation imaging.

Science.gov (United States)

Persoons, Tim; O'Donovan, Tadhg S

2011-01-01

The dynamic velocity range of particle image velocimetry (PIV) is determined by the maximum and minimum resolvable particle displacement. Various techniques have extended the dynamic range, however flows with a wide velocity range (e.g., impinging jets) still challenge PIV algorithms. A new technique is presented to increase the dynamic velocity range by over an order of magnitude. The multiple pulse separation (MPS) technique (i) records series of double-frame exposures with different pulse separations, (ii) processes the fields using conventional multi-grid algorithms, and (iii) yields a composite velocity field with a locally optimized pulse separation. A robust criterion determines the local optimum pulse separation, accounting for correlation strength and measurement uncertainty. Validation experiments are performed in an impinging jet flow, using laser-Doppler velocimetry as reference measurement. The precision of mean flow and turbulence quantities is significantly improved compared to conventional PIV, due to the increase in dynamic range. In a wide range of applications, MPS PIV is a robust approach to increase the dynamic velocity range without restricting the vector evaluation methods.

Acceleration Characteristics of a Rock Slide Using the Particle Image Velocimetry Technique

Directory of Open Access Journals (Sweden)

Guoqing Chen

2016-01-01

Full Text Available The Particle Image Velocimetry (PIV technique with high precision and spatial resolution is a suitable sensor for flow field experiments. In this paper, the PIV technology was used to monitor the development of a displacement field, velocity field and acceleration field of a rock slide. It was found that the peak acceleration of the sliding surface appeared earlier than the peak acceleration of the sliding body. The characteristics of the rock slide including the short failure time, high velocities, and large accelerations indicate that the sliding forces and energy release rate of the slope are high. The deformation field showed that the sliding body was sliding outwards along the sliding surface while the sliding bed moved in an opposite direction. Moving upwards at the top of the sliding bed can be one of the warning signs for rock slide failure.

PIV Uncertainty Quantification and Beyond

NARCIS (Netherlands)

Wieneke, B.F.A.

2017-01-01

The fundamental properties of computed flow fields using particle imaging velocimetry (PIV) have been investigated, viewing PIV processing as a black box without going in detail into algorithmic details. PIV processing can be analyzed using a linear filter model, i.e. assuming that the computed

Comparison of Tomo-PIV and 3D-PTV for microfluidic flows

International Nuclear Information System (INIS)

Kim, Hyoungsoo; Westerweel, Jerry; Elsinga, Gerrit E

2013-01-01

Two 3D-3C velocimetry techniques for micro-scale measurements are compared: tomographic particle image velocimetry (Tomo-PIV) and 3D particle-tracking velocimetry (3D-PTV). Both methods are applied to experimental data from a confined shear-driven liquid droplet over a moving surface. The droplet has 200 μm height and 2 mm diameter. Micro 3D-PTV and Tomo-PIV are used to obtain the tracer particle distribution and the flow velocity field for the same set of images. It is shown that the reconstructed particle distributions are distinctly different, where Tomo-PIV returns a nearly uniform distribution over the height of the volume, as expected, and PTV reveals a clear peak in the particle distribution near the plane of focus. In Tomo-PIV, however, the reconstructed particle peak intensity decreases in proportion to the distance from the plane of focus. Due to the differences in particle distributions, the measured flow velocities are also different. In particular, we observe Tomo-PIV to be in closer agreement with mass conservation. Furthermore, the random noise level is found to increase with distance to the plane of focus at a higher rate for 3D-PTV as compared to Tomo-PIV. Thus, for a given noise threshold value, the latter method can measure reliably over a thicker volume. (paper)

High resolution measurement of the velocity profiles of channel flows using the particle image velocimetry technique

International Nuclear Information System (INIS)

Nor Azizi Mohamed

2000-01-01

The high resolution velocity profiles of a uniform steady channel flow and a flow beneath waves were obtained using the particle image velocimetry (PIV) technique. The velocity profiles for each flow were calculated for both components. It is shown that the profiles obtained are very precise, displaying the point velocities from a few millimeters from the bottom of the channel up to the water surface across the water depth. In the case of the wave-induced flow, the profiles are shown under the respective wave phases and given in a plane representation. High resolution measurement of point velocities in a flow is achievable using PIV and invaluable when applied to a complex flow. (Author)

Analysis of bubbly flow using particle image velocimetry

Energy Technology Data Exchange (ETDEWEB)

Todd, D.R.; Ortiz-Villafuerte, J.; Schmidl, W.D.; Hassan, Y.A. [Texas A and M University, Nuclear Engineering Dept., College Stagion, TX (United States); Sanchez-Silva, F. [ESIME, INP (Mexico)

2001-07-01

The local phasic velocities can be determined in two-phase flows if the phases can be separated during analysis. The continuous liquid velocity field can be captured using standard Particle Image Velocimetry (PIV) techniques in two-phase flows. PIV is now a well-established, standard flow measurement technique, which provides instantaneous velocity fields in a two-dimensional plane of finite thickness. PIV can be extended to three dimensions within the plane with special considerations. A three-dimensional shadow PIV (SPIV) measurement apparatus can be used to capture the dispersed phase flow parameters such as velocity and interfacial area. The SPIV images contain only the bubble images, and can be easily analyzed and the results used to separate the dispersed phase from the continuous phase in PIV data. An experimental system that combines the traditional PIV technique with SPIV will be described and sample data will be analyzed to demonstrate an advanced turbulence measurement method in a two-phase bubbly flow system. Also, a qualitative error analysis method that allows users to reduce the number of erroneous vectors obtained from the PIV measurements will be discussed. (authors)

Analysis of bubbly flow using particle image velocimetry

International Nuclear Information System (INIS)

Todd, D.R.; Ortiz-Villafuerte, J.; Schmidl, W.D.; Hassan, Y.A.; Sanchez-Silva, F.

2001-01-01

The local phasic velocities can be determined in two-phase flows if the phases can be separated during analysis. The continuous liquid velocity field can be captured using standard Particle Image Velocimetry (PIV) techniques in two-phase flows. PIV is now a well-established, standard flow measurement technique, which provides instantaneous velocity fields in a two-dimensional plane of finite thickness. PIV can be extended to three dimensions within the plane with special considerations. A three-dimensional shadow PIV (SPIV) measurement apparatus can be used to capture the dispersed phase flow parameters such as velocity and interfacial area. The SPIV images contain only the bubble images, and can be easily analyzed and the results used to separate the dispersed phase from the continuous phase in PIV data. An experimental system that combines the traditional PIV technique with SPIV will be described and sample data will be analyzed to demonstrate an advanced turbulence measurement method in a two-phase bubbly flow system. Also, a qualitative error analysis method that allows users to reduce the number of erroneous vectors obtained from the PIV measurements will be discussed. (authors)

Particle image velocimetry - Principles and first results

International Nuclear Information System (INIS)

Laporta, A.; Marechal, J.P.

1997-01-01

Particle Image Velocimetry (PIV) is a measurement technique elaborated towards the end of the 1970's, but which has developed considerably in recent years. The general principle of PIV is very simple and enables access to instantaneous velocity fields. It consists in recording images of tracer-particles injected into the flow and determining the distance covered by these particles. Since we know the time lapse between successive images of the same particle, we can derive the local fluid velocity. Among the many existing image acquisition and processing methods, the image inter-correlation analysis techniques, used with a pulsed laser source, is the most effective. Since we know the influence of different parameters (number of particles, beam power, time lapse between two successive images, size of query zones, etc.) on the quality of the final result, we can optimize practical adjustment of the PIV measurement scheme. The PIV was tested on the LAVITA hydraulic mockup (simulating the operation of a tangential fan). First results are, all in all, highly satisfactory. These have enabled the rapid drafting of instantaneous mean velocity field maps (20 images acquired in less than 90 seconds, with a post-processing time of about 10 minutes). Observation of the instantaneous fields has evidenced the presence of low frequency non-stationary phenomena which are not revealed by Laser Doppler Velocimetry (LDV). Quantitative comparison between LDV and PIV, concerning average fields, showed close results, with, however, local divergences which could be relatively marked. It must nevertheless be noted that the PIV measurements performed on LAVITA have not been optimized with a view to obtaining a consistently good accuracy level. Priority in the present case was given to the scope of the field explored, with a view to observing the large non-stationary structures within a flow. The PIV measurement technique is thus operational for prompt flow characterization. However

Time-resolved X-ray PIV technique for diagnosing opaque biofluid flow with insufficient X-ray fluxes.

Science.gov (United States)

Jung, Sung Yong; Park, Han Wook; Kim, Bo Heum; Lee, Sang Joon

2013-05-01

X-ray imaging is used to visualize the biofluid flow phenomena in a nondestructive manner. A technique currently used for quantitative visualization is X-ray particle image velocimetry (PIV). Although this technique provides a high spatial resolution (less than 10 µm), significant hemodynamic parameters are difficult to obtain under actual physiological conditions because of the limited temporal resolution of the technique, which in turn is due to the relatively long exposure time (~10 ms) involved in X-ray imaging. This study combines an image intensifier with a high-speed camera to reduce exposure time, thereby improving temporal resolution. The image intensifier amplifies light flux by emitting secondary electrons in the micro-channel plate. The increased incident light flux greatly reduces the exposure time (below 200 µs). The proposed X-ray PIV system was applied to high-speed blood flows in a tube, and the velocity field information was successfully obtained. The time-resolved X-ray PIV system can be employed to investigate blood flows at beamlines with insufficient X-ray fluxes under specific physiological conditions. This method facilitates understanding of the basic hemodynamic characteristics and pathological mechanism of cardiovascular diseases.

MacCormack's technique-based pressure reconstruction approach for PIV data in compressible flows with shocks

Science.gov (United States)

Liu, Shun; Xu, Jinglei; Yu, Kaikai

2017-06-01

This paper proposes an improved approach for extraction of pressure fields from velocity data, such as obtained by particle image velocimetry (PIV), especially for steady compressible flows with strong shocks. The principle of this approach is derived from Navier-Stokes equations, assuming adiabatic condition and neglecting viscosity of flow field boundaries measured by PIV. The computing method is based on MacCormack's technique in computational fluid dynamics. Thus, this approach is called the MacCormack method. Moreover, the MacCormack method is compared with several approaches proposed in previous literature, including the isentropic method, the spatial integration and the Poisson method. The effects of velocity error level and PIV spatial resolution on these approaches are also quantified by using artificial velocity data containing shock waves. The results demonstrate that the MacCormack method has higher reconstruction accuracy than other approaches, and its advantages become more remarkable with shock strengthening. Furthermore, the performance of the MacCormack method is also validated by using synthetic PIV images with an oblique shock wave, confirming the feasibility and advantage of this approach in real PIV experiments. This work is highly significant for the studies on aerospace engineering, especially the outer flow fields of supersonic aircraft and the internal flow fields of ramjets.

Tomographic PIV: particles versus blobs

International Nuclear Information System (INIS)

Champagnat, Frédéric; Cornic, Philippe; Besnerais, Guy Le; Plyer, Aurélien; Cheminet, Adam; Leclaire, Benjamin

2014-01-01

We present an alternative approach to tomographic particle image velocimetry (tomo-PIV) that seeks to recover nearly single voxel particles rather than blobs of extended size. The baseline of our approach is a particle-based representation of image data. An appropriate discretization of this representation yields an original linear forward model with a weight matrix built with specific samples of the system’s point spread function (PSF). Such an approach requires only a few voxels to explain the image appearance, therefore it favors much more sparsely reconstructed volumes than classic tomo-PIV. The proposed forward model is general and flexible and can be embedded in a classical multiplicative algebraic reconstruction technique (MART) or a simultaneous multiplicative algebraic reconstruction technique (SMART) inversion procedure. We show, using synthetic PIV images and by way of a large exploration of the generating conditions and a variety of performance metrics, that the model leads to better results than the classical tomo-PIV approach, in particular in the case of seeding densities greater than 0.06 particles per pixel and of PSFs characterized by a standard deviation larger than 0.8 pixels. (paper)

Ensemble correlation PIV applied to bubble plumes rising in a bubble column.

NARCIS (Netherlands)

Delnoij, E.; Westerweel, J.; Deen, N.G.; Kuipers, J.A.M.; van Swaaij, Willibrordus Petrus Maria

1999-01-01

This paper discusses an ensemble correlation, double-exposure single-frame, particle image velocimetry (PIV) technique that can be applied to study dispersed gas¿liquid two-phase flows. The essentials of this technique will be reviewed and several important issues concerning the implementation of

Remote measurement of river discharge using thermal particle image velocimetry (PIV) and various sources of bathymetric information

Science.gov (United States)

Legleiter, Carl; Kinzel, Paul J.; Nelson, Jonathan M.

2017-01-01

Although river discharge is a fundamental hydrologic quantity, conventional methods of streamgaging are impractical, expensive, and potentially dangerous in remote locations. This study evaluated the potential for measuring discharge via various forms of remote sensing, primarily thermal imaging of flow velocities but also spectrally-based depth retrieval from passive optical image data. We acquired thermal image time series from bridges spanning five streams in Alaska and observed strong agreement between velocities measured in situ and those inferred by Particle Image Velocimetry (PIV), which quantified advection of thermal features by the flow. The resulting surface velocities were converted to depth-averaged velocities by applying site-specific, calibrated velocity indices. Field spectra from three clear-flowing streams provided strong relationships between depth and reflectance, suggesting that, under favorable conditions, spectrally-based bathymetric mapping could complement thermal PIV in a hybrid approach to remote sensing of river discharge; this strategy would not be applicable to larger, more turbid rivers, however. A more flexible and efficient alternative might involve inferring depth from thermal data based on relationships between depth and integral length scales of turbulent fluctuations in temperature, captured as variations in image brightness. We observed moderately strong correlations for a site-aggregated data set that reduced station-to-station variability but encompassed a broad range of depths. Discharges calculated using thermal PIV-derived velocities were within 15% of in situ measurements when combined with depths measured directly in the field or estimated from field spectra and within 40% when the depth information also was derived from thermal images. The results of this initial, proof-of-concept investigation suggest that remote sensing techniques could facilitate measurement of river discharge.

PIV Measurements in Weakly Buoyant Gas Jet Flames

Science.gov (United States)

Sunderland, Peter B.; Greenbberg, Paul S.; Urban, David L.; Wernet, Mark P.; Yanis, William

2001-01-01

Despite numerous experimental investigations, the characterization of microgravity laminar jet diffusion flames remains incomplete. Measurements to date have included shapes, temperatures, soot properties, radiative emissions and compositions, but full-field quantitative measurements of velocity are lacking. Since the differences between normal-gravity and microgravity diffusion flames are fundamentally influenced by changes in velocities, it is imperative that the associated velocity fields be measured in microgravity flames. Velocity measurements in nonbuoyant flames will be helpful both in validating numerical models and in interpreting past microgravity combustion experiments. Pointwise velocity techniques are inadequate for full-field velocity measurements in microgravity facilities. In contrast, Particle Image Velocimetry (PIV) can capture the entire flow field in less than 1% of the time required with Laser Doppler Velocimetry (LDV). Although PIV is a mature diagnostic for normal-gravity flames , restrictions on size, power and data storage complicate these measurements in microgravity. Results from the application of PIV to gas jet flames in normal gravity are presented here. Ethane flames burning at 13, 25 and 50 kPa are considered. These results are presented in more detail in Wernet et al. (2000). The PIV system developed for these measurements recently has been adapted for on-rig use in the NASA Glenn 2.2-second drop tower.

Measurement of fluid velocity development behind a circular cylinder using particle image velocimetry (PIV)

International Nuclear Information System (INIS)

Goharzadeh, Afshin; Molki, Arman

2015-01-01

In this paper we present a non-intrusive experimental approach for obtaining a two-dimensional velocity distribution around a 22 mm diameter circular cylinder mounted in a water tunnel. Measurements were performed for a constant Reynolds number of 7670 using a commercial standard particle image velocimetry (PIV) system. Different flow patterns generated behind the circular cylinder are discussed. Both instantaneous and time-averaged velocity distributions with corresponding streamlines are obtained. Key concepts in fluid mechanics, such as contra-rotating vortices, von Kármán vortex street, and laminar-turbulent flow, are discussed. In addition, brief historical information pertaining to the development of flow measurement techniques—in particular, PIV—is described. (paper)

Application and evaluation of LS-PIV technique for the monitoring of river surface velocities in high flow conditions

OpenAIRE

Jodeau , M.; Hauet , A.; Paquier , A.; Le Coz , J.; Dramais , G.

2008-01-01

Large Scale Particle Image Velocimetry (LS-PIV) is used to measure the surface flow velocities in a mountain stream during high flow conditions due to a reservoir release. A complete installation including video acquisition from a mobile elevated viewpoint and artificial flow seeding has been developed and implemented. The LS-PIV method was adapted in order to take into account the specific constraints of these high flow conditions. Using a usual LS-PIV data processing, significant variations...

Tomographic PIV: principles and practice

International Nuclear Information System (INIS)

Scarano, F

2013-01-01

A survey is given of the major developments in three-dimensional velocity field measurements using the tomographic particle image velocimetry (PIV) technique. The appearance of tomo-PIV dates back seven years from the present review (Elsinga et al 2005a 6th Int. Symp. PIV (Pasadena, CA)) and this approach has rapidly spread as a versatile, robust and accurate technique to investigate three-dimensional flows (Arroyo and Hinsch 2008 Topics in Applied Physics vol 112 ed A Schröder and C E Willert (Berlin: Springer) pp 127–54) and turbulence physics in particular. A considerable number of applications have been achieved over a wide range of flow problems, which requires the current status and capabilities of tomographic PIV to be reviewed. The fundamental aspects of the technique are discussed beginning from hardware considerations for volume illumination, imaging systems, their configurations and system calibration. The data processing aspects are of uppermost importance: image pre-processing, 3D object reconstruction and particle motion analysis are presented with their fundamental aspects along with the most advanced approaches. Reconstruction and cross-correlation algorithms, attaining higher measurement precision, spatial resolution or higher computational efficiency, are also discussed. The exploitation of 3D and time-resolved (4D) tomographic PIV data includes the evaluation of flow field pressure on the basis of the flow governing equation. The discussion also covers a-posteriori error analysis techniques. The most relevant applications of tomo-PIV in fluid mechanics are surveyed, covering experiments in air and water flows. In measurements in flow regimes from low-speed to supersonic, most emphasis is given to the complex 3D organization of turbulent coherent structures. (topical review)

Large scale particle image velocimetry with helium filled soap bubbles

Energy Technology Data Exchange (ETDEWEB)

Bosbach, Johannes; Kuehn, Matthias; Wagner, Claus [German Aerospace Center (DLR), Institute of Aerodynamics and Flow Technology, Goettingen (Germany)

2009-03-15

The application of particle image velocimetry (PIV) to measurement of flows on large scales is a challenging necessity especially for the investigation of convective air flows. Combining helium filled soap bubbles as tracer particles with high power quality switched solid state lasers as light sources allows conducting PIV on scales of the order of several square meters. The technique was applied to mixed convection in a full scale double aisle aircraft cabin mock-up for validation of computational fluid dynamics simulations. (orig.)

Large scale particle image velocimetry with helium filled soap bubbles

Science.gov (United States)

Bosbach, Johannes; Kühn, Matthias; Wagner, Claus

2009-03-01

The application of Particle Image Velocimetry (PIV) to measurement of flows on large scales is a challenging necessity especially for the investigation of convective air flows. Combining helium filled soap bubbles as tracer particles with high power quality switched solid state lasers as light sources allows conducting PIV on scales of the order of several square meters. The technique was applied to mixed convection in a full scale double aisle aircraft cabin mock-up for validation of Computational Fluid Dynamics simulations.

PIV/HPIV Film Analysis Software Package

Science.gov (United States)

Blackshire, James L.

1997-01-01

A PIV/HPIV film analysis software system was developed that calculates the 2-dimensional spatial autocorrelations of subregions of Particle Image Velocimetry (PIV) or Holographic Particle Image Velocimetry (HPIV) film recordings. The software controls three hardware subsystems including (1) a Kodak Megaplus 1.4 camera and EPIX 4MEG framegrabber subsystem, (2) an IEEE/Unidex 11 precision motion control subsystem, and (3) an Alacron I860 array processor subsystem. The software runs on an IBM PC/AT host computer running either the Microsoft Windows 3.1 or Windows 95 operating system. It is capable of processing five PIV or HPIV displacement vectors per second, and is completely automated with the exception of user input to a configuration file prior to analysis execution for update of various system parameters.

Tomographic Particle Image Velocimetry Using Colored Shadow Imaging

KAUST Repository

Alarfaj, Meshal K.

2016-02-01

Tomographic Particle Image Velocimetry Using Colored Shadow Imaging by Meshal K Alarfaj, Master of Science King Abdullah University of Science & Technology, 2015 Tomographic Particle image velocimetry (PIV) is a recent PIV method capable of reconstructing the full 3D velocity field of complex flows, within a 3-D volume. For nearly the last decade, it has become the most powerful tool for study of turbulent velocity fields and promises great advancements in the study of fluid mechanics. Among the early published studies, a good number of researches have suggested enhancements and optimizations of different aspects of this technique to improve the effectiveness. One major aspect, which is the core of the present work, is related to reducing the cost of the Tomographic PIV setup. In this thesis, we attempt to reduce this cost by using an experimental setup exploiting 4 commercial digital still cameras in combination with low-cost Light emitting diodes (LEDs). We use two different colors to distinguish the two light pulses. By using colored shadows with red and green LEDs, we can identify the particle locations within the measurement volume, at the two different times, thereby allowing calculation of the velocities. The present work tests this technique on the flows patterns of a jet ejected from a tube in a water tank. Results from the images processing are presented and challenges discussed.

Probabilistic Extraction Of Vectors In PIV

Science.gov (United States)

Humphreys, William M., Jr.

1994-01-01

Probabilistic technique for extraction of velocity vectors in particle-image velocimetry (PIV) implemented with much less computation. Double-exposure photograph of particles in flow illuminated by sheet of light provides data on velocity field of flow. Photograph converted into video image then digitized and processed by computer into velocity-field data. Velocity vectors in interrogation region chosen from magnitude and angle histograms constructed from centroid map of region.

PIV measurements in a microfluidic 3D-sheathing structure with three-dimensional flow behaviour

DEFF Research Database (Denmark)

Klank, Henning; Goranovic, Goran; Kutter, Jörg Peter

2002-01-01

. The structures are often of complex geometry and include strongly three-dimensional flow behaviour, which poses a challenge for the micro particle image velocimetry (micro-PIV) technique. The flow in a microfluidic 3D-sheathing structure has been measured throughout the volume using micro-PIV. In addition......, a stereoscopic principle was applied to obtain all three velocity components, showing the feasibility of obtaining full volume mapping (x, y, z, U, V, W) from micro-PIV measurements. The results are compared with computational fluid dynamics (CFD) simulations....

PIV Measurements in Pumps

National Research Council Canada - National Science Library

Wulff, Detlev L

2006-01-01

.... In contrast to Particle Image Velocimetry (PIV), which utilizes analogue imaging and therefore time-consuming post processing, for DPIV digital video recording is encountered which is ideally suited for digital data processing...

Real-time particle image velocimetry based on FPGA technology;Velocimetria PIV en tiempo real basada en logica programable FPGA

Energy Technology Data Exchange (ETDEWEB)

Iriarte Munoz, Jose Miguel [Universidad Nacional de Cuyo, Instituto Balseiro, Centro Atomico Bariloche (Argentina)

2008-07-01

Particle image velocimetry (PIV), based on laser sheet, is a method for image processing and calculation of distributed velocity fields.It is well established as a fluid dynamics measurement tool, being applied to liquid, gases and multiphase flows.Images of particles are processed by means of computationally demanding algorithms, what makes its real-time implementation difficult.The most probable displacements are found applying two dimensional cross-correlation function. In this work, we detail how it is possible to achieve real-time visualization of PIV method by designing an adaptive embedded architecture based on FPGA technology.We show first results of a physical field of velocity calculated by this platform system in a real-time approach.;La velocimetria por imagenes de particulas (PIV), basada en plano laser, es una potente herramienta de medicion en dinamica de fluidos, capaz de medir sin grandes errores, un campo de velocidades distribuido en liquidos, gases y flujo multifase.Los altos requerimientos computacionales de los algoritmos PIV dificultan su empleo en tiempo-real.En este trabajo presentamos el diseno de una plataforma basada en tecnologia FPGA para capturar video y procesar en tiempo real el algoritmo de correlacion cruzada bidimensional.Mostramos resultados de un primer abordaje de la captura de imagenes y procesamiento de un campo fisico de velocidades en tiempo real.

Particle Image Velocimetry (PIV) Measurements of Suspension-Feeding Velocities

Science.gov (United States)

Du Clos, K.; Jones, I. T.; Carrier, T. J.; Jumars, P. A.

2016-02-01

Active suspension feeders, such as bivalves and tunicates, connect benthic and pelagic ecosystems by packaging suspended matter into larger fecal and pseudofecal particles, greatly enhancing the flux of carbon and nutrients from the water column to the benthos. The volume of water processed by a population of suspension feeders is commonly estimated by scaling up results from experiments that measure the clearance rate (the volume of water cleared of particles per time) of one or a few individual suspension feeders. Clearance rates vary, however, between species, within a species, and over time for a single individual; and the velocity fields produced by suspension feeders are likely to interact in complex ways. We measured the water velocity fields produced by two species of bivalve, Mya arenaria and Mercenaria mercenaria, and the tunicate Ciona intestinalis, using particle image velocimetry (PIV). We used these measurements to calculate flow rates and Reynolds numbers of inhalant and exhalant siphons. We also observed strong entrainment of water by M. arenaria's exhalant siphon jet that may help to explain how the clam avoids depleting the water around it of particles and oxygen as it feeds. We are using these measurements to inform computational fluid mechanics (CFD) models of suspension feeding, allowing us to examine the interactions of flow fields produced by multiple suspension feeders and other effects not quantified by clearance-rate measurements.

Measurements of wall-shear-stress distribution on an NACA0018 airfoil by liquid-crystal coating and near-wall particle image velocimetry (PIV)

International Nuclear Information System (INIS)

Fujisawa, N; Oguma, Y; Nakano, T

2009-01-01

Measurements of wall-shear-stress distributions along curved surfaces are carried out using non-intrusive experimental methods, such as liquid-crystal coating and near-wall particle image velocimetry (PIV). The former method relies on the color change of the liquid-crystal coating sensitive to the wall shear stress, while the latter is based on the direct evaluation of shear stresses through the near-wall PIV measurement in combination with the image deformation technique. These experimental methods are applied to the measurement of wall-shear-stress distributions of air flow at a free-stream velocity of 15 m s −1 on a flat plate and an NACA0018 airfoil. The experiments are carried out at zero angle of attack for the flat plate and at 0° and ±6° angles of attack for the airfoil, and then the variations of shear-stress distribution along these surfaces are studied. These measurements in wall shear stresses agree with each other within their experimental uncertainties, suggesting the validity of experimental methods for non-intrusive shear-stress measurements. It is found that the wall-shear-stress distribution shows a small negative value upstream of the reattachment point on the NACA0018 airfoil, which is followed by an increase in shear stresses downstream due to laminar–turbulent transition of boundary layers. Such behavior of wall-shear-stress distribution is well correlated with the mean flow and turbulence characteristics along the airfoil surfaces, which are measured by PIV

Surge Flow in a Centrifugal Compressor Measured by Digital Particle Image Velocimetry

Science.gov (United States)

Wernet, Mark P.

2000-01-01

A planar optical velocity measurement technique known as Particle Image Velocimetry (PIV) is being used to study transient events in compressors. In PIV, a pulsed laser light sheet is used to record the positions of particles entrained in a fluid at two instances in time across a planar region of the flow. Determining the recorded particle displacement between exposures yields an instantaneous velocity vector map across the illuminated plane. Detailed flow mappings obtained using PIV in high-speed rotating turbomachinery components are used to improve the accuracy of computational fluid dynamics (CFD) simulations, which in turn, are used to guide advances in state-of-the-art aircraft engine hardware designs.

Bridging PIV spatial and temporal resolution using governing equations and development of the coaxial volumetric velocimeter

NARCIS (Netherlands)

Schneiders, J.F.G.

2017-01-01

A series of techniques is proposed for volumetric air flow measurements that are based upon the principles of particle image velocimetry (PIV). The proposed techniques fall in two categories; part 1 of this dissertation considers measurement data processing using constitutive laws and part 2 focuses

Veiligheidsrapport voor de PIV-goot in het Laboratorium voor Vloeistofmechanica

NARCIS (Netherlands)

Hofland, B.

2002-01-01

Bevat een veiligheidsvoorschrift voor de PIV (particle-image velocimetry) goot. Het rapport is vooral gericht op het gebruik van de krachtige Nd: YAG laser (veiligheidsklasse 4) die gebruikt wordt voor de PIV techniek.

Endoscopic PIV measurements in a low pressure turbine rig

Energy Technology Data Exchange (ETDEWEB)

Kegalj, Martin; Schiffer, Heinz-Peter [Technische Universitaet Darmstadt (Germany). Department of Gas Turbines and Aerospace Propulsion

2009-10-15

Particle-Image-Velocimetry (PIV) is a useful way to acquire information about the flow in turbomachinery. Several premises have to be fulfilled to achieve high-quality data, for example, optical access, low vibrations and low reflections. However, not all test facilities comply with these requirements. If there is no optical access to the test area, measurements cannot be performed. The use of borescopic optics is a possible solution to this issue, as the access required is very small. Several different techniques can be used to measure the three components of the velocity vector, one of which is Stereo-PIV. These techniques require either large optical access from several viewing angles or highly complex setups. Orthogonal light sheet orientations in combination with borescopic optics using Planar-PIV can deliver sufficient information about the flow. This study will show the feasibility of such an approach in an enclosed test area, such as the interblade space in a Low-Pressure-Turbine-Rig. The results from PIV will be compared with data collected with conventional techniques, such as the Five-Hole-Probe and the 2-component Hot-Wire-Anemometry. An analysis of time- and phase-averaged data will be performed. (orig.)

Particle Image Velocimetry

DEFF Research Database (Denmark)

Zhang, Chen; Vasilevskis, Sandijs; Kozlowski, Bartosz

Particle image velocimetry (PIV) is a non-intrusive, whole filed optical method providing instantaneous velocity information in fluids. The flow is seeded with tracer particles. The particles are illuminated in the target area with a light sheet at least twice within a short time interval....... The camera images the target area and captures each light pulse in separate image frames. The displacement of the particle between the light pulses can be used to determine the velocity vectors. This guideline introduces the principle of the PIV system and the system configuration. The measurement procedure...

A posteriori uncertainty quantification of PIV-based pressure data

NARCIS (Netherlands)

Azijli, I.; Sciacchitano, A.; Ragni, D.; Palha Da Silva Clérigo, A.; Dwight, R.P.

2016-01-01

A methodology for a posteriori uncertainty quantification of pressure data retrieved from particle image velocimetry (PIV) is proposed. It relies upon the Bayesian framework, where the posterior distribution (probability distribution of the true velocity, given the PIV measurements) is obtained from

Optical PIV and LDV Comparisons of Internal Flow Investigations in SHF Impeller

Directory of Open Access Journals (Sweden)

G. Wuibaut

2006-01-01

Full Text Available The paper presents a comparison between two sets of experimental results in a centrifugal flow pump. The tested impeller is the so-called SHF impeller for which many experimental data have been continuously produced to built databases for CFD code validations with various levels of approximation. Measurements have been performed using optical techniques: 2D particle image velocimetry (PIV technique on an air test model and 2D laser doppler velocimetry (LDV technique on a water model, both for different flow rates. For the present study, results obtained by these optical techniques are compared together in terms of phase averaged velocity and velocity fluctuations inside the impeller flow passage for design flow rate.

Particle and speckle imaging velocimetry applied to a monostatic LIDAR

Science.gov (United States)

Halldorsson, Thorsteinn; Langmeier, Andreas; Prücklmeier, Andreas; Banakh, Viktor; Falits, Andrey

2006-11-01

A novel backscatter-lidar imaging method of visualization of air movement in the atmosphere is discussed in the paper. The method is based on the particle image velocimetry (PIV) principle, namely: pairs of image of laser illuminated thin atmospheric layers are recorded by CCD camera and then are cross correlated to obtain velocity information from these records. Both the way of computer simulation of atmospheric version of PIV technique and the first concept proof experiments are described in the paper. It is proposed that the method can find an application for visualization of wake vortices arising behind large aircrafts.

Estudos de Reaeração com Velocimetria por Imagens de Partículas - Sistema S-PIV-3D Rearation Studies with Particle Image Velocimetry - S-PIV-3D System

Directory of Open Access Journals (Sweden)

Marcos Rogério Szeliga

2009-12-01

Full Text Available Particle Image Velocimetry (PIV é uma técnica recente de medição não-intrusiva de campos de velocidades em escoamentos. Neste trabalho, foi desenvolvido um equipamento de medição com características similares aos convencionais, porém com algumas características exclusivas, como o método óptico de aquisição de imagens e a calibração de coordenadas, que resultaram na utilização de uma única câmera convencional para obtenção de imagens e dados tridimensionais em escoamentos de baixa turbulência, proporcionando significativa economia na implantação. Foi desenvolvido um software específico e os resultados consistem em campos de velocidades tridimensionais. A aplicação destinou-se à medição de velocidades na superfície do escoamento em um tanque de grades oscilantes de forma a correlacionar a turbulência superficial com a capacidade de reaeração dos corpos da água.Particle Image Velocimetry (PIV is a recent technique of flow measurement labeled as a non-intrusive methodology. The system developed in this paper used principles similar to conventional systems including some exclusive characteristics as the optical method of image acquisition and the calibration process of the coordinate system. The measurement system, resulted from these characteristics, uses a single conventional digital video camera to obtain three-dimensional data in low turbulence flow, which provided significant economy in the system implantation. A specific software was developed and the results consist of fields of three-dimensional velocities obtained from the digital video file. The application was destined to the measurement of velocities on the flow surface in a tank of oscillating grids in order to correlate the surface turbulence with the rearation capacity of the bodies of water.

PIV measurements of flow structures in a spray dryer

DEFF Research Database (Denmark)

Meyer, Knud Erik; Velte, Clara Marika; Ullum, Thorvald

2011-01-01

Stereoscopic Particle Image Velocimetry (PIV) measurements are made in horizontal planes in a simplified scale model of a spray dryer using water as fluid. The sample rate was sufficient to resolve phenomena at lower frequencies. Data reveal asymmetric velocity fields in both mean fields and dyna......Stereoscopic Particle Image Velocimetry (PIV) measurements are made in horizontal planes in a simplified scale model of a spray dryer using water as fluid. The sample rate was sufficient to resolve phenomena at lower frequencies. Data reveal asymmetric velocity fields in both mean fields...

Multiparticle imaging velocimetry measurements in two-phase flow

International Nuclear Information System (INIS)

Hassan, Y.A.

1998-01-01

The experimental flow visualization tool, Particle Image Velocimetry (PIV), is being extended to determine the velocity fields in two and three-dimensional, two-phase fluid flows. In the past few years, the technique has attracted quite a lot of interest. PIV enables fluid velocities across a region of a flow to be measured at a single instant in time in global domain. This instantaneous velocity profile of a given flow field is determined by digitally recording particle (microspheres or bubbles) images within the flow over multiple successive video frames and then conducting flow pattern identification and analysis of the data. This paper presents instantaneous velocity measurements in various two and three- dimensional, two-phase flow situations. (author)

Experimental investigation of the velocity field in buoyant diffusion flames using PIV and TPIV algorithm

Science.gov (United States)

L. Sun; X. Zhou; S.M. Mahalingam; D.R. Weise

2005-01-01

We investigated a simultaneous temporally and spatially resolved 2-D velocity field above a burning circular pan of alcohol using particle image velocimetry (PIV). The results obtained from PIV were used to assess a thermal particle image velocimetry (TPIV) algorithm previously developed to approximate the velocity field using the temperature field, simultaneously...

Particle displacement tracking for PIV

Science.gov (United States)

Wernet, Mark P.

1990-01-01

A new Particle Imaging Velocimetry (PIV) data acquisition and analysis system, which is an order of magnitude faster than any previously proposed system has been constructed and tested. The new Particle Displacement Tracing (PDT) system is an all electronic technique employing a video camera and a large memory buffer frame-grabber board. Using a simple encoding scheme, a time sequence of single exposure images are time coded into a single image and then processed to track particle displacements and determine velocity vectors. Application of the PDT technique to a counter-rotating vortex flow produced over 1100 velocity vectors in 110 seconds when processed on an 80386 PC.

The application of particle image velocimetry for the analysis of high-speed craft hydrodynamics

NARCIS (Netherlands)

Jacobi, G.; Thill, C.H.; Huijsmans, R.H.M.; Huijsmans, R.H.M.

2016-01-01

The particle image velocimetry (PIV) technique has become a reliable method for capturing the velocity field and its derivatives, even in complex flows and is now also widely used for validation of numerical codes. As the imaging system is sensitive to vibrations, the application in environments

Peak-locking reduction for particle image velocimetry

International Nuclear Information System (INIS)

Michaelis, Dirk; Wieneke, Bernhard; Neal, Douglas R

2016-01-01

A parametric study of the factors contributing to peak-locking, a known bias error source in particle image velocimetry (PIV), is conducted using synthetic data that are processed with a state-of-the-art PIV algorithm. The investigated parameters include: particle image diameter, image interpolation techniques, the effect of asymmetric versus symmetric window deformation, number of passes and the interrogation window size. Some of these parameters are found to have a profound effect on the magnitude of the peak-locking error. The effects for specific PIV cameras are also studied experimentally using a precision turntable to generate a known rotating velocity field. Image time series recorded using this experiment show a linear range of pixel and sub-pixel shifts ranging from 0 to  ±4 pixels. Deviations in the constant vorticity field (ω z ) reveal how peak-locking can be affected systematically both by varying parameters of the detection system such as the focal distance and f -number, and also by varying the settings of the PIV analysis. A new a priori technique for reducing the bias errors associated with peak-locking in PIV is introduced using an optical diffuser to avoid undersampled particle images during the recording of the raw images. This technique is evaluated against other a priori approaches using experimental data and is shown to perform favorably. Finally, a new a posteriori anti peak-locking filter (APLF) is developed and investigated, which shows promising results for both synthetic data and real measurements for very small particle image sizes. (paper)

Characterization of the activity of ultrasound emitted in a perpendicular liquid flow using Particle Image Velocimetry (PIV) and electrochemical mass transfer measurements.

Science.gov (United States)

Barthès, Magali; Mazue, Gerald; Bonnet, Dimitri; Viennet, Remy; Hihn, Jean-Yves; Bailly, Yannick

2015-05-01

The present work is dedicated to the study of the interactions between a liquid circulation and a perpendicular acoustic wave propagation. A specific experimental setup was designed to study one transducer operating at 20 kHz, with the help of electrochemical mass transfer measurements combined with Particle Image Velocimetry (PIV) determination. Electrodes were located on the wall opposite to the acoustic emission. Experiments were performed for various Reynolds numbers: from 0 to 21700 (different liquid flow rates and viscosities). Both PIV and electrochemical measurements methods were found to be relevant, and had delivered complementary information. Even if PIV showed that the plume due to streaming was highly deflected by the additional flow, electrochemical measurements showed that there was still an activity, higher than in silent conditions, on the wall facing the transducer. Thus the ultrasound contribution remained noticeable on the surface opposite to the transducer even for a disturbed hydrodynamic environment due to the presence of a liquid circulation perpendicular to the wave propagation. Copyright © 2015 Elsevier B.V. All rights reserved.

Investigation of fluid flow in various geometries related to nuclear reactor using PIV system

International Nuclear Information System (INIS)

Kansal, A.K.; Maheshwari, N.K.; Singh, R.K.; Vijayan, P.K.; Saha, D.; Singh, R.K.; Joshi, V.M.

2011-01-01

Particle Image Velocimetry (PIV) is a non-intrusive technique for simultaneously measuring the velocities at many points in a fluid flow. The PIV system used is comprised of Nd:YAG laser source, CCD (Charged Coupled Device) camera, timing controller (to control the laser and camera) and software used for analyzing the flow velocities. Several case studies related to nuclear reactor were performed with the PIV system. Some of the cases like flow in circular tube, submerged jet, natural convection in a water pool, flow field of moderator inlet diffuser of 500 MWe Pressurised Heavy Water Reactor (PHWR) and fluidic flow control device (FFCD) used in advanced accumulator of Emergency Core Cooling System (ECCS) have been studied using PIV system. Theoretical studies have been performed and comparisons with PIV results are also given in the present studies. (author)

Hybrid micro-/nano-particle image velocimetry for 3D3C multi-scale velocity field measurement in microfluidics

International Nuclear Information System (INIS)

Min, Young Uk; Kim, Kyung Chun

2011-01-01

The conventional two-dimensional (2D) micro-particle image velocimetry (micro-PIV) technique has inherent bias error due to the depth of focus along the optical axis to measure the velocity field near the wall of a microfluidics device. However, the far-field measurement of velocity vectors yields good accuracy for micro-scale flows. Nano-PIV using the evanescent wave of total internal reflection fluorescence microscopy can measure near-field velocity vectors within a distance of around 200 nm from the solid surface. A micro-/nano-hybrid PIV system is proposed to measure both near- and far-field velocity vectors simultaneously in microfluidics. A near-field particle image can be obtained by total internal reflection fluorescence microscopy using nanoparticles, and the far-field velocity vectors are measured by three-hole defocusing micro-particle tracking velocimetry (micro-PTV) using micro-particles. In order to identify near- and far-field particle images, lasers of different wavelengths are adopted and tested in a straight microchannel for acquiring the three-dimensional three-component velocity field. We found that the new technique gives superior accuracy for the velocity profile near the wall compared to that of conventional nano-PIV. This method has been successfully applied to precisely measure wall shear stress in 2D microscale Poiseulle flows

Time-resolved PIV technique for high temporal resolution measurement of mechanical prosthetic aortic valve fluid dynamics.

Science.gov (United States)

Kaminsky, R; Morbiducci, U; Rossi, M; Scalise, L; Verdonck, P; Grigioni, M

2007-02-01

Prosthetic heart valves (PHVs) have been used to replace diseased native valves for more than five decades. Among these, mechanical PHVs are the most frequently implanted. Unfortunately, these devices still do not achieve ideal behavior and lead to many complications, many of which are related to fluid mechanics. The fluid dynamics of mechanical PHVs are particularly complex and the fine-scale characteristics of such flows call for very accurate experimental techniques. Adequate temporal resolution can be reached by applying time-resolved PIV, a high-resolution dynamic technique which is able to capture detailed chronological changes in the velocity field. The aim of this experimental study is to investigate the evolution of the flow field in a detailed time domain of a commercial bileaflet PHV in a mock-loop mimicking unsteady conditions, by means of time-resolved 2D Particle Image Velocimetry (PIV). The investigated flow field corresponded to the region immediately downstream of the valve plane. Spatial resolution as in "standard" PIV analysis of prosthetic valve fluid dynamics was used. The combination of a Nd:YLF high-repetition-rate double-cavity laser with a high frame rate CMOS camera allowed a detailed, highly temporally resolved acquisition (up to 10000 fps depending on the resolution) of the flow downstream of the PHV. Features that were observed include the non-homogeneity and unsteadiness of the phenomenon and the presence of large-scale vortices within the field, especially in the wake of the valve leaflets. Furthermore, we observed that highly temporally cycle-resolved analysis allowed the different behaviors exhibited by the bileaflet valve at closure to be captured in different acquired cardiac cycles. By accurately capturing hemodynamically relevant time scales of motion, time-resolved PIV characterization can realistically be expected to help designers in improving PHV performance and in furnishing comprehensive validation with experimental data

Flow evolution of a turbulent submerged two-dimensional rectangular free jet of air. Average Particle Image Velocimetry (PIV) visualizations and measurements

International Nuclear Information System (INIS)

Gori, Fabio; Petracci, Ivano; Angelino, Matteo

2013-01-01

Highlights: • Zone of flow establishment contains a newly identified undisturbed region of flow. • In the undisturbed region of flow the velocity profile is similar to the exit one. • In undisturbed region of flow the height of average PIV visualizations is constant. • In the undisturbed region of flow the turbulence on the centerline is equal to exit. • Length of undisturbed region of flow decreases with Reynolds number increase. -- Abstract: The paper presents average flow visualizations and measurements, obtained with the Particle Image Velocimetry (PIV) technique, of a submerged rectangular free jet of air in the range of Reynolds numbers from Re = 35,300 to Re = 2200, where the Reynolds number is defined according to the hydraulic diameter of a rectangular slot of height H. According to the literature, just after the exit of the jet there is a zone of flow, called zone of flow establishment, containing the region of mixing fluid, at the border with the stagnant fluid, and the potential core, where velocity on the centerline maintains a value almost equal to the exit one. After this zone is present the zone of established flow or fully developed region. The goal of the paper is to show, with average PIV visualizations and measurements, that, before the zone of flow establishment is present a region of flow, never mentioned by the literature and called undisturbed region of flow, with a length, L U , which decreases with the increase of the Reynolds number. The main characteristics of the undisturbed region is the fact that the velocity profile maintains almost equal to the exit one, and can also be identified by a constant height of the average PIV visualizations, with length, L CH , or by a constant turbulence on the centerline, with length L CT . The average PIV velocity and turbulence measurements are compared to those performed with the Hot Film Anemometry (HFA) technique. The average PIV visualizations show that the region of constant height has

Development of dynamic PIV for droplet jet flow

International Nuclear Information System (INIS)

Okamoto, K.; Hong, S. D.; Bi, W. T.; Sugii, Y.; Madarame, H.; Hayami, H.

2003-01-01

The Particle Image Velocimetry (PIV) can capture velocity vector fields with high spatial resolution. In this study, the Dynamic PIV system up to 10kHz temporal resolution was developed with combining the High-speed camera and high speed Laser with Double pulse option. The 1024 x 1024 pixel images with frame straddling were captured in 2kHz. Also, PIV data were measured in 512 x 256 pixel in 10kHz. The system had been applied to capture the water droplet flow. The transient characteristics of the droplet flow can be clearly captured using the developed Dynamic PIV System

Simultaneous measurement of internal and surrounding flows of a moving droplet using multicolour confocal micro-particle image velocimetry (micro-PIV)

International Nuclear Information System (INIS)

Oishi, M; Kinoshita, H; Fujii, T; Oshima, M

2011-01-01

This paper presents a micro-multiphase flow measurement technique, 'multicolour confocal micro-particle image velocimetry (PIV), and its application to the internal and surrounding flow measurement of a droplet moving through a microchannel. The present system measures the dynamic interaction between flows in two different phases, such as solid–liquid or liquid–liquid, simultaneously and separately. Unlike conventional confocal micro-PIV, this system features a wavelength separation optical device. The optical components (e.g., filters and dichroic mirror) are designed to separate fluorescent lights of tracer particles and to eliminate unnecessary scattered light depending on the characteristic wavelengths. The system can record a sequence of images at up to 2000 frames per second. It also has an in-plane spatial resolution of 0.284 µm/pixel in a field of 227.2 µm × 170.4 µm and a confocal depth of 3.43 µm using 1.0 µm particles and a 40× objective lens. This paper examines the performance of the present system, such as its ability to separate wavelengths. Furthermore, this system is applied to liquid–liquid two-phase flow, which consists of a water droplet and surrounding oil flow, in a microchannel. We succeeded in measuring each phase movement separately and simultaneously. As a result of the estimation of the out-of-plane velocity component, a three-dimensional flow structure is obtained and the interaction between each phase is investigated

On the feasibility of tomographic-PIV with low pulse energy illumination in a lifted turbulent jet flame

Science.gov (United States)

Boxx, I.; Carter, C. D.; Meier, W.

2014-08-01

Tomographic particle image velocimetry (tomographic-PIV) is a recently developed measurement technique used to acquire volumetric velocity field data in liquid and gaseous flows. The technique relies on line-of-sight reconstruction of the rays between a 3D particle distribution and a multi-camera imaging system. In a turbulent flame, however, index-of-refraction variations resulting from local heat-release may inhibit reconstruction and thereby render the technique infeasible. The objective of this study was to test the efficacy of tomographic-PIV in a turbulent flame. An additional goal was to determine the feasibility of acquiring usable tomographic-PIV measurements in a turbulent flame at multi-kHz acquisition rates with current-generation laser and camera technology. To this end, a setup consisting of four complementary metal oxide semiconductor cameras and a dual-cavity Nd:YAG laser was implemented to test the technique in a lifted turbulent jet flame. While the cameras were capable of kHz-rate image acquisition, the laser operated at a pulse repetition rate of only 10 Hz. However, use of this laser allowed exploration of the required pulse energy and thus power for a kHz-rate system. The imaged region was 29 × 28 × 2.7 mm in size. The tomographic reconstruction of the 3D particle distributions was accomplished using the multiplicative algebraic reconstruction technique. The results indicate that volumetric velocimetry via tomographic-PIV is feasible with pulse energies of 25 mJ, which is within the capability of current-generation kHz-rate diode-pumped solid-state lasers.

Flow mapping of multiphase flows using a novel single stem endoscopic particle image velocimetry instrument

International Nuclear Information System (INIS)

Lad, N; Adebayo, D; Aroussi, A

2011-01-01

Particle image velocimetry (PIV) is a successful flow mapping technique which can optically quantify large portions of a flow regime. This enables the method to be completely non-intrusive. The ability to be non-intrusive to any flow has allowed PIV to be used in a large range of industrial sectors for many applications. However, a fundamental disadvantage of the conventional PIV technique is that it cannot easily be used with flows which have no or limited optical access. Flows which have limited optical access for PIV measurement have been addressed using endoscopic PIV techniques. This system uses two separate probes which relay a light sheet and imaging optics to a planar position within the desired flow regime. This system is effective in medical and engineering applications. The present study has been involved in the development of a new endoscopic PIV system which integrates the illumination and imaging optics into one rigid probe. This paper focuses on the validation of the images taken from the novel single stem endoscopic PIV system. The probe is used within atomized spray flow and is compared with conventional PIV measurement and also pitot-static data. The endoscopic PIV system provides images which create localized velocity maps that are comparable with the global measurement of the conventional PIV system. The velocity information for both systems clearly show similar results for the spray characterization and are also validated using the pitot-static data

An optical flow algorithm based on gradient constancy assumption for PIV image processing

International Nuclear Information System (INIS)

Zhong, Qianglong; Yang, Hua; Yin, Zhouping

2017-01-01

Particle image velocimetry (PIV) has matured as a flow measurement technique. It enables the description of the instantaneous velocity field of the flow by analyzing the particle motion obtained from digitally recorded images. Correlation based PIV evaluation technique is widely used because of its good accuracy and robustness. Although very successful, correlation PIV technique has some weakness which can be avoided by optical flow based PIV algorithms. At present, most of the optical flow methods applied to PIV are based on brightness constancy assumption. However, some factors of flow imaging technology and the nature property of the fluids make the brightness constancy assumption less appropriate in real PIV cases. In this paper, an implementation of a 2D optical flow algorithm (GCOF) based on gradient constancy assumption is introduced. The proposed GCOF assumes the edges of the illuminated PIV particles are constant during motion. It comprises two terms: a combined local-global gradient data term and a first-order divergence and vorticity smooth term. The approach can provide accurate dense motion fields. The approach are tested on synthetic images and on two experimental flows. The comparison of GCOF with other optical flow algorithms indicates the proposed method is more accurate especially in conditions of illumination variation. The comparison of GCOF with correlation PIV technique shows that the proposed GCOF has advantages on preserving small divergence and vorticity structures of the motion field and getting less outliers. As a consequence, the GCOF acquire a more accurate and better topological description of the turbulent flow. (paper)

Systematic Error of Acoustic Particle Image Velocimetry and Its Correction

Directory of Open Access Journals (Sweden)

Mickiewicz Witold

2014-08-01

Full Text Available Particle Image Velocimetry is getting more and more often the method of choice not only for visualization of turbulent mass flows in fluid mechanics, but also in linear and non-linear acoustics for non-intrusive visualization of acoustic particle velocity. Particle Image Velocimetry with low sampling rate (about 15Hz can be applied to visualize the acoustic field using the acquisition synchronized to the excitation signal. Such phase-locked PIV technique is described and used in experiments presented in the paper. The main goal of research was to propose a model of PIV systematic error due to non-zero time interval between acquisitions of two images of the examined sound field seeded with tracer particles, what affects the measurement of complex acoustic signals. Usefulness of the presented model is confirmed experimentally. The correction procedure, based on the proposed model, applied to measurement data increases the accuracy of acoustic particle velocity field visualization and creates new possibilities in observation of sound fields excited with multi-tonal or band-limited noise signals.

PIV Data Validation Software Package

Science.gov (United States)

Blackshire, James L.

1997-01-01

A PIV data validation and post-processing software package was developed to provide semi-automated data validation and data reduction capabilities for Particle Image Velocimetry data sets. The software provides three primary capabilities including (1) removal of spurious vector data, (2) filtering, smoothing, and interpolating of PIV data, and (3) calculations of out-of-plane vorticity, ensemble statistics, and turbulence statistics information. The software runs on an IBM PC/AT host computer working either under Microsoft Windows 3.1 or Windows 95 operating systems.

Study on flow-induced acoustic resonance in symmetrically located side-branches using dynamic PIV technique

International Nuclear Information System (INIS)

Li, Yanrong; Inagaki, Terumi; Nishi, Yasuyuki; Someya, Satoshi; Okamoto, Koji

2014-01-01

Flow-induced acoustic resonance in a piping system containing closed coaxial side-branches was investigated experimentally. Resonance characteristics of the piping system were examined by a microphone. The results revealed that the resonance frequencies of the shear layer instability were locked in corresponding to the natural frequencies of the side-branches. Phase-averaged velocity fields were obtained two-dimensionally in the junction of coaxial side-branches by dynamic particle image velocimetry (PIV), while the acoustic resonance was induced at the first and second hydrodynamic modes. Patterns of jet correspond to two hydrodynamic modes were derived from the phase-averaged velocity fields. The dynamic PIV can acquire time-series velocity fluctuations, then, two-dimensional phase delay maps under resonance and off-resonance conditions in the junction of coaxial side-branches were obtained. Experimental results show that the proposed phase delay map method costs less experiment and computation time and achieves a better accuracy and repetition than the phase-locking technique. In addition, the phase delay map method can obtain phase difference under the different frequency components. This is important when two different acoustic modes were induced in one experimental condition. (author)

Experimental approach to investigate the dynamics of mixing coolant flow in complex geometry using PIV and PLIF techniques

Directory of Open Access Journals (Sweden)

Hutli Ezddin

2015-01-01

Full Text Available The aim of this work is to investigate experimentally the increase of mixing phenomenon in a coolant flow in order to improve the heat transfer, the economical operation and the structural integrity of Light Water Reactors-Pressurized Water Reactors (LWRs-PWRs. Thus the parameters related to the heat transfer process in the system will be investigated. Data from a set of experiments, obtained by using high precision measurement techniques, Particle Image Velocimetry and Planar Laser-Induced Fluorescence (PIV and PLIF, respectively are to improve the basic understanding of turbulent mixing phenomenon and to provide data for CFD code validation. The coolant mixing phenomenon in the head part of a fuel assembly which includes spacer grids has been investigated (the fuel simulator has half-length of a VVER 440 reactor fuel. The two-dimensional velocity vector and temperature fields in the area of interest are obtained by PIV and PLIF technique, respectively. The measurements of the turbulent flow in the regular tube channel around the thermocouple proved that there is rotation and asymmetry in the coolant flow caused by the mixing grid and the geometrical asymmetry of the fuel bundle. Both PIV and PLIF results showed that at the level of the core exit thermocouple the coolant is homogeneous. The discrepancies that could exist between the outlet average temperature of the coolant and the temperature at in-core thermocouple were clarified. Results of the applied techniques showed that both of them can be used as good provider for data base and to validate CFD results.

Schlieren image velocimetry measurements in a rocket engine exhaust plume

Science.gov (United States)

Morales, Rudy; Peguero, Julio; Hargather, Michael

2017-11-01

Schlieren image velocimetry (SIV) measures velocity fields by tracking the motion of naturally-occurring turbulent flow features in a compressible flow. Here the technique is applied to measuring the exhaust velocity profile of a liquid rocket engine. The SIV measurements presented include discussion of visibility of structures, image pre-processing for structure visibility, and ability to process resulting images using commercial particle image velocimetry (PIV) codes. The small-scale liquid bipropellant rocket engine operates on nitrous oxide and ethanol as propellants. Predictions of the exhaust velocity are obtained through NASA CEA calculations and simple compressible flow relationships, which are compared against the measured SIV profiles. Analysis of shear layer turbulence along the exhaust plume edge is also presented.

Particle Image Velocimetry Applications of Fluorescent Dye-Doped Particles

OpenAIRE

Petrosky, Brian Joseph

2015-01-01

Laser flare can often be a major issue in particle image velocimetry (PIV) involving solid boundaries in a flow or a gas-liquid interface. The use of fluorescent light from dye-doped particles has been demonstrated in water applications, but reproducing the technique in an airflow is more difficult due to particle size constraints and safety concerns. The following thesis is formatted in a hybrid manuscript style, including a full paper presenting the applications of fluorescent Kiton R...

PIV Measurements of He II Counterflow Around a Cylinder

International Nuclear Information System (INIS)

Fuzier, S.; Van Stiver, S. W.; Zhang, T.

2006-01-01

The induced flow field of counterflow He II across a circular cylinder has been quantitatively studied using the particle image velocimetry (PIV) technique. Two different size cylinders (6.35 mm and 2 mm in diameter) were used and placed in a 20 mm wide rectangular channel. In these experiments, large-scale eddy motion generated by the He II counterflow was observed both in front of and behind the cylinder, an effect which has no analogue in classical fluids

Collaborative framework for PIV uncertainty quantification: comparative assessment of methods

International Nuclear Information System (INIS)

Sciacchitano, Andrea; Scarano, Fulvio; Neal, Douglas R; Smith, Barton L; Warner, Scott O; Vlachos, Pavlos P; Wieneke, Bernhard

2015-01-01

A posteriori uncertainty quantification of particle image velocimetry (PIV) data is essential to obtain accurate estimates of the uncertainty associated with a given experiment. This is particularly relevant when measurements are used to validate computational models or in design and decision processes. In spite of the importance of the subject, the first PIV uncertainty quantification (PIV-UQ) methods have been developed only in the last three years. The present work is a comparative assessment of four approaches recently proposed in the literature: the uncertainty surface method (Timmins et al 2012), the particle disparity approach (Sciacchitano et al 2013), the peak ratio criterion (Charonko and Vlachos 2013) and the correlation statistics method (Wieneke 2015). The analysis is based upon experiments conducted for this specific purpose, where several measurement techniques are employed simultaneously. The performances of the above approaches are surveyed across different measurement conditions and flow regimes. (paper)

The measurements of water flow rates in the straight microchannel based on the scanning micro-PIV technique

Science.gov (United States)

Wang, H. L.; Han, W.; Xu, M.

2011-12-01

Measurement of the water flow rate in microchannel has been one of the hottest points in the applications of microfluidics, medical, biological, chemical analyses and so on. In this study, the scanning microscale particle image velocimetry (scanning micro-PIV) technique is used for the measurements of water flow rates in a straight microchannel of 200μm width and 60μm depth under the standard flow rates ranging from 2.481μL/min to 8.269μL/min. The main effort of this measurement technique is to obtain three-dimensional velocity distribution on the cross sections of microchannel by measuring velocities of the different fluid layers along the out-of-plane direction in the microchannel, so the water flow rates can be evaluated from the discrete surface integral of velocities on the cross section. At the same time, the three-dimensional velocity fields in the measured microchannel are simulated numerically using the FLUENT software in order to verify the velocity accuracy of measurement results. The results show that the experimental values of flow rates are well consistent to the standard flow rates input by the syringe pump and the compared results between numerical simulation and experiment are consistent fundamentally. This study indicates that the micro-flow rate evaluated from three-dimensional velocity by the scanning micro-PIV technique is a promising method for the micro-flow rate research.

Structure analysis of bubble driven flow by time-resolved PIV and POD techniques

International Nuclear Information System (INIS)

Kim, Hyun Dong; Yi, Seung Jae; Kim, Jong Wook; Kim, Kyung Chun

2010-01-01

In this paper, the recirculation flow motion and turbulence characteristics of liquid flow driven by air bubble stream in a rectangular water tank are studied. The time-resolved Particle Image Velocimetry (PIV) technique is adopted for the quantitative visualization and analysis. 532nm Diode CW laser is used for illumination and orange fluorescent (λex = 540nm, λem = 584nm) particle images are acquired by a 1280X1024 high-speed camera. To obtain clean particle images, 545nm long pass optical filter and an image intensifier are employed and the flow rate of compressed air is 3/min at 0.5MPa. The recirculation and mixing flow field is further investigated by timeresolved Proper Orthogonal Decomposition (POD) analysis technique. It is observed that the large scale recirculation resulting from the interaction between rising bubble stream and side wall is the most dominant flow structure and there are small scale vortical structures moving along with the large scale recirculation flow. It is also verified that the sum of 20 modes of velocity field has about 67.4% of total turbulent energy

Development of Uncertainty Quantification Method for MIR-PIV Measurement using BOS Technique

International Nuclear Information System (INIS)

Seong, Jee Hyun; Song, Min Seop; Kim, Eung Soo

2014-01-01

Matching Index of Refraction (MIR) is frequently used for obtaining high quality PIV measurement data. ven small distortion by unmatched refraction index of test section can result in uncertainty problems. In this context, it is desirable to construct new concept for checking errors of MIR and following uncertainty of PIV measurement. This paper proposes a couple of experimental concept and relative results. This study developed an MIR uncertainty quantification method for PIV measurement using SBOS technique. From the reference data of the BOS, the reliable SBOS experiment procedure was constructed. Then with the combination of SBOS technique with MIR-PIV technique, velocity vector and refraction displacement vector field was measured simultaneously. MIR errors are calculated through mathematical equation, in which PIV and SBOS data are put. These errors are also verified by another BOS experiment. Finally, with the applying of calculated MIR-PIV uncertainty, correct velocity vector field can be obtained regardless of MIR errors

Flow field study in a bulb turbine runner using LDV and endoscopic S-PIV measurements

International Nuclear Information System (INIS)

Lemay, S; Fraser, R; Ciocan, G D; Aeschlimann, V; Deschênes, C

2014-01-01

The flow in the inter-blade channels of a bulb turbine was measured using two different techniques. The first involved a classical laser Doppler velocimetry (LDV) setup whereas the second integrated endoscopic cameras to a stereoscopic particle image velocimetry (S-PIV) system. This paper presents results from both measurement campaigns and also provides some key conclusions based on the two datasets. Before getting into the thick of the data though, the technical aspect of both measurement configurations is addressed. A quick overview of the LDV setup is presented, but the main focus is on the novelties and challenges brought by the use of endoscopic cameras to achieve S-PIV measurements between the runner blades. Endoscopic PIV systems have already led to successful measurements of flow fields in a few studies concerning turbomachinery, especially in aerodynamics. However, to the author's knowledge, the realisation of such measurements in a hydraulic turbine is a first. After this outline of the techniques used, the results and conclusions are shown. First, the influence of the guide vanes wakes on the runner flow is described. The size, localisation, strength and dissipation of those structures are inferred from the information coming from both measurement techniques. Then, a flow imbalance is assessed circumferentially. On another subject, the blade tip vortices are identified and characterized using the LDV data. The size, position and direction of rotation of those structures are all extracted from the measured flow field. Finally, the PIV data allows the identification of yet another vortex located near the suction side of the blades and originating from the corner between the leading edge and the hub when operating the bulb turbine at part load

Quantification of tomographic PIV uncertainty using controlled experimental measurements.

Science.gov (United States)

Liu, Ning; Wu, Yue; Ma, Lin

2018-01-20

The goal of this work was to experimentally quantify the uncertainty of three-dimensional (3D) and three-component (3C) velocity measurements using tomographic particle image velocimetry (tomo-PIV). Controlled measurements were designed using tracer particles embedded in a solid sample, and tomo-PIV measurements were performed on the sample while it was moved both translationally and rotationally to simulate various known displacement fields, so the 3D3C displacements measured by tomo-PIV can be directly compared to the known displacements created by the sample. The results illustrated that (1) the tomo-PIV technique was able to reconstruct the 3D3C velocity with an averaged error of 0.8-1.4 voxels in terms of magnitude and 1.7°-1.9° in terms of orientation for the velocity fields tested; (2) view registration (VR) plays a significant role in tomo-PIV, and by reducing VR error from 0.6° to 0.1°, the 3D3C measurement accuracy can be improved by at least 2.5 times in terms of both magnitude and orientation; and (3) the use of additional cameras in tomo-PIV can extend the 3D3C velocity measurement to a larger volume, while maintaining acceptable accuracy. These results obtained from controlled tests are expected to aid the error analysis and the design of tomo-PIV measurements.

Simultaneous measurements with 3D PIV and Acoustic Doppler Velocity Profiler

NARCIS (Netherlands)

Blanckaert, K.J.F.; McLelland, S.J.

2009-01-01

Simultaneous velocity measurements were taken using Particle Image Velocimetry (PIV) and an Acoustic Doppler Velocity Profiler (ADVP) in a sharp open-channel bend with an immobile gravel bed. The PIV measures 3D velocity vectors in a vertical plane (~40cm x 20cm) at a frequency of 7.5 Hz, whereas

Error Propagation dynamics: from PIV-based pressure reconstruction to vorticity field calculation

Science.gov (United States)

Pan, Zhao; Whitehead, Jared; Richards, Geordie; Truscott, Tadd; USU Team; BYU Team

2017-11-01

Noninvasive data from velocimetry experiments (e.g., PIV) have been used to calculate vorticity and pressure fields. However, the noise, error, or uncertainties in the PIV measurements would eventually propagate to the calculated pressure or vorticity field through reconstruction schemes. Despite the vast applications of pressure and/or vorticity field calculated from PIV measurements, studies on the error propagation from the velocity field to the reconstructed fields (PIV-pressure and PIV-vorticity are few. In the current study, we break down the inherent connections between PIV-based pressure reconstruction and PIV-based vorticity calculation. The similar error propagation dynamics, which involve competition between physical properties of the flow and numerical errors from reconstruction schemes, are found in both PIV-pressure and PIV-vorticity reconstructions.

Error Propagation Dynamics of PIV-based Pressure Field Calculations: How well does the pressure Poisson solver perform inherently?

Science.gov (United States)

Pan, Zhao; Whitehead, Jared; Thomson, Scott; Truscott, Tadd

2016-08-01

Obtaining pressure field data from particle image velocimetry (PIV) is an attractive technique in fluid dynamics due to its noninvasive nature. The application of this technique generally involves integrating the pressure gradient or solving the pressure Poisson equation using a velocity field measured with PIV. However, very little research has been done to investigate the dynamics of error propagation from PIV-based velocity measurements to the pressure field calculation. Rather than measure the error through experiment, we investigate the dynamics of the error propagation by examining the Poisson equation directly. We analytically quantify the error bound in the pressure field, and are able to illustrate the mathematical roots of why and how the Poisson equation based pressure calculation propagates error from the PIV data. The results show that the error depends on the shape and type of boundary conditions, the dimensions of the flow domain, and the flow type.

Error propagation dynamics of PIV-based pressure field calculations: How well does the pressure Poisson solver perform inherently?

International Nuclear Information System (INIS)

Pan, Zhao; Thomson, Scott; Whitehead, Jared; Truscott, Tadd

2016-01-01

Obtaining pressure field data from particle image velocimetry (PIV) is an attractive technique in fluid dynamics due to its noninvasive nature. The application of this technique generally involves integrating the pressure gradient or solving the pressure Poisson equation using a velocity field measured with PIV. However, very little research has been done to investigate the dynamics of error propagation from PIV-based velocity measurements to the pressure field calculation. Rather than measure the error through experiment, we investigate the dynamics of the error propagation by examining the Poisson equation directly. We analytically quantify the error bound in the pressure field, and are able to illustrate the mathematical roots of why and how the Poisson equation based pressure calculation propagates error from the PIV data. The results show that the error depends on the shape and type of boundary conditions, the dimensions of the flow domain, and the flow type. (paper)

Error Propagation Dynamics of PIV-based Pressure Field Calculations: How well does the pressure Poisson solver perform inherently?

Science.gov (United States)

Pan, Zhao; Whitehead, Jared; Thomson, Scott; Truscott, Tadd

2016-01-01

Obtaining pressure field data from particle image velocimetry (PIV) is an attractive technique in fluid dynamics due to its noninvasive nature. The application of this technique generally involves integrating the pressure gradient or solving the pressure Poisson equation using a velocity field measured with PIV. However, very little research has been done to investigate the dynamics of error propagation from PIV-based velocity measurements to the pressure field calculation. Rather than measure the error through experiment, we investigate the dynamics of the error propagation by examining the Poisson equation directly. We analytically quantify the error bound in the pressure field, and are able to illustrate the mathematical roots of why and how the Poisson equation based pressure calculation propagates error from the PIV data. The results show that the error depends on the shape and type of boundary conditions, the dimensions of the flow domain, and the flow type. PMID:27499587

Time-Resolved PIV for Space-Time Correlations in Hot Jets

Science.gov (United States)

Wernet, Mark P.

2007-01-01

Temporally Resolved Particle Image Velocimetry (TR-PIV) is being used to characterize the decay of turbulence in jet flows a critical element for understanding the acoustic properties of the flow. A TR-PIV system, developed in-house at the NASA Glenn Research Center, is capable of acquiring planar PIV image frame pairs at up to 10 kHz. The data reported here were collected at Mach numbers of 0.5 and 0.9 and at temperature ratios of 0.89 and 1.76. The field of view of the TR-PIV system covered 6 nozzle diameters along the lip line of the 50.8 mm diameter jet. The cold flow data at Mach 0.5 were compared with hotwire anemometry measurements in order to validate the new TR-PIV technique. The axial turbulence profiles measured across the shear layer using TR-PIV were thinner than those measured using hotwire anemometry and remained centered along the nozzle lip line. The collected TR-PIV data illustrate the differences in the single point statistical flow properties of cold and hot jet flows. The planar, time-resolved velocity records were then used to compute two-point space-time correlations of the flow at the Mach 0.9 flow condition. The TR-PIV results show that there are differences in the convective velocity and growth rate of the turbulent structures between cold and hot flows at the same Mach number.

Micro-PIV (micro particle image velocimetry) visualization of red blood cells (RBCs) sucked by a female mosquito

International Nuclear Information System (INIS)

Kikuchi, K; Mochizuki, O

2011-01-01

A mosquito's pump is a highly effective system in the small suction domain. To understand a mosquito's blood suction mechanism, we analysed the characteristics of red blood cells (RBCs) in human blood during and after suction by a female mosquito. Focussing on the flow patterns of the RBCs in human blood being sucked by a mosquito, we visualized blood flow by using a micro-particle image velocimetry (μ-PIV) system, which combines an optical microscope and a PIV method. In an ex vivo experiment, a female mosquito was supplied diluted blood at the tip of the proboscis. We examined the blood flow around the tip of the proboscis and observed that RBCs were periodically sucked towards a hole around the tip. The sucked RBCs then homogeneously flowed parallel to the inner surface of the proboscis without adhering to the wall. Furthermore, using a bioelectric recording system, we directly measured electrical signals generated during suction by the pump muscles located in the mosquito's head. We found that the electrical signal power was synchronized with the acceleration of the RBCs in the sucking phase. A histological stain method was adapted for the observation of the form and internal structure of RBCs in the mosquito. Although the blood flow analysis revealed that the RBCs underwent shear stress during suction, RBCs in the mosquito's stomach maintained their original shape

A fast all-in-one method for automated post-processing of PIV data.

Science.gov (United States)

Garcia, Damien

2011-05-01

Post-processing of PIV (particle image velocimetry) data typically contains three following stages: validation of the raw data, replacement of spurious and missing vectors, and some smoothing. A robust post-processing technique that carries out these steps simultaneously is proposed. The new all-in-one method (DCT-PLS), based on a penalized least squares approach (PLS), combines the use of the discrete cosine transform (DCT) and the generalized cross-validation, thus allowing fast unsupervised smoothing of PIV data. The DCT-PLS was compared with conventional methods, including the normalized median test, for post-processing of simulated and experimental raw PIV velocity fields. The DCT-PLS was shown to be more efficient than the usual methods, especially in the presence of clustered outliers. It was also demonstrated that the DCT-PLS can easily deal with a large amount of missing data. Because the proposed algorithm works in any dimension, the DCT-PLS is also suitable for post-processing of volumetric three-component PIV data.

A fast all-in-one method for automated post-processing of PIV data

Science.gov (United States)

Garcia, Damien

2013-01-01

Post-processing of PIV (particle image velocimetry) data typically contains three following stages: validation of the raw data, replacement of spurious and missing vectors, and some smoothing. A robust post-processing technique that carries out these steps simultaneously is proposed. The new all-in-one method (DCT-PLS), based on a penalized least squares approach (PLS), combines the use of the discrete cosine transform (DCT) and the generalized cross-validation, thus allowing fast unsupervised smoothing of PIV data. The DCT-PLS was compared with conventional methods, including the normalized median test, for post-processing of simulated and experimental raw PIV velocity fields. The DCT-PLS was shown to be more efficient than the usual methods, especially in the presence of clustered outliers. It was also demonstrated that the DCT-PLS can easily deal with a large amount of missing data. Because the proposed algorithm works in any dimension, the DCT-PLS is also suitable for post-processing of volumetric three-component PIV data. PMID:24795497

Computationally efficient storage of 3D particle intensity and position data for use in 3D PIV and 3D PTV

International Nuclear Information System (INIS)

Atkinson, C; Buchmann, N A; Soria, J

2013-01-01

Three-dimensional (3D) volumetric velocity measurement techniques, such as tomographic or holographic particle image velocimetry (PIV), rely upon the computationally intensive formation, storage and localized interrogation of multiple 3D particle intensity fields. Calculation of a single velocity field typically requires the extraction of particle intensities into tens of thousands of 3D sub-volumes or discrete particle clusters, the processing of which can significantly affect the performance of 3D cross-correlation based PIV and 3D particle tracking velocimetry (PTV). In this paper, a series of popular and customized volumetric data formats are presented and investigated using synthetic particle volumes and experimental data arising from tomographic PIV measurements of a turbulent boundary layer. Results show that the use of a sub-grid ordered non-zero intensity format with a sub-grid size of 16 × 16 × 16 points provides the best performance for cross-correlation based PIV analysis, while a particle clustered non-zero intensity format provides the best format for PTV applications. In practical tomographic PIV measurements the sub-grid ordered non-zero intensity format offered a 29% improvement in reconstruction times, while providing a 93% reduction in volume data requirements and a 28% overall improvement in cross-correlation based velocity analysis and validation times. (paper)

Laboratory observations of sediment transport using combined particle image and tracking velocimetry (Conference Presentation)

Science.gov (United States)

Frank, Donya; Calantoni, Joseph

2017-05-01

Improved understanding of coastal hydrodynamics and morphology will lead to more effective mitigation measures that reduce fatalities and property damage caused by natural disasters such as hurricanes. We investigated sediment transport under oscillatory flow over flat and rippled beds with phase-separated stereoscopic Particle Image Velocimetry (PIV). Standard PIV techniques severely limit measurements at the fluid-sediment interface and do not allow for the observation of separate phases in multi-phase flow (e.g. sand grains in water). We have implemented phase-separated Particle Image Velocimetry by adding fluorescent tracer particles to the fluid in order to observe fluid flow and sediment transport simultaneously. While sand grains scatter 532 nm wavelength laser light, the fluorescent particles absorb 532 nm laser light and re-emit light at a wavelength of 584 nm. Optical long-pass filters with a cut-on wavelength of 550 nm were installed on two cameras configured to perform stereoscopic PIV to capture only the light emitted by the fluorescent tracer particles. A third high-speed camera was used to capture the light scattered by the sand grains allowing for sediment particle tracking via particle tracking velocimetry (PTV). Together, these overlapping, simultaneously recorded images provided sediment particle and fluid velocities at high temporal and spatial resolution (100 Hz sampling with 0.8 mm vector spacing for the 2D-3C fluid velocity field). Measurements were made under a wide range of oscillatory flows over flat and rippled sand beds. The set of observations allow for the investigation of the relative importance of pressure gradients and shear stresses on sediment transport.

CFD and PIV analysis of hemodynamics in a growing intracranial aneurysm.

Science.gov (United States)

Raschi, Marcelo; Mut, Fernando; Byrne, Greg; Putman, Christopher M; Tateshima, Satoshi; Viñuela, Fernando; Tanoue, Tetsuya; Tanishita, Kazuo; Cebral, Juan R

2012-02-01

Hemodynamics is thought to be a fundamental factor in the formation, progression, and rupture of cerebral aneurysms. Understanding these mechanisms is important to improve their rupture risk assessment and treatment. In this study, we analyze the blood flow field in a growing cerebral aneurysm using experimental particle image velocimetry (PIV) and computational fluid dynamics (CFD) techniques. Patient-specific models were constructed from longitudinal 3D computed tomography angiography images acquired at 1-y intervals. Physical silicone models were constructed from the computed tomography angiography images using rapid prototyping techniques, and pulsatile flow fields were measured with PIV. Corresponding CFD models were created and run under matching flow conditions. Both flow fields were aligned, interpolated, and compared qualitatively by inspection and quantitatively by defining similarity measures between the PIV and CFD vector fields. Results showed that both flow fields were in good agreement. Specifically, both techniques provided consistent representations of the main intra-aneurysmal flow structures and their change during the geometric evolution of the aneurysm. Despite differences observed mainly in the near wall region, and the inherent limitations of each technique, the information derived is consistent and can be used to study the role of hemodynamics in the natural history of intracranial aneurysms.

Estimating Horizontal Displacement between DEMs by Means of Particle Image Velocimetry Techniques

Directory of Open Access Journals (Sweden)

Juan F. Reinoso

2015-12-01

Full Text Available To date, digital terrain model (DTM accuracy has been studied almost exclusively by computing its height variable. However, the largely ignored horizontal component bears a great influence on the positional accuracy of certain linear features, e.g., in hydrological features. In an effort to fill this gap, we propose a means of measurement different from the geomatic approach, involving fluid mechanics (water and air flows or aerodynamics. The particle image velocimetry (PIV algorithm is proposed as an estimator of horizontal differences between digital elevation models (DEM in grid format. After applying a scale factor to the displacement estimated by the PIV algorithm, the mean error predicted is around one-seventh of the cell size of the DEM with the greatest spatial resolution, and around one-nineteenth of the cell size of the DEM with the least spatial resolution. Our methodology allows all kinds of DTMs to be compared once they are transformed into DEM format, while also allowing comparison of data from diverse capture methods, i.e., LiDAR versus photogrammetric data sources.

Beam stability and warm-up effects of Nd:YAG lasers used in particle image velocimetry

International Nuclear Information System (INIS)

Grayson, K; De Silva, C M; Hutchins, N; Marusic, I

2017-01-01

The characteristics and causes of Nd:YAG laser warm-up transients and steady state beam stability effects are investigated in this study. Dynamic laser performance has a particularly noticeable impact on particle image velocimetry (PIV) and other laser-based flow visualisation techniques, where changes in beam pointing can influence the overlap between laser light sheets and thereby degrade the correlation of PIV image pairs. Despite anecdotal knowledge or experience of laser warm-up effects, they have not been formally documented or quantified to date for PIV applications. In this study, the nature of these laser transients are analysed and compared among a selection of typical PIV laser equipment. An investigation into the cause of these transients during the laser warm-up sequence is also presented. Furthermore, the degree of dual cavity transient coupling within a PIV laser system is analysed to determine a practical limit to the laser light sheet overlap that can be expected from PIV experiments. Finally, the results from this study inform a series of recommendations for PIV best practice, which aim to minimise the impact of laser transients on experimental data. (paper)

PIV-based load determination in aircraft propellers

NARCIS (Netherlands)

Ragni, D.

2012-01-01

The thesis describes the application of particle image velocimetry (PIV) to study the aerodynamic loads of airfoils and aircraft propellers. The experimental work focuses on the development of a measurement procedure to infer the pressure of the flow field from the velocity distribution obtained by

Flow characteristics of guide vane of diffuser pump by PIV measurement

International Nuclear Information System (INIS)

Kim, J. H.; Lee, Young Ho; Choi, J. W.; Kim, M. Y.; Lee, H.

2000-01-01

The present experimental study is focused on the application of multi-point simultaneous measurement by PIV(Particle Image Velocimetry) to guide vane region within a diffuser pump. Various different kinds of clearance were selected as experimental conditions. Optimized cross correlation identification to obtain velocity vectors was implemented with direct calculation of correlation coefficients. Fine optical setup important in PIV performance is arranged for the accurate PIV measurement of high-speed complex flow. Various flow patterns are represented quantitatively at the stator passages

Application of PIV to the Measurement of High Speed Jet Flows

Science.gov (United States)

Lourenco, L.

1999-01-01

The Particle Image Velocimetry, PIV, has been implemented for the investigation of high-speed jet flows at the NASA Langley Research Center. In this approach the velocity (displacement) is found as the location of a peak in the correlation map of particle images acquired in quick succession. In the study, the technique for the correct seeding of the flow field were developed and implemented and the operational parameters influencing the accuracy of the measurement have been optimized.

Time Resolved PIV for Space-Time Correlations in Hot Jets

Science.gov (United States)

Wernet, Mark P.

2007-01-01

Temporally Resolved Particle Image Velocimetry (TR-PIV) is the newest and most exciting tool recently developed to support our continuing efforts to characterize and improve our understanding of the decay of turbulence in jet flows -- a critical element for understanding the acoustic properties of the flow. A new TR-PIV system has been developed at the NASA Glenn Research Center which is capable of acquiring planar PIV image frame pairs at up to 25 kHz. The data reported here were collected at Mach numbers of 0.5 and 0.9 and at temperature ratios of 0.89 and 1.76. The field of view of the TR-PIV system covered 6 nozzle diameters along the lip line of the 50.8 mm diameter jet. The cold flow data at Mach 0.5 were compared with hotwire anemometry measurements in order to validate the new TR-PIV technique. The axial turbulence profiles measured across the shear layer using TR-PIV were thinner than those measured using hotwire anemometry and remained centered along the nozzle lip line. The collected TR-PIV data illustrate the differences in the single point statistical flow properties of cold and hot jet flows. The planar, time-resolved velocity records were then used to compute two-point space-time correlations of the flow at the Mach 0.9 flow condition. The TR-PIV results show that there are differences in the convective velocity and growth rate of the turbulent structures between cold and hot flows at the same Mach number

A multi-time-step noise reduction method for measuring velocity statistics from particle tracking velocimetry

Science.gov (United States)

Machicoane, Nathanaël; López-Caballero, Miguel; Bourgoin, Mickael; Aliseda, Alberto; Volk, Romain

2017-10-01

We present a method to improve the accuracy of velocity measurements for fluid flow or particles immersed in it, based on a multi-time-step approach that allows for cancellation of noise in the velocity measurements. Improved velocity statistics, a critical element in turbulent flow measurements, can be computed from the combination of the velocity moments computed using standard particle tracking velocimetry (PTV) or particle image velocimetry (PIV) techniques for data sets that have been collected over different values of time intervals between images. This method produces Eulerian velocity fields and Lagrangian velocity statistics with much lower noise levels compared to standard PIV or PTV measurements, without the need of filtering and/or windowing. Particle displacement between two frames is computed for multiple different time-step values between frames in a canonical experiment of homogeneous isotropic turbulence. The second order velocity structure function of the flow is computed with the new method and compared to results from traditional measurement techniques in the literature. Increased accuracy is also demonstrated by comparing the dissipation rate of turbulent kinetic energy measured from this function against previously validated measurements.

Particle image velocimetry measurements in an anatomical vascular model fabricated using inkjet 3D printing

Science.gov (United States)

Aycock, Kenneth I.; Hariharan, Prasanna; Craven, Brent A.

2017-11-01

For decades, the study of biomedical fluid dynamics using optical flow visualization and measurement techniques has been limited by the inability to fabricate transparent physical models that realistically replicate the complex morphology of biological lumens. In this study, we present an approach for producing optically transparent anatomical models that are suitable for particle image velocimetry (PIV) using a common 3D inkjet printing process (PolyJet) and stock resin (VeroClear). By matching the index of refraction of the VeroClear material using a room-temperature mixture of water, sodium iodide, and glycerol, and by printing the part in an orientation such that the flat, optical surfaces are at an approximately 45° angle to the build plane, we overcome the challenges associated with using this 3D printing technique for PIV. Here, we summarize our methodology and demonstrate the process and the resultant PIV measurements of flow in an optically transparent anatomical model of the human inferior vena cava.

A histogram-based technique for rapid vector extraction from PIV photographs

Science.gov (United States)

Humphreys, William M., Jr.

1991-01-01

A new analysis technique, performed totally in the image plane, is proposed which rapidly extracts all available vectors from individual interrogation regions on PIV photographs. The technique avoids the need for using Fourier transforms with the associated computational burden. The data acquisition and analysis procedure is described, and results of a preliminary simulation study to evaluate the accuracy of the technique are presented. Recently obtained PIV photographs are analyzed.

PIV measurement at the blowdown pipe outlet. [Particle Image Velocimetry

Energy Technology Data Exchange (ETDEWEB)

Puustinen, M.; Laine, J.; Raesaenen, A.; Pyy, L.; Telkkae, J. [Lappeenranta Univ. of Technology, Lappeenranta (Finland)

2013-04-15

This report summarizes the findings of the PIV measurement tests carried out in January - February 2013 with the scaled down PPOOLEX test facility at LUT. The main objective of the tests was to find out the operational limits of the PIV system regarding suitable test conditions and correct values of different adjustable PIV parameters. An additional objective was to gather CFD grade data for verification/validation of numerical models. Both water and steam injection tests were carried out. PIV measurements with cold water injection succeeded well. Raw images were of high quality, averaging over the whole measurement period could be done and flow fields close to the blowdown pipe outlet could be determined. In the warm water injection cases the obtained averaged velocity field images were harder to interpret, especially if the blowdown pipe was also filled with warm water in the beginning of the measurement period. The absolute values of the velocity vectors seemed to be smaller than in the cold water injection cases. With very small steam flow rates the steam/water interface was inside the blowdown pipe and quite stable in nature. The raw images were of good quality but due to some fluctuation in the velocity field averaging of the velocity images over the whole measured period couldn't be done. Condensation of steam in the vicinity of the pipe exit probably caused these fluctuations. A constant outflow was usually followed by a constant inflow towards the pipe exit. Vector field images corresponding to a certain phase of the test could be extracted and averaged but this would require a very careful analysis so that the images could be correctly categorized. With higher steam flow rates rapid condensation of large steam bubbles created small gas bubbles which were in front of the measurement area of the PIV system. They disturbed the measurements by reflecting laser light like seeding particles and therefore the raw images were of poor quality and they couldn

Automated and temperature-controlled micro-PIV measurements enabling long-term-stable microchannel acoustophoresis characterization

DEFF Research Database (Denmark)

Augustsson, Per; Barnkob, Rune; Wereley, Steven T.

2011-01-01

We present a platform for micro particle image velocimetry (μPIV), capable of carrying out full-channel, temperature-controlled, long-term-stable, and automated μPIV-measurement of microchannel acoustophoresis with uncertainties below 5% and a spatial resolution in the order of 20 μm. A method to...

Pressure from particle image velocimetry for convective flows: a Taylor’s hypothesis approach

International Nuclear Information System (INIS)

De Kat, R; Ganapathisubramani, B

2013-01-01

Taylor’s hypothesis is often applied in turbulent flow analysis to map temporal information into spatial information. Recent efforts in deriving pressure from particle image velocimetry (PIV) have proposed multiple approaches, each with its own weakness and strength. Application of Taylor’s hypothesis allows us to counter the weakness of an Eulerian approach that is described by de Kat and van Oudheusden (2012 Exp. Fluids 52 1089–106). Two different approaches of using Taylor’s hypothesis in determining planar pressure are investigated: one where pressure is determined from volumetric PIV data and one where pressure is determined from time-resolved stereoscopic PIV data. A performance assessment on synthetic data shows that application of Taylor’s hypothesis can improve determination of pressure from PIV data significantly compared with a time-resolved volumetric approach. The technique is then applied to time-resolved PIV data taken in a cross-flow plane of a turbulent jet (Ganapathisubramani et al 2007 Exp. Fluids 42 923–39). Results appear to indicate that pressure can indeed be obtained from PIV data in turbulent convective flows using the Taylor’s hypothesis approach, where there are no other methods to determine pressure. The role of convection velocity in determination of pressure is also discussed. (paper)

New adaptive sampling method in particle image velocimetry

International Nuclear Information System (INIS)

Yu, Kaikai; Xu, Jinglei; Tang, Lan; Mo, Jianwei

2015-01-01

This study proposes a new adaptive method to enable the number of interrogation windows and their positions in a particle image velocimetry (PIV) image interrogation algorithm to become self-adapted according to the seeding density. The proposed method can relax the constraint of uniform sampling rate and uniform window size commonly adopted in the traditional PIV algorithm. In addition, the positions of the sampling points are redistributed on the basis of the spring force generated by the sampling points. The advantages include control of the number of interrogation windows according to the local seeding density and smoother distribution of sampling points. The reliability of the adaptive sampling method is illustrated by processing synthetic and experimental images. The synthetic example attests to the advantages of the sampling method. Compared with that of the uniform interrogation technique in the experimental application, the spatial resolution is locally enhanced when using the proposed sampling method. (technical design note)

Reconstruction of an acoustic pressure field in a resonance tube by particle image velocimetry.

Science.gov (United States)

Kuzuu, K; Hasegawa, S

2015-11-01

A technique for estimating an acoustic field in a resonance tube is suggested. The estimation of an acoustic field in a resonance tube is important for the development of the thermoacoustic engine, and can be conducted employing two sensors to measure pressure. While this measurement technique is known as the two-sensor method, care needs to be taken with the location of pressure sensors when conducting pressure measurements. In the present study, particle image velocimetry (PIV) is employed instead of a pressure measurement by a sensor, and two-dimensional velocity vector images are extracted as sequential data from only a one- time recording made by a video camera of PIV. The spatial velocity amplitude is obtained from those images, and a pressure distribution is calculated from velocity amplitudes at two points by extending the equations derived for the two-sensor method. By means of this method, problems relating to the locations and calibrations of multiple pressure sensors are avoided. Furthermore, to verify the accuracy of the present method, the experiments are conducted employing the conventional two-sensor method and laser Doppler velocimetry (LDV). Then, results by the proposed method are compared with those obtained with the two-sensor method and LDV.

Three-dimensional measurement and visualization of internal flow of a moving droplet using confocal micro-PIV.

Science.gov (United States)

Kinoshita, Haruyuki; Kaneda, Shohei; Fujii, Teruo; Oshima, Marie

2007-03-01

This paper presents a micro-flow diagnostic technique, 'high-speed confocal micro-particle image velocimetry (PIV)', and its application to the internal flow measurement of a droplet passing through a microchannel. A confocal micro-PIV system has been successfully constructed wherein a high-speed confocal scanner is combined with the conventional micro-PIV technique. The confocal micro-PIV system enables us to obtain a sequence of sharp and high-contrast cross-sectional particle images at 2000 frames s(-1). This study investigates the confocal depth, which is a significant parameter to determine the out-of-plane measurement resolution in confocal micro-PIV. Using the present confocal micro-PIV system, we can measure velocity distributions of micro-flows in a 228 microm x 171 microm region with a confocal depth of 1.88 microm. We also propose a three-dimensional velocity measurement method based on the confocal micro-PIV and the equation of continuity. This method enables us to measure three velocity components in a three-dimensional domain of micro flows. The confocal micro-PIV system is applied to the internal flow measurement of a droplet. We have measured three-dimensional distributions of three-component velocities of a droplet traveling in a 100 microm (width) x 58 microm (depth) channel. A volumetric velocity distribution inside a droplet is obtained by the confocal micro-PIV and the three-dimensional flow structure inside the droplet is investigated. The measurement results suggest that a three-dimensional and complex circulating flow is formed inside the droplet.

Instantaneous planar pressure determination from PIV in turbulent flow

NARCIS (Netherlands)

De Kat, R.; Van Oudheusden, B.W.

2011-01-01

This paper deals with the determination of instantaneous planar pressure fields from velocity data obtained by particle image velocimetry (PIV) in turbulent flow. The operating principles of pressure determination using a Eulerian or a Lagrangian approach are described together with theoretical

PIV measurement of internal structure of diesel fuel spray

Energy Technology Data Exchange (ETDEWEB)

Cao, Z M [Ecotechnology System Lab., Yokohama National Univ. (Japan); Nishino, K [Div. of Artificial Environment and Systems, Yokohama National Univ. (Japan); Mizuno, S [Yokohama National Univ. (Japan); Torii, K [Dept. of Mechanical Engineering and Materials Science, Yokohama National Univ. (Japan)

2000-12-01

This paper reports particle image velocimetry (PIV) measurements of diesel fuel spray injected from a single-hole nozzle at injection pressures ranging from 30 to 70 MPa, which are comparable to partial-load operating conditions of commercial diesel engines. The fuel is injected into a non-combusting environment pressurized up to 2.0 MPa. A laser-induced fluorescent (LIF) technique is utilized to visualize internal structures of fuel sprays formed by densely-distributing droplets. A specially designed synchronization system is developed to acquire double-frame spray images at an arbitrary time delay after injection. A direct cross-correlation PIV technique is applied to measure instantaneous droplet velocity distribution. Unique large-scale structures in droplet concentration, called 'branch-like structures' by Azetsu et al. (1990), are observed and shown to be associated with active vortical motions, which appear to be responsible for the mixing between droplets and the surrounding gas. It is found that the droplets tend to move out of the vortical structures and accumulate in the regions of low vorticity. Some other interesting features concerning droplet velocity fields are also presented. (orig.)

Measurements of a high-luminosity flame structure by a shuttered PIV system

International Nuclear Information System (INIS)

Li, Yueh-Heng; Wu, Chih-Yung; Chen, Bi-Chian; Chao, Yei-Chin

2008-01-01

It is difficult to measure the velocity distribution inside a high-luminosity flame by using the particle image velocimetry (PIV) system with a double-shutter mode CCD camera. The second raw image of the PIV image pair is usually contaminated by flame emission. The main cause of the problem is an excess exposure time which lets the flame emission overlap the particle image in the second frame. If the flame-contamination problem is not significant, for example in faint flames, digital image processing can improve the image to an acceptable level. Nevertheless, when the PIV technique is applied to high-luminosity flames, the second raw particle image would be contaminated by flame emission. In this paper, incorporating a mechanical shutter in the PIV system with a double-shutter CCD camera is proposed to improve PIV measurements in high-luminosity flames. Measurements in faint, high-luminosity as well as very bright flames were tested. The results show that the present setup can accurately resolve the flow velocity field inside the flame cone, through the flame and in the post flame zone for all the flame conditions analyzed. The velocity distributions and streamline patterns measured by the present equipment are reasonable and meaningful

Development of two-dimensional velocity field measurement using particle tracking velocimetry on neutron radiography

International Nuclear Information System (INIS)

Saito, Y.; Mishima, K.; Suzuki, T.; Matsubayashi, M.

2003-01-01

The structures of liquid metal two-phase flow are investigated for analyzing the core meltdown accident of fast reactor. The experiments of high-density ratio two-phase flow for lead-bismuth molten metal and nitrogen gases are conducted to understand in detail. The liquid phase velocity distributions of lead-bismuth molten metal are measured by neutron radiography using Au-Cd tracer particles. The liquid phase velocity distributions are obtained usually by using particle image velocimetry (PIV) on the neutron radiography. The PIV, however is difficult to get the velocity vector distribution quantitatively. An image of neutron radiography is divided into two images of the bubbles and the tracer particles each in particle tracking velocimetry (PTV), which distinguishes tracer contents in the bubble from them in the liquid phase. The locations of tracer particles in the liquid phase are possible to determine by particle mask correlation method, in which the bubble images are separated from the tracer images by Σ-scaling method. The particle tracking velocimetry give a full detail of the velocity vector distributions of the liquid phase in two-phase flow, in comparison with the PIV method. (M. Suetake)

Internal flow measurement in transonic compressor by PIV technique

Science.gov (United States)

Wang, Tongqing; Wu, Huaiyu; Liu, Yin

2001-11-01

The paper presents some research works conducted in National Key Laboratory of Aircraft Engine of China on the shock containing supersonic flow measurement as well as the internal flow measurement of transoijc compressor by PIC technique. A kind of oil particles in diameter about 0.3 micrometers containing in the flow was discovered to be a very good seed for the PIV measurement of supersonic jet flow. The PIV measurement in over-expanded supersonic free jet and in the flow over wages show a very clear shock wave structure. In the PIV internal flow measurement of transonic compressor a kind of liquid particle of glycol was successful to be used as the seed. An illumination periscope with sheet forming optics was designed and manufactured, it leaded the laser shot generated from an integrate dual- cavity Nd:YAG laser of TSI PIV results of internal flow of an advanced low aspect ratio transonic compressor were shown and discussed briefly.

Cross-Stream PIV Measurements of Jets With Internal Lobed Mixers

Science.gov (United States)

Bridges, James; Wernet, Mark P.

2004-01-01

With emphasis being placed on enhanced mixing of jet plumes for noise reduction and on predictions of jet noise based upon turbulent kinetic energy, unsteady measurements of jet plumes are a very important part of jet noise studies. Given that hot flows are of most practical interest, optical techniques such as Particle Image Velocimetry (PIV) are applicable. When the flow has strong azimuthal features, such as those generated by chevrons or lobed mixers, traditional PIV, which aligns the measurement plane parallel to the dominant flow direction is very inefficient, requiring many planes of data to be acquired and stacked up to produce the desired flow cross-sections. This paper presents PIV data acquired in a plane normal to the jet axis, directly measuring the cross-stream gradients and features of an internally mixed nozzle operating at aircraft engine flow conditions. These nozzle systems included variations in lobed mixer penetration, lobe count, lobe scalloping, and nozzle length. Several cases validating the accuracy of the PIV data are examined along with examples of its use in answering questions about the jet noise generation processes in these nozzles. Of most interest is the relationship of low frequency aft-directed noise with turbulence kinetic energy and mean velocity.

Particle image velocimetry (PIV) study of rotating cylindrical filters for animal cell perfusion processes.

Science.gov (United States)

Figueredo-Cardero, Alvio; Chico, Ernesto; Castilho, Leda; de Andrade Medronho, Ricardo

2012-01-01

In the present work, the main fluid flow features inside a rotating cylindrical filtration (RCF) system used as external cell retention device for animal cell perfusion processes were investigated using particle image velocimetry (PIV). The motivation behind this work was to provide experimental fluid dynamic data for such turbulent flow using a high-permeability filter, given the lack of information about this system in the literature. The results shown herein gave evidence that, at the boundary between the filter mesh and the fluid, a slip velocity condition in the tangential direction does exist, which had not been reported in the literature so far. In the RCF system tested, this accounted for a fluid velocity 10% lower than that of the filter tip, which could be important for the cake formation kinetics during filtration. Evidence confirming the existence of Taylor vortices under conditions of turbulent flow and high permeability, typical of animal cell perfusion RCF systems, was obtained. Second-order turbulence statistics were successfully calculated. The radial behavior of the second-order turbulent moments revealed that turbulence in this system is highly anisotropic, which is relevant for performing numerical simulations of this system. Copyright © 2012 American Institute of Chemical Engineers (AIChE).

Investigating fundamental properties of wind turbine wake structure using particle image velocimetry

Energy Technology Data Exchange (ETDEWEB)

Whale, J. [Univ. of Edinburgh, Dept. of Mechanical Engineering, Edinburgh (United Kingdom)

1997-08-01

Low Reynolds number flow visualization tests are often used for showing the flow pattern changes associated with changes in lift-coefficients at a higher Reynolds number. In wind turbine studies, analysis of measured wake structures at small scale may reveal fundamental properties of the wake which will offer wake modellers a more complete understanding of rotor flows. Measurements are presented from experiments on a model wind turbine rig conducted in a water channel. The laser-optics technique of Particle Image Velocimetry (PIV) is used to make simultaneous multi-point measurements of the wake flow behind small-scale rotors. Analysis of the PIV data shows trends in velocity and vorticity structure in the wake. Study of the flow close to the rotor plane reveals information on stalled flow and blade performance. (au)

Pulsed operation of high-power light emitting diodes for imaging flow velocimetry

International Nuclear Information System (INIS)

Willert, C; Klinner, J; Moessner, S; Stasicki, B

2010-01-01

High-powered light emitting diodes (LED) are investigated for possible uses as light sources in flow diagnostics, in particular, as an alternative to laser-based illumination in particle imaging flow velocimetry in side-scatter imaging arrangements. Recent developments in solid state illumination resulted in mass-produced LEDs that provide average radiant power in excess of 10 W. By operating these LEDs with short duration, pulsed currents that are considerably beyond their continuous current damage threshold, light pulses can be generated that are sufficient to illuminate and image micron-sized particles in flow velocimetry. Time-resolved PIV measurements in water at a framing rate of 2kHz are presented. The feasibility of LED-based PIV measurements in air is also demonstrated

Analysis of particle kinematics in spheronization via particle image velocimetry.

Science.gov (United States)

Koester, Martin; Thommes, Markus

2013-02-01

Spheronization is a wide spread technique in pellet production for many pharmaceutical applications. Pellets produced by spheronization are characterized by a particularly spherical shape and narrow size distribution. The particle kinematic during spheronization is currently not well-understood. Therefore, particle image velocimetry (PIV) was implemented in the spheronization process to visualize the particle movement and to identify flow patterns, in order to explain the influence of various process parameters. The spheronization process of a common formulation was recorded with a high-speed camera, and the images were processed using particle image velocimetry software. A crosscorrelation approach was chosen to determine the particle velocity at the surface of the pellet bulk. Formulation and process parameters were varied systematically, and their influence on the particle velocity was investigated. The particle stream shows a torus-like shape with a twisted rope-like motion. It is remarkable that the overall particle velocity is approximately 10-fold lower than the tip speed of the friction plate. The velocity of the particle stream can be correlated to the water content of the pellets and the load of the spheronizer, while the rotation speed was not relevant. In conclusion, PIV was successfully applied to the spheronization process, and new insights into the particle velocity were obtained. Copyright © 2012 Elsevier B.V. All rights reserved.

A Dual-Plane PIV Study of Turbulent Heat Transfer Flows

Science.gov (United States)

Wernet, Mark P.; Wroblewski, Adam C.; Locke, Randy J.

2016-01-01

Thin film cooling is a widely used technique in turbomachinery and rocket propulsion applications, where cool injection air protects a surface from hot combustion gases. The injected air typically has a different velocity and temperature from the free stream combustion flow, yielding a flow field with high turbulence and large temperature differences. These thin film cooling flows provide a good test case for evaluating computational model prediction capabilities. The goal of this work is to provide a database of flow field measurements for validating computational flow prediction models applied to turbulent heat transfer flows. In this work we describe the application of a Dual-Plane Particle Image Velocimetry (PIV) technique in a thin film cooling wind tunnel facility where the injection air stream velocity and temperatures are varied in order to provide benchmark turbulent heat transfer flow field measurements. The Dual-Plane PIV data collected include all three components of velocity and all three components of vorticity, spanning the width of the tunnel at multiple axial measurement planes.

Development of PIV for Microgravity Diffusion Flames

Science.gov (United States)

Greenberg, Paul S.; Wernet, Mark P.; Yanis, William; Urban, David L.; Sunderland, Peter B.

2003-01-01

Results are presented from the application of Particle Image Velocimetry(PIV) to the overfire region of a laminar gas jet diffusion flame in normal gravity. A methane flame burning in air at 0.98 bar was considered. The apparatus demonstrated here is packaged in a drop rig designed for use in the 2.2 second drop tower.

Study on applicability of PIV measurement to natural convection in a scaled reactor vessel model

International Nuclear Information System (INIS)

Murakami, Takahiro; Koga, Tomonari; Eguchi, Yuzuru; Watanabe, Osamu

2009-01-01

The applicability of Particle Image Velocimetry (PIV) to natural convection in the plenum of a scaled water test model of the Japan Sodium-cooled Fast Reactor (JSFR) is studied in the paper. PIV measurement of such a buoyancy-driven flow in a geometrically complicated vessel is difficult in general, because the detection rate of tracer particles tends to decrease, and the noisy optical reflection to increase. In our measurements, tracer particles are adequately seeded in the hot plenum and particle images are captured by using a double-pulsed Nd:YAG laser and a high-speed camera. Then, image-processing techniques are employed to eliminate unphysical velocity vectors and unnecessary background images. The PIV results have shown that clear flow pattern can be extracted by time-averaging 300 sets of instantaneous PIV data in spite of highly fluctuating features of velocity in space and time. Moreover, the evaluation of the statistical quantities such as variance, skewness, and kurtosis has revealed the characteristic of the non-stationary spouting flows at the heater outlet. (author)

Study of flow around model of cooling tower by means of 2D Particle Image Velocimetry measurement

Science.gov (United States)

Barraclough, Veronika; Novotný, Jan; Šafařík, Pavel

This paper deals with flow around a bluff body of hyperboloid shape. It combines results gathered in the course of research by means of Particle Image Velocimetry (PIV). The experiments were carried out by means of low-frequency 2D PIV and the Reynolds number was 43 000.

3D Flow reconstruction using ultrasound PIV

Science.gov (United States)

Poelma, C.; Mari, J. M.; Foin, N.; Tang, M.-X.; Krams, R.; Caro, C. G.; Weinberg, P. D.; Westerweel, J.

2011-04-01

Ultrasound particle image velocimetry (PIV) can be used to obtain velocity fields in non-transparent geometries and/or fluids. In the current study, we use this technique to document the flow in a curved tube, using ultrasound contrast bubbles as flow tracer particles. The performance of the technique is first tested in a straight tube, with both steady laminar and pulsatile flows. Both experiments confirm that the technique is capable of reliable measurements. A number of adaptations are introduced that improve the accuracy and applicability of ultrasound PIV. Firstly, due to the method of ultrasound image acquisition, a correction is required for the estimation of velocities from tracer displacements. This correction accounts for the fact that columns in the image are recorded at slightly different instances. The second improvement uses a slice-by-slice scanning approach to obtain three-dimensional velocity data. This approach is here demonstrated in a strongly curved tube. The resulting flow profiles and wall shear stress distribution shows a distinct asymmetry. To meaningfully interpret these three-dimensional results, knowledge of the measurement thickness is required. Our third contribution is a method to determine this quantity, using the correlation peak heights. The latter method can also provide the third (out-of-plane) component if the measurement thickness is known, so that all three velocity components are available using a single probe.

PIV tracer behavior on propagating shock fronts

International Nuclear Information System (INIS)

Glazyrin, Fyodor N; Mursenkova, Irina V; Znamenskaya, Irina A

2016-01-01

The present work was aimed at the quantitative particle image velocimetry (PIV) measurement of a velocity field near the front of a propagating shock wave and the study of the dynamics of liquid tracers crossing the shock front. For this goal, a shock tube with a rectangular cross-section (48  ×  24 mm) was used. The flat shock wave with Mach numbers M  =  1.4–2.0 propagating inside the tube channel was studied as well as an expanding shock wave propagating outside the channel with M  =  1.2–1.8 at its main axis. The PIV imaging of the shock fronts was carried out with an aerosol of dioctyl sebacate (DEHS) as tracer particles. The pressures of the gas in front of the shock waves studied ranged from 0.013 Mpa to 0.1 MPa in the series of experiments. The processed PIV data, compared to the 1D normal shock theory, yielded consistent values of wake velocity immediately behind the plain shock wave. Special attention was paid to the blurring of the velocity jump on the shock front due to the inertial particle lag and peculiarities of the PIV technique. A numerical algorithm was developed for analysis and correction of the PIV data on the shock fronts, based on equations of particle-flow interaction. By application of this algorithm, the effective particle diameter of the DEHS aerosol tracers was estimated as 1.03  ±  0.12 μm. A number of different formulations for particle drag were tested with this algorithm, with varying success. The results show consistency with previously reported experimental data obtained for cases of stationary shock waves. (paper)

Study of flow around model of cooling tower by means of 2D Particle Image Velocimetry measurement

Directory of Open Access Journals (Sweden)

Barraclough Veronika

2017-01-01

Full Text Available This paper deals with flow around a bluff body of hyperboloid shape. It combines results gathered in the course of research by means of Particle Image Velocimetry (PIV. The experiments were carried out by means of low-frequency 2D PIV and the Reynolds number was 43 000.

Analysis of propeller-induced ground vortices by particle image velocimetry

NARCIS (Netherlands)

Yang, Y.; Sciacchitano, A.; Veldhuis, L.L.M.; Eitelberg, G.

2017-01-01

Abstract: The interaction between a propeller and its self-induced vortices originating on the ground is investigated in a scaled experiment. The velocity distribution in the flow field in two different planes containing the self-induced vortices is measured by particle image velocimetry (PIV).

Stereo-particle image velocimetry uncertainty quantification

International Nuclear Information System (INIS)

Bhattacharya, Sayantan; Vlachos, Pavlos P; Charonko, John J

2017-01-01

Particle image velocimetry (PIV) measurements are subject to multiple elemental error sources and thus estimating overall measurement uncertainty is challenging. Recent advances have led to a posteriori uncertainty estimation methods for planar two-component PIV. However, no complete methodology exists for uncertainty quantification in stereo PIV. In the current work, a comprehensive framework is presented to quantify the uncertainty stemming from stereo registration error and combine it with the underlying planar velocity uncertainties. The disparity in particle locations of the dewarped images is used to estimate the positional uncertainty of the world coordinate system, which is then propagated to the uncertainty in the calibration mapping function coefficients. Next, the calibration uncertainty is combined with the planar uncertainty fields of the individual cameras through an uncertainty propagation equation and uncertainty estimates are obtained for all three velocity components. The methodology was tested with synthetic stereo PIV data for different light sheet thicknesses, with and without registration error, and also validated with an experimental vortex ring case from 2014 PIV challenge. Thorough sensitivity analysis was performed to assess the relative impact of the various parameters to the overall uncertainty. The results suggest that in absence of any disparity, the stereo PIV uncertainty prediction method is more sensitive to the planar uncertainty estimates than to the angle uncertainty, although the latter is not negligible for non-zero disparity. Overall the presented uncertainty quantification framework showed excellent agreement between the error and uncertainty RMS values for both the synthetic and the experimental data and demonstrated reliable uncertainty prediction coverage. This stereo PIV uncertainty quantification framework provides the first comprehensive treatment on the subject and potentially lays foundations applicable to volumetric

A temporal PIV study of flame/obstacle generated vortex interactions within a semi-confined combustion chamber

Science.gov (United States)

Jarvis, S.; Hargrave, G. K.

2006-01-01

Experimental data obtained using a new multiple-camera digital particle image velocimetry (PIV) technique are presented for the interaction between a propagating flame and the turbulent recirculating velocity field generated during flame-solid obstacle interaction. The interaction between the gas movement and the obstacle creates turbulence by vortex shedding and local wake recirculations. The presence of turbulence in a flammable gas mixture can wrinkle a flame front, increasing the flame surface area and enhancing the burning rate. To investigate propagating flame/turbulence interaction, a novel multiple-camera digital PIV technique was used to provide high spatial and temporal characterization of the phenomenon for the turbulent flow field in the wake of three sequential obstacles. The technique allowed the quantification of the local flame speed and local flow velocity. Due to the accelerating nature of the explosion flow field, the wake flows develop 'transient' turbulent fields. Multiple-camera PIV provides data to define the spatial and temporal variation of both the velocity field ahead of the propagating flame and the flame front to aid the understanding of flame-vortex interaction. Experimentally obtained values for flame displacement speed and flame stretch are presented for increasing vortex complexity.

Investigation of the hydrodynamic behavior of diatom aggregates using particle image velocimetry.

Science.gov (United States)

Xiao, Feng; Li, Xiaoyan; Lam, Kitming; Wang, Dongsheng

2012-01-01

The hydrodynamic behavior of diatom aggregates has a significant influence on the interactions and flocculation kinetics of algae. However, characterization of the hydrodynamics of diatoms and diatom aggregates in water is rather difficult. In this laboratory study, an advanced visualization technique in particle image velocimetry (PIV) was employed to investigate the hydrodynamic properties of settling diatom aggregates. The experiments were conducted in a settling column filled with a suspension of fluorescent polymeric beads as seed tracers. A laser light sheet was generated by the PIV setup to illuminate a thin vertical planar region in the settling column, while the motions of particles were recorded by a high speed charge-coupled device (CCD) camera. This technique was able to capture the trajectories of the tracers when a diatom aggregate settled through the tracer suspension. The PIV results indicated directly the curvilinear feature of the streamlines around diatom aggregates. The rectilinear collision model largely overestimated the collision areas of the settling particles. Algae aggregates appeared to be highly porous and fractal, which allowed streamlines to penetrate into the aggregate interior. The diatom aggregates have a fluid collection efficiency of 10%-40%. The permeable feature of aggregates can significantly enhance the collisions and flocculation between the aggregates and other small particles including algal cells in water.

POD as tool for comparison of PIV and LES data

DEFF Research Database (Denmark)

Meyer, Knud Erik; Cavar, Dalibor; Pedersen, Jakob Martin

2007-01-01

Both Particle Image Velocimetry (PIV) and Large Eddy Simulation (LES) provides instantaneous velocity fields which can contain dynamical flow structures that occur systematically. Turbulent flows also contain random flow structures, and therefore there is a need for tools that can identify the sy...... on the crossflow velocity and pipe diameter is 2400 and the jet to crossflow velocity ratio is R = 3.3. The POD is able to identify two dynamic flow structures: jet shear-layer vortices and wake vortices. A good agreement for the dynamical content is found between PIV and LES....

MODELLING MANTLE TANKS FOR SDHW SYSTEMS USING PIV AND CFD

DEFF Research Database (Denmark)

Shah, Louise Jivan; Morrison, G.L.; Behnia, Masud

1999-01-01

Characteristics of vertical mantle heat exchanger tanks for SDHW systems have been investigated experimentally and theoretically using particle image velocimetry (PIV) and CFD modelling. A glass model of a mantle heat exchanger tank was constructed so that the flow distribution in the mantle could...... be studied using the PIV test facility. Two transient three-dimensional CFD-models of the glass model mantle tank were developed using the CFD-programmes CFX and FLUENT.The experimental results illustrate that the mantle flow structure in the mantle is complicated and the distribution of flow in the mantle...

Eulerian-Lagrangian analysis for particle velocities and trajectories in a pure wave motion using particle image velocimetry.

Science.gov (United States)

Umeyama, Motohiko

2012-04-13

This paper investigates the velocity and the trajectory of water particles under surface waves, which propagate at a constant water depth, using particle image velocimetry (PIV). The vector fields and vertical distributions of velocities are presented at several phases in one wave cycle. The third-order Stokes wave theory was employed to express the physical quantities. The PIV technique's ability to measure both temporal and spatial variations of the velocity was proved after a series of attempts. This technique was applied to the prediction of particle trajectory in an Eulerian scheme. Furthermore, the measured particle path was compared with the positions found theoretically by integrating the Eulerian velocity to the higher order of a Taylor series expansion. The profile of average travelling distance is also presented with a solution of zero net mass flux in a closed wave flume.

Optimization of in-line phase contrast particle image velocimetry using a laboratory x-ray source

International Nuclear Information System (INIS)

Ng, I.; Fouras, A.; Paganin, D. M.

2012-01-01

Phase contrast particle image velocimetry (PIV) using a laboratory x-ray microfocus source is investigated using a numerical model. Phase contrast images of 75 μm air bubbles, embedded within water exhibiting steady-state vortical flow, are generated under the paraxial approximation using a tungsten x-ray spectrum at 30 kVp. Propagation-based x-ray phase-contrast speckle images at a range of source-object and object-detector distances are generated, and used as input into a simulated PIV measurement. The effects of source-size-induced penumbral blurring, together with the finite dynamic range of the detector, are accounted for in the simulation. The PIV measurement procedure involves using the cross-correlation between temporally sequential speckle images to estimate the transverse displacement field for the fluid. The global error in the PIV reconstruction, for the set of simulations that was performed, suggests that geometric magnification is the key parameter for designing a laboratory-based x-ray phase-contrast PIV system. For the modeled system, x-ray phase-contrast PIV data measurement can be optimized to obtain low error ( 15 μm) of the detector, high geometric magnification (>2.5) is desired, while for large source size system (FWHM > 30 μm), low magnification (<1.5) would be suggested instead. The methods developed in this paper can be applied to optimizing phase-contrast velocimetry using a variety of laboratory x-ray sources.

Flow structures in large-angle conical diffusers measured by PIV

DEFF Research Database (Denmark)

Meyer, Knud Erik; Nielsen, L.; Nielsen, N.F.

2004-01-01

Flow in two different conical diffusers with large opening angles (30° and 18°) have been measured with stereoscopic Particle Image Velocimetry (PIV). The measurements were done in a cross section just after the exit of the diffuser. The Reynolds number was 100000 based on upstream diameter...

Measurements of liquid-phase turbulence in gas–liquid two-phase flows using particle image velocimetry

International Nuclear Information System (INIS)

Zhou, Xinquan; Doup, Benjamin; Sun, Xiaodong

2013-01-01

Liquid-phase turbulence measurements were performed in an air–water two-phase flow loop with a circular test section of 50 mm inner diameter using a particle image velocimetry (PIV) system. An optical phase separation method-–planar laser-induced fluorescence (PLIF) technique—which uses fluorescent particles and an optical filtration technique, was employed to separate the signals of the fluorescent seeding particles from those due to bubbles and other noises. An image pre-processing scheme was applied to the raw PIV images to remove the noise residuals that are not removed by the PLIF technique. In addition, four-sensor conductivity probes were adopted to measure the radial distribution of the void fraction. Two benchmark tests were performed: the first was a comparison of the PIV measurement results with those of similar flow conditions using thermal anemometry from previous studies; the second quantitatively compared the superficial liquid velocities calculated from the local liquid velocity and void fraction measurements with the global liquid flow rate measurements. The differences of the superficial liquid velocity obtained from the two measurements were bounded within ±7% for single-phase flows and two-phase bubbly flows with the area-average void fraction up to 18%. Furthermore, a preliminary uncertainty analysis was conducted to investigate the accuracy of the two-phase PIV measurements. The systematic uncertainties due to the circular pipe curvature effects, bubble surface reflection effects and other potential uncertainty sources of the PIV measurements were discussed. The purpose of this work is to facilitate the development of a measurement technique (PIV-PLIF) combined with image pre-processing for the liquid-phase turbulence in gas–liquid two-phase flows of relatively high void fractions. The high-resolution data set can be used to more thoroughly understand two-phase flow behavior, develop liquid-phase turbulence models, and assess high

Visual hull method for tomographic PIV measurement of flow around moving objects

Energy Technology Data Exchange (ETDEWEB)

Adhikari, D.; Longmire, E.K. [University of Minnesota, Department of Aerospace Engineering and Mechanics, Minneapolis, MN (United States)

2012-10-15

Tomographic particle image velocimetry (PIV) is a recently developed method to measure three components of velocity within a volumetric space. We present a visual hull technique that automates identification and masking of discrete objects within the measurement volume, and we apply existing tomographic PIV reconstruction software to measure the velocity surrounding the objects. The technique is demonstrated by considering flow around falling bodies of different shape with Reynolds number {proportional_to}1,000. Acquired image sets are processed using separate routines to reconstruct both the volumetric mask around the object and the surrounding tracer particles. After particle reconstruction, the reconstructed object mask is used to remove any ghost particles that otherwise appear within the object volume. Velocity vectors corresponding with fluid motion can then be determined up to the boundary of the visual hull without being contaminated or affected by the neighboring object velocity. Although the visual hull method is not meant for precise tracking of objects, the reconstructed object volumes nevertheless can be used to estimate the object location and orientation at each time step. (orig.)

Validation and application of Acoustic Mapping Velocimetry

Science.gov (United States)

Baranya, Sandor; Muste, Marian

2016-04-01

The goal of this paper is to introduce a novel methodology to estimate bedload transport in rivers based on an improved bedform tracking procedure. The measurement technique combines components and processing protocols from two contemporary nonintrusive instruments: acoustic and image-based. The bedform mapping is conducted with acoustic surveys while the estimation of the velocity of the bedforms is obtained with processing techniques pertaining to image-based velocimetry. The technique is therefore called Acoustic Mapping Velocimetry (AMV). The implementation of this technique produces a whole-field velocity map associated with the multi-directional bedform movement. Based on the calculated two-dimensional bedform migration velocity field, the bedload transport estimation is done using the Exner equation. A proof-of-concept experiment was performed to validate the AMV based bedload estimation in a laboratory flume at IIHR-Hydroscience & Engineering (IIHR). The bedform migration was analysed at three different flow discharges. Repeated bed geometry mapping, using a multiple transducer array (MTA), provided acoustic maps, which were post-processed with a particle image velocimetry (PIV) method. Bedload transport rates were calculated along longitudinal sections using the streamwise components of the bedform velocity vectors and the measured bedform heights. The bulk transport rates were compared with the results from concurrent direct physical samplings and acceptable agreement was found. As a first field implementation of the AMV an attempt was made to estimate bedload transport for a section of the Ohio river in the United States, where bed geometry maps, resulted by repeated multibeam echo sounder (MBES) surveys, served as input data. Cross-sectional distributions of bedload transport rates from the AMV based method were compared with the ones obtained from another non-intrusive technique (due to the lack of direct samplings), ISSDOTv2, developed by the US Army

Flow Mapping of a Jet in Crossflow with Stereoscopic PIV

DEFF Research Database (Denmark)

Meyer, Knud Erik; Özcan, Oktay; Westergaard, C. H.

2002-01-01

Stereoscopic Particle Image Velocimetry (PIV) has been used to make a three-dimensional flow mapping of a jet in crossflow. The Reynolds number based on the free stream velocity and the jet diameter was nominally 2400. A jet-to-crossflow velocity ratio of 3.3 was used. Details of the formation...

QUANTITATIVE FLOW-ANALYSIS AROUND AQUATIC ANIMALS USING LASER SHEET PARTICLE IMAGE VELOCIMETRY

NARCIS (Netherlands)

STAMHUIS, EJ; VIDELER, JJ

Two alternative particle image velocimetry (PIV) methods have been developed, applying laser light sheet illumination of particle-seeded flows around marine organisms, Successive video images, recorded perpendicular to a light sheet parallel to the main stream, were digitized and processed to map

Aeroacoustic analysis of an airfoil with Gurney flap based on time-resolved particle image velocimetry measurements

Science.gov (United States)

Zhang, Xueqing; Sciacchitano, Andrea; Pröbsting, Stefan

2018-05-01

Particle image velocimetry for the experimental assessment of trailing edge noise sources has become focus of research in recent years. The present study investigates the feasibility of the noise prediction for high-lift devices based on time-resolved particle image velocimetry (PIV). The model under investigation is a NACA 0015 airfoil with a Gurney flap with a height of 6% of the chord length. The velocity fields around and downstream of the Gurney flap were measured by PIV and used to compute the corresponding pressure fields by solving the Poisson equation for incompressible flows. The reconstructed pressure fluctuations on the airfoil surface constitute the source term for Curle's aeroacoustic analogy, which was employed in both the distributed and compact formulation to estimate the noise emission from PIV. The results of the two formulations are compared with the simultaneous far-field microphone measurements in the temporal and spectral domains. Both formulations of Curle's analogy yield acoustic sound pressure levels in good agreement with the simultaneous microphone measurements for the tonal component. The estimated far-field sound power spectra (SPL) from the PIV measurements reproduce the peak at the vortex shedding frequency, which also agrees well with the acoustic measurements.

3D velocity measurements in a premixed flame by tomographic PIV

International Nuclear Information System (INIS)

Tokarev, M P; Sharaborin, D K; Lobasov, A S; Chikishev, L M; Dulin, V M; Markovich, D M

2015-01-01

Tomographic particle image velocimetry (PIV) has become a standard tool for 3D velocity measurements in non-reacting flows. However, the majority of the measurements in flows with combustion are limited to small resolved depth compared to the size of the field of view (typically 1 : 10). The limitations are associated with inhomogeneity of the volume illumination and the non-uniform flow seeding, the optical distortions and errors in the 3D calibration, and the unwanted flame luminosity. In the present work, the above constraints were overcome for the tomographic PIV experiment in a laminar axisymmetric premixed flame. The measurements were conducted for a 1 : 1 depth-to-size ratio using a system of eight CCD cameras and a 200 mJ pulsed laser. The results show that camera calibration based on the triangulation of the tracer particles in the non-reacting conditions provided reliable accuracy for the 3D image reconstruction in the flame. The modification of the tomographic reconstruction allowed a posteriori removal of unwanted bright objects, which were located outside of the region of interest but affected the reconstruction quality. This study reports on a novel experience for the instantaneous 3D velocimetry in laboratory-scale flames by using tomographic PIV. (paper)

Correcting for particle size effects on plasma actuator particle image velocimetry measurements

Science.gov (United States)

Masati, A.; Sedwick, R. J.

2018-01-01

Particle image velocimetry (PIV) is often used to characterize plasma actuator flow, but particle charging effects are rarely taken into account. A parametric study was conducted to determine the effects of particle size on the velocity results of plasma actuator PIV experiments. Results showed that smaller particles more closely match air flow velocities than larger particles. The measurement uncertainty was quantified by deconvolving the particle image diameter from the correlation diameter. The true air velocity was calculated by linearly extrapolating to the zero-size particle diameter.

Load estimation from planar PIV measurement in vortex dominated flows

Science.gov (United States)

McClure, Jeffrey; Yarusevych, Serhiy

2017-11-01

Control volume-based loading estimates are employed on experimental and synthetic numerical planar Particle Image Velocimetry (PIV) data of a stationary cylinder and a cylinder undergoing one degree-of-freedom (1DOF) Vortex Induced Vibration (VIV). The results reveal the necessity of including out of plane terms, identified from a general formulation of the control volume momentum balance, when evaluating loads from planar measurements in three-dimensional flows. Reynolds stresses from out of plane fluctuations are shown to be significant for both instantaneous and mean force estimates when the control volume encompasses vortex dominated regions. For planar measurement, invoking a divergence-free assumption allows accurate estimation of half the identified terms. Towards evaluating the fidelity of PIV-based loading estimates for obtaining the forcing function unobtrusively in VIV experiments, the accuracy of the control volume-based loading methodology is evaluated using the numerical data with synthetically generated experimental PIV error, and a comparison is made between experimental PIV-based estimates and simultaneous force balance measurements.

Three-dimensional particle image velocimetry in a generic can-type gas turbine combustor

CSIR Research Space (South Africa)

Meyers, BC

2009-09-01

Full Text Available The three-dimensional flow field inside a generic can-type, forward flow, experimental combustor was measured. A stereoscopic Particle Image Velocimetry (PIV) system was used to obtain the flow field of the combustor in the non-reacting condition...

Development of a Large Field-of-View PIV System for Rotorcraft Testing in the 14- x 22-Foot Subsonic Tunnel

Science.gov (United States)

Jenkins, Luther N.; Yao, Chung-Sheng; Bartram, Scott M.; Harris, Jerome; Allan, Brian; Wong, Oliver; Mace, W. Derry

2009-01-01

A Large Field-of-View Particle Image Velocimetry (LFPIV) system has been developed for rotor wake diagnostics in the 14-by 22-Foot Subsonic Tunnel. The system has been used to measure three components of velocity in a plane as large as 1.524 meters by 0.914 meters in both forward flight and hover tests. Overall, the system performance has exceeded design expectations in terms of accuracy and efficiency. Measurements synchronized with the rotor position during forward flight and hover tests have shown that the system is able to capture the complex interaction of the body and rotor wakes as well as basic details of the blade tip vortex at several wake ages. Measurements obtained with traditional techniques such as multi-hole pressure probes, Laser Doppler Velocimetry (LDV), and 2D Particle Image Velocimetry (PIV) show good agreement with LFPIV measurements.

PIV for the characterization of focused field induced acoustic streaming: seeding particle choice evaluation.

Science.gov (United States)

Ben Haj Slama, Rafika; Gilles, Bruno; Ben Chiekh, Maher; Béra, Jean-Christophe

2017-04-01

This research evaluates the use of Particle Image Velocimetry (PIV) technique for characterizing acoustic streaming flow generated by High Intensity Focused Ultrasound (HIFU). PIV qualification tests, focusing on the seeding particle size (diameter of 5, 20 and 50μm) were carried out in degassed water subjected to a focused field of 550kHz-frequency with an acoustic pressure amplitude of 5.2, 10.5 and 15.7bar at the focus. This study shows that the ultrasonic field, especially the radiation force, can strongly affect seeding particle behavior. Large particles (50μm-diameter) are repelled from the focal zone and gathered at radiation pressure convergence lines on either side of the focus. The calculation of the acoustic radiation pressure applied on these particles explains the observed phenomenon. PIV measurements do not, therefore, properly characterize the streaming flow in this case. On the contrary, small particles (5μm-diameter) velocity measurements were in good agreement with the Computational Fluid Dynamics (CFD) simulations of the water velocity field. A simple criterion approximating the diameter threshold below which seeding particles are qualified for PIV in presence of focused ultrasound is then proposed. Copyright © 2017 Elsevier B.V. All rights reserved.

PIV and LIF study of slot continuous jet at low Reynolds number

Directory of Open Access Journals (Sweden)

Broučková Zuzana

2016-01-01

Full Text Available This study deals with a continuous jet issuing from a small narrow slot with a width of 0.36 mm. The experimental arrangement is based on the piezoelectric synthetic jet actuator studied previously for easy comparisons. The working fluid is water at room temperature. The experiments were performed using methods of particle image velocimetry (PIV and flow visualization (laser induced fluorescence, LIF. The time-mean volume flux through the exit nozzle was quantified using precise scales. The mean velocity and the Reynolds number were evaluated as Um = 0.12 m/s and Re = 90, respectively. The results of LIF and PIV techniques revealed the three-dimensional character of the flow field, namely the saddle-shape velocity profiles. This behavior is typical for steady jets from a rectangular nozzle. The obtained results were compared with previous measurements of the synthetic jet issuing from the same cavity and the slot nozzle.

Demonstration of Clean Particle Seeding for Particle Image Velocimetry in a Closed Circuit Supersonic Wind Tunnel

National Research Council Canada - National Science Library

McNiel, Charles M

2007-01-01

The purpose of this research was to determine whether solid carbon dioxide (CO2) particles might provide a satisfactory, and cleaner, alternative to traditional seed material for Particle Image Velocimetry (PIV...

Irrigant flow during photon-induced photoacoustic streaming (PIPS) using Particle Image Velocimetry (PIV).

Science.gov (United States)

Koch, Jon D; Jaramillo, David E; DiVito, Enrico; Peters, Ove A

2016-03-01

This study aimed to compare fluid movements generated from photon-induced photoacoustic streaming (PIPS) and passive ultrasonic irrigation (PUI). Particle Image Velocimetry (PIV) was performed using 6-μm melamine spheres in water. Measurement areas were 3-mm-long sections of the canal in the coronal, midroot and apical regions for PIPS (erbium/yttrium-aluminium garnet (Er:YAG) laser set at 15 Hz with 20 mJ), or passive ultrasonic irrigation (PUI, non-cutting insert at 30% unit power) was performed in simulated root canals prepared to an apical size #30/0.04 taper. Fluid movement was analysed directly subjacent to the apical ends of ultrasonic insert or fiber optic tips as well as at midroot and apically. During PUI, measured average velocities were around 0.03 m/s in the immediate vicinity of the sides and tip of the ultrasonic file. Speeds decayed to non-measureable values at a distance of about 2 mm from the sides and tip. During PIPS, typical average speeds were about ten times higher than those measured for PUI, and they were measured throughout the length of the canal, at distances up to 20 mm away. PIPS caused higher average fluid speeds when compared to PUI, both close and distant from the instrument. The findings of this study could be relevant to the debriding and disinfecting stage of endodontic therapy. Irrigation enhancement beyond needle irrigation is relevant to more effectively eradicate microorganisms from root canal systems. PIPS may be an alternative approach due to its ability to create high streaming velocities further away from the activation source compared to ultrasonic activation.

Pulse-burst PIV in a high-speed wind tunnel

International Nuclear Information System (INIS)

Beresh, Steven; Kearney, Sean; Wagner, Justin; Guildenbecher, Daniel; Henfling, John; Spillers, Russell; Pruett, Brian; Jiang, Naibo; Slipchenko, Mikhail; Mance, Jason; Roy, Sukesh

2015-01-01

Time-resolved particle image velocimetry (TR-PIV) has been achieved in a high-speed wind tunnel, providing velocity field movies of compressible turbulence events. The requirements of high-speed flows demand greater energy at faster pulse rates than possible with the TR-PIV systems developed for low-speed flows. This has been realized using a pulse-burst laser to obtain movies at up to 50 kHz, with higher speeds possible at the cost of spatial resolution. The constraints imposed by use of a pulse-burst laser are limited burst duration of 10.2 ms and a low duty cycle for data acquisition. Pulse-burst PIV has been demonstrated in a supersonic jet exhausting into a transonic crossflow and in transonic flow over a rectangular cavity. The velocity field sequences reveal the passage of turbulent structures and can be used to find velocity power spectra at every point in the field, providing spatial distributions of acoustic modes. The present work represents the first use of TR-PIV in a high-speed ground-test facility. (paper)

Temperature and velocity fields in natural convection by PIV and LIF

DEFF Research Database (Denmark)

Meyer, Knud Erik; Larsen, Poul Scheel; Westergaard, C. H.

2002-01-01

plate and cooled walls is 1.4×10^10. The flow is turbulent and is similar to some indoor room flows. Combined Particle Image Velocimetry (PIV) and Planar Light Induced Fluorescence (LIF) are used to measure local velocities and temperatures. Data measured in a symmetry plane parallel to a sidewall...

Automated and temperature-controlled micro-PIV measurements enabling long-term-stable microchannel acoustophoresis characterization.

Science.gov (United States)

Augustsson, Per; Barnkob, Rune; Wereley, Steven T; Bruus, Henrik; Laurell, Thomas

2011-12-21

We present a platform for micro particle image velocimetry (μPIV), capable of carrying out full-channel, temperature-controlled, long-term-stable, and automated μPIV-measurement of microchannel acoustophoresis with uncertainties below 5% and a spatial resolution in the order of 20 μm. A method to determine optimal μPIV-settings for obtaining high-quality results of the spatially inhomogeneous acoustophoretic velocity fields of large dynamical range is presented. In particular we study the dependence of the results on the μPIV interrogation window size and the number of repeated experiments. The μPIV-method was further verified by comparing it with our previously published particle tracking method. Using the μPIV platform we present a series of high-resolution measurements of the acoustophoretic velocity field as a function of the driving frequency, the driving voltage, and the resonator temperature. Finally, we establish a direct and consistent connection between the obtained acoustophoretic velocity fields, and continuous flow mode acoustophoresis, commonly used in applications.

Performing particle image velocimetry using artificial neural networks: a proof-of-concept

Science.gov (United States)

Rabault, Jean; Kolaas, Jostein; Jensen, Atle

2017-12-01

Traditional programs based on feature engineering are underperforming on a steadily increasing number of tasks compared with artificial neural networks (ANNs), in particular for image analysis. Image analysis is widely used in fluid mechanics when performing particle image velocimetry (PIV) and particle tracking velocimetry (PTV), and therefore it is natural to test the ability of ANNs to perform such tasks. We report for the first time the use of convolutional neural networks (CNNs) and fully connected neural networks (FCNNs) for performing end-to-end PIV. Realistic synthetic images are used for training the networks and several synthetic test cases are used to assess the quality of each network’s predictions and compare them with state-of-the-art PIV software. In addition, we present tests on real-world data that prove ANNs can be used not only with synthetic images but also with more noisy, imperfect images obtained in a real experimental setup. While the ANNs we present have slightly higher root mean square error than state-of-the-art cross-correlation methods, they perform better near edges and allow for higher spatial resolution than such methods. In addition, it is likely that one could with further work develop ANNs which perform better that the proof-of-concept we offer.

A tracer liquid image velocimetry for multi-layer radial flow in bioreactors.

Science.gov (United States)

Gao, Yu-Bao; Liang, Jiu-Xing; Luo, Yu-Xi; Yan, Jia

2015-02-13

This paper presents a Tracer Liquid Image Velocimetry (TLIV) for multi-layer radial flow in bioreactors used for cells cultivation of tissue engineering. The goal of this approach is to use simple devices to get good measuring precision, specialized for the case in which the uniform level of fluid shear stress was required while fluid velocity varied smoothly. Compared to the widely used Particles Image Velocimetry (PIV), this method adopted a bit of liquid as tracer, without the need of laser source. Sub-pixel positioning algorithm was used to overcome the adverse effects of the tracer liquid deformation. In addition, a neighborhood smoothing algorithm was used to restrict the measurement perturbation caused by diffusion. Experiments were carried out in a parallel plates flow chamber. And mathematical models of the flow chamber and Computational Fluid Dynamics (CFD) simulation were separately employed to validate the measurement precision of TLIV. The mean relative error between the simulated and measured data can be less than 2%, while in similar validations using PIV, the error was around 8.8%. TLIV avoided the contradiction between the particles' visibility and following performance with tested fluid, which is difficult to overcome in PIV. And TLIV is easier to popularize for its simple experimental condition and low cost.

PIV measurement of a contraction flow using micro-bubble tracer

International Nuclear Information System (INIS)

Ishikawa, Masaaki; Irabu, Kunio; Teruya, Isao; Nitta, Munehiro

2009-01-01

Recently, a technique using the micro-bubbles is focused. It was applied to many fields such as purification of rivers and lakes, washing the industrial parts, growth of plants and marine products. The characteristics of micro-bubbles are small size, wide surface area, low terminal velocity, and so on. If this micro-bubble is available as tracer of PIV (Particle Image Velocimetry), environment load would become lower because it doesn't need to discard particle. In this paper, we make a micro-bubble generator with Venturi type mechanism. The generated micro-bubbles are applied to a vertical channel flow with contraction. We validate about traceability of the micro-bubble tracer in comparison with the particle tracer.

Errors in mean and fluctuating velocity due to PIV bias and precision uncertainties

International Nuclear Information System (INIS)

Wilson, B.; Smith, B.L.

2011-01-01

Particle Image Velocimetry is a powerful fluid velocity measurement tool that has recently become important for CFD validation experiments. Knowledge of experimental uncertainty is important to CFD validation, but the uncertainty of PIV is very complex and not well understood. Previous work has shown that PIV measurements can become 'noisy' in regions of high shear as well as regions of small displacement. This paper aims to demonstrate the impact of these effects on validation data by comparing PIV data to data acquired using hot-wire anemometry, which does not suffer from the same issues. It is confirmed that shear and insufficient particle displacements can result in elevated measurements of turbulence levels. (author)

Collaborative framework for PIV uncertainty quantification: the experimental database

International Nuclear Information System (INIS)

Neal, Douglas R; Sciacchitano, Andrea; Scarano, Fulvio; Smith, Barton L

2015-01-01

The uncertainty quantification of particle image velocimetry (PIV) measurements has recently become a topic of great interest as shown by the recent appearance of several different methods within the past few years. These approaches have different working principles, merits and limitations, which have been speculated upon in subsequent studies. This paper reports a unique experiment that has been performed specifically to test the efficacy of PIV uncertainty methods. The case of a rectangular jet, as previously studied by Timmins et al (2012) and Wilson and Smith (2013b), is used. The novel aspect of the experiment is simultaneous velocity measurements using two different time-resolved PIV systems and a hot-wire anemometry (HWA) system. The first PIV system, called the PIV measurement system (‘PIV-MS’), is intended for nominal measurements of which the uncertainty is to be evaluated. It is based on a single camera and features a dynamic velocity range (DVR) representative of typical PIV experiments. The second PIV system, called the ‘PIV-HDR’ (high dynamic range) system, features a significantly higher DVR obtained with a higher digital imaging resolution. The hot-wire is placed in close proximity to the PIV measurement domain. The three measurement systems were carefully set to simultaneously measure the flow velocity at the same time and location. The comparison between the PIV-HDR system and the HWA provides an estimate of the measurement precision of the reference velocity for evaluation of the instantaneous error in the measurement system. The discrepancy between the PIV-MS and the reference data provides the measurement error, which is later used to assess the different uncertainty quantification methods proposed in the literature. A detailed comparison of the uncertainty estimation methods based on the present datasets is presented in a second paper from Sciacchitano et al (2015). Furthermore, this database offers the potential to be used for

Real-time particle image velocimetry based on FPGA technology

International Nuclear Information System (INIS)

Iriarte Munoz, Jose Miguel

2008-01-01

Particle image velocimetry (PIV), based on laser sheet, is a method for image processing and calculation of distributed velocity fields.It is well established as a fluid dynamics measurement tool, being applied to liquid, gases and multiphase flows.Images of particles are processed by means of computationally demanding algorithms, what makes its real-time implementation difficult.The most probable displacements are found applying two dimensional cross-correlation function. In this work, we detail how it is possible to achieve real-time visualization of PIV method by designing an adaptive embedded architecture based on FPGA technology.We show first results of a physical field of velocity calculated by this platform system in a real-time approach. [es

Software for Acquiring Image Data for PIV

Science.gov (United States)

Wernet, Mark P.; Cheung, H. M.; Kressler, Brian

2003-01-01

PIV Acquisition (PIVACQ) is a computer program for acquisition of data for particle-image velocimetry (PIV). In the PIV system for which PIVACQ was developed, small particles entrained in a flow are illuminated with a sheet of light from a pulsed laser. The illuminated region is monitored by a charge-coupled-device camera that operates in conjunction with a data-acquisition system that includes a frame grabber and a counter-timer board, both installed in a single computer. The camera operates in "frame-straddle" mode where a pair of images can be obtained closely spaced in time (on the order of microseconds). The frame grabber acquires image data from the camera and stores the data in the computer memory. The counter/timer board triggers the camera and synchronizes the pulsing of the laser with acquisition of data from the camera. PIVPROC coordinates all of these functions and provides a graphical user interface, through which the user can control the PIV data-acquisition system. PIVACQ enables the user to acquire a sequence of single-exposure images, display the images, process the images, and then save the images to the computer hard drive. PIVACQ works in conjunction with the PIVPROC program which processes the images of particles into the velocity field in the illuminated plane.

Investigation and visualization of internal flow through particle aggregates and microbial flocs using particle image velocimetry.

Science.gov (United States)

Xiao, Feng; Lam, Kit Ming; Li, Xiao-yan

2013-05-01

An advanced particle-tracking and flow-visualization technology, particle image velocimetry (PIV), was utilized to investigate the hydrodynamic properties of large aggregates in water. The laser-based PIV system was used together with a settling column to capture the streamlines around two types of aggregates: latex particle aggregates and activated sludge (AS) flocs. Both types of the aggregates were highly porous and fractal with fractal dimensions of 2.13±0.31 for the latex particle aggregates (1210-2144 μm) and 1.78±0.24 for the AS flocs (1265-3737 μm). The results show that PIV is a powerful flow visualization technique capable of determining flow field details at the micrometer scale around and through settling aggregates and flocs. The PIV streamlines provided direct experimental proof of internal flow through the aggregate interiors. According to the PIV images, fluid collection efficiency ranged from 0.052 to 0.174 for the latex particle aggregates and from 0.008 to 0.126 for AS flocs. AS flocs are apparently less permeable than the particle aggregates, probably due to the extracellular polymeric substances (EPSs) produced by bacteria clogging the pores within the flocs. The internal permeation of fractal aggregates and bio-flocs would enhance flocculation between particles and material transport into the aggregates. Copyright © 2013 Elsevier Inc. All rights reserved.

Height profile of particle concentration in an aeolian saltating cloud: A wind tunnel investigation by PIV MSD

Science.gov (United States)

Dong, Zhibao; Wang, Hongtao; Zhang, Xiaohang; Ayrault, Michael

2003-10-01

Attempt is made to define the particle concentration in an aeolian saltating cloud and its variation with height using artificial spherical quartz sand in a wind tunnel. The height profiles of the relative particle concentration in aeolian saltating cloud at three wind velocities were detected by the state of the art PIV (Particle Image Velocimetry) MSD (Mie Scattering Diffusion) technique, and converted to actual concentration based on sand transport rate and the variation with height of velocity of the saltating cloud. The particle concentration was found to decay exponentially with height and to increase with wind velocity. It decayed more rapidly when the wind velocity decreased. The volume/volume concentration in the near-surface layer was at the order of 10-4. The results obtained by PIV MSD technique were in good agreement with those derived from the sand flux and velocity profiles, the former being about 15% greater than the later.

Sub-piexl methods for improving vector quality in echo PIV flow, imaging technology.

Science.gov (United States)

Niu, Lili; Wang, Jing; Qian, Ming; Zheng, Hairong

2009-01-01

Developments of many cardiovascular problems have been shown to have a close relationship with arterial flow conditions. An ultrasound-based particle image velocimetry technique(Echo PIV) was recently developed to measure multi-component velocity vectors and local shear rates in arteries and opaque fluid flows by identifying and tracking flow tracers (ultrasound contrast microbubbles) within these flow fields. To improve the measurement accuracy, sub-pixel calculation method was adopted in this paper to maximize the ultrasound RF signal and B mode image correlation accuracy and increase the image spatial resolution. This algorithm is employed in processing both computer-generated particle image patterns and the B-mode images of microbubbles in rotating flows obtained by a high frame rate (up to 1000 frames per second) ultrasound imaging system. The results show the correlation of particle patterns and individual flow vector quality are improved and the overall flow mappings are also improved significantly. This would help the Echo PIV system to provide better multi-component velocity accuracy.

Confocal micro-PIV measurement of droplet formation in a T-shaped micro-junction

International Nuclear Information System (INIS)

Oishi, M; Kinoshita, H; Fujii, T; Oshima, M

2009-01-01

This paper aims to investigate a mechanism of microdroplet formation using 'multicolor confocal micro particle image velocimetry (PIV)' technique. The present system can measure dynamical behavior of multiphase flow separately and simultaneously. It also enables to identify the interactions between two immiscible fluids. We have applied this system to measure the water droplet formation at a micro T-shaped junction. We have also succeeded in dispersing fluorescent tracer particles into both phases. The interaction between the internal flow of to-be-dispersed water phase and of continuous oil phase is measured as a liquid-liquid multiphase flow. As a result of PIV measurement and interface scanning, the relationship between flow structure of each phase and interface shape is clarified. It indicates that the gap between the tip of to-be-dispersed phase and capillary wall, and interface area play an important role in the flow structure and shear stress on the interface.

Development and assessment of transparent soil and particle image velocimetry in dynamic soil-structure interaction

Science.gov (United States)

2007-02-01

This research combines Particle Image Velocimetry (PIV) and transparent soil to investigate the dynamic rigid block and soil interaction. In order to get a low viscosity pore fluid for the transparent soil, 12 different types of chemical solvents wer...

Visualization by PIV of dynamic stall on a vertical axis wind turbine

NARCIS (Netherlands)

Ferreira, C.J.S.; Kuik, van G.A.M.; Bussel, van G.J.W.; Scarano, F.

2009-01-01

The aerodynamic behavior of a vertical axis wind turbine (VAWT) is analyzed by means of 2D particle image velocimetry (PIV), focusing on the development of dynamic stall at different tip speed ratios. The VAWT has an unsteady aerodynamic behavior due to the variation with the azimuth angle ¿ of the

Design considerations for large field particle image velocimetery (LF-PIV)

International Nuclear Information System (INIS)

Pol, S U; Balakumar, B J

2013-01-01

We discuss the challenges and limitations associated with the development of a large field of view particle image velocimetry (LF-PIV) diagnostic, capable of resolving large-scale motions (>1 m per camera) in gas phase laboratory and field experiments. While this diagnostic is developed for the measurement of wakes and local inflow conditions around research wind turbines, the design considerations provided here are also relevant for the application of LF-PIV to atmospheric boundary layer, rotorcraft dynamics and large-scale wind tunnel flows. Measurements over an area of 0.75 m × 1.0 m on a confined vortex were obtained using a standard 2MP camera, with the potential for increasing this area significantly using 11MP cameras. The cameras in this case were oriented orthogonal to the measurement plane receiving only the side-scattered component of light from the particles. Scaling laws associated with LF-PIV systems are also presented along with the performance analysis of low-density, large diameter Expancel particles, that appear to be promising candidates for LF-PIV seeding. (paper)

PIV Uncertainty Methodologies for CFD Code Validation at the MIR Facility

Energy Technology Data Exchange (ETDEWEB)

Sabharwall, Piyush [Idaho National Lab. (INL), Idaho Falls, ID (United States); Skifton, Richard [Idaho National Lab. (INL), Idaho Falls, ID (United States); Stoots, Carl [Idaho National Lab. (INL), Idaho Falls, ID (United States); Kim, Eung Soo [Idaho National Lab. (INL), Idaho Falls, ID (United States); Conder, Thomas [Idaho National Lab. (INL), Idaho Falls, ID (United States)

2013-12-01

Currently, computational fluid dynamics (CFD) is widely used in the nuclear thermal hydraulics field for design and safety analyses. To validate CFD codes, high quality multi dimensional flow field data are essential. The Matched Index of Refraction (MIR) Flow Facility at Idaho National Laboratory has a unique capability to contribute to the development of validated CFD codes through the use of Particle Image Velocimetry (PIV). The significance of the MIR facility is that it permits non intrusive velocity measurement techniques, such as PIV, through complex models without requiring probes and other instrumentation that disturb the flow. At the heart of any PIV calculation is the cross-correlation, which is used to estimate the displacement of particles in some small part of the image over the time span between two images. This image displacement is indicated by the location of the largest peak. In the MIR facility, uncertainty quantification is a challenging task due to the use of optical measurement techniques. Currently, this study is developing a reliable method to analyze uncertainty and sensitivity of the measured data and develop a computer code to automatically analyze the uncertainty/sensitivity of the measured data. The main objective of this study is to develop a well established uncertainty quantification method for the MIR Flow Facility, which consists of many complicated uncertainty factors. In this study, the uncertainty sources are resolved in depth by categorizing them into uncertainties from the MIR flow loop and PIV system (including particle motion, image distortion, and data processing). Then, each uncertainty source is mathematically modeled or adequately defined. Finally, this study will provide a method and procedure to quantify the experimental uncertainty in the MIR Flow Facility with sample test results.

Experimental PIV and CFD studies of UV-peroxide advanced oxidation reactors for water treatment

International Nuclear Information System (INIS)

Sozzi, A.; Taghipour, F.

2004-01-01

An experimental and numerical study of the flow characteristics in an annular UV reactor, as used for drinking water disinfection or Advanced Oxidation Processes, was carried out using Particle Image Velocimetry (PIV) and Computational Fluid Dynamics (CFD). The influence of different turbulence models and mesh structures on the CFD results was investigated. By qualitative and quantitative comparison of CFD and PIV experimental data, it was shown that the Realizable k-e- turbulence model is best suited for simulating the hydrodynamics of this geometry. (author)

A comparative experimental evaluation of uncertainty estimation methods for two-component PIV

Science.gov (United States)

Boomsma, Aaron; Bhattacharya, Sayantan; Troolin, Dan; Pothos, Stamatios; Vlachos, Pavlos

2016-09-01

Uncertainty quantification in planar particle image velocimetry (PIV) measurement is critical for proper assessment of the quality and significance of reported results. New uncertainty estimation methods have been recently introduced generating interest about their applicability and utility. The present study compares and contrasts current methods, across two separate experiments and three software packages in order to provide a diversified assessment of the methods. We evaluated the performance of four uncertainty estimation methods, primary peak ratio (PPR), mutual information (MI), image matching (IM) and correlation statistics (CS). The PPR method was implemented and tested in two processing codes, using in-house open source PIV processing software (PRANA, Purdue University) and Insight4G (TSI, Inc.). The MI method was evaluated in PRANA, as was the IM method. The CS method was evaluated using DaVis (LaVision, GmbH). Utilizing two PIV systems for high and low-resolution measurements and a laser doppler velocimetry (LDV) system, data were acquired in a total of three cases: a jet flow and a cylinder in cross flow at two Reynolds numbers. LDV measurements were used to establish a point validation against which the high-resolution PIV measurements were validated. Subsequently, the high-resolution PIV measurements were used as a reference against which the low-resolution PIV data were assessed for error and uncertainty. We compared error and uncertainty distributions, spatially varying RMS error and RMS uncertainty, and standard uncertainty coverages. We observed that qualitatively, each method responded to spatially varying error (i.e. higher error regions resulted in higher uncertainty predictions in that region). However, the PPR and MI methods demonstrated reduced uncertainty dynamic range response. In contrast, the IM and CS methods showed better response, but under-predicted the uncertainty ranges. The standard coverages (68% confidence interval) ranged from

A comparative experimental evaluation of uncertainty estimation methods for two-component PIV

International Nuclear Information System (INIS)

Boomsma, Aaron; Troolin, Dan; Pothos, Stamatios; Bhattacharya, Sayantan; Vlachos, Pavlos

2016-01-01

Uncertainty quantification in planar particle image velocimetry (PIV) measurement is critical for proper assessment of the quality and significance of reported results. New uncertainty estimation methods have been recently introduced generating interest about their applicability and utility. The present study compares and contrasts current methods, across two separate experiments and three software packages in order to provide a diversified assessment of the methods. We evaluated the performance of four uncertainty estimation methods, primary peak ratio (PPR), mutual information (MI), image matching (IM) and correlation statistics (CS). The PPR method was implemented and tested in two processing codes, using in-house open source PIV processing software (PRANA, Purdue University) and Insight4G (TSI, Inc.). The MI method was evaluated in PRANA, as was the IM method. The CS method was evaluated using DaVis (LaVision, GmbH). Utilizing two PIV systems for high and low-resolution measurements and a laser doppler velocimetry (LDV) system, data were acquired in a total of three cases: a jet flow and a cylinder in cross flow at two Reynolds numbers. LDV measurements were used to establish a point validation against which the high-resolution PIV measurements were validated. Subsequently, the high-resolution PIV measurements were used as a reference against which the low-resolution PIV data were assessed for error and uncertainty. We compared error and uncertainty distributions, spatially varying RMS error and RMS uncertainty, and standard uncertainty coverages. We observed that qualitatively, each method responded to spatially varying error (i.e. higher error regions resulted in higher uncertainty predictions in that region). However, the PPR and MI methods demonstrated reduced uncertainty dynamic range response. In contrast, the IM and CS methods showed better response, but under-predicted the uncertainty ranges. The standard coverages (68% confidence interval) ranged from

Application of particle image velocimetry measurement techniques to study turbulence characteristics of oscillatory flows around parallel-plate structures in thermoacoustic devices

International Nuclear Information System (INIS)

Mao, Xiaoan; Jaworski, Artur J

2010-01-01

This paper describes the development of the experimental setup and measurement methodologies to study the physics of oscillatory flows in the vicinity of parallel-plate stacks by using the particle image velocimetry (PIV) techniques. Parallel-plate configurations often appear as internal structures in thermoacoustic devices and are responsible for the hydrodynamic energy transfer processes. The flow around selected stack configurations is induced by a standing acoustic wave, whose amplitude can be varied. Depending on the direction of the flow within the acoustic cycle, relative to the stack, it can be treated as an entrance flow or a wake flow. The insight into the flow behaviour, its kinematics, dynamics and scales of turbulence, is obtained using the classical Reynolds decomposition to separate the instantaneous velocity fields into ensemble-averaged mean velocity fields and fluctuations in a set of predetermined phases within an oscillation cycle. The mean velocity field and the fluctuation intensity distributions are investigated over the acoustic oscillation cycle. The velocity fluctuation is further divided into large- and small-scale fluctuations by using fast Fourier transform (FFT) spatial filtering techniques

On the applicability of numerical image mapping for PIV image analysis near curved interfaces

International Nuclear Information System (INIS)

Masullo, Alessandro; Theunissen, Raf

2017-01-01

This paper scrutinises the general suitability of image mapping for particle image velocimetry (PIV) applications. Image mapping can improve PIV measurement accuracy by eliminating overlap between the PIV interrogation windows and an interface, as illustrated by some examples in the literature. Image mapping transforms the PIV images using a curvilinear interface-fitted mesh prior to performing the PIV cross correlation. However, degrading effects due to particle image deformation and the Jacobian transformation inherent in the mapping along curvilinear grid lines have never been deeply investigated. Here, the implementation of image mapping from mesh generation to image resampling is presented in detail, and related error sources are analysed. Systematic comparison with standard PIV approaches shows that image mapping is effective only in a very limited set of flow conditions and geometries, and depends strongly on a priori knowledge of the boundary shape and streamlines. In particular, with strongly curved geometries or streamlines that are not parallel to the interface, the image-mapping approach is easily outperformed by more traditional image analysis methodologies invoking suitable spatial relocation of the obtained displacement vector. (paper)

Development of Hydroxyl Tagging Velocimetry for Low Velocity Flows

Science.gov (United States)

Andre, Matthieu A.; Bardet, Philippe M.; Burns, Ross A.; Danehy, Paul M.

2016-01-01

Hydroxyl tagging velocimetry (HTV) is a molecular tagging technique that relies on the photo-dissociation of water vapor into OH radicals and their subsequent tracking using laser induced fluorescence. Velocities are then obtained from time-of-flight calculations. At ambient temperature in air, the OH species lifetime is relatively short (<50 µs), making it suited for high speed flows. Lifetime and radicals formation increases with temperature, which allows HTV to also probe low-velocity, high-temperature flows or reacting flows such as flames. The present work aims at extending the domain of applicability of HTV, particularly towards low-speed (<10 m/s) and moderate (<500 K) temperature flows. Results are compared to particle image velocimetry (PIV) measurements recorded in identical conditions. Single shot and averaged velocity profiles are obtained in an air jet at room temperature. By modestly raising the temperature (100-200 degC) the OH production increases, resulting in an improvement of the signal-to-noise ratio (SNR). Use of nitrogen - a non-reactive gas with minimal collisional quenching - extends the OH species lifetime (to over 500 µs), which allows probing of slower flows or, alternately, increases the measurement precision at the expense of spatial resolution. Instantaneous velocity profiles are resolved in a 100degC nitrogen jet (maximum jet-center velocity of 6.5 m/s) with an uncertainty down to 0.10 m/s (1.5%) at 68% confidence level. MTV measurements are compared with particle image velocimetry and show agreement within 2%.

Wall shear stress measurement of near-wall flow over inclined and curved boundaries by stereo interfacial particle image velocimetry

International Nuclear Information System (INIS)

Nguyen, Thien Duy; Wells, John Craig; Nguyen, Chuong Vinh

2010-01-01

In investigations of laminar or turbulent flows, wall shear is often important. Nevertheless, conventional particle image velocimetry (PIV) is difficult in near-wall regions. A near-wall measurement technique, named interfacial PIV (IPIV) [Nguyen, C., Nguyen, T., Wells, J., Nakayama, A., 2008. Proposals for PIV of near-wall flow over curved boundaries. In: Proceedings of 14th International Symposium on Applications of Laser Technique to Fluid Mechanics], handles curved boundaries by means of conformal transformation, directly measures the wall gradient, and yields the near-wall tangential velocity profile at one-pixel resolution. In this paper, we show the feasibility of extending IPIV to measure wall gradients by stereo reconstruction. First, we perform a test on synthetic images generated from a direct numerical simulation (DNS) snapshot of turbulent flow over sinusoidal bed. Comparative assessment of wall gradients derived by IPIV, stereo-IPIV and particle image distortion (PID) [Huang, H.T., Fiedler, H.E., Wang, J.J., 1993. Limitation and improvement of PIV. Experiments in Fluids 15(4), 263-273] is evaluated with DNS data. Also, the sensitivity of IPIV and stereo-IPIV results to the uncertainty of identified wall position is examined. As a practical application of IPIV and stereo-IPIV to experimental images, results from turbulent open channel flow over a backward-facing step are discussed in detail.

Liquid Crystals, PIV and IR-Photography in Selected Technical and Biomedical Applications

Science.gov (United States)

Stasiek, Jan; Jewartowski, Marcin

2017-10-01

Thermochromic liquid crystals (TLC), Particle Image Velocimetry (PIV), Infrared Imaging Themography (IR) and True-Colour Digital Image Processing (TDIP) have been successfully used in non-intrusive technical, industrial and biomedical studies and applications. These four tools (based on the desktop computers) have come together during the past two decades to produce a powerful advanced experimental technique as a judgment of quality of information that cannot be obtained from any other imaging procedure. The brief summary of the history of this technique is reviewed, principal methods and tools are described and some examples are presented. With this objective, a new experimental technique have been developed and applied to the study of heat and mass transfer and for biomedical diagnosis. Automated evaluation allows determining the heat and flow visualisation and locate the area of suspicious tissue of human body.

Characterization of an evaporating direct-injected gasoline spray using laser-induced exciplex fluorescence and particle image velocimetry techniques

Energy Technology Data Exchange (ETDEWEB)

Dong-Seok Choi; Choongsik Bae [Korea Advanced Institute of Science and Technology, Taejon (Korea). Dept. of Mechanical Engineering; Duck-Jool Kim [Pusan National University (Korea). School of Mechanical Engineering

2004-07-01

The purpose of this study is to characterize an evaporating direct-injected (DI) gasoline spray from a high-pressure swirl injector using the laser-induced exciplex fluorescence (LIEF) technique and particle image velocimetry (PIV). A fluorobenzene/diethylmethylamine (DEMA) system was used as the exciplex-forming dopants. The behaviour of the liquid and vapour phases was analysed by image processing. For the analysis of vorticity inside the spray, droplet velocity data obtained by PIV were used. The experiments were performed at two ambient temperatures (293 and 473 K) and three different ambient pressures (0.1, 0.5 and 1.0 MPa). It was found that ambient temperature had a significant effect on the axial and radial growth of the liquid phase of the evaporating spray at atmospheric pressure while it had little effect under elevated pressures. Radial growth of the vapour phase of the evaporating spray was more dominant than axial growth under high temperature and pressure conditions. As the ambient pressure was elevated, the liquid phase of the spray transformed from a hollow cone to a solid cone of bell shape, while the vapour phase varied from a widespread distribution to a compact shape with a locally richer mixture. The evaporating spray could be divided into two spray regions from the analysis of vorticity and the distributions of liquid and vapour phases. The cone region (penetrations of 0.3-0.5) was mainly liquid phase and disappeared rapidly at the end of injection. The mixing region contained the active interaction between entrained air and fuel vapour. (author)

Measurement of flow velocity fields in small vessel-mimic phantoms and vessels of small animals using micro ultrasonic particle image velocimetry (micro-EPIV).

Science.gov (United States)

Qian, Ming; Niu, Lili; Wang, Yanping; Jiang, Bo; Jin, Qiaofeng; Jiang, Chunxiang; Zheng, Hairong

2010-10-21

Determining a multidimensional velocity field within microscale opaque fluid flows is needed in areas such as microfluidic devices, biofluid mechanics and hemodynamics research in animal studies. The ultrasonic particle image velocimetry (EchoPIV) technique is appropriate for measuring opaque flows by taking advantage of PIV and B-mode ultrasound contrast imaging. However, the use of clinical ultrasound systems for imaging flows in small structures or animals has limitations associated with spatial resolution. This paper reports on the development of a high-resolution EchoPIV technique (termed as micro-EPIV) and its application in measuring flows in small vessel-mimic phantoms and vessels of small animals. Phantom experiments demonstrate the validity of the technique, providing velocity estimates within 4.1% of the analytically derived values with regard to the flows in a small straight vessel-mimic phantom, and velocity estimates within 5.9% of the computationally simulated values with regard to the flows in a small stenotic vessel-mimic phantom. Animal studies concerning arterial and venous flows of living rats and rabbits show that the micro-EPIV-measured peak velocities within several cardiac cycles are about 25% below the values measured by the ultrasonic spectral Doppler technique. The micro-EPIV technique is able to effectively measure the flow fields within microscale opaque fluid flows.

Measurement of flow velocity fields in small vessel-mimic phantoms and vessels of small animals using micro ultrasonic particle image velocimetry (micro-EPIV)

International Nuclear Information System (INIS)

Qian Ming; Niu Lili; Jiang Bo; Jin Qiaofeng; Jiang Chunxiang; Zheng Hairong; Wang Yanping

2010-01-01

Determining a multidimensional velocity field within microscale opaque fluid flows is needed in areas such as microfluidic devices, biofluid mechanics and hemodynamics research in animal studies. The ultrasonic particle image velocimetry (EchoPIV) technique is appropriate for measuring opaque flows by taking advantage of PIV and B-mode ultrasound contrast imaging. However, the use of clinical ultrasound systems for imaging flows in small structures or animals has limitations associated with spatial resolution. This paper reports on the development of a high-resolution EchoPIV technique (termed as micro-EPIV) and its application in measuring flows in small vessel-mimic phantoms and vessels of small animals. Phantom experiments demonstrate the validity of the technique, providing velocity estimates within 4.1% of the analytically derived values with regard to the flows in a small straight vessel-mimic phantom, and velocity estimates within 5.9% of the computationally simulated values with regard to the flows in a small stenotic vessel-mimic phantom. Animal studies concerning arterial and venous flows of living rats and rabbits show that the micro-EPIV-measured peak velocities within several cardiac cycles are about 25% below the values measured by the ultrasonic spectral Doppler technique. The micro-EPIV technique is able to effectively measure the flow fields within microscale opaque fluid flows.

Time Resolved Scanning PIV measurements at fine scales in a turbulent jet

International Nuclear Information System (INIS)

Cheng, Y.; Torregrosa, M.M.; Villegas, A.; Diez, F.J.

2011-01-01

The temporal and spatial complexity of turbulent flows at intermediate and small scales has prevented the acquisition of full three-dimensional experimental data sets for validating classical turbulent theory and Direct Numerical Simulations (DNS). Experimental techniques like Particle Velocimetry, PIV, allow non-intrusive planar measurements of turbulent flows. The present work applied a Time Resolved Scanning PIV system, TRS-PIV, capable of obtaining three-dimensional two-component velocities to measure the small scales of a turbulent jet. When probing the small scales of these flows with PIV, the uncertainty of the measured turbulent properties are determined by the characteristics of the PIV system and specially the thickness of the laser sheet. A measurement of the particle distribution across the thickness of the laser sheet is proposed as a more detailed description of the PIV sheet thickness. The high temporal and spatial resolution of the TRS-PIV system allowed obtaining quasi-instantaneous volumetric vector fields at the far field of a round turbulent jet in water, albeit for a low Reynolds number of 1478 due to the speed limitations of the present camera and scanning system. Six of the nine components of the velocity gradient tensor were calculated from the velocity measurements. This allowed the visualization with near Kolmogorov-scale resolution of the velocity gradient structures in three-dimensional space. In general, these structures had a complex geometry corresponding to elongated shapes in the form of sheets and tubes. An analysis of the probability density function, pdf, of the velocity gradients calculated showed that the on-diagonal (off-diagonal) velocity gradient components were very similar to each other even for events at the tails of the pdfs, as required for homogeneous isotropy. The root mean square of the components of the velocity gradients is also calculated and their ratio of off-diagonal components to on-diagonal components

Fluid Flow Characterization of High Turbulent Intensity Compressible Flow Using Particle Image Velocimetry

Science.gov (United States)

2015-08-01

completed in order to begin further experimentation. A 10 kHz Time Resolved Particle Image Velocimetry (TR-PIV) system and a 3 kHz Planer Laser ...9 2.3.2 Planar Laser Induced Fluorescence (PLIF...35 Figure 4.4: Solenoid valve (a), proportional control valve (b) and flowmeter (c) ...................................... 36 Figure 4.5

Evaluación del PIV como método de medida en Geotecnia

OpenAIRE

Ruiz Morales, Alvaro Eduardo

2014-01-01

El PIV(Particle Image Velocimetry), metodología desarrollada en el campo de la mecánica de fluidos y usada por varios investigadores en la Geotecnia, es una metodología que promete ser una herramienta muy útil en los trabajos de investigación desarrollados en el departamento de Ingeniería del Terreno, Cartográfica y Geofísica de la Universidad Politécnica de Cataluña. Esta investigación tuvo como principal objetivo lograr implementar una metodología para el uso del PIV como instrumento de med...

A study on the application of two different acoustic analogies to experimental PIV data

NARCIS (Netherlands)

Koschatzky, V.; Westerweel, J.; Boersma, B.J.

2011-01-01

The aim of the present study is to compare two different acoustic analogies applied to time-resolved particle image velocimetry (PIV) data for the prediction of the acoustic far-field generated by the flow over a rectangular cavity. We consider the model problem of sound radiating from an open,

A study of plunging breaker mechanics by PIV measurements and a Navier-Stokes solver

DEFF Research Database (Denmark)

Emarat, Narumon; Forehand, David I. M.; Christensen, Erik Damgaard

2000-01-01

The mechanics of a surf-zone plunging breaker are studied from Particle Image Velocimetry (PIV) measurements and a numerical model based on the Navier-Stokes equations, using a Volume of Fluid (VOF) method. An additional numerical model using a Boundary-Integral Method (BIM) is also used in order...

An overview of CFD and PIV application in investigation of solar thermal systems

DEFF Research Database (Denmark)

Ai, Ning; Fan, Jianhua; Ji, Jianbing

2007-01-01

. The most promising solution to this challenge is the use of computational fluid dynamics (CFD) in combination with particle image velocimetry (PIV)，which will be the future trend in the investigation of solar thermal systems. The aim of this work is to give an overview of the status of the CFD...

PIV Analysis of Ludwig Prandtl's Historic Flow Visualization Films

OpenAIRE

Willert, Christian; Kompenhans, Jürgen

2010-01-01

Around 1930 Ludwig Prandtl and his colleagues O. Tietjens and W. M\\"uller published two films with visualizations of flows around surface piercing obstacles to illustrate the unsteady process of flow separation. These visualizations were achieved by recording the motion of fine particles sprinkled onto the water surface in water channels. The resulting images meet the relevant criteria of properly seeded recordings for particle image velocimetry (PIV). Processing these image sequences with mo...

Uncertainty on PIV mean and fluctuating velocity due to bias and random errors

International Nuclear Information System (INIS)

Wilson, Brandon M; Smith, Barton L

2013-01-01

Particle image velocimetry is a powerful and flexible fluid velocity measurement tool. In spite of its widespread use, the uncertainty of PIV measurements has not been sufficiently addressed to date. The calculation and propagation of local, instantaneous uncertainties on PIV results into the measured mean and Reynolds stresses are demonstrated for four PIV error sources that impact uncertainty through the vector computation: particle image density, diameter, displacement and velocity gradients. For the purpose of this demonstration, velocity data are acquired in a rectangular jet. Hot-wire measurements are compared to PIV measurements with velocity fields computed using two PIV algorithms. Local uncertainty on the velocity mean and Reynolds stress for these algorithms are automatically estimated using a previously published method. Previous work has shown that PIV measurements can become ‘noisy’ in regions of high shear as well as regions of small displacement. This paper also demonstrates the impact of these effects by comparing PIV data to data acquired using hot-wire anemometry, which does not suffer from the same issues. It is confirmed that flow gradients, large particle images and insufficient particle image displacements can result in elevated measurements of turbulence levels. The uncertainty surface method accurately estimates the difference between hot-wire and PIV measurements for most cases. The uncertainty based on each algorithm is found to be unique, motivating the use of algorithm-specific uncertainty estimates. (paper)

Microparticle image velocimetry approach to flow measurements in isolated contracting lymphatic vessels.

Science.gov (United States)

Margaris, Konstantinos N; Nepiyushchikh, Zhanna; Zawieja, David C; Moore, James; Black, Richard A

2016-02-01

We describe the development of an optical flow visualization method for resolving the flow velocity vector field in lymphatic vessels in vitro. The aim is to develop an experimental protocol for accurately estimating flow parameters, such as flow rate and shear stresses, with high spatial and temporal resolution. Previous studies in situ have relied on lymphocytes as tracers, but their low density resulted in a reduced spatial resolution whereas the assumption that the flow was fully developed in order to determine the flow parameters of interest may not be valid, especially in the vicinity of the valves, where the flow is undoubtedly more complex. To overcome these issues, we have applied the time-resolved microparticle image velocimetry (μ -PIV) technique, a well-established method that can provide increased spatial and temporal resolution that this transient flow demands. To that end, we have developed a custom light source, utilizing high-power light-emitting diodes, and associated control and image processing software. This paper reports the performance of the system and the results of a series of preliminary experiments performed on vessels isolated from rat mesenteries, demonstrating, for the first time, the successful application of the μ -PIV technique in these vessels.

Comparative assessment of pressure field reconstructions from particle image velocimetry measurements and Lagrangian particle tracking

NARCIS (Netherlands)

van Gent, P.L.; Michaelis, D; van Oudheusden, B.W.; Weiss, P.E.; de Kat, R.; Laskari, A.; Jeon, Y.J.; David, L; Schanz, D; Huhn, F.; Gesemann, S; Novara, M.; McPhaden, C.; Neeteson, N. J.; Rival, David E.; Schneiders, J.F.G.; Schrijer, F.F.J.

2017-01-01

A test case for pressure field reconstruction from particle image velocimetry (PIV) and Lagrangian particle tracking (LPT) has been developed by constructing a simulated experiment from a zonal detached eddy simulation for an axisymmetric base flow at Mach 0.7. The test case comprises sequences

Optical fibre laser velocimetry: a review

International Nuclear Information System (INIS)

Charrett, Thomas O H; James, Stephen W; Tatam, Ralph P

2012-01-01

The applications of optical fibre technology to laser velocimetry are diverse and often critical to their successful implementation, particularly in harsh environments. Applications range from the use of optical fibres for beam delivery and scattered light collection, aiding the miniaturization of instrument probes, to the use of imaging fibre bundles for imaging the flow field in planar velocimetry systems. Optical fibre techniques have also been used in signal processing, for example fibre frequency shifters, and optical fibre devices such as amplifiers and lasers have been exploited. This paper will review the use of optical fibres in point-wise laser velocimetry techniques such as laser Doppler velocimetry and laser transit anemometry, as well as in planar measurement techniques such as particle imaging velocimetry and planar Doppler velocimetry. (topical review)

Echo Particle Image Velocimetry for Estimation of Carotid Artery Wall Shear Stress: Repeatability, Reproducibility and Comparison with Phase-Contrast Magnetic Resonance Imaging.

Science.gov (United States)

Gurung, Arati; Gates, Phillip E; Mazzaro, Luciano; Fulford, Jonathan; Zhang, Fuxing; Barker, Alex J; Hertzberg, Jean; Aizawa, Kunihiko; Strain, William D; Elyas, Salim; Shore, Angela C; Shandas, Robin

2017-08-01

Measurement of hemodynamic wall shear stress (WSS) is important in investigating the role of WSS in the initiation and progression of atherosclerosis. Echo particle image velocimetry (echo PIV) is a novel ultrasound-based technique for measuring WSS in vivo that has previously been validated in vitro using the standard optical PIV technique. We evaluated the repeatability and reproducibility of echo PIV for measuring WSS in the human common carotid artery. We measured WSS in 28 healthy participants (18 males and 10 females, mean age: 56 ± 12 y). Echo PIV was highly repeatable, with an intra-observer variability of 1.0 ± 0.1 dyn/cm 2 for peak systolic (maximum), 0.9 dyn/cm 2 for mean and 0.5 dyn/cm 2 for end-diastolic (minimum) WSS measurements. Likewise, echo PIV was reproducible, with a low inter-observer variability (max: 2.0 ± 0.2 dyn/cm 2 , mean: 1.3 ± 0.1 dyn/cm 2 , end-diastolic: 0.7 dyn/cm 2 ) and more variable inter-scan (test-retest) variability (max: 7.1 ± 2.3 dyn/cm 2 , mean: 2.9 ± 0.4 dyn/cm 2 , min: 1.5 ± 0.1 dyn/cm 2 ). We compared echo PIV with the reference method, phase-contrast magnetic resonance imaging (PC-MRI); echo PIV-based WSS measurements agreed qualitatively with PC-MRI measurements (r = 0.89, p PIV vs. PC-MRI): WSS at peak systole: 21 ± 7.0 dyn/cm 2 vs. 15 ± 5.0 dyn/cm 2 ; time-averaged WSS: 8.9 ± 3.0 dyn/cm 2 vs. 7.1 ± 3.0 dyn/cm 2 (p  0.05). For the first time, we report that echo PIV can measure WSS with good repeatability and reproducibility in adult humans with a broad age range. Echo PIV is feasible in humans and offers an easy-to-use, ultrasound-based, quantitative technique for measuring WSS in vivo in humans with good repeatability and reproducibility. Copyright © 2017. Published by Elsevier Inc.

CCD image sensor induced error in PIV applications

Science.gov (United States)

Legrand, M.; Nogueira, J.; Vargas, A. A.; Ventas, R.; Rodríguez-Hidalgo, M. C.

2014-06-01

The readout procedure of charge-coupled device (CCD) cameras is known to generate some image degradation in different scientific imaging fields, especially in astrophysics. In the particular field of particle image velocimetry (PIV), widely extended in the scientific community, the readout procedure of the interline CCD sensor induces a bias in the registered position of particle images. This work proposes simple procedures to predict the magnitude of the associated measurement error. Generally, there are differences in the position bias for the different images of a certain particle at each PIV frame. This leads to a substantial bias error in the PIV velocity measurement (˜0.1 pixels). This is the order of magnitude that other typical PIV errors such as peak-locking may reach. Based on modern CCD technology and architecture, this work offers a description of the readout phenomenon and proposes a modeling for the CCD readout bias error magnitude. This bias, in turn, generates a velocity measurement bias error when there is an illumination difference between two successive PIV exposures. The model predictions match the experiments performed with two 12-bit-depth interline CCD cameras (MegaPlus ES 4.0/E incorporating the Kodak KAI-4000M CCD sensor with 4 megapixels). For different cameras, only two constant values are needed to fit the proposed calibration model and predict the error from the readout procedure. Tests by different researchers using different cameras would allow verification of the model, that can be used to optimize acquisition setups. Simple procedures to obtain these two calibration values are also described.

CCD image sensor induced error in PIV applications

International Nuclear Information System (INIS)

Legrand, M; Nogueira, J; Vargas, A A; Ventas, R; Rodríguez-Hidalgo, M C

2014-01-01

The readout procedure of charge-coupled device (CCD) cameras is known to generate some image degradation in different scientific imaging fields, especially in astrophysics. In the particular field of particle image velocimetry (PIV), widely extended in the scientific community, the readout procedure of the interline CCD sensor induces a bias in the registered position of particle images. This work proposes simple procedures to predict the magnitude of the associated measurement error. Generally, there are differences in the position bias for the different images of a certain particle at each PIV frame. This leads to a substantial bias error in the PIV velocity measurement (∼0.1 pixels). This is the order of magnitude that other typical PIV errors such as peak-locking may reach. Based on modern CCD technology and architecture, this work offers a description of the readout phenomenon and proposes a modeling for the CCD readout bias error magnitude. This bias, in turn, generates a velocity measurement bias error when there is an illumination difference between two successive PIV exposures. The model predictions match the experiments performed with two 12-bit-depth interline CCD cameras (MegaPlus ES 4.0/E incorporating the Kodak KAI-4000M CCD sensor with 4 megapixels). For different cameras, only two constant values are needed to fit the proposed calibration model and predict the error from the readout procedure. Tests by different researchers using different cameras would allow verification of the model, that can be used to optimize acquisition setups. Simple procedures to obtain these two calibration values are also described. (paper)

Aeroacoustic analysis of a NACA 0015 airfoil with Gurney flap based on time-resolved PIV measurements

NARCIS (Netherlands)

Zhang, Xueqing; Sciacchitano, A.; Pröbsting, S.; von Estorff, O.; Kropp, W.; Schulte-Fortkamp, B.

2016-01-01

The present study investigates the feasibility of high-lift devices noise prediction based on measurements of time-resolved particle image velocimetry (TR-PIV). The model under investigation is a NACA 0015 airfoil with Gurney flap with height of 6% chord length. The velocity fields around and

PIV in a model wind turbine rotor wake

DEFF Research Database (Denmark)

Meyer, Knud Erik; Naumov, Igor; Karbadin, Ivan

2013-01-01

Stereoscopic particle image velocimetry (PIV) measurements of the flow in the wake of scale model of a horizontal axis wind turbine is presented Near the rotor, measurements are made in vertical planes intersecting the rotor axis These planes capture flow effect from the tip and root vortices...... perpendicular to the rotor axis is used to investigate the dynamics in the far wake Here, a precessing core is found and data indicate that the Strouhal number of the precessing is independent of the rotor speed...

A physics-enabled flow restoration algorithm for sparse PIV and PTV measurements

Science.gov (United States)

Vlasenko, Andrey; Steele, Edward C. C.; Nimmo-Smith, W. Alex M.

2015-06-01

The gaps and noise present in particle image velocimetry (PIV) and particle tracking velocimetry (PTV) measurements affect the accuracy of the data collected. Existing algorithms developed for the restoration of such data are only applicable to experimental measurements collected under well-prepared laboratory conditions (i.e. where the pattern of the velocity flow field is known), and the distribution, size and type of gaps and noise may be controlled by the laboratory set-up. However, in many cases, such as PIV and PTV measurements of arbitrarily turbid coastal waters, the arrangement of such conditions is not possible. When the size of gaps or the level of noise in these experimental measurements become too large, their successful restoration with existing algorithms becomes questionable. Here, we outline a new physics-enabled flow restoration algorithm (PEFRA), specially designed for the restoration of such velocity data. Implemented as a ‘black box’ algorithm, where no user-background in fluid dynamics is necessary, the physical structure of the flow in gappy or noisy data is able to be restored in accordance with its hydrodynamical basis. The use of this is not dependent on types of flow, types of gaps or noise in measurements. The algorithm will operate on any data time-series containing a sequence of velocity flow fields recorded by PIV or PTV. Tests with numerical flow fields established that this method is able to successfully restore corrupted PIV and PTV measurements with different levels of sparsity and noise. This assessment of the algorithm performance is extended with an example application to in situ submersible 3D-PTV measurements collected in the bottom boundary layer of the coastal ocean, where the naturally-occurring plankton and suspended sediments used as tracers causes an increase in the noise level that, without such denoising, will contaminate the measurements.

A physics-enabled flow restoration algorithm for sparse PIV and PTV measurements

International Nuclear Information System (INIS)

Vlasenko, Andrey; Steele, Edward C C; Nimmo-Smith, W Alex M

2015-01-01

The gaps and noise present in particle image velocimetry (PIV) and particle tracking velocimetry (PTV) measurements affect the accuracy of the data collected. Existing algorithms developed for the restoration of such data are only applicable to experimental measurements collected under well-prepared laboratory conditions (i.e. where the pattern of the velocity flow field is known), and the distribution, size and type of gaps and noise may be controlled by the laboratory set-up. However, in many cases, such as PIV and PTV measurements of arbitrarily turbid coastal waters, the arrangement of such conditions is not possible. When the size of gaps or the level of noise in these experimental measurements become too large, their successful restoration with existing algorithms becomes questionable. Here, we outline a new physics-enabled flow restoration algorithm (PEFRA), specially designed for the restoration of such velocity data. Implemented as a ‘black box’ algorithm, where no user-background in fluid dynamics is necessary, the physical structure of the flow in gappy or noisy data is able to be restored in accordance with its hydrodynamical basis. The use of this is not dependent on types of flow, types of gaps or noise in measurements. The algorithm will operate on any data time-series containing a sequence of velocity flow fields recorded by PIV or PTV. Tests with numerical flow fields established that this method is able to successfully restore corrupted PIV and PTV measurements with different levels of sparsity and noise. This assessment of the algorithm performance is extended with an example application to in situ submersible 3D-PTV measurements collected in the bottom boundary layer of the coastal ocean, where the naturally-occurring plankton and suspended sediments used as tracers causes an increase in the noise level that, without such denoising, will contaminate the measurements. (paper)

Velocity and turbulence measurements of oil-water flow in horizontal and slightly inclined pipes using PIV

OpenAIRE

Kumara, W.A.S.; Halvorsen, Britt; Melaaen, Morten Christian

2009-01-01

Oil-water flows in horizontal and slightly inclined pipes are investigated using Particle Image Velocimetry (PIV). PIV offers a powerful non-invasive tool to study such flow fields. The experiments are conducted in a 15 m long, 56 mm diameter, inclinable steel pipe using Exxsol D60 oil (viscosity 1.64 mPa s, density 790 kg/m3) and water (viscosity 1.0 mPa s, density 996 kg/m3) as test fluids. The test pipe inclination is changed in the range from 5° upward to 5° downward. The experiments are ...

Traversing field of view and AR-PIV for mid-field wake vortex investigation in a towing tank

Science.gov (United States)

Scarano, F.; van Wijk, C.; Veldhuis, L. L. M.

2002-08-01

Wake vortex flow experiments are performed in a water tank where a 1:48 scaled model of a large transport aircraft A340-300 is towed at the speed of 3 and 5 ms-1 with values of the angle of attack α={2°, 4°, 8°}. Particle image velocimetry (PIV) measurements are performed in a plane perpendicular to the towing direction describing the streamwise component of the wake vorticity. The instantaneous field of view (I-FOV) is traversed vertically with an underwater moving-camera device tracking the vortex core during the downward motion. An adaptive resolution (AR) image-processing technique is introduced that enhances the PIV interrogation in terms of spatial resolution and accuracy. The main objectives of the investigation are to demonstrate the applicability of PIV diagnostics in wake vortex research with towing-tank facilities. The specific implementation of the traversing field-of-view (T-FOV) technique and the AR image processing are driven by the need to characterize the vortex wake global properties as well as the vortex decay phenomenon in the mid- and far-field. Relevant aerodynamic information is obtained in the mid-field where the time evolution of the vortex structure (core radius and tangential velocity) and of the overall vortex wake (vortex trajectory, descent velocity, circulation) are discussed.

Particle image velocimetry measurements of the flow in the converging region of two parallel jets

Energy Technology Data Exchange (ETDEWEB)

Wang, Huhu, E-mail: huhuwang@tamu.edu; Lee, Saya, E-mail: sayalee@tamu.edu; Hassan, Yassin A., E-mail: y-hassan@tamu.edu

2016-09-15

Highlights: • The flow behaviors in the converging region were non-intrusively investigated using PIV. • The PIV results using two measuring scales and LDV data matched very well. • Significant momentum transfer was observed in the merging region right after the merging point. • Instantaneous vector field revealed characteristic interacting patterns of the jets. - Abstract: The interaction between parallel jets plays a critical role in determining the characteristics of the momentum and heat transfer in the flow. Specifically for next generation VHTR, the output temperature will be about 900 °C, and any thermal oscillations will create safety issues. The mixing variations of the coolants in the reactor core may influence these power oscillations. Numerous numerical tools such as computational fluid dynamics (CFD) simulations have been used to support the reactor design. The validation of CFD method is important to ensure the fidelity of the calculations. This requires high-fidelity, qualified benchmark data. Particle image velocimetry (PIV), a non-intrusive measuring technique, was used to provide benchmark data for resolving a simultaneous flow field in the converging region of two submerged parallel jets issued from rectangular channels. The jets studied in this work had an equal discharge velocity at room temperature. The turbulent characteristics including the distributions of mean velocities, turbulence intensities, Reynolds stresses and z-component vorticity were studied. The streamwise mean velocity measured by PIV and LDV were compared, and they agreed very well.

Flow visualization through particle image velocimetry in realistic model of rhesus monkey's upper airway.

Science.gov (United States)

Kim, Ji-Woong; Phuong, Nguyen Lu; Aramaki, Shin-Ichiro; Ito, Kazuhide

2018-05-01

Studies concerning inhalation toxicology and respiratory drug-delivery systems require biological testing involving experiments performed on animals. Particle image velocimetry (PIV) is an effective in vitro technique that reveals detailed inhalation flow patterns, thereby assisting analyses of inhalation exposure to various substances. A realistic model of a rhesus-monkey upper airway was developed to investigate flow patterns in its oral and nasal cavities through PIV experiments performed under steady-state constant inhalation conditions at various flow rates-4, 10, and 20 L/min. Flow rate of the fluid passing through the inlet into the trachea was measured to obtain characteristic flow mechanisms, and flow phenomena in the model were confirmed via characterized flow fields. It was observed that increase in flow rate leads to constant velocity profiles in upper and lower trachea regions. It is expected that the results of this study would contribute to future validation of studies aimed at developing in silico models, especially those involving computational fluid dynamic (CFD) analysis. Copyright © 2018 Elsevier B.V. All rights reserved.

High-speed PIV applied to the wake of the NASA CRM model in ETW at high Re-number stall conditions for sub- and transonic speeds

OpenAIRE

Konrath, Robert; Geisler, Reinhard; Otter, Dirk; Philipp, Florian; Ehlers, Hauke; Agocs, Janos; Quest, Jürgen

2015-01-01

Within the framework of the EU project ESWIRP the Particle Image Velocimetry (PIV) using high-speed camera and laser has been used to measure the turbulent flow in the wake of a stalled aircraft wing. The measurements took place on the Common Research Model (CRM) provided by NASA in the pressurized cryogenic European Transonic Wind tunnel (ETW). A specific cryo-PIV system has been used and adapted for using high-speed PIV components under the cryogenic conditions of the wind tunnel faci...

Flow field investigations in rotating facilities by means of stationary PIV systems

International Nuclear Information System (INIS)

Armellini, A; Mucignat, C; Casarsa, L; Giannattasio, P

2012-01-01

The flow field inside rotating test sections can be investigated by means of particle image velocimetry (PIV) operated in the phase-locked mode. With this experimental approach, the measurement system is kept fixed and it is synchronized with the periodical passage of the test section. Therefore, the direct output of the PIV measurements is the absolute velocity field, while the relative one is indirectly obtained from proper data processing that relies on accurate knowledge of the peripheral velocity field. This work provides an uncertainty analysis about the evaluation of the peripheral displacement field in phase-locked PIV measurements. The analysis leads to the detection of the levels of accuracy required in the estimation of both the angular velocity and the position of the center of rotation to ensure correct evaluation of the peripheral displacement field. In this regard, a simple methodology is proposed to evaluate the center of rotation position with an accuracy below 1 px. Finally, a procedure to pre-process the PIV images by subtracting the peripheral displacement is described. The advantages of its implementation are highlighted by the comparison with the performance of a more standard methodology where the peripheral field is subtracted from the absolute velocity field and not directly from the PIV raw data

Utilization of MatPIV program to different geotechnical models

Science.gov (United States)

Aklik, P.; Idinger, G.

2009-04-01

The Particle Imaging Velocimetry (PIV) technique is being used to measure soil displacements. PIV has been used for many years in fluid mechanics; but for physical modeling in geotechnical engineering, this technique is still relatively new. PIV is a worldwide growth in soil mechanics over the last decade owing to the developments in digital cameras and laser technologies. The use of PIV is feasible provided the surface contains sufficient texture. A Cambridge group has shown that natural sand contains enough texture for applying PIV. In a texture-based approach, the only requirement is for any patch, big or small to be sufficiently unique so that statistical tracking of this patch is possible. In this paper, some of the soil mechanic's models were investigated such as retaining walls, slope failures, and foundations. The photographs were taken with the help of the high resolution digital camera, the displacements of soils were evaluated with free software named as MatPIV and the displacement graphics between the two images were obtained. Nikon D60 digital camera is 10.2 MB and it has special properties which makes it possible to use in PIV applications. These special properties are Airflow Control System and Image Sensor cleaning for protection against dust, Active D-Lighting for highlighted or shadowy areas while shooting, advanced three-point AF system for fast, efficient and precise autofocus. Its fast and continuous shooting mode enables up to 100 JPEG images at three frames per second. Norm Sand (DIN 1164) was used for all the models in a glass rectangular box. For every experiment, MatPIV was used to calculate the velocities from the two images. MatPIV program was used in two ways such as easy way and difficult way: In the easy way, the two images with 64*64 pixels with 50% or 75% overlap of the interrogation windows were taken into consideration and the calculation was performed with a single iteration through the images and the result consisted of four

Effects of Injection Timing on Fluid Flow Characteristics of Partially Premixed Combustion Based on High-Speed Particle Image Velocimetry

KAUST Repository

Izadi Najafabadi, Mohammad; Tanov, Slavey; Wang, Hua; Somers, Bart; Johansson, Bengt; Dam, Nico

2017-01-01

behavior. The scope of the present study is to investigate the fluid flow characteristics of PPC at different injection timings. To this end, high-speed Particle Image Velocimetry (PIV) is implemented in a light-duty optical engine to measure fluid flow

Replacement of the Ectodomains of the Hemagglutinin-Neuraminidase and Fusion Glycoproteins of Recombinant Parainfluenza Virus Type 3 (PIV3) with Their Counterparts from PIV2 Yields Attenuated PIV2 Vaccine Candidates

OpenAIRE

Tao, Tao; Skiadopoulos, Mario H.; Davoodi, Fatemeh; Riggs, Jeffrey M.; Collins, Peter L.; Murphy, Brian R.

2000-01-01

We sought to develop a live attenuated parainfluenza virus type 2 (PIV2) vaccine strain for use in infants and young children, using reverse genetic techniques that previously were used to rapidly produce a live attenuated PIV1 vaccine candidate. The PIV1 vaccine candidate, designated rPIV3-1cp45, was generated by substituting the full-length HN and F proteins of PIV1 for those of PIV3 in the attenuated cp45 PIV3 vaccine candidate (T. Tao et al., J. Virol. 72:2955–2961, 1998; M. H. Skiadopoul...

PIV technique implementation for wind mapping in complex topographies

International Nuclear Information System (INIS)

Siddiqui, Kamran; Hangan, Horia; Rasouli, Ashkan

2008-01-01

An experimental study was conducted to demonstrate PIV's capability to provide a detailed characterization of the flow field over complex topographic terrain in a large boundary layer wind tunnel setup. Two-dimensional velocity fields were measured in horizontal and vertical planes over a 1:3000 scaled topographic model. The non-uniform seed distribution was found to be a major issue which could affect the PIV velocity vectors. A novel scheme was developed to automatically detect the regions with low seed density and exclude them from further analysis. The mean and turbulent velocities obtained from PIV and previous hotwire measurements are compared and show good agreement. The study shows that PIV can be successfully used to measure flow over complex geometries in large wind tunnel setups, enabling the flow structure to be mapped with a very high spatial resolution

Simultaneous density-field visualization and PIV of a shock-accelerated gas curtain

Energy Technology Data Exchange (ETDEWEB)

Prestridge, K.; Rightley, P.M.; Vorobieff, P. [Los Alamos Nat. Lab., NM (United States). Dynamic Exp. Div.; Benjamin, R.F.; Kurnit, N.A.

2000-10-01

We describe a highly-detailed experimental characterization of the Richtmyer-Meshkov instability (the impulsively driven Rayleigh-Taylor instability) (Meshkov 1969; Richtmyer 1960). In our experiment, a vertical curtain of heavy gas (SF{sub 6}) flows into the test section of an air-filled, horizontal shock tube. The instability evolves after a Mach 1.2 shock passes through the curtain. For visualization, we pre-mix the SF{sub 6} with a small ({proportional_to}10{sup -5}) volume fraction of sub-micron-sized glycol/water droplets. A horizontal section of the flow is illuminated by a light sheet produced by a combination of a customized, burst-mode Nd:YAG laser and a commercial pulsed laser. Three CCD cameras are employed in visualization. The ''dynamic imaging camera'' images the entire test section, but does not detect the individual droplets. It produces a sequence of instantaneous images of local droplet concentration, which in the post-shock flow is proportional to density. The gas curtain is convected out of the test section about 1 ms after the shock passes through the curtain. A second camera images the initial conditions with high resolution, since the initial conditions vary from test to test. The third camera, ''PIV camera,'' has a spatial resolution sufficient to detect the individual droplets in the light sheet. Images from this camera are interrogated using particle image velocimetry (PIV) to recover instantaneous snapshots of the velocity field in a small (19 x 14 mm) field of view. The fidelity of the flow-seeding technique for density-field acquisition and the reliability of the PIV technique are both quantified in this paper. In combination with wide-field density data, PIV measurements give us additional physical insight into the evolution of the Richtmyer-Meshkov instability in a problem which serves as an excellent test case for general transition-to-turbulence studies. (orig.)

Simultaneous particle image velocimetry and infrared imagery of microscale breaking waves

International Nuclear Information System (INIS)

Siddiqui, M.H. Kamran; Loewen, Mark R.; Richardson, Christine; Asher, William E.; Jessup, Andrew T.

2001-01-01

We report the results from a laboratory investigation in which microscale breaking waves were detected using an infrared (IR) imager and two-dimensional (2-D) velocity fields were simultaneously measured using particle image velocimetry (PIV). In addition, the local heat transfer velocity was measured using the controlled flux technique. To the best of our knowledge these are the first measurements of the instantaneous 2-D velocity fields generated beneath microscale breaking waves. Careful measurements of the water surface profile enabled us to make accurate estimates of the near-surface velocities using PIV. Previous experiments have shown that behind the leading edge of a microscale breaker the cool skin layer is disrupted creating a thermal signature in the IR image [Jessup et al., J. Geophys. Res. 102, 23145 (1997)]. The simultaneously sampled IR images and PIV data enabled us to show that these disruptions or wakes are typically produced by a series of vortices that form behind the leading edge of the breaker. When the vortices are first formed they are very strong and coherent but as time passes, and they move from the crest region to the back face of the wave, they become weaker and less coherent. The near-surface vorticity was correlated with both the fractional area coverage of microscale breaking waves and the local heat transfer velocity. The strong correlations provide convincing evidence that the wakes produced by microscale breaking waves are regions of high near-surface vorticity that are in turn responsible for enhancing air-water heat transfer rates

Measurement of velocity field in pipe with classic twisted tape using matching refractive index technique

Energy Technology Data Exchange (ETDEWEB)

Song, Min Seop; Park, So Hyun; Kim, Eung Soo [Seoul National Univ., Seoul (Korea, Republic of)

2014-10-15

Many researchers conducted experiments and numerical simulations to measure or predict a Nusselt number or a friction factor in a pipe with a twisted tape while some other studies focused on the heat transfer performance enhancement using various twisted tape configurations. However, since the optical access to the inner space of a pipe with a twisted tape was limited, the detailed flow field data were not obtainable so far. Thus, researchers mainly relied on the numerical simulations to obtain the data of the flow field. In this study, a 3D printing technique was used to manufacture a transparent test section for optical access. And also, a noble refractive index matching technique was used to eliminate optical distortion. This two combined techniques enabled to measure the velocity profile with Particle Image Velocimetry (PIV). The measured velocity field data can be used either to understand the fundamental flow characteristics around a twisted tape or to validate turbulence models in Computational Fluid Dynamics (CFD). In this study, the flow field in the test-section was measured for various flow conditions and it was finally compared with numerically calculated data. Velocity fields in a pipe with a classic twisted tape was measured using a particle image velocimetry (PIV) system. To obtain undistorted particle images, a noble optical technique, refractive index matching, was used and it was proved that high-quality image can be obtained from this experimental equipment. The velocity data from the PIV was compared with the CFD simulations.

Measurement of velocity field in pipe with classic twisted tape using matching refractive index technique

International Nuclear Information System (INIS)

Song, Min Seop; Park, So Hyun; Kim, Eung Soo

2014-01-01

Many researchers conducted experiments and numerical simulations to measure or predict a Nusselt number or a friction factor in a pipe with a twisted tape while some other studies focused on the heat transfer performance enhancement using various twisted tape configurations. However, since the optical access to the inner space of a pipe with a twisted tape was limited, the detailed flow field data were not obtainable so far. Thus, researchers mainly relied on the numerical simulations to obtain the data of the flow field. In this study, a 3D printing technique was used to manufacture a transparent test section for optical access. And also, a noble refractive index matching technique was used to eliminate optical distortion. This two combined techniques enabled to measure the velocity profile with Particle Image Velocimetry (PIV). The measured velocity field data can be used either to understand the fundamental flow characteristics around a twisted tape or to validate turbulence models in Computational Fluid Dynamics (CFD). In this study, the flow field in the test-section was measured for various flow conditions and it was finally compared with numerically calculated data. Velocity fields in a pipe with a classic twisted tape was measured using a particle image velocimetry (PIV) system. To obtain undistorted particle images, a noble optical technique, refractive index matching, was used and it was proved that high-quality image can be obtained from this experimental equipment. The velocity data from the PIV was compared with the CFD simulations

Tomo-PIV measurements of the flow field in the wake of a sphere

Science.gov (United States)

Eshbal, Lior; David, Tom; Rinsky, Vladislav; van Hout, Rene; Greenblatt, David

2017-11-01

A sphere can be considered as a prototypical 3D bluff body. In order to improve our understanding of its 3D wake flow, a combination of time-resolved planar particle image velocimetry (PIV) and tomographic PIV (tomo-PIV) was implemented. Experiments were performed in a closed-loop water channel facility and sphere Reynolds numbers ReD = UD/ ν = 400, 800, 1200 and 2000, where U is the free-stream velocity, ν the kinematic viscosity and D the sphere diameter. The measurement volume (Height x Length x Width, 5 x 5 x 1.5 D3) comprised the sphere and the downstream wake. Tomo-PIV snap-shots were correlated with the time-resolved PIV such that the 3D temporal evolution of the shed vortices became clear. At ReD = 400, this procedure revealed shed hairpin vortices having a vertical plane of symmetry in agreement with many dye visualization studies. However, the measurements also revealed weaker induced hairpins resulting from the interaction of the near-wake flow and the surrounding free stream. These induced vortices were not visible in previous dye and smoke visualizations and have only been observed in simulations. Data processing of the data at higher ReD is currently ongoing. Israel Science Foundation Grant No. 1596/14.

Development of a compact x-ray particle image velocimetry for measuring opaque flows.

Science.gov (United States)

Lee, Sang Joon; Kim, Guk Bae; Yim, Dae Hyun; Jung, Sung Yong

2009-03-01

A compact x-ray particle image velocimetry (PIV) system employing a medical x-ray tube as a light source was developed to measure quantitative velocity field information of opaque flows. The x-ray PIV system consists of a medical x-ray tube, an x-ray charge coupled device camera, a programmable shutter for a pulse-type x ray, and a synchronization device. Through performance tests, the feasibility of the developed x-ray PIV system as a flow measuring device was verified. To check the feasibility of the developed system, we tested a tube flow at two different mean velocities of 1 and 2 mm/s. The x-ray absorption of tracer particles must be quite different from that of working fluid to have a good contrast in x-ray images. All experiments were performed under atmospheric pressure condition. This system is unique and useful for investigating various opaque flows or flows inside opaque conduits.

Development of a compact x-ray particle image velocimetry for measuring opaque flows

International Nuclear Information System (INIS)

Lee, Sang Joon; Kim, Guk Bae; Yim, Dae Hyun; Jung, Sung Yong

2009-01-01

A compact x-ray particle image velocimetry (PIV) system employing a medical x-ray tube as a light source was developed to measure quantitative velocity field information of opaque flows. The x-ray PIV system consists of a medical x-ray tube, an x-ray charge coupled device camera, a programmable shutter for a pulse-type x ray, and a synchronization device. Through performance tests, the feasibility of the developed x-ray PIV system as a flow measuring device was verified. To check the feasibility of the developed system, we tested a tube flow at two different mean velocities of 1 and 2 mm/s. The x-ray absorption of tracer particles must be quite different from that of working fluid to have a good contrast in x-ray images. All experiments were performed under atmospheric pressure condition. This system is unique and useful for investigating various opaque flows or flows inside opaque conduits.

Flow measurements in a model centrifugal pump by 3-D PIV

International Nuclear Information System (INIS)

Yang, H; Xu, H R; Liu, C

2012-01-01

PIV (Particle Image Velocimetry), as an non-intrusive flow measurements technology, is widely used to investigate the flow fields in many areas. 3-D (three Dimensional) PIV has seldom been used to measure flow field in rotational impeller of centrifugal pump due to the difficulty of calibration in samll space. In this article, a specially manufactured water tank was used to perform the calibration for 3-D PIV measurement. The instantaneous absolute velocity in one impeller passage was obtained by merging of three sub zones and the relative velocity was acquired by velocity decomposition. The result shows that, when the pump runs at the condition of design flow rate, the radial component velocity W r appears a concave distribution except the condition of R=45 mm. With the increase of radius, the circumference location of the minimum radial component velocity W r moves from the pressure side to the suction side. At the same time, the tangential component velocity W θ on the suction side decreases gradually with the increase of radius, while the component on the pressure side increases gradually. The secondary flow in different radius section has also been shown. At last, the error of PIV measurements was analyzed, which shows that the test results are accurate and the measured data is reliable.

Determine of velocity field with PIV and CFD during the flow around of bridge piers

Directory of Open Access Journals (Sweden)

Picka D.

2013-04-01

Full Text Available The article describes the processing of specific junior research FAST-J-11-51/1456 which dealt with physical and CFD of the velocity field during the flow around of bridge piers. Physical modelling has been carried out in Laboratory of water management research in Institute of Water Structures in Brno University of Technology – Faculty of Civil Engineering. To measure of the velocity field in profile of bridge piers were used laser measuring method PIV (Particle Image Velocimetry. The results of PIV served as a basis for comparing experimental data with CFD results of this type of flow in the commercial software ANSYS CFX.

Tomographic Particle Image Velocimetry using Pulsed, High Power LED Volume Illumination

OpenAIRE

Buchmann, N. A.; Willert, C.; Soria, J.

2011-01-01

This paper investigates the use of high-power light emitting diode (LED) illumination in Particle Image Velocimetry (PIV) as an alternative to traditional laser-based illumination. The solid-state LED devices can provide averaged radiant power in excess of 10W and by operating the LEDs with short current pulses, considerably higher than in continuous operation, light pulses of sufficient energy suitable for imaging micron-sized particles can be generated. The feasibility of this LED-based ill...

Track benchmarking method for uncertainty quantification of particle tracking velocimetry interpolations

International Nuclear Information System (INIS)

Schneiders, Jan F G; Sciacchitano, Andrea

2017-01-01

The track benchmarking method (TBM) is proposed for uncertainty quantification of particle tracking velocimetry (PTV) data mapped onto a regular grid. The method provides statistical uncertainty for a velocity time-series and can in addition be used to obtain instantaneous uncertainty at increased computational cost. Interpolation techniques are typically used to map velocity data from scattered PTV (e.g. tomographic PTV and Shake-the-Box) measurements onto a Cartesian grid. Recent examples of these techniques are the FlowFit and VIC+  methods. The TBM approach estimates the random uncertainty in dense velocity fields by performing the velocity interpolation using a subset of typically 95% of the particle tracks and by considering the remaining tracks as an independent benchmarking reference. In addition, also a bias introduced by the interpolation technique is identified. The numerical assessment shows that the approach is accurate when particle trajectories are measured over an extended number of snapshots, typically on the order of 10. When only short particle tracks are available, the TBM estimate overestimates the measurement error. A correction to TBM is proposed and assessed to compensate for this overestimation. The experimental assessment considers the case of a jet flow, processed both by tomographic PIV and by VIC+. The uncertainty obtained by TBM provides a quantitative evaluation of the measurement accuracy and precision and highlights the regions of high error by means of bias and random uncertainty maps. In this way, it is possible to quantify the uncertainty reduction achieved by advanced interpolation algorithms with respect to standard correlation-based tomographic PIV. The use of TBM for uncertainty quantification and comparison of different processing techniques is demonstrated. (paper)

Modification of the ultrasound induced activity by the presence of an electrode in a sono-reactor working at two low frequencies (20 and 40 kHz). Part II: Mapping flow velocities by particle image velocimetry (PIV).

Science.gov (United States)

Mandroyan, A; Doche, M L; Hihn, J Y; Viennet, R; Bailly, Y; Simonin, L

2009-01-01

Sonoelectrochemical experiments differ from sonochemical ones by the introduction of electrodes in the sonicated reaction vessel. The aim of the study is to characterize the changes in the ultrasonic activity induced by the presence of an electrode located in front of the transducer. The scope of our investigations concerns two low frequency vibration modes: 20 and 40 kHz. For this purpose, two laser visualization techniques have been used. The first part of the study, described in a previous paper (Part I), deals with the laser tomography technique which provides an accurate picture of the reactor active zones, related to numerous cavitation events. The second part of the paper (Part II) will describe the particle image velocimetry (PIV) technique used to measure the velocity vector field in the fluid portion between the horn and the electrode. As for the previous study, two parameters were studied: the electrical power supplied to the transducer and the electrode/transducer distance. The velocity vector fields show a main flow in the reactor axis. This flow seems to correspond to the conical cavitation bubbles structure which is observed on the laser tomography pictures. When an electrode is introduced into the reactor, two additional symmetric transversal flows can be quantified on both sides of the electrode.

Channel flow structure measurements using particle image velocimetry

International Nuclear Information System (INIS)

Norazizi Mohamed; Noraeini Mokhtar; Aziz Ibrahim; Ramli Abu Hassan

1996-01-01

Two different flow structures in a laboratory channel were examined using a flow visualization technique, known as Particle Image Velocimetry (PIV). The first channel flow structure was that of a steady flow over a horizontal channel bottom. Photographs of particle displacements were taken in the boundary layer in a plane parallel to the flow. These photographs were analyzed to give simultaneous measurements of two components of the velocity at hundreds of points in the plane. Averaging these photographs gave the velocity profile a few millimeters from the bottom of the channel to the water surface. The results gave good agreement with the known boundary layer theory. This technique is extended to the study of the structure under a progressive wave in the channel. A wavelength of the propagating wave is divided into sections by photographing it continously for a number of frames. Each frame is analyzed and a velocity field under this wave at various phase points were produced with their respective directions. The results show that velocity vectors in a plane under the wave could be achieved instantaneously and in good agreement with the small amplitude wave theory

DeepPIV: Particle image velocimetry measurements using deep-sea, remotely operated vehicles

Science.gov (United States)

Katija, Kakani; Sherman, Alana; Graves, Dale; Klimov, Denis; Kecy, Chad; Robison, Bruce

2015-11-01

The midwater region of the ocean (below the euphotic zone and above the benthos) is one of the largest ecosystems on our planet, yet remains one of the least explored. Little-known marine organisms that inhabit midwater have developed life strategies that contribute to their evolutionary success, and may inspire engineering solutions for societally relevant challenges. Although significant advances in underwater vehicle technologies have improved access to midwater, small-scale, in situ fluid mechanics measurement methods that seek to quantify the interactions that midwater organisms have with their physical environment are lacking. Here we present DeepPIV, an instrumentation package affixed to remotely operated vehicles that quantifies fluid motions from the surface of the ocean down to 4000 m depths. Utilizing ambient suspended particulate, fluid-structure interactions are evaluated on a range of marine organisms in midwater. Initial science targets include larvaceans, biological equivalents of flapping flexible foils, that create mucus houses to filter food. Little is known about the structure of these mucus houses and the function they play in selectively filtering particles, and these dynamics can serve as particle-mucus models for human health. Using DeepPIV, we reveal the complex structures and flows generated within larvacean mucus houses, and elucidate how these structures function. Funding is gratefully acknowledged from the Packard Foundation.

Aerodynamic Performance Degradation Induced by Ice Accretion. PIV Technique Assessment in Icing Wind Tunnel

Science.gov (United States)

Gregorio, Fabrizio De

The aim of the present chapter is to consider the use of PIV technique in an industrial icing wind tunnel (IWT) and the potentiality/advantages of applying the PIV technique to this specific field. The purpose of icing wind tunnels is to simulate the aircraft flight condition through cloud formations. In this operational condition ice accretions appear on the aircraft exposed surfaces due to the impact of the water droplets present in the clouds and the subsequent solidification. The investigation of aircraft aerodynamic performances and flight safety in icing condition is a fundamental aspect in the phase of design, development and certification of new aircrafts. The description of this unusual ground testing facility is reported. The assessment of PIV in CIRA-IWT has been investigated. Several technological problems have been afforded and solved by developing the components of the measurement system, such as the laser system and the recording apparatus, both fully remotely controlled, equipped with several traversing mechanism and protected by the adverse environment conditions (temperature and pressure). The adopted solutions are described. Furthermore, a complete test campaign on a full-scale aircraft wing tip, equipped with moving slat and deicing system has been carried out by PIV. Two regions have been investigated. The wing leading-edge (LE) area has been studied with and without ice accretion and for different cloud characteristics. The second activitiy was aimed at the investigation of the wing-wake behavior. The measurements were aimed to characterize the wake for the model in cruise condition without ice formation and during the ice formation.

Validation of a CFD methodology for positive displacement LVAD analysis using PIV data.

Science.gov (United States)

Medvitz, Richard B; Reddy, Varun; Deutsch, Steve; Manning, Keefe B; Paterson, Eric G

2009-11-01

Computational fluid dynamics (CFD) is used to asses the hydrodynamic performance of a positive displacement left ventricular assist device. The computational model uses implicit large eddy simulation direct resolution of the chamber compression and modeled valve closure to reproduce the in vitro results. The computations are validated through comparisons with experimental particle image velocimetry (PIV) data. Qualitative comparisons of flow patterns, velocity fields, and wall-shear rates demonstrate a high level of agreement between the computations and experiments. Quantitatively, the PIV and CFD show similar probed velocity histories, closely matching jet velocities and comparable wall-strain rates. Overall, it has been shown that CFD can provide detailed flow field and wall-strain rate data, which is important in evaluating blood pump performance.

Enhancing PIV image and fractal descriptor for velocity and shear stresses propagation around a circular pier

Directory of Open Access Journals (Sweden)

Alireza Keshavarzi

2017-07-01

Full Text Available In this study, the fractal dimensions of velocity fluctuations and the Reynolds shear stresses propagation for flow around a circular bridge pier are presented. In the study reported herein, the fractal dimension of velocity fluctuations (u′, v′, w′ and the Reynolds shear stresses (u′v′ and u′w′ of flow around a bridge pier were computed using a Fractal Interpolation Function (FIF algorithm. The velocity fluctuations of flow along a horizontal plane above the bed were measured using Acoustic Doppler Velocity meter (ADV and Particle Image Velocimetry (PIV. The PIV is a powerful technique which enables us to attain high resolution spatial and temporal information of turbulent flow using instantaneous time snapshots. In this study, PIV was used for detection of high resolution fractal scaling around a bridge pier. The results showed that the fractal dimension of flow fluctuated significantly in the longitudinal and transverse directions in the vicinity of the pier. It was also found that the fractal dimension of velocity fluctuations and shear stresses increased rapidly at vicinity of pier at downstream whereas it remained approximately unchanged far downstream of the pier. The higher value of fractal dimension was found at a distance equal to one times of the pier diameter in the back of the pier. Furthermore, the average fractal dimension for the streamwise and transverse velocity fluctuations decreased from the centreline to the side wall of the flume. Finally, the results from ADV measurement were consistent with the result from PIV, therefore, the ADV enables to detect turbulent characteristics of flow around a circular bridge pier.

Laboratory experiment on the 3D tide-induced Lagrangian residual current using the PIV technique

Science.gov (United States)

Chen, Yang; Jiang, Wensheng; Chen, Xu; Wang, Tao; Bian, Changwei

2017-12-01

The 3D structure of the tide-induced Lagrangian residual current was studied using the particle image velocimetry (PIV) technique in a long shallow narrow tank in the laboratory. At the mouth of the tank, a wave generator was used to make periodic wave which represents the tide movement, and at the head of the tank, a laterally sloping topography with the length of one fifth of the water tank was installed, above which the tide-induced Lagrangian residual current was studied. Under the weakly nonlinear condition in the present experiment setup, the results show that the Lagrangian residual velocity (LRV) field has a three-layer structure. The residual current flows inwards (towards the head) in the bottom layer and flows outwards in the middle layer, while in the surface layer, it flows inwards along the shallow side of the sloping topography and outwards along the deep side. The depth-averaged and breadth-averaged LRV are also analyzed based on the 3D LRV observations. Our results are in good agreement with the previous experiment studies, the analytical solutions with similar conditions and the observational results in real bays. Moreover, the volume flux comparison between the Lagrangian and Eulerian residual currents shows that the Eulerian residual velocity violates the mass conservation law while the LRV truly represents the inter-tidal water transport. This work enriches the laboratory studies of the LRV and offers valuable references for the LRV studies in real bays.

PIV as a method for quantifying root cell growth and particle displacement in confocal images.

Science.gov (United States)

Bengough, A Glyn; Hans, Joachim; Bransby, M Fraser; Valentine, Tracy A

2010-01-01

Particle image velocimetry (PIV) quantifies displacement of patches of pixels between successive images. We evaluated PIV as a tool for microscopists by measuring displacements of cells and of a surrounding granular medium in confocal laser scanning microscopy images of Arabidopsis thaliana roots labeled with cell-membrane targeted green fluorescent protein. Excellent accuracy (e.g., displacement standard deviation PIV-predicted and actual displacements (r(2) > 0.83). Root mean squared error for these distorted images was 0.4-1.1 pixels, increasing at higher magnification factors. Cell growth and rhizosphere deformation were tracked with good temporal (e.g., 1-min interval) and spatial resolution, with PIV patches located on recognizable cell features being tracked more successfully. Appropriate choice of GFP-label was important to decrease small-scale biological noise due to intracellular motion. PIV of roots grown in stiff 2% versus 0.7% agar showed patterns of cell expansion consistent with physically impeded roots of other species. Roots in glass ballotini underwent rapid changes in growth direction on a timescale of minutes, associated with localized arching of ballotini. By tracking cell vertices, we monitored automatically cell length, width, and area every minute for 0.5 h for cells in different stages of development. In conclusion, PIV measured displacements successfully in images of living root cells and the external granular medium, revealing much potential for use by microscopists. (c) 2009 Wiley-Liss, Inc.

Impact of mismatched and misaligned laser light sheet profiles on PIV performance

Science.gov (United States)

Grayson, K.; de Silva, C. M.; Hutchins, N.; Marusic, I.

2018-01-01

The effect of mismatched or misaligned laser light sheet profiles on the quality of particle image velocimetry (PIV) results is considered in this study. Light sheet profiles with differing widths, shapes, or alignment can reduce the correlation between PIV images and increase experimental errors. Systematic PIV simulations isolate these behaviours to assess the sensitivity and implications of light sheet mismatch on measurements. The simulations in this work use flow fields from a turbulent boundary layer; however, the behaviours and impacts of laser profile mismatch are highly relevant to any fluid flow or PIV application. Experimental measurements from a turbulent boundary layer facility are incorporated, as well as additional simulations matched to experimental image characteristics, to validate the synthetic image analysis. Experimental laser profiles are captured using a modular laser profiling camera, designed to quantify the distribution of laser light sheet intensities and inform any corrective adjustments to an experimental configuration. Results suggest that an offset of just 1.35 standard deviations in the Gaussian light sheet intensity distributions can cause a 40% reduction in the average correlation coefficient and a 45% increase in spurious vectors. Errors in measured flow statistics are also amplified when two successive laser profiles are no longer well matched in alignment or intensity distribution. Consequently, an awareness of how laser light sheet overlap influences PIV results can guide faster setup of an experiment, as well as achieve superior experimental measurements.

Decompositions of bubbly flow PIV velocity fields using discrete wavelets multi-resolution and multi-section image method

International Nuclear Information System (INIS)

Choi, Je-Eun; Takei, Masahiro; Doh, Deog-Hee; Jo, Hyo-Jae; Hassan, Yassin A.; Ortiz-Villafuerte, Javier

2008-01-01

Currently, wavelet transforms are widely used for the analyses of particle image velocimetry (PIV) velocity vector fields. This is because the wavelet provides not only spatial information of the velocity vectors, but also of the time and frequency domains. In this study, a discrete wavelet transform is applied to real PIV images of bubbly flows. The vector fields obtained by a self-made cross-correlation PIV algorithm were used for the discrete wavelet transform. The performances of the discrete wavelet transforms were investigated by changing the level of power of discretization. The images decomposed by wavelet multi-resolution showed conspicuous characteristics of the bubbly flows for the different levels. A high spatial bubble concentrated area could be evaluated by the constructed discrete wavelet transform algorithm, in which high-leveled wavelets play dominant roles in revealing the flow characteristics

Comparison of PIV with 4D-Flow in a physiological accurate flow phantom

Science.gov (United States)

Sansom, Kurt; Balu, Niranjan; Liu, Haining; Aliseda, Alberto; Yuan, Chun; Canton, Maria De Gador

2016-11-01

Validation of 4D MRI flow sequences with planar particle image velocimetry (PIV) is performed in a physiologically-accurate flow phantom. A patient-specific phantom of a carotid artery is connected to a pulsatile flow loop to simulate the 3D unsteady flow in the cardiovascular anatomy. Cardiac-cycle synchronized MRI provides time-resolved 3D blood velocity measurements in clinical tool that is promising but lacks a robust validation framework. PIV at three different Reynolds numbers (540, 680, and 815, chosen based on +/- 20 % of the average velocity from the patient-specific CCA waveform) and four different Womersley numbers (3.30, 3.68, 4.03, and 4.35, chosen to reflect a physiological range of heart rates) are compared to 4D-MRI measurements. An accuracy assessment of raw velocity measurements and a comparison of estimated and measureable flow parameters such as wall shear stress, fluctuating velocity rms, and Lagrangian particle residence time, will be presented, with justification for their biomechanics relevance to the pathophysiology of arterial disease: atherosclerosis and intimal hyperplasia. Lastly, the framework is applied to a new 4D-Flow MRI sequence and post processing techniques to provide a quantitative assessment with the benchmarked data. Department of Education GAANN Fellowship.

POD Mode Robustness for the Turbulent Jet Sampled with PIV

DEFF Research Database (Denmark)

Hodzic, Azur; Meyer, Knud Erik; Velte, Clara Marika

2017-01-01

An important challenge in the description and simulation of turbulence is the large amount of information that is needed to describe even relatively simple flows in detail. The frequent disagreement between Reynolds averaged Navier–Stokes-based simulations and experiments is well known. Albeit, d...... and even high speed volumetric PIV systems providing fully three dimensional velocity fields. Another challenge is how do we verify simulations against experiments and ensure that we indeed have simulated the same flow that we have measured?......An important challenge in the description and simulation of turbulence is the large amount of information that is needed to describe even relatively simple flows in detail. The frequent disagreement between Reynolds averaged Navier–Stokes-based simulations and experiments is well known. Albeit......, direct numerical simulations and in certain cases large eddy simulations tend to agree fairly well with experiments, their practical implementation introduces the problem of data storage. The experimentalist, however, experiences the same problem, using highspeed particle image velocimetry (PIV) systems...

On the extraction of pressure fields from PIV velocity measurements in turbines

Science.gov (United States)

Villegas, Arturo; Diez, Fancisco J.

2012-11-01

In this study, the pressure field for a water turbine is derived from particle image velocimetry (PIV) measurements. Measurements are performed in a recirculating water channel facility. The PIV measurements include calculating the tangential and axial forces applied to the turbine by solving the integral momentum equation around the airfoil. The results are compared with the forces obtained from the Blade Element Momentum theory (BEMT). Forces are calculated by using three different methods. In the first method, the pressure fields are obtained from PIV velocity fields by solving the Poisson equation. The boundary conditions are obtained from the Navier-Stokes momentum equations. In the second method, the pressure at the boundaries is determined by spatial integration of the pressure gradients along the boundaries. In the third method, applicable only to incompressible, inviscid, irrotational, and steady flow, the pressure is calculated using the Bernoulli equation. This approximated pressure is known to be accurate far from the airfoil and outside of the wake for steady flows. Additionally, the pressure is used to solve for the force from the integral momentum equation on the blade. From the three methods proposed to solve for pressure and forces from PIV measurements, the first one, which is solved by using the Poisson equation, provides the best match to the BEM theory calculations.

PIV validation of blood-heart valve leaflet interaction modelling.

Science.gov (United States)

Kaminsky, R; Dumont, K; Weber, H; Schroll, M; Verdonck, P

2007-07-01

The aim of this study was to validate the 2D computational fluid dynamics (CFD) results of a moving heart valve based on a fluid-structure interaction (FSI) algorithm with experimental measurements. Firstly, a pulsatile laminar flow through a monoleaflet valve model with a stiff leaflet was visualized by means of Particle Image Velocimetry (PIV). The inflow data sets were applied to a CFD simulation including blood-leaflet interaction. The measurement section with a fixed leaflet was enclosed into a standard mock loop in series with a Harvard Apparatus Pulsatile Blood Pump, a compliance chamber and a reservoir. Standard 2D PIV measurements were made at a frequency of 60 bpm. Average velocity magnitude results of 36 phase-locked measurements were evaluated at every 10 degrees of the pump cycle. For the CFD flow simulation, a commercially available package from Fluent Inc. was used in combination with inhouse developed FSI code based on the Arbitrary Lagrangian-Eulerian (ALE) method. Then the CFD code was applied to the leaflet to quantify the shear stress on it. Generally, the CFD results are in agreement with the PIV evaluated data in major flow regions, thereby validating the FSI simulation of a monoleaflet valve with a flexible leaflet. The applicability of the new CFD code for quantifying the shear stress on a flexible leaflet is thus demonstrated.

Comparative assessment of PIV-based pressure evaluation techniques applied to a transonic base flow

NARCIS (Netherlands)

Blinde, P; Michaelis, D; van Oudheusden, B.W.; Weiss, P.E.; de Kat, R.; Laskari, A.; Jeon, Y.J.; David, L; Schanz, D; Huhn, F.; Gesemann, S; Novara, M.; McPhaden, C.; Neeteson, N.; Rival, D.; Schneiders, J.F.G.; Schrijer, F.F.J.

2016-01-01

A test case for PIV-based pressure evaluation techniques has been developed by constructing a simulated experiment from a ZDES simulation for an axisymmetric base flow at Mach 0.7. The test case comprises sequences of four subsequent particle images (representing multi-pulse data) as well as

Characterization of the Inlet Port Flow under Steady-State Conditions Using PIV and POD

Directory of Open Access Journals (Sweden)

Mohammed El-Adawy

2017-11-01

Full Text Available The current study demonstrates an experimental investigation of the tumble flow structures using Particle Image Velocimetry (PIV under steady-state conditions considering the central vertical tumble plane. The experiments were carried out on a four-valve, pent-roof Gasoline Direct Injection (GDI engine head at different valve lifts and with a pressure difference of 150 mmH2O across the intake valves. Furthermore, the Proper Orthogonal Decomposition (POD analytical technique was applied to PIV-measured velocity vector maps to characterize the flow structures at various valve lifts, and hence the different rig tumble values. The results show that at low valve lifts (1 to 5 mm, 48.9 to 46.6% of the flow energy is concentrated in the large (mode 1 eddies with only 8.4 to 11.46% in mode 2 and 7.2 to 7.5 in mode 3. At high valve lifts, it can be clearly seen that some of the energy in the large eddies of mode 1 is transferred to the smaller flow structures of modes 2 and 3. This can be clearly seen at valve lift 10 mm where the values of the flow energy were 40.6%, 17.3%, and 8.0% for modes 1, 2, and 3, respectively.

Particle image velocimetry measurements of 2-dimensional velocity field around twisted tape

Energy Technology Data Exchange (ETDEWEB)

Song, Min Seop; Park, So Hyun; Kim, Eung Soo, E-mail: kes7741@snu.ac.kr

2016-11-01

Highlights: • Measurements of the flow field in a pipe with twisted tape were conducted by particle image velocimetry (PIV). • A novel matching index of refraction technique utilizing 3D printing and oil mixture was adopted to make the test section transparent. • Undistorted particle images were clearly captured in the presence of twisted tape. • 2D flow field in the pipe with twisted tape revealed the characteristic two-peak velocity profile. - Abstract: Twisted tape is a passive component used to enhance heat exchange in various devices. It induces swirl flow that increases the mixing of fluid. Thus, ITER selected the twisted tape as one of the candidates for turbulence promoting in the divertor cooling. Previous study was mainly focused on the thermohydraulic performance of the twisted tape. As detailed data on the velocity field around the twisted tape was insufficient, flow visualization study was performed to provide fundamental data on velocity field. To visualize the flow in a complex structure, novel matching index of refraction technique was used with 3-D printing and mixture of anise and mineral oil. This technique enables the camera to capture undistorted particle image for velocity field measurement. Velocity fields at Reynolds number 1370–9591 for 3 different measurement plane were obtained through particle image velocimetry. The 2-dimensional averaged velocity field data were obtained from 177 pair of instantaneous velocity fields. It reveals the characteristic two-peak flow motion in axial direction. In addition, the normalized velocity profiles were converged with increase of Reynolds numbers. Finally, the uncertainty of the result data was analyzed.

A three-dimensional strain measurement method in elastic transparent materials using tomographic particle image velocimetry.

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Azuma Takahashi

Full Text Available The mechanical interaction between blood vessels and medical devices can induce strains in these vessels. Measuring and understanding these strains is necessary to identify the causes of vascular complications. This study develops a method to measure the three-dimensional (3D distribution of strain using tomographic particle image velocimetry (Tomo-PIV and compares the measurement accuracy with the gauge strain in tensile tests.The test system for measuring 3D strain distribution consists of two cameras, a laser, a universal testing machine, an acrylic chamber with a glycerol water solution for adjusting the refractive index with the silicone, and dumbbell-shaped specimens mixed with fluorescent tracer particles. 3D images of the particles were reconstructed from 2D images using a multiplicative algebraic reconstruction technique (MART and motion tracking enhancement. Distributions of the 3D displacements were calculated using a digital volume correlation. To evaluate the accuracy of the measurement method in terms of particle density and interrogation voxel size, the gauge strain and one of the two cameras for Tomo-PIV were used as a video-extensometer in the tensile test. The results show that the optimal particle density and interrogation voxel size are 0.014 particles per pixel and 40 × 40 × 40 voxels with a 75% overlap. The maximum measurement error was maintained at less than 2.5% in the 4-mm-wide region of the specimen.We successfully developed a method to experimentally measure 3D strain distribution in an elastic silicone material using Tomo-PIV and fluorescent particles. To the best of our knowledge, this is the first report that applies Tomo-PIV to investigate 3D strain measurements in elastic materials with large deformation and validates the measurement accuracy.

Water flow experiment using the PIV technique and the thermal hydraulic analysis on the cross-flow type mercury target model

International Nuclear Information System (INIS)

Haga, Katsuhiro; Terada, Atsuhiko; Kaminaga, Masanori; Hino, Ryutaro

2001-01-01

In this study the effectiveness of the cross-flow type mercury target structure was evaluated experimentally and analytically. The average water flow velocity field in the target mock-up model, which was fabricated with plexiglass, was measured at room temperature using the PIV (Particle Image Velocimetry) technique. The water flow analyses were conducted and the analytical results were compared with the experimental results. The experimental results showed that the cross-flow could be realized in the former part of the proton beam path where the heat load by the spallation reaction is large, and the analytical result of the water flow velocity field showed good correspondence to the experimental result in the case of the Reynolds number of more than 4.83 x 10 5 at the model inlet. With these results, the effectiveness of the cross-flow type mercury target structure and the present analysis code system was demonstrated. Then the mercury flow field and the temperature distribution in the target container were analyzed assuming the proton beam energy and power of 3 GeV and 5 MW. The analytical result showed that the cross-flow field of mercury, which is similar to the water flow field, could also be attained. (author)

Development of flow velocity measurement techniques in visible images. Improvement of particle image velocimetry techniques on image process

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Kimura, Nobuyuki; Nishimura, Motohiko; Kamide, Hideki; Hishida, Koichi

1999-10-01

Noise reduction system was developed to improve applicability of Particle Image Velocimetry (PIV) to complicated configure bounded flows. For fast reactor safety and thermal hydraulic studies, experiments are performed in scale models which usually have rather complicated geometry and structures such as fuel subassemblies, heat exchangers, etc. The structures and stuck dusts on the view window of the models obscure the particle image. Thus the image except the moving particles can be regarded as a noise. In the present study, two noise reduction techniques are proposed. The one is the Time-averaged Light Intensity Subtraction method (TIS) which subtracts the time-averaged light intensity of each pixel in the sequential images from the each corresponding pixel. The other one is the Minimum Light Intensity Subtraction method (MIS) which subtracts the minimum light intensity of each pixel in the sequential images from the each corresponding pixel. Both methods are examined on their capabilities of noise reduction. As for the original 'bench mark' image, the image made from Large Eddy Simulation was used. To the bench mark image, noises are added which are referred as sample images. Both methods reduce the rate of vector with the error of more than one pixel from 90% to less than 5%. Also, more than 50% of the vectors have the error of less than 0.2 pixel. The analysis of uncertainty shows that these methods enhances the accuracy of vector measurement 3 ∼ 12 times if the image with noise were processed, and the MIS method has 1.1 ∼ 2.1 times accuracy compared to the TIS. Thus the present noise reduction methods are quite efficient to enhance the accuracy of flow velocity fields measured with particle images including structures and deposits on the view window. (author)

Velocity Fields Measurement of Natural Circulation Flow inside a Pool Using PIV Technique

International Nuclear Information System (INIS)

Kim, Seok; Kim, Dong Eok; Youn, Young Jung; Euh, Dong Jin; Song, Chul Hwa

2012-01-01

Thermal stratification is encountered in large pool of water increasingly being used as heat sink in new generation of advanced reactors. These large pools at near atmospheric pressure provide a heat sink for heat removal from the reactor or steam generator, and the containment by natural circulation as well as a source of water for core cooling. For examples, the PAFS (passive auxiliary feedwater system) is one of the advanced safety features adopted in the APR+ (Advanced Power Reactor Plus), which is intended to completely replace the conventional active auxiliary feedwater system. The PAFS cools down the steam generator secondary side and eventually removes the decay heat from the reactor core by adopting a natural convection mechanism. In a pool, the heat transfer from the PCHX (passive condensation heat exchanger) contributed to increase the pool temperature up to the saturation condition and induce the natural circulation flow of the PCCT (passive condensate cooling tank) pool water. When a heat rod is placed horizontally in a pool of water, the fluid adjacent to the heat rod gets heated up. In the process, its density reduces and by virtue of the buoyancy force, the fluid in this region moves up. After reaching the top free surface, the heated water moves towards the other side wall of the pool along the free surface. Since this heated water is cooling, it goes downward along the wall at the other side wall. Above heater rod, a natural circulation flow is formed. However, there is no flow below heater rod until pool water temperature increases to saturation temperature. In this study, velocity measurement was conducted to reveal a natural circulation flow structure in a small pool using PIV (particle image velocimetry) measurement technique

Using PIV to determine relative pressures in a stenotic phantom under steady flow based on the pressure-poisson equation.

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Khodarahmi, Iman; Shakeri, Mostafa; Sharp, M; Amini, Amir A

2010-01-01

Pressure gradient across a Gaussian-shaped 87% area stenosis phantom was estimated by solving the pressure Poisson equation (PPE) for a steady flow mimicking the blood flow through the human iliac artery. The velocity field needed to solve the pressure equation was obtained using particle image velocimetry (PIV). A steady flow rate of 46.9 ml/s was used, which corresponds to a Reynolds number of 188 and 595 at the inlet and stenosis throat, respectively (in the range of mean Reynolds number encountered in-vivo). In addition, computational fluid dynamics (CFD) simulation of the same flow was performed. Pressure drops across the stenosis predicted by PPE/PIV and CFD were compared with those measured by a pressure catheter transducer. RMS errors relative to the measurements were 17% and 10% for PPE/PIV and CFD, respectively.

Continuous and simultaneous measurement of the tank-treading motion of red blood cells and the surrounding flow using translational confocal micro-particle image velocimetry (micro-PIV) with sub-micron resolution

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Oishi, M; Utsubo, K; Kinoshita, H; Fujii, T; Oshima, M

2012-01-01

In this study, a translational confocal micro-particle image velocimetry (PIV) system is introduced to measure the microscopic interaction between red blood cells (RBCs) and the surrounding flow. Since the macroscopic behavior of RBCs, such as the tank-treading motion, is closely related to the axial migration and other flow characteristics in arterioles, the measurement method must answer the conflicting demands of sub-micron resolution, continuous measurement and applicability for high-speed flow. In order to avoid loss of the measurement target, i.e. RBCs, from the narrow field of view during high-magnification measurement, the translation stage with the flow device moves in the direction opposite the direction of flow. The proposed system achieves the measurement of higher absolute velocities compared with a conventional confocal micro-PIV system without the drawbacks derived from stage vibration. In addition, we have applied a multicolor separation unit, which can measure different phases simultaneously using different fluorescent particles, in order to clarify the interaction between RBCs and the surrounding flow. Based on our measurements, the tank-treading motion of RBCs depends on the shear stress gradient of the surrounding flow. Although, the relationship between the tank-treading frequency and the shear rate of the surrounding flow is of the same order as in the previous uniform shear rate experiments, our results reveal the remarkable behavior of the non-uniform membrane velocities and lateral velocity component of flow around the RBCs. (paper)

Quantitative flow characteristics for side-by-side square cylinders via PIV

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Dogan Sercan

2012-04-01

Full Text Available In this study, instantaneous and time-averaged flow structures downstream of the sharp-edged single and two and three side-by-side square cylinders (SCs immersed in a uniform open channel water flow were studied by a technique of particle image velocimetry (PIV. Experimental results of wake flow structures were presented for gap ratios (G/D in the range of 1.0”G/D”3.0 for Reynolds number values of 1050, 2450 and 3400. Flow structures depending on the square cylinder (SC configurations and Reynolds number were discussed. It has been found that the development of the vortex shedding as well as the flow structure were substantially altered for side-by-side SCs comparing to the single SC. Asymmetrical and biased wake structures were observed because of the jetlike flow between the SCs for two SCs cases for the gap ratio less than 2.0. Depending on the gap spacing between the SCs, the interaction results of time2 averaged vorticity, velocity vector field, Reynolds stress correlations and streamline patterns in the wake region form a distinguished flow structure. Strouhal numbers for the single square cylinder for 1050≤Re≤3400 are found in the range of 0.12-0.13. The present results have supported the previous works by providing detailed quantitative experimental information with PIV in the wake region of the SC and might be helpful for validation of numerical studies and designers.

A translating stage system for µ-PIV measurements surrounding the tip of a migrating semi-infinite bubble.

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Smith, B J; Yamaguchi, E; Gaver, D P

2010-01-01

We have designed, fabricated and evaluated a novel translating stage system (TSS) that augments a conventional micro particle image velocimetry (µ-PIV) system. The TSS has been used to enhance the ability to measure flow fields surrounding the tip of a migrating semi-infinite bubble in a glass capillary tube under both steady and pulsatile reopening conditions. With conventional µ-PIV systems, observations near the bubble tip are challenging because the forward progress of the bubble rapidly sweeps the air-liquid interface across the microscopic field of view. The translating stage mechanically cancels the mean bubble tip velocity, keeping the interface within the microscope field of view and providing a tenfold increase in data collection efficiency compared to fixed-stage techniques. This dramatic improvement allows nearly continuous observation of the flow field over long propagation distances. A large (136-frame) ensemble-averaged velocity field recorded with the TSS near the tip of a steadily migrating bubble is shown to compare well with fixed-stage results under identical flow conditions. Use of the TSS allows the ensemble-averaged measurement of pulsatile bubble propagation flow fields, which would be practically impossible using conventional fixed-stage techniques. We demonstrate our ability to analyze these time-dependent two-phase flows using the ensemble-averaged flow field at four points in the oscillatory cycle.

A maximum entropy reconstruction technique for tomographic particle image velocimetry

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Bilsky, A V; Lozhkin, V A; Markovich, D M; Tokarev, M P

2013-01-01

This paper studies a novel approach for reducing tomographic PIV computational complexity. The proposed approach is an algebraic reconstruction technique, termed MENT (maximum entropy). This technique computes the three-dimensional light intensity distribution several times faster than SMART, using at least ten times less memory. Additionally, the reconstruction quality remains nearly the same as with SMART. This paper presents the theoretical computation performance comparison for MENT, SMART and MART, followed by validation using synthetic particle images. Both the theoretical assessment and validation of synthetic images demonstrate significant computational time reduction. The data processing accuracy of MENT was compared to that of SMART in a slot jet experiment. A comparison of the average velocity profiles shows a high level of agreement between the results obtained with MENT and those obtained with SMART. (paper)

Comparison of particle image velocimetry and phase contrast MRI in a patient-specific extracardiac total cavopulmonary connection.

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Kitajima, Hiroumi D; Sundareswaran, Kartik S; Teisseyre, Thomas Z; Astary, Garrett W; Parks, W James; Skrinjar, Oskar; Oshinski, John N; Yoganathan, Ajit P

2008-08-01

Particle image velocimetry (PIV) and phase contrast magnetic resonance imaging (PC-MRI) have not been compared in complex biofluid environments. Such analysis is particularly useful to investigate flow structures in the correction of single ventricle congenital heart defects, where fluid dynamic efficiency is essential. A stereolithographic replica of an extracardiac total cavopulmonary connection (TCPC) is studied using PIV and PC-MRI in a steady flow loop. Volumetric two-component PIV is compared to volumetric three-component PC-MRI at various flow conditions. Similar flow structures are observed in both PIV and PC-MRI, where smooth flow dominates the extracardiac TCPC, and superior vena cava flow is preferential to the right pulmonary artery, while inferior vena cava flow is preferential to the left pulmonary artery. Where three-component velocity is available in PC-MRI studies, some helical flow in the extracardiac TCPC is observed. Vessel cross sections provide an effective means of validation for both experiments, and velocity magnitudes are of the same order. The results highlight similarities to validate flow in a complex patient-specific extracardiac TCPC. Additional information obtained by velocity in three components further describes the complexity of the flow in anatomic structures.

4D blood flow mapping using SPIM-microPIV in the developing zebrafish heart

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Zickus, Vytautas; Taylor, Jonathan M.

2018-02-01

Fluid-structure interaction in the developing heart is an active area of research in developmental biology. However, investigation of heart dynamics is mostly limited to computational uid dynamics simulations using heart wall structure information only, or single plane blood ow information - so there is a need for 3D + time resolved data to fully understand cardiac function. We present an imaging platform combining selective plane illumination microscopy (SPIM) with micro particle image velocimetry (μPIV) to enable 3D-resolved flow mapping in a microscopic environment, free from many of the sources of error and bias present in traditional epi uorescence-based μPIV systems. By using our new system in conjunction with optical heart beat synchronization, we demonstrate the ability obtain non-invasive 3D + time resolved blood flow measurements in the heart of a living zebrafish embryo.

Time-resolved Particle Image Velocimetry measurements of the 3D random Richtmyer-Meshkov Instability

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Sewell, Everest; Krivets, Vitaliy; Jacobs, Jeffrey

2017-11-01

The vertical shock tube at the University of Arizona is used to perform experiments on the multi-mode three-dimensional Richtmyer-Meshkov Instability (RMI). An interface of air and sulfur hexafluoride is formed in a counter flow configuration, and is excited using voice coils to produce faraday-like multi-modal perturbations.This interface is shock accelerated by an approximately Mach 1.2 shockwave to form the RMI. Time resolved Particle Image Velocimetry (PIV) is used to perform analysis of the evolving instability.

PIV measurements in a compact return diffuser under multi-conditions

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Zhou, L.; Lu, W. G.; Shi, W. D.

2013-12-01

Due to the complex three-dimensional geometries of impellers and diffusers, their design is a delicate and difficult task. Slight change could lead to significant changes in hydraulic performance and internal flow structure. Conversely, the grasp of the pump's internal flow pattern could benefit from pump design improvement. The internal flow fields in a compact return diffuser have been investigated experimentally under multi-conditions. A special Particle Image Velocimetry (PIV) test rig is designed, and the two-dimensional PIV measurements are successfully conducted in the diffuser mid-plane to capture the complex flow patterns. The analysis of the obtained results has been focused on the flow structure in diffuser, especially under part-load conditions. The vortex and recirculation flow patterns in diffuser are captured and analysed accordingly. Strong flow separation and back flow appeared at the part-load flow rates. Under the design and over-load conditions, the flow fields in diffuser are uniform, and the flow separation and back flow appear at the part-load flow rates, strong back flow is captured at one diffuser passage under 0.2Qdes.

Micro-PIV Study of Supercritical CO2-Water Interactions in Porous Micromodels

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Kazemifar, Farzan; Blois, Gianluca; Christensen, Kenneth T.

2015-11-01

Multiphase flow of immiscible fluids in porous media is encountered in numerous natural systems and engineering applications such as enhanced oil recovery (EOR), and CO2 sequestration among others. Geological sequestration of CO2 in saline aquifers has emerged as a viable option for reducing CO2 emissions, and thus it has been the subject of numerous studies in recent years. A key objective is improving the accuracy of numerical models used for field-scale simulations by incorporation/better representation of the pore-scale flow physics. This necessitates experimental data for developing, testing and validating such models. We have studied drainage and imbibition processes in a homogeneous, two-dimensional porous micromodel with CO2 and water at reservoir-relevant conditions. Microscopic particle image velocimetry (micro-PIV) technique was applied to obtain spatially- and temporally-resolved velocity vector fields in the aqueous phase. The results provide new insight into the flow processes at the pore scale.

Development of a Dual-PIV system for high-speed flow applications

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Schreyer, Anne-Marie; Lasserre, Jean J.; Dupont, Pierre

2015-10-01

A new Dual-particle image velocimetry (Dual-PIV) system for application in supersonic flows was developed. The system was designed for shock wave/turbulent boundary layer interactions with separation. This type of flow places demanding requirements on the system, from the large range of characteristic frequencies O(100 Hz-100 kHz) to spatial and temporal resolutions necessary for the measurement of turbulent quantities (Dolling in AIAA J 39(8):1517-1531, 2001; Dupont et al. in J Fluid Mech 559:255-277, 2006; Smits and Dussauge in Turbulent shear layers in supersonic flow, 2nd edn. Springer, New York, 2006). While classic PIV systems using high-resolution CCD sensors allow high spatial resolution, these systems cannot provide the required temporal resolution. Existing high-speed PIV systems provide temporal and CMOS sensor resolutions, and even laser pulse energies, that are not adapted to our needs. The only obvious solution allowing sufficiently high spatial resolution, access to high frequencies, and a high laser pulse energy is a multi-frame system: a Dual-PIV system, consisting of two synchronized PIV systems observing the same field of view, will give access to temporal characteristics of the flow. The key technology of our system is frequency-based image separation: two lasers of different wavelengths illuminate the field of view. The cross-pollution with laser light from the respective other branches was quantified during system validation. The overall system noise was quantified, and the prevailing error of only 2 % reflects the good spatial and temporal alignment. The quality of the measurement system is demonstrated with some results on a subsonic jet flow including the spatio-temporal inter-correlation functions between the systems. First measurements in a turbulent flat-plate boundary layer at Mach 2 show the same satisfactory data quality and are also presented and discussed.

Variational 3D-PIV with sparse descriptors

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Lasinger, Katrin; Vogel, Christoph; Pock, Thomas; Schindler, Konrad

2018-06-01

3D particle imaging velocimetry (3D-PIV) aims to recover the flow field in a volume of fluid, which has been seeded with tracer particles and observed from multiple camera viewpoints. The first step of 3D-PIV is to reconstruct the 3D locations of the tracer particles from synchronous views of the volume. We propose a new method for iterative particle reconstruction, in which the locations and intensities of all particles are inferred in one joint energy minimization. The energy function is designed to penalize deviations between the reconstructed 3D particles and the image evidence, while at the same time aiming for a sparse set of particles. We find that the new method, without any post-processing, achieves significantly cleaner particle volumes than a conventional, tomographic MART reconstruction, and can handle a wide range of particle densities. The second step of 3D-PIV is to then recover the dense motion field from two consecutive particle reconstructions. We propose a variational model, which makes it possible to directly include physical properties, such as incompressibility and viscosity, in the estimation of the motion field. To further exploit the sparse nature of the input data, we propose a novel, compact descriptor of the local particle layout. Hence, we avoid the memory-intensive storage of high-resolution intensity volumes. Our framework is generic and allows for a variety of different data costs (correlation measures) and regularizers. We quantitatively evaluate it with both the sum of squared differences and the normalized cross-correlation, respectively with both a hard and a soft version of the incompressibility constraint.

Investigation on convective mixing of triple-jet. Evaluation of turbulent quantities using particle image velocimetry and direct numerical simulation

International Nuclear Information System (INIS)

Kimura, Nobuyuki; Igarashi, Minoru; Kamide, Hideki

2002-01-01

We performed a water experiment on parallel triple-jet and a calculation using a direct numerical simulation (DNS) for a quantification of thermal striping. The local temperatures and velocities were measured by using thermocouples and the particle image velocimetry (PIV), respectively. The calculation was carried out using the quasi-DNS code, DINUS-3, which was based on the finite difference method. The oscillation of the jets obtained from the flow visualization was related to the movements of the twin vortices between the jets by using the PIV. The experimental temperatures/velocities results were close to the numerical results. The heat transportation among the jets was evaluated by using the turbulent heat fluxes obtained from the quasi-DNS. (author)

Tomographic PIV behind a prosthetic heart valve

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Hasler, D.; Landolt, A.; Obrist, D.

2016-05-01

The instantaneous three-dimensional velocity field past a bioprosthetic heart valve was measured using tomographic particle image velocimetry. Two digital cameras were used together with a mirror setup to record PIV images from four different angles. Measurements were conducted in a transparent silicone phantom with a simplified geometry of the aortic root. The refraction indices of the silicone phantom and the working fluid were matched to minimize optical distortion from the flow field to the cameras. The silicone phantom of the aorta was integrated in a flow loop driven by a piston pump. Measurements were conducted for steady and pulsatile flow conditions. Results of the instantaneous, ensemble and phase-averaged flow field are presented. The three-dimensional velocity field reveals a flow topology, which can be related to features of the aortic valve prosthesis.

Can echocardiographic particle image velocimetry correctly detect motion patterns as they occur in blood inside heart chambers? A validation study using moving phantoms

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Prinz Christian

2012-06-01

Full Text Available Abstract Aims To validate Echo Particle Image Velocimetry (PIV Methods High fidelity string and rotating phantoms moving with different speed patterns were imaged with different high-end ultrasound systems at varying insonation angles and frame rates. Images were analyzed for velocity and direction and for complex motion patterns of blood flow with dedicated software. Post-processing was done with MATLAB-based tools (Dflow, JUV, University Leuven. Results Velocity estimation was accurate up to a velocity of 42 cm/s (r = 0.99, p  Conclusion Echo-PIV appears feasible. Velocity estimates are accurate, but the maximal detectable velocity depends strongly on acquisition parameters. Direction estimation works sufficiently, even at higher velocities. Echo-PIV appears to be a promising technical approach to investigate flow patterns by echocardiography.

Performance test on 2-dimensional PIV and 3-dimensional PIV using standard images

International Nuclear Information System (INIS)

Hwang, Tae Gyu; Doh, Deog Hee

2004-01-01

Quantitative performance test on the conventional 2D-PIV and the hybrid angular 3D-PIV (Stereoscopic PIV) was carried out. LES Data sets on an impinging jet which are provided on the webpage(http://www.vsj.or.jp/piv) for the PIV Standard Project were used for the generation of virtual images. The generated virtual images were used for the 2D-PIV and 3D-PIV measurements test. It has been shown that the results obtained by 2D-PIV on average values are slightly closer to the LES data than those obtained by 3D-PIV, but the turbulent properties obtained by 2D-PIV are largely underestimated than those obtained by 3D-PIV

A fast multi-resolution approach to tomographic PIV

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Discetti, Stefano; Astarita, Tommaso

2012-03-01

Tomographic particle image velocimetry (Tomo-PIV) is a recently developed three-component, three-dimensional anemometric non-intrusive measurement technique, based on an optical tomographic reconstruction applied to simultaneously recorded images of the distribution of light intensity scattered by seeding particles immersed into the flow. Nowadays, the reconstruction process is carried out mainly by iterative algebraic reconstruction techniques, well suited to handle the problem of limited number of views, but computationally intensive and memory demanding. The adoption of the multiplicative algebraic reconstruction technique (MART) has become more and more accepted. In the present work, a novel multi-resolution approach is proposed, relying on the adoption of a coarser grid in the first step of the reconstruction to obtain a fast estimation of a reliable and accurate first guess. A performance assessment, carried out on three-dimensional computer-generated distributions of particles, shows a substantial acceleration of the reconstruction process for all the tested seeding densities with respect to the standard method based on 5 MART iterations; a relevant reduction in the memory storage is also achieved. Furthermore, a slight accuracy improvement is noticed. A modified version, improved by a multiplicative line of sight estimation of the first guess on the compressed configuration, is also tested, exhibiting a further remarkable decrease in both memory storage and computational effort, mostly at the lowest tested seeding densities, while retaining the same performances in terms of accuracy.

CH PLIF and PIV implementation using C-X (0,0) and intra-vibrational band filtered detection

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Hammack, Stephen D.; Skiba, Aaron W.; Lee, Tonghun; Carter, Campbell D.

2018-02-01

This study demonstrates advancement in a low-pulse energy methylidyne (CH) planar laser-induced fluorescence (PLIF) method that facilitates its application alongside flows seeded for particle image velocimetry (PIV) or other particle scattering based methods, as well as in high scattering environments. The C-X (0,0) R-branch excitation and filtered detection are carefully selected such that the laser line frequency is heavily attenuated by an edge filter while allowing transmission of most of the (0,0) band fluorescence. There are strong OH A-X (0,0) lines in the vicinity, but they can be avoided or utilized through dye laser tuning. As a demonstration of efficacy, PIV is performed simultaneously with the PLIF imaging. Using the edge filter, particle scattering signal is reduced to sub-fluorescence levels, allowing for flame-front analysis. This achievement enables flame-front tracking at high repetition rates (due to the low-pulse energy required) in combination with a scattering method such as PIV or use in high scattering environments such as enclosed combustors or near burner surfaces.

The Application of EIS and PIV Methods to the Measurement of Aerated Flow

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Fejfarová M.

2013-04-01

Full Text Available The paper describes measurements in the aerated water medium using modern methods PIV (Particle Image Velocimetry and EIS (Electrical Impedance Spectrometry, which are applied in the Laboratory of Water Management Research (LVV of the Department of Water Structures (UVST at the Faculty of Civil Engineering (FAST of Brno University of Technology (VUT. Measurements of the water medium were carried out for three different aeration intensities at special experimental workplaces. The experiment was focused on the capability of the methods to monitor the air content in the water.

On the effect of velocity gradients on the depth of correlation in μPIV

International Nuclear Information System (INIS)

Mustin, B; Stoeber, B

2016-01-01

The present work revisits the effect of velocity gradients on the depth of the measurement volume (depth of correlation) in microscopic particle image velocimetry (μPIV). General relations between the μPIV weighting functions and the local correlation function are derived from the original definition of the weighting functions. These relations are used to investigate under which circumstances the weighting functions are related to the curvature of the local correlation function. Furthermore, this work proposes a modified definition of the depth of correlation that leads to more realistic results than previous definitions for the case when flow gradients are taken into account. Dimensionless parameters suitable to describe the effect of velocity gradients on μPIV cross correlation are derived and visual interpretations of these parameters are proposed. We then investigate the effect of the dimensionless parameters on the weighting functions and the depth of correlation for different flow fields with spatially constant flow gradients and with spatially varying gradients. Finally this work demonstrates that the results and dimensionless parameters are not strictly bound to a certain model for particle image intensity distributions but are also meaningful when other models for particle images are used. (paper)

Computational fluid dynamics analysis and PIV validation of a bionic vortex flow pulsatile LVAD.

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Xu, Liang; Yang, Ming; Ye, Lin; Dong, Zhaopeng

2015-01-01

Hemocompatibility is highly affected by the flow field in Left Ventricular Assistant Devices (LVAD). An asymmetric inflow and outflow channel arrangement with a 45° intersection angle with respect to the blood chamber is proposed to approximate the vascular structure of the aorta and left atrium on the left ventricle. The structure is expected to develop uninterruptible vortex flow state which is similar to the flow state in human left ventricle. The Computational Fluid Dynamics (CFD) asymmetric model is simulated using ANSYS workbench. To validate the velocity field calculated by CFD, a Particle Image Velocimetry (PIV) experiment is conducted. The CFD results show that the proposed blood chamber could generate a shifting vortex flow that would be redirected to the aorta during ejection to form a persistent recirculating flow state, which is similar to the echocardiographic flow state in left ventricle. Both the PIV and the CFD results show the development of a persistent vortex during the pulsatile period. Comparison of the qualitative flow pattern and quantitative probed velocity histories in a pulsatile period shows a good agreement between the CFD and PIV data. The goal of developing persistent quasi intra-ventricle vortex flow state in LVAD is realized.

On the effect of velocity gradients on the depth of correlation in μPIV

Science.gov (United States)

Mustin, B.; Stoeber, B.

2016-03-01

The present work revisits the effect of velocity gradients on the depth of the measurement volume (depth of correlation) in microscopic particle image velocimetry (μPIV). General relations between the μPIV weighting functions and the local correlation function are derived from the original definition of the weighting functions. These relations are used to investigate under which circumstances the weighting functions are related to the curvature of the local correlation function. Furthermore, this work proposes a modified definition of the depth of correlation that leads to more realistic results than previous definitions for the case when flow gradients are taken into account. Dimensionless parameters suitable to describe the effect of velocity gradients on μPIV cross correlation are derived and visual interpretations of these parameters are proposed. We then investigate the effect of the dimensionless parameters on the weighting functions and the depth of correlation for different flow fields with spatially constant flow gradients and with spatially varying gradients. Finally this work demonstrates that the results and dimensionless parameters are not strictly bound to a certain model for particle image intensity distributions but are also meaningful when other models for particle images are used.

In vitro blood flow in a rectangular PDMS microchannel: experimental observations using a confocal micro-PIV system.

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Lima, Rui; Wada, Shigeo; Tanaka, Shuji; Takeda, Motohiro; Ishikawa, Takuji; Tsubota, Ken-ichi; Imai, Yohsuke; Yamaguchi, Takami

2008-04-01

Progress in microfabricated technologies has attracted the attention of researchers in several areas, including microcirculation. Microfluidic devices are expected to provide powerful tools not only to better understand the biophysical behavior of blood flow in microvessels, but also for disease diagnosis. Such microfluidic devices for biomedical applications must be compatible with state-of-the-art flow measuring techniques, such as confocal microparticle image velocimetry (PIV). This confocal system has the ability to not only quantify flow patterns inside microchannels with high spatial and temporal resolution, but can also be used to obtain velocity measurements for several optically sectioned images along the depth of the microchannel. In this study, we investigated the ability to obtain velocity measurements using physiological saline (PS) and in vitro blood in a rectangular polydimethysiloxane (PDMS) microchannel (300 microm wide, 45 microm deep) using a confocal micro-PIV system. Applying this combination, measurements of trace particles seeded in the flow were performed for both fluids at a constant flow rate (Re = 0.02). Velocity profiles were acquired by successive measurements at different depth positions to obtain three-dimensional (3-D) information on the behavior of both fluid flows. Generally, the velocity profiles were found to be markedly blunt in the central region, mainly due to the low aspect ratio (h/w = 0.15) of the rectangular microchannel. Predictions using a theoretical model for the rectangular microchannel corresponded quite well with the experimental micro-PIV results for the PS fluid. However, for the in vitro blood with 20% hematocrit, small fluctuations were found in the velocity profiles. The present study clearly shows that confocal micro-PIV can be effectively integrated with a PDMS microchannel and used to obtain blood velocity profiles along the full depth of the microchannel because of its unique 3-D optical sectioning ability

PIV pictures of stream field predict haemolysis index of centrifugal pump with streamlined impeller.

Science.gov (United States)

Qian, K X; Feng, Z G; Ru, W M; Zeng, P; Yuan, H Y

2007-01-01

Previously it has been found by pump haemolysis testing that the flow rate has a remarkable effect on index of haemolysis (IH), while pressure head does not affect IH. Recent investigation with particle image velocimetry (PIV) technology has demonstrated that IH is directly related to the flow pattern of stream field in impeller vane channels. PIV is a visible approach showing the real flow status in the pump. The different positions of a tracer particle in two PIV pictures taken at 20 micros intervals decide the velocity value and direction. The velocity vectors of many particles draw the flow pattern of the stream field. The same pictures are taken at 2, 4 and 6 l min(-1) flow rates while the pressure head is kept unchanged at 100 mmHg; then the pictures are taken at 4 l min(-1) flow with different pressure heads of 80, 100 and 120 mmHg. Results reveal that the flow rate of 4 l min(-1) (IH = 0.030) has the best stream field, and neither turbulence nor separation can be seen. In other flow rates (IH: 0.048 - 0.082), there is obviously second flow. Meanwhile, no significant difference can be seen among the PIV pictures of different pressure heads pumped, which agrees with the results of haemolysis testing showing that pressure has no effect on pump haemolysis. It may be concluded that the haemolysis property of a centrifugal pump can be assessed approximately by PIV pictures, which are much easier to take than haemolysis tests.

Investigation of the hydrodynamic model test of forced rolling for a barge using PIV

Directory of Open Access Journals (Sweden)

WANG Xiaoqiang

2017-03-01

Full Text Available In order to study the physical details of viscous flow in ship roll motions and improve the accuracy of ship roll damping numerical simulation, the application of the Particle Image Velocimetry (PIV technique is investigated in model tests of forced ship rolling in calm water. The hydrodynamic force and flow field at the bilge region are simultaneously measured for barges at different amplitudes and frequencies in which the self-made forced rolling facility was used. In the model test, the viscous flow variation with the time around the bilge region was studied during ship rolling motion. The changes in ship roll damping coefficients with the rolling amplitude and period were also investigated. A comparison of the model test results with the Computational Fluid Dynamics(CFDresults shows that the numerical ship roll damping coefficients agree well with the model test results, while the differences in the local flow details exist between the CFD results and model test results. Further research into the model test technique and CFD application is required.

PIV and LDA measurements of the wake behind a wind turbine model

DEFF Research Database (Denmark)

Naumov, I. V.; Mikkelsen, Robert Flemming; Okulov, Valery

2014-01-01

=5 with a constant design lift coefficient along the span, CLdesign= 0.8. The measurements include dye visualization, Particle Image Velocimetry and Laser Doppler Anemometry. The wake instability has been studied in the range λ =3 – 9 at different cross-sections from the very near wake up to 10 rotor...... diameters downstream from the rotor. The initial flume flow was subject to a very low turbulence level with a uniform velocity profile, limiting the influence of external disturbances on the development of the inherent vortex instability. Using PIV measurements and visualizations, special attention was paid...

Ultrasonic particle image velocimetry for improved flow gradient imaging: algorithms, methodology and validation

International Nuclear Information System (INIS)

Niu Lili; Qian Ming; Yu Wentao; Jin Qiaofeng; Ling Tao; Zheng Hairong; Wan Kun; Gao Shen

2010-01-01

This paper presents a new algorithm for ultrasonic particle image velocimetry (Echo PIV) for improving the flow velocity measurement accuracy and efficiency in regions with high velocity gradients. The conventional Echo PIV algorithm has been modified by incorporating a multiple iterative algorithm, sub-pixel method, filter and interpolation method, and spurious vector elimination algorithm. The new algorithms' performance is assessed by analyzing simulated images with known displacements, and ultrasonic B-mode images of in vitro laminar pipe flow, rotational flow and in vivo rat carotid arterial flow. Results of the simulated images show that the new algorithm produces much smaller bias from the known displacements. For laminar flow, the new algorithm results in 1.1% deviation from the analytically derived value, and 8.8% for the conventional algorithm. The vector quality evaluation for the rotational flow imaging shows that the new algorithm produces better velocity vectors. For in vivo rat carotid arterial flow imaging, the results from the new algorithm deviate 6.6% from the Doppler-measured peak velocities averagely compared to 15% of that from the conventional algorithm. The new Echo PIV algorithm is able to effectively improve the measurement accuracy in imaging flow fields with high velocity gradients.

PIV-measured versus CFD-predicted flow dynamics in anatomically realistic cerebral aneurysm models.

Science.gov (United States)

Ford, Matthew D; Nikolov, Hristo N; Milner, Jaques S; Lownie, Stephen P; Demont, Edwin M; Kalata, Wojciech; Loth, Francis; Holdsworth, David W; Steinman, David A

2008-04-01

Computational fluid dynamics (CFD) modeling of nominally patient-specific cerebral aneurysms is increasingly being used as a research tool to further understand the development, prognosis, and treatment of brain aneurysms. We have previously developed virtual angiography to indirectly validate CFD-predicted gross flow dynamics against the routinely acquired digital subtraction angiograms. Toward a more direct validation, here we compare detailed, CFD-predicted velocity fields against those measured using particle imaging velocimetry (PIV). Two anatomically realistic flow-through phantoms, one a giant internal carotid artery (ICA) aneurysm and the other a basilar artery (BA) tip aneurysm, were constructed of a clear silicone elastomer. The phantoms were placed within a computer-controlled flow loop, programed with representative flow rate waveforms. PIV images were collected on several anterior-posterior (AP) and lateral (LAT) planes. CFD simulations were then carried out using a well-validated, in-house solver, based on micro-CT reconstructions of the geometries of the flow-through phantoms and inlet/outlet boundary conditions derived from flow rates measured during the PIV experiments. PIV and CFD results from the central AP plane of the ICA aneurysm showed a large stable vortex throughout the cardiac cycle. Complex vortex dynamics, captured by PIV and CFD, persisted throughout the cardiac cycle on the central LAT plane. Velocity vector fields showed good overall agreement. For the BA, aneurysm agreement was more compelling, with both PIV and CFD similarly resolving the dynamics of counter-rotating vortices on both AP and LAT planes. Despite the imposition of periodic flow boundary conditions for the CFD simulations, cycle-to-cycle fluctuations were evident in the BA aneurysm simulations, which agreed well, in terms of both amplitudes and spatial distributions, with cycle-to-cycle fluctuations measured by PIV in the same geometry. The overall good agreement

Application of Stereo PIV on a Supersonic Parachute Model

Science.gov (United States)

Wernet, Mark P.; Locke, Randy J.; Wroblewski, Adam; Sengupta, Anita

2009-01-01

The Mars Science Laboratory (MSL) is the next step in NASA's Mars Exploration Program, currently scheduled for 2011. The spacecraft's descent into the Martian atmosphere will be slowed from Mach 2 to subsonic speeds via a large parachute system with final landing under propulsive control. A Disk-Band-Gap (DBG) parachute will be used on MSL similar to the designs that have been used on previous missions, however; the DBG parachute used by MSL will be larger (21.5 m) than in any of the previous missions due to the weight of the payload and landing site requirements. The MSL parachute will also deploy at higher Mach number (M 2) than previous parachutes, which can lead to instabilities in canopy performance. Both the increased size of the DBG above previous demonstrated configurations and deployment at higher Mach numbers add uncertainty to the deployment, structural integrity and performance of the parachute. In order to verify the performance of the DBG on MSL, experimental testing, including acquisition of Stereo Particle Imaging Velocimetry (PIV) measurements were required for validating CFD predictions of the parachute performance. A rigid model of the DBG parachute was tested in the 10x10 foot wind tunnel at GRC. Prior to the MSL tests, a PIV system had never been used in the 10x10 wind tunnel. In this paper we discuss some of the technical challenges overcome in implementing a Stereo PIV system with a 750x400 mm field-of-view in the 10x10 wind tunnel facility and results from the MSL hardshell canopy tests.

Performance and analysis by particle image velocimetry (PIV) of cooker-top burners in Thailand

International Nuclear Information System (INIS)

Makmool, U.; Jugjai, S.; Tia, S.; Vallikul, P.; Fungtammasan, B.

2007-01-01

Cooker-top burners are used extensively in Thailand because of the rapid combustion and high heating-rates created by an impinging flame, which is characteristic of these types of burners. High thermal efficiency with low level of CO emissions is the most important performance criteria for these burners. The wide variation in reported performances of the burners appears to be due to the ad hoc knowledge gained through trial and error of the local manufacturers rather than sound scientific principles. This is extremely undesirable in view of safety, energy conservation and environmental protection. In the present work, a nationwide cooker-top burner performance survey and an implementation of a PIV technique to analyze the burner performance as well as advising local manufacturers were carried out. Experimental data were reported for the base line value of thermal efficiency of all the burners. The thermal performance parameters and dynamic properties of the flow field at a flame impingement area, i.e. velocity magnitude, turbulent intensity, vorticity and strain rate were also reported as a function of burner type, which was categorized into four types based on the configuration of the burner head: radial flow burners, swirling flow burners, vertical flow burners and porous radiant burners

Validation of a numerical FSI simulation of an aortic BMHV by in vitro PIV experiments.

Science.gov (United States)

Annerel, S; Claessens, T; Degroote, J; Segers, P; Vierendeels, J

2014-08-01

In this paper, a validation of a recently developed fluid-structure interaction (FSI) coupling algorithm to simulate numerically the dynamics of an aortic bileaflet mechanical heart valve (BMHV) is performed. This validation is done by comparing the numerical simulation results with in vitro experiments. For the in vitro experiments, the leaflet kinematics and flow fields are obtained via the particle image velocimetry (PIV) technique. Subsequently, the same case is numerically simulated by the coupling algorithm and the resulting leaflet kinematics and flow fields are obtained. Finally, the results are compared, revealing great similarity in leaflet motion and flow fields between the numerical simulation and the experimental test. Therefore, it is concluded that the developed algorithm is able to capture very accurately all the major leaflet kinematics and dynamics and can be used to study and optimize the design of BMHVs. Copyright © 2014 IPEM. Published by Elsevier Ltd. All rights reserved.

Three-dimensional temporally resolved measurements of turbulence-flame interactions using orthogonal-plane cinema-stereoscopic PIV

Energy Technology Data Exchange (ETDEWEB)

Steinberg, Adam Michael; Driscoll, James F. [University of Michigan, Department of Aerospace Engineering, Ann Arbor, MI (United States); Ceccio, Steven L. [University of Michigan, Department of Mechanical Engineering, Ann Arbor, MI (United States)

2009-09-15

A new orthogonal-plane cinema-stereoscopic particle image velocimetry (OPCS-PIV) diagnostic has been used to measure the dynamics of three-dimensional turbulence-flame interactions. The diagnostic employed two orthogonal PIV planes, with one aligned perpendicular and one aligned parallel to the streamwise flow direction. In the plane normal to the flow, temporally resolved slices of the nine-component velocity gradient tensor were determined using Taylor's hypothesis. Volumetric reconstruction of the 3D turbulence was performed using these slices. The PIV plane parallel to the streamwise flow direction was then used to measure the evolution of the turbulence; the path and strength of 3D turbulent structures as they interacted with the flame were determined from their image in this second plane. Structures of both vorticity and strain-rate magnitude were extracted from the flow. The geometry of these structures agreed well with predictions from direct numerical simulations. The interaction of turbulent structures with the flame also was observed. In three dimensions, these interactions had complex geometries that could not be reflected in either planar measurements or simple flame-vortex configurations. (orig.)

Time-Resolved Particle Image Velocimetry Measurements with Wall Shear Stress and Uncertainty Quantification for the FDA Nozzle Model.

Science.gov (United States)

Raben, Jaime S; Hariharan, Prasanna; Robinson, Ronald; Malinauskas, Richard; Vlachos, Pavlos P

2016-03-01

We present advanced particle image velocimetry (PIV) processing, post-processing, and uncertainty estimation techniques to support the validation of computational fluid dynamics analyses of medical devices. This work is an extension of a previous FDA-sponsored multi-laboratory study, which used a medical device mimicking geometry referred to as the FDA benchmark nozzle model. Experimental measurements were performed using time-resolved PIV at five overlapping regions of the model for Reynolds numbers in the nozzle throat of 500, 2000, 5000, and 8000. Images included a twofold increase in spatial resolution in comparison to the previous study. Data was processed using ensemble correlation, dynamic range enhancement, and phase correlations to increase signal-to-noise ratios and measurement accuracy, and to resolve flow regions with large velocity ranges and gradients, which is typical of many blood-contacting medical devices. Parameters relevant to device safety, including shear stress at the wall and in bulk flow, were computed using radial basis functions. In addition, in-field spatially resolved pressure distributions, Reynolds stresses, and energy dissipation rates were computed from PIV measurements. Velocity measurement uncertainty was estimated directly from the PIV correlation plane, and uncertainty analysis for wall shear stress at each measurement location was performed using a Monte Carlo model. Local velocity uncertainty varied greatly and depended largely on local conditions such as particle seeding, velocity gradients, and particle displacements. Uncertainty in low velocity regions in the sudden expansion section of the nozzle was greatly reduced by over an order of magnitude when dynamic range enhancement was applied. Wall shear stress uncertainty was dominated by uncertainty contributions from velocity estimations, which were shown to account for 90-99% of the total uncertainty. This study provides advancements in the PIV processing methodologies over

Towed underwater PIV measurement for free-surface effects on turbulent wake of a surface-piercing body

Directory of Open Access Journals (Sweden)

Dong Myung Seol

2013-09-01

Full Text Available In the present study, a towed underwater particle image velocimetry (PIV system was validated in uniform flow and used to investigate the free-surface effects on the turbulent wake of a simple surface-piercing body. The selected test model was a cylindrical geometry formed by extruding the Wigley hull's waterplane shape in the vertical direction. Due to the constraints of the two-dimensional (2D PIV system used for the present study, the velocity field measurements were done separately for the vertical and horizontal planes. Using the measured data at several different locations, it was possible to identify the free-surface effects on the turbulent wake in terms of the mean velocity components and turbulence quantities. In order to provide an accuracy level of the data, uncertainty assessment was done following the International Towing Tank Conference standard procedure.

Characterization of extrusion flow using particle image velocimetry

Directory of Open Access Journals (Sweden)

2009-09-01

Full Text Available The aim of this study was the characterization of polymer flows within an extrusion die using particle image velocimetry (PIV in very constraining conditions (high temperature, pressure and velocity. Measurements were realized on semi-industrial equipments in order to have test conditions close to the industrial ones. Simple flows as well as disrupted ones were studied in order to determine the capabilities and the limits of the method. The analysis of the velocity profiles pointed out significant wall slip, which was confirmed by rheological measurements based on Mooney's method. Numerical simulations were used to connect the two sets of measurements and to simulate complex velocity profiles for comparison to the experimental ones. A good agreement was found between simulations and experiments providing wall slip is taken into account in the simulation.

Measurement of rotation and strain-rate tensors by using stereoscopic PIV

DEFF Research Database (Denmark)

Özcan, O.; Meyer, Knud Erik; Larsen, Poul Scheel

2004-01-01

A simple technique is described for measuring the mean rate-of-displacement (velocity gradient) tensor in a plane by using a conventional stereoscopic PIV system. The technique involves taking PIV data in two or three closely-spaced parallel planes at different times. All components of the mean...... are presented to show the applicability of the proposed technique. The PIV cameras and light sheet optics shown in Fig. 1a are mounted on the same traverse mechanism in order to displace the measurement plane accurately. Data obtained in constant-y and -z planes are presented. Fig. 1b shows a contour plot...

Investigation of Aerodynamic Interference in a Multirotor by PIV Method

Directory of Open Access Journals (Sweden)

Zbigniew Czyż

2018-03-01

Full Text Available This paper presents part of the investigation into aerodynamics of the vertical take-off and landing multirotor. There are described the technology to design a research object and the Particle Image Velocimetry (PIV setup to measure airflow around the aircraft. The around-the-aircraft speed distribution was investigated for an angle of attack of 0o and for four different configurations. The results are presented in form of vector velocity field of airflow on the plane of symmetry of the test object. The results enabled the characteristics of speed vs. the distance from the fuselage. It was observed that the push propeller and the main rotor impact the speed field around the fuselage.

An efficient simultaneous reconstruction technique for tomographic particle image velocimetry

Science.gov (United States)

Atkinson, Callum; Soria, Julio

2009-10-01

To date, Tomo-PIV has involved the use of the multiplicative algebraic reconstruction technique (MART), where the intensity of each 3D voxel is iteratively corrected to satisfy one recorded projection, or pixel intensity, at a time. This results in reconstruction times of multiple hours for each velocity field and requires considerable computer memory in order to store the associated weighting coefficients and intensity values for each point in the volume. In this paper, a rapid and less memory intensive reconstruction algorithm is presented based on a multiplicative line-of-sight (MLOS) estimation that determines possible particle locations in the volume, followed by simultaneous iterative correction. Reconstructions of simulated images are presented for two simultaneous algorithms (SART and SMART) as well as the now standard MART algorithm, which indicate that the same accuracy as MART can be achieved 5.5 times faster or 77 times faster with 15 times less memory if the processing and storage of the weighting matrix is considered. Application of MLOS-SMART and MART to a turbulent boundary layer at Re θ = 2200 using a 4 camera Tomo-PIV system with a volume of 1,000 × 1,000 × 160 voxels is discussed. Results indicate improvements in reconstruction speed of 15 times that of MART with precalculated weighting matrix, or 65 times if calculation of the weighting matrix is considered. Furthermore the memory needed to store a large weighting matrix and volume intensity is reduced by almost 40 times in this case.

PIV measurements in a compact return diffuser under multi-conditions

International Nuclear Information System (INIS)

Zhou, L; Lu, W G; Shi, W D

2013-01-01

Due to the complex three-dimensional geometries of impellers and diffusers, their design is a delicate and difficult task. Slight change could lead to significant changes in hydraulic performance and internal flow structure. Conversely, the grasp of the pump's internal flow pattern could benefit from pump design improvement. The internal flow fields in a compact return diffuser have been investigated experimentally under multi-conditions. A special Particle Image Velocimetry (PIV) test rig is designed, and the two-dimensional PIV measurements are successfully conducted in the diffuser mid-plane to capture the complex flow patterns. The analysis of the obtained results has been focused on the flow structure in diffuser, especially under part-load conditions. The vortex and recirculation flow patterns in diffuser are captured and analysed accordingly. Strong flow separation and back flow appeared at the part-load flow rates. Under the design and over-load conditions, the flow fields in diffuser are uniform, and the flow separation and back flow appear at the part-load flow rates, strong back flow is captured at one diffuser passage under 0.2Q des

DHMPIV and Tomo-PIV measurements of three-dimensional structures in a turbulent boundary layer

Science.gov (United States)

Amili, O.; Atkinson, C.; Soria, J.

In turbulent boundary layers, a large portion of total turbulence production happens in the near wall region, y/δ memory intensive reconstruction algorithm. It is based on a multiplicative line-of-sight (MLOS) estimation that determines possible particle locations in the volume, followed by simultaneous iterative correction. Application of MLOS-SART and MART to a turbulent boundary layer at Refθ=2200 using a 4 camera Tomo-PIV system with a volume of 1000×1000×160 voxels is discussed. In addition, near wall velocity measurement attempt made by digital holographic microscopic particle image velocimetry (DHMPIV). The technique provides a solution to overcome the poor axial accuracy and the low spatial resolution which are common problems in digital holography [5]. By reducing the depth of focus by at least one order of magnitude as well as increasing the lateral spatial resolution, DHMPIV provides the opportunity to resolve the small-scale structures existing in near wall layers.

Investigation of the shape change of bio-flocs and its influence on mass transport using particle image velocimetry.

Science.gov (United States)

Ren, T T; Xiao, F; Sun, W J; Sun, F Y; Lam, K M; Li, X Y

2014-01-01

In this laboratory study, an advanced flow visualization technique - particle image velocimetry (PIV) - was employed to investigate the change of shape of activated sludge flocs in water and its influence on the material transport characteristics of the flocs. The continuous shape change of the bio-flocs that occurred within a very short period of time could be captured by the PIV system. The results demonstrate that the fluid turbulence caused the shift of parts of a floc from one side to the other in less than 200 ms. During the continuous shape change, the liquid within the floc was forced out of the floc, which was then refilled with the liquid from the surrounding flow. For the bio-flocs saturated with a tracer dye, it was shown that the dye could be released from the flocs at a faster rate when the flocs were swayed around in water. The experimental results indicate that frequent shape change of bio-flocs facilitates the exchange of fluid and materials between the floc interior and the surrounding water. This mass transfer mechanism can be more important than molecular diffusion and internal permeation to the function and behavior of particle aggregates, including bio-flocs, in natural waters and treatment systems.

Simultaneous wall-shear-stress and wide-field PIV measurements in a turbulent boundary layer

Science.gov (United States)

Gomit, Guillaume; Fourrie, Gregoire; de Kat, Roeland; Ganapathisubramani, Bharathram

2015-11-01

Simultaneous particle image velocimetry (PIV) and hot-film shear stress sensor measurements were performed to study the large-scale structures associated with shear stress events in a flat plate turbulent boundary layer at a high Reynolds number (Reτ ~ 4000). The PIV measurement was performed in a streamwise-wall normal plane using an array of six high resolution cameras (4 ×16MP and 2 ×29MP). The resulting field of view covers 8 δ (where δ is the boundary layer thickness) in the streamwise direction and captures the entire boundary layer in the wall-normal direction. The spatial resolution of the measurement is approximately is approximately 70 wall units (1.8 mm) and sampled each 35 wall units (0.9 mm). In association with the PIV setup, a spanwise array of 10 skin-friction sensors (spanning one δ) was used to capture the footprint of the large-scale structures. This combination of measurements allowed the analysis of the three-dimensional conditional structures in the boundary layer. Particularly, from conditional averages, the 3D organisation of the wall normal and streamwise velocity components (u and v) and the Reynolds shear stress (-u'v') related to a low and high shear stress events can be extracted. European Research Council Grant No-277472-WBT.

Three-dimensional three-component particle velocimetry for microscale flows using volumetric scanning

International Nuclear Information System (INIS)

Klein, S A; Moran, J L; Posner, J D; Frakes, D H

2012-01-01

We present a diagnostic platform for measuring three-dimensional three-component (3D3C) velocity fields in microscopic volumes. The imaging system uses high-speed Nipkow spinning disk confocal microscopy. Confocal microscopy provides optical sectioning using pinhole spatial filtering which rejects light originating from out-of-focus objects. The system accomplishes volumetric scanning by rapid translation of the high numerical aperture objective using a piezo objective positioner. The motion of fluorescent microspheres is quantified using 3D3C super resolution particle-imaging velocimetry with instantaneous spatial resolutions of the order of 5 µm or less in all three dimensions. We examine 3D3C flow in a PDMS microchannel with an expanding section at 3D acquisition rates of 30 Hz, and find strong agreement with a computational model. Equations from the PIV and PTV literature adapted for a scanning objective provide estimates of maximum measurable velocity. The technique allows for isosurface visualization of 3D particle motion and robust high spatial resolution velocity measurements without requiring a calibration step or reconstruction algorithms. (paper)

Velocity field measurements in an evaporating sessile droplet by means of micro-PIV technique

Directory of Open Access Journals (Sweden)

Yagodnitsyna Anna

2016-01-01

Full Text Available Velocity fields are measured in evaporating sessile droplets on two substrates with different contact angles and contact angle hysteresis using micro resolution particle image velocimetry technique. Different flow patterns are observed in different stages of droplet evaporation: a flow with vortices and a radial flow. Flow structure is found to be similar for droplets on different substrates.

PIV measurement of the flow field in a domestic refrigerator model: Comparison with 3D simulations

Energy Technology Data Exchange (ETDEWEB)

Ben Amara, S.; Laguerre, O.; Flick, D. [UMR Genie Industriel Alimentaire (Cemagref-AgroParisTech-INRA) - Cemagref, Parc de Tourvoie, BP 44, 92185 Antony Cedex (France); Charrier-Mojtabi, M.-C.; Lartigue, B. [Universite Paul Sabatier, Laboratoire PHASE, E.A. 3208, 118 route de Narbonne, 31062 Toulouse Cedex 4 (France)

2008-12-15

PIV (particle image velocimetry) measurements of flow field due to natural convection in a parallelepipedic enclosure representing a domestic refrigerator model (scale 1) have been undertaken in order to determine the thickness of the hydrodynamic boundary layers and to study the flow motions depending on the boundary conditions applied on the vertical walls. One of the vertical walls is maintained at a negative and constant temperature either on the totality or on one part of its surface: this wall acts as the evaporator. The other walls are in contact with external air at constant temperature. The velocity measurements have been made in the symmetry plane of the enclosure. Unsteady recirculations have been observed at the bottom of the cavity. The influence of both the temperature and the dimension of the cold wall has been studied. Numerical simulations using CFD software (Fluent) have been then performed. In the numerical model, we assumed that the temperature of the evaporator is constant while an uniform global heat transfer coefficient has been used to describe the heat exchange with the external air at constant temperature. We considered laminar 3D flows and took into account the heat transfer by radiation between the different walls of the cavity. The results obtained with the 3D numerical simulations are in quite good agreement with the experimental airflow measurements using the PIV technique. (author)

Proper orthogonal decomposition-based estimations of the flow field from particle image velocimetry wall-gradient measurements in the backward-facing step flow

International Nuclear Information System (INIS)

Nguyen, Thien Duy; Wells, John Craig; Mokhasi, Paritosh; Rempfer, Dietmar

2010-01-01

In this paper, particle image velocimetry (PIV) results from the recirculation zone of a backward-facing step flow, of which the Reynolds number is 2800 based on bulk velocity upstream of the step and step height (h = 16.5 mm), are used to demonstrate the capability of proper orthogonal decomposition (POD)-based measurement models. Three-component PIV velocity fields are decomposed by POD into a set of spatial basis functions and a set of temporal coefficients. The measurement models are built to relate the low-order POD coefficients, determined from an ensemble of 1050 PIV fields by the 'snapshot' method, to the time-resolved wall gradients, measured by a near-wall measurement technique called stereo interfacial PIV. These models are evaluated in terms of reconstruction and prediction of the low-order temporal POD coefficients of the velocity fields. In order to determine the estimation coefficients of the measurement models, linear stochastic estimation (LSE), quadratic stochastic estimation (QSE), principal component regression (PCR) and kernel ridge regression (KRR) are applied. We denote such approaches as LSE-POD, QSE-POD, PCR-POD and KRR-POD. In addition to comparing the accuracy of measurement models, we introduce multi-time POD-based estimations in which past and future information of the wall-gradient events is used separately or combined. The results show that the multi-time estimation approaches can improve the prediction process. Among these approaches, the proposed multi-time KRR-POD estimation with an optimized window of past wall-gradient information yields the best prediction. Such a multi-time KRR-POD approach offers a useful tool for real-time flow estimation of the velocity field based on wall-gradient data

Air flow measurement techniques applied to noise reduction of a centrifugal blower

Science.gov (United States)

Laage, John W.; Armstrong, Ashli J.; Eilers, Daniel J.; Olsen, Michael G.; Mann, J. Adin

2005-09-01

The air flow in a centrifugal blower was studied using a variety of flow and sound measurement techniques. The flow measurement techniques employed included Particle Image Velocimetry (PIV), pitot tubes, and a five hole spherical probe. PIV was used to measure instantaneous and ensemble-averaged velocity fields over large area of the outlet duct as a function of fan position, allowing for the visualization of the flow as it leave the fan blades and progressed downstream. The results from the flow measurements were reviewed along side the results of the sound measurements with the goal of identifying sources of noise and inefficiencies in flow performance. The radiated sound power was divided into broadband and tone noise and measures of the flow. The changes in the tone and broadband sound were compared to changes in flow quantities such as the turbulent kinetic energy and Reynolds stress. Results for each method will be presented to demonstrate the strengths of each flow measurement technique as well as their limitations. Finally, the role that each played in identifying noise sources is described.

Surface pressure and aerodynamic loads determination of a transonic airfoil based on particle image velocimetry

International Nuclear Information System (INIS)

Ragni, D; Ashok, A; Van Oudheusden, B W; Scarano, F

2009-01-01

The present investigation assesses a procedure to extract the aerodynamic loads and pressure distribution on an airfoil in the transonic flow regime from particle image velocimetry (PIV) measurements. The wind tunnel model is a two-dimensional NACA-0012 airfoil, and the PIV velocity data are used to evaluate pressure fields, whereas lift and drag coefficients are inferred from the evaluation of momentum contour and wake integrals. The PIV-based results are compared to those derived from conventional loads determination procedures involving surface pressure transducers and a wake rake. The method applied in this investigation is an extension to the compressible flow regime of that considered by van Oudheusden et al (2006 Non-intrusive load characterization of an airfoil using PIV Exp. Fluids 40 988–92) at low speed conditions. The application of a high-speed imaging system allows the acquisition in relatively short time of a sufficient ensemble size to compute converged velocity statistics, further translated in turbulent fluctuations included in the pressure and loads calculation, notwithstanding their verified negligible influence in the computation. Measurements are performed at varying spatial resolution to optimize the loads determination in the wake region and around the airfoil, further allowing us to assess the influence of spatial resolution in the proposed procedure. Specific interest is given to the comparisons between the PIV-based method and the conventional procedures for determining the pressure coefficient on the surface, the drag and lift coefficients at different angles of attack. Results are presented for the experiments at a free-stream Mach number M = 0.6, with the angle of attack ranging from 0° to 8°

Measurement of acoustic velocity components in a turbulent flow using LDV and high-repetition rate PIV

Science.gov (United States)

Léon, Olivier; Piot, Estelle; Sebbane, Delphine; Simon, Frank

2017-06-01

The present study provides theoretical details and experimental validation results to the approach proposed by Minotti et al. (Aerosp Sci Technol 12(5):398-407, 2008) for measuring amplitudes and phases of acoustic velocity components (AVC) that are waveform parameters of each component of velocity induced by an acoustic wave, in fully turbulent duct flows carrying multi-tone acoustic waves. Theoretical results support that the turbulence rejection method proposed, based on the estimation of cross power spectra between velocity measurements and a reference signal such as a wall pressure measurement, provides asymptotically efficient estimators with respect to the number of samples. Furthermore, it is shown that the estimator uncertainties can be simply estimated, accounting for the characteristics of the measured flow turbulence spectra. Two laser-based measurement campaigns were conducted in order to validate the acoustic velocity estimation approach and the uncertainty estimates derived. While in previous studies estimates were obtained using laser Doppler velocimetry (LDV), it is demonstrated that high-repetition rate particle image velocimetry (PIV) can also be successfully employed. The two measurement techniques provide very similar acoustic velocity amplitude and phase estimates for the cases investigated, that are of practical interest for acoustic liner studies. In a broader sense, this approach may be beneficial for non-intrusive sound emission studies in wind tunnel testings.

Neural network approaches to tracer identification as related to PIV research

International Nuclear Information System (INIS)

Seeley, C.H. Jr.

1992-12-01

Neural networks have become very powerful tools in many fields of interest. This thesis examines the application of neural networks to another rapidly growing field flow visualization. Flow visualization research is used to experimentally determine how fluids behave and to verify computational results obtained analytically. A form of flow visualization, particle image velocimetry (PIV). determines the flow movement by tracking neutrally buoyant particles suspended in the fluid. PIV research has begun to improve rapidly with the advent of digital imagers, which can quickly digitize an image into arrays of grey levels. These grey level arrays are analyzed to determine the location of the tracer particles. Once the particles positions have been determined across multiple image frames, it is possible to track their movements, and hence, the flow of the fluid. This thesis explores the potential of several different neural networks to identify the positions of the tracer particles. Among these networks are Backpropagation, Kohonen (counter-propagation), and Cellular. Each of these algorithms were employed in their basic form, and training and testing were performed on a synthetic grey level array. Modifications were then made to them in attempts to improve the results

Neural network approaches to tracer identification as related to PIV research

Energy Technology Data Exchange (ETDEWEB)

Seeley, C.H. Jr.

1992-12-01

Neural networks have become very powerful tools in many fields of interest. This thesis examines the application of neural networks to another rapidly growing field flow visualization. Flow visualization research is used to experimentally determine how fluids behave and to verify computational results obtained analytically. A form of flow visualization, particle image velocimetry (PIV). determines the flow movement by tracking neutrally buoyant particles suspended in the fluid. PIV research has begun to improve rapidly with the advent of digital imagers, which can quickly digitize an image into arrays of grey levels. These grey level arrays are analyzed to determine the location of the tracer particles. Once the particles positions have been determined across multiple image frames, it is possible to track their movements, and hence, the flow of the fluid. This thesis explores the potential of several different neural networks to identify the positions of the tracer particles. Among these networks are Backpropagation, Kohonen (counter-propagation), and Cellular. Each of these algorithms were employed in their basic form, and training and testing were performed on a synthetic grey level array. Modifications were then made to them in attempts to improve the results.

Investigation of Unsteady Flow Behavior in Transonic Compressor Rotors with LES and PIV Measurements

Science.gov (United States)

Hah, Chunill; Voges, Melanie; Mueller, Martin; Schiffer, Heinz-Peter

2009-01-01

In the present study, unsteady flow behavior in a modern transonic axial compressor rotor is studied in detail with large eddy simulation (LES) and particle image velocimetry (PIV). The main purpose of the study is to advance the current understanding of the flow field near the blade tip in an axial transonic compressor rotor near the stall and peak-efficiency conditions. Flow interaction between the tip leakage vortex and the passage shock is inherently unsteady in a transonic compressor. Casing-mounted unsteady pressure transducers have been widely applied to investigate steady and unsteady flow behavior near the casing. Although many aspects of flow have been revealed, flow structures below the casing cannot be studied with casing-mounted pressure transducers. In the present study, unsteady velocity fields are measured with a PIV system and the measured unsteady flow fields are compared with LES simulations. The currently applied PIV measurements indicate that the flow near the tip region is not steady even at the design condition. This self-induced unsteadiness increases significantly as the compressor rotor operates near the stall condition. Measured data from PIV show that the tip clearance vortex oscillates substantially near stall. The calculated unsteady characteristics of the flow from LES agree well with the PIV measurements. Calculated unsteady flow fields show that the formation of the tip clearance vortex is intermittent and the concept of vortex breakdown from steady flow analysis does not seem to apply in the current flow field. Fluid with low momentum near the pressure side of the blade close to the leading edge periodically spills over into the adjacent blade passage. The present study indicates that stall inception is heavily dependent on unsteady behavior of the flow field near the leading edge of the blade tip section for the present transonic compressor rotor.

PIV study of flow around unsteady airfoil with dynamic trailing-edge flap deflection

Energy Technology Data Exchange (ETDEWEB)

Gerontakos, P.; Lee, T. [McGill University, Department of Mechanical Engineering, Montreal, Quebec (Canada)

2008-12-15

The flow around an oscillating NACA 0015 airfoil with prescheduled trailing-edge flap motion control was investigated by using particle image velocimetry (PIV). Aerodynamic load coefficients, obtained via surface pressure measurements, were also acquired to supplement the PIV results. The results demonstrate that upward flap deflections led to an improved negative peak pitching moment coefficient C{sub m,peak}, mainly as a consequence of the increased suction pressure on the lower surface of the flap. The behavior of the leading-edge vortex (LEV) was largely unaffected. Its strength was, however, reduced slightly compared to that of the uncontrolled airfoil. No trailing-edge vortex was observed. For downward flap deflection, the strength of the LEV was found to be slightly increased. A favorable increase in C{sub l,max}, as a consequence of downward flap-induced positive camber effects, accompanied by a detrimental increase in the nose-down C{sub m,peak}, due to the large pressure increase on the lower surface of the flap, was also observed. (orig.)

Tomographic particle image velocimetry of a water-jet for low volume harvesting of fat tissue for regenerative medicine

Directory of Open Access Journals (Sweden)

Drobek Christoph

2015-09-01

Full Text Available Particle Image Velocimetry (PIV measurements of a water-jet for water-assisted liposuction (WAL are carried out to investigate the distribution of velocity and therefore momentum and acting force on the human sub-cutaneous fat tissue. These results shall validate CFD simulations and force sensor measurements of the water-jet and support the development of a new WAL device that is able to harvest low volumes of fat tissue for regenerative medicine even gentler than regular WAL devices.

TR-PIV Performance Test for a Flow Field Measurement in a Single Rod Test Section

International Nuclear Information System (INIS)

Park, Ju Yong; Shin, Chang Hwan; Lee, Chi Young; Oh, Dong Seok; In, Wang Kee

2011-01-01

For large enhancement of performance of Pressurized Water Reactor(PWR), dual-cooled fuel is being developed in Korea Atomic Energy Research Institute(KAERI). This nuclear fuel is a ring shape fuel which is different from conventional cylindrical nuclear fuel and cooling water flows both inner and outer channel. For this fuel, it widens the surface area. But it is bigger outer diameter of fuel rods. So, interval between fuel rods narrows. This because of outer channel flow is unstable. So, measurement of turbulence flow and perturbation that influence in heat transfer elevation is important.. To understand heat transfer characteristics by turbulence, measurement of flow perturbation element is necessary. To measure these turbulence characteristics, hot wire anemometer is widely used. However, it has many disadvantages such as low durability of prove, and big probe size. For these reasons, TR-PIV(Time-Resolved Particle Image Velocimetry) system is employed for better flow measurement in our research institute. TR-PIV system is consisted of laser system and high-speed camera that have high frequency. So, was judged that can measurement complicated turbulence flow and perturbation. In this paper, introduce TR-PIV system, and with results acquiring in single rod flow through this system, and wish to introduce about after this practical use plan

PIV measurement of the complex and transient cross-flow over a circular cylinder

International Nuclear Information System (INIS)

Kuwabara, Joji; Someya, Satoshi; Okamoto, Koji

2007-01-01

This paper describe about measurement for the complex and transient cross-flow over a circular cylinder with the dynamic (time resolved) PIV (particle image velocimetry) techniques. The experiment was carried out water flow tunnel with a working section of 50x50 mm, at the Reynolds number 6.7 x 10 3 to 2.7 x 10 4 . This circular cylinder constructed with MEXFLON resin, the end of circular cylinder is rigidly supported and the other is free. The MEXFLON is fluorine resin; its refractive index is almost same as the water with high transparency. Very high speed water flow among the test section had been clearly visualized and captured by high speed camera. The fluctuations of the flow structure also are clearly obtained with high spatial and high temporal resolution, 512x512pixel with 10,000fps. It corresponds to set up number of thousands LDV array at the test section. Consequently, we found there are asynchronous vibration between parallel-ward and perpendicular-ward to main flow. (author)

Development and Application of PIV in Supersonic flows

Science.gov (United States)

Rong, Z.; Liu, H.; Chen, F.

2011-09-01

This paper presents PIV measurements obtained in Mach 4.0 flowfields performed in the SJTU Hypersonic wind tunnel (HWT). In order to certificate this technique, PIV experiments were conducted to the empty test section to provide uniform flow data for comparison with analysis data. Dynamical properties of particle tracers were investigated to measure the particle response across an oblique shock wave. The flow over a sharp cone at Ma = 4.0 were tested in comparasion with the CFD and schlieren visualization. It is shown that shock wave angles measured with PIV are in good agreement with theory and schlieren visualization, in addition the overall flow is consistent with the CFD results.

A method for three-dimensional interfacial particle image velocimetry (3D-IPIV) of an air–water interface

International Nuclear Information System (INIS)

Turney, Damon E; Anderer, Angelika; Banerjee, Sanjoy

2009-01-01

A new stereoscopic method for collecting particle image velocimetry (PIV) measurements within ∼1 mm of a wavy air–water interface with simultaneous measurements of the morphology of the interface is described. The method, termed three-dimensional interfacial particle image velocimetry (3D-IPIV), is tested in a wind wave channel with a wind speed of 5.8 m s −1 , water depth of 10 cm and a fetch of ∼9 m. Microscale breaking waves populate the interface and their flow patterns are clearly visible in the velocimetry results. The associated capillary waves and surface divergence patterns are observed. Several statistical measurements of the flow are compared with independent measurements and good agreement is found. The method shows great promise for investigating the transfer of momentum, heat and gases across an air–water interface, both in the laboratory and in field settings. Additional methods are described for manufacturing the flow tracers needed for the 3D-IPIV method. These tracers are likely to be useful for other researchers, and have the characteristics of being fluorescent, neutrally buoyant, non-toxic, monodisperse, inexpensive and easy to manufacture

A high-order time-accurate interrogation method for time-resolved PIV

International Nuclear Information System (INIS)

Lynch, Kyle; Scarano, Fulvio

2013-01-01

A novel method is introduced for increasing the accuracy and extending the dynamic range of time-resolved particle image velocimetry (PIV). The approach extends the concept of particle tracking velocimetry by multiple frames to the pattern tracking by cross-correlation analysis as employed in PIV. The working principle is based on tracking the patterned fluid element, within a chosen interrogation window, along its individual trajectory throughout an image sequence. In contrast to image-pair interrogation methods, the fluid trajectory correlation concept deals with variable velocity along curved trajectories and non-zero tangential acceleration during the observed time interval. As a result, the velocity magnitude and its direction are allowed to evolve in a nonlinear fashion along the fluid element trajectory. The continuum deformation (namely spatial derivatives of the velocity vector) is accounted for by adopting local image deformation. The principle offers important reductions of the measurement error based on three main points: by enlarging the temporal measurement interval, the relative error becomes reduced; secondly, the random and peak-locking errors are reduced by the use of least-squares polynomial fits to individual trajectories; finally, the introduction of high-order (nonlinear) fitting functions provides the basis for reducing the truncation error. Lastly, the instantaneous velocity is evaluated as the temporal derivative of the polynomial representation of the fluid parcel position in time. The principal features of this algorithm are compared with a single-pair iterative image deformation method. Synthetic image sequences are considered with steady flow (translation, shear and rotation) illustrating the increase of measurement precision. An experimental data set obtained by time-resolved PIV measurements of a circular jet is used to verify the robustness of the method on image sequences affected by camera noise and three-dimensional motions. In

Enhancing Tomo-PIV reconstruction quality by reducing ghost particles

International Nuclear Information System (INIS)

De Silva, C M; Baidya, R; Marusic, I

2013-01-01

A technique to enhance the reconstruction quality and consequently the accuracy of the velocity vector field obtained in Tomo-PIV experiments is presented here. The methodology involves detecting and eliminating spurious outliers in the reconstructed intensity field (ghost particles). A simulacrum matching-based reconstruction enhancement (SMRE) technique is proposed, which utilizes the characteristic shape and size of actual particles to remove ghost particles in the reconstructed intensity field. An assessment of SMRE is performed by a quantitative comparison of Tomo-PIV simulation results and DNS data, together with a comparison to Tomo-PIV experimental data measured in a turbulent channel flow at a matched Reynolds number (Re τ = 937) to the DNS study. For the simulation data, a comparative study is performed on the reconstruction quality based on an ideal reconstruction determined from known particle positions. The results suggest that a significant improvement in the reconstruction quality and flow statistics is achievable at typical seeding densities used in Tomo-PIV experiments. This improvement is further amplified at higher seeding densities, enabling the use of up to twice the typical seeding densities currently used in Tomo-PIV experiments. A reduction of spurious vectors present in the velocity field is also observed based on a median outlier detection criterion. The application of SMRE to Tomo-PIV experimental data shows an improvement in flow statistics, comparable to the improvement seen in simulations. Finally, due to the non-iterative nature of SMRE, the increase in processing time is marginal since only a single pass of the reconstruction algorithm is required. (paper)

A LIF-PIV investigation of turbulence induced by sprays

Science.gov (United States)

van der Voort, Dennis; Dam, Nico; van de Water, Willem; Clercx, Herman

2017-11-01

During the breakup of a high-speed liquid jet, it drags along and mixes the air surrounding it, creating turbulence. This turbulence can, in turn, influence the dispersion of the droplets in the resulting spray. Very little is known about the small-scale characteristics of the ambient turbulent flow. This work investigated spray-induced turbulence using (gas-phase) laser-induced fluorescent tracer particle image velocimetry (LIF-PIV), which suppresses the strong light scattering of jet and droplets on the images. The results for both a heptane (h) and water (w) spray (135 m/s and 125 m/s respectively) show that the heptane spray generates stronger turbulence due to the difference in breakup between the two fluids. Using a large-eddy estimation, carefully compensating for the finite size of the PIV windows, the dissipation rate ɛ and the small-scale turbulence characteristics are estimated as ɛh = 190 +/-25 m2s-3, ɛw = 120 +/-30 m2s-3, Reλ,h = 380 +/-40, Reλ,w = 290 +/-40, ηh = 65 +/-3 μm, and ηw = 75 +/-5 μm. We will discuss the influence of the turbulent fluctuations in the surrounding air on the dispersion of droplets. This work is part of the research programme of the Foundation for Fundamental Research on Matter (FOM), which is part of the Dutch Organisation for Scientific Research (NWO).

20  kHz CH2O and OH PLIF with stereo PIV.

Science.gov (United States)

Hammack, Stephen D; Carter, Campbell D; Skiba, Aaron W; Fugger, Christopher A; Felver, Josef J; Miller, Joseph D; Gord, James R; Lee, Tonghun

2018-03-01

Planar laser-induced fluorescence (PLIF) of hydroxyl (OH) and formaldehyde (CH 2 O) radicals was performed alongside stereo particle image velocimetry (PIV) at a 20 kHz repetition rate in a highly turbulent Bunsen flame. A dual-pulse burst-mode laser generated envelopes of 532 nm pulse pairs for PIV as well as a pair of 355 nm pulses, the first of which was used for CH 2 O PLIF. A diode-pumped solid-state Nd:YAG/dye laser system produced the excitation beam for the OH PLIF. The combined diagnostics produced simultaneous, temporally resolved two-dimensional fields of OH and CH 2 O and two-dimensional, three-component velocity fields, facilitating the observation of the interaction of fluid dynamics with flame fronts and preheat layers. The high-fidelity data acquired surpass the previous state of the art and demonstrate dual-pulse burst-mode laser technology with the ability to provide pulse pairs at both 532 and 355 nm with sufficient energy for scattering and fluorescence measurement at 20 kHz.

PIV Investigations of the Flow Field in the Volute of a Rotary Blood Pump

Science.gov (United States)

Sankovic, John M.; Kadambi, Jaikrishnan R.; Smith, William A.; Wernet, Mark P.

2004-01-01

A full-size acrylic model of a rotary blood pump was developed in order to utilize Particle Image Velocimetry (PIV) to make measurements of the fluid velocities and turbulent stresses throughout the device. The development of an understanding of the hemodynamics within the blood pump is critical to the development and validation of computational models. A blood analog solution, consisting of sodium iodide solution and glycerin, was developed to match physiological kinematic viscosity. The refractive indices of the fluid, the pump casing, and the impeller were matched to facilitate the use of PIV to make velocity measurements. Velocity measurements made in the volute exit/diffuser region are presented for pumps speeds of 3000-3850 rpm. At each speed data were obtained at a physiological pressure of 12 kPa and at a maximum flow condition. Four hundred data pairs were used for each resultant mean velocity vector value, representing greater than an order of magnitude more data pairs than reported previously in the literature on similar devices and resulting in velocity uncertainty levels of approximately 22.9%.

Ground-based PIV and numerical flow visualization results from the Surface Tension Driven Convection Experiment

Science.gov (United States)

Pline, Alexander D.; Werner, Mark P.; Hsieh, Kwang-Chung

1991-01-01

The Surface Tension Driven Convection Experiment (STDCE) is a Space Transportation System flight experiment to study both transient and steady thermocapillary fluid flows aboard the United States Microgravity Laboratory-1 (USML-1) Spacelab mission planned for June, 1992. One of the components of data collected during the experiment is a video record of the flow field. This qualitative data is then quantified using an all electric, two dimensional Particle Image Velocimetry (PIV) technique called Particle Displacement Tracking (PDT), which uses a simple space domain particle tracking algorithm. Results using the ground based STDCE hardware, with a radiant flux heating mode, and the PDT system are compared to numerical solutions obtained by solving the axisymmetric Navier Stokes equations with a deformable free surface. The PDT technique is successful in producing a velocity vector field and corresponding stream function from the raw video data which satisfactorily represents the physical flow. A numerical program is used to compute the velocity field and corresponding stream function under identical conditions. Both the PDT system and numerical results were compared to a streak photograph, used as a benchmark, with good correlation.

Experimental research on intraocular aqueous flow by PIV method.

Science.gov (United States)

Yang, Hongyu; Song, Hongfang; Mei, Xi; Li, Lin; Fu, Xineng; Zhang, Mindi; Liu, Zhicheng

2013-10-21

Aqueous humor flows regularly from posterior chamber to anterior chamber, and this flow much involves intraocular pressure, the eye tissue nutrition and metabolism. To visualize and measure the intraocular flow regular pattern of aqueous humor. Intraocular flow in the vitro eyeball is driven to simulate the physiological aqueous humor flow, and the flow field is measured by Particle Image Velocimetry(PIV). Fluorescent particle solution of a certain concentration was infused into the root of Posterior Chamber(PC) of vitro rabbit eye to simulate the generation of aqueous and was drained out at a certain hydrostatic pressure from the angle of Anterior Chamber(AC) to represent the drainage of aqueous. PIV method was used to record and calculate the flow on the midsagittal plane of the eyeball. Velocity vector distribution in AC has been obtained, and the distribution shows symmetry feature to some extent. Fluorescent particle solution first fills the PC as it is continuously infused, then surges into AC through the pupil, flows upwards toward the central cornea, reflecting and scattering, and eventually converges along the inner cornea surface towards the outflow points at the periphery of the eyeball. Velocity values around the pupillary margin are within the range of 0.008-0.012 m/s, which are close to theoretical values of 0.0133 m/s, under the driving rate of 100 μl/min. Flow field of aqueous humor can be measured by PIV method, which makes it possible to study the aqueous humor dynamics by experimental method. Our study provides a basis for experimental research on aqueous humor flow; further, it possibly helps to diagnose and treat eye diseases as shear force damage of ocular tissues and destructions on corneal endothelial cells from the point of intraocular flow field.

THE APPLICATION OF LASERS IN MEASUREMENT OF FLUID FLOW THROUGH DRILLING BIT NOZZLES

Directory of Open Access Journals (Sweden)

Radenko Drakulić

1993-12-01

Full Text Available Two optical methods based on laser and video technology and digital signal and image processing techniques - Laser Doppler velocimetry (LDV and Particle image velocimetry (PIV were applied in highly accurate fluid flow measurement. Their application in jet velocity measurement of flows through drilling bit nozzles is presented. The role of nozzles in drilling technology together with procedures and tests performed on their optimization are reviewed. In addition, some experimental results for circular nozzle obtained both with LDV and PIV are elaborated. The experimental set-up and the testing procedure arc briefly discussed, as well as potential improvements in the design. Possible other applications of LDV and PIV in the domain of petroleum engineering are suggested (the paper is published in Croatian.

PIV Measurements in the 14 x 22 Low Speed Tunnel: Recommendations for Future Testing

Science.gov (United States)

Watson, Ralph D.; Jenkins, Luther N.; Yao, Chung-Sheng; McGinley, Catherine B.; Paschal, Keith B.; Neuhart, Dan H.

2003-01-01

During the period from February 4 to March 21, 2003 stereo digital particle imaging velocimetry measurements were made on a generic high lift model, the Trap Wing, as part of the High Lift Flow Physics Experiment. These measurements were the first PIV measurements made in the NASA, Langley Research Center 14 x 22 Foot Low Speed Tunnel, and several problems were encountered and solved in the acquisition of the data. It is the purpose of this paper to document the solutions to these problems and to make recommendations for further improvements to the tunnel/setup in order to facilitate future measurements of this type.

Particle image velocimetry correlation signal-to-noise ratio metrics and measurement uncertainty quantification

International Nuclear Information System (INIS)

Xue, Zhenyu; Charonko, John J; Vlachos, Pavlos P

2014-01-01

In particle image velocimetry (PIV) the measurement signal is contained in the recorded intensity of the particle image pattern superimposed on a variety of noise sources. The signal-to-noise-ratio (SNR) strength governs the resulting PIV cross correlation and ultimately the accuracy and uncertainty of the resulting PIV measurement. Hence we posit that correlation SNR metrics calculated from the correlation plane can be used to quantify the quality of the correlation and the resulting uncertainty of an individual measurement. In this paper we extend the original work by Charonko and Vlachos and present a framework for evaluating the correlation SNR using a set of different metrics, which in turn are used to develop models for uncertainty estimation. Several corrections have been applied in this work. The SNR metrics and corresponding models presented herein are expanded to be applicable to both standard and filtered correlations by applying a subtraction of the minimum correlation value to remove the effect of the background image noise. In addition, the notion of a ‘valid’ measurement is redefined with respect to the correlation peak width in order to be consistent with uncertainty quantification principles and distinct from an ‘outlier’ measurement. Finally the type and significance of the error distribution function is investigated. These advancements lead to more robust and reliable uncertainty estimation models compared with the original work by Charonko and Vlachos. The models are tested against both synthetic benchmark data as well as experimental measurements. In this work, U 68.5 uncertainties are estimated at the 68.5% confidence level while U 95 uncertainties are estimated at 95% confidence level. For all cases the resulting calculated coverage factors approximate the expected theoretical confidence intervals, thus demonstrating the applicability of these new models for estimation of uncertainty for individual PIV measurements. (paper)

Particle image velocimetry correlation signal-to-noise ratio metrics and measurement uncertainty quantification

Science.gov (United States)

Xue, Zhenyu; Charonko, John J.; Vlachos, Pavlos P.

2014-11-01

In particle image velocimetry (PIV) the measurement signal is contained in the recorded intensity of the particle image pattern superimposed on a variety of noise sources. The signal-to-noise-ratio (SNR) strength governs the resulting PIV cross correlation and ultimately the accuracy and uncertainty of the resulting PIV measurement. Hence we posit that correlation SNR metrics calculated from the correlation plane can be used to quantify the quality of the correlation and the resulting uncertainty of an individual measurement. In this paper we extend the original work by Charonko and Vlachos and present a framework for evaluating the correlation SNR using a set of different metrics, which in turn are used to develop models for uncertainty estimation. Several corrections have been applied in this work. The SNR metrics and corresponding models presented herein are expanded to be applicable to both standard and filtered correlations by applying a subtraction of the minimum correlation value to remove the effect of the background image noise. In addition, the notion of a ‘valid’ measurement is redefined with respect to the correlation peak width in order to be consistent with uncertainty quantification principles and distinct from an ‘outlier’ measurement. Finally the type and significance of the error distribution function is investigated. These advancements lead to more robust and reliable uncertainty estimation models compared with the original work by Charonko and Vlachos. The models are tested against both synthetic benchmark data as well as experimental measurements. In this work, {{U}68.5} uncertainties are estimated at the 68.5% confidence level while {{U}95} uncertainties are estimated at 95% confidence level. For all cases the resulting calculated coverage factors approximate the expected theoretical confidence intervals, thus demonstrating the applicability of these new models for estimation of uncertainty for individual PIV measurements.

Three-dimensional investigation of the two-phase flow structure in a bubbly pipe flow

International Nuclear Information System (INIS)

Hassan, Y.A.; Schmidl, W.D.; Ortiz-Villafuerte, J.

1997-01-01

Particle Image Velocimetry (PIV) is a non-intrusive measurement technique, which can be used to study the structure of various fluid flows. PIV is used to measure the time varying full field velocity data of a particle-seeded flow field within either a two-dimensional plane or three-dimensional volume. PIV is a very efficient measurement technique since it can obtain both qualitative and quantitative spatial information about the flow field being studied. This information can be further processed into information such as vorticity and pathlines. Other flow measurement techniques (Laser Doppler Velocimetry, Hot Wire Anemometry, etc...) only provide quantitative information at a single point. PIV can be used to study turbulence structures if a sufficient amount of data can be acquired and analyzed, and it can also be extended to study two-phase flows if both phases can be distinguished. In this study, the flow structure around a bubble rising in a pipe filled with water was studied in three-dimensions. The velocity of the rising bubble and the velocity field of the surrounding water was measured. Then the turbulence intensities and Reynolds stresses were calculated from the experimental data. (author)

High fidelity phase locked PIV measurements analysing the flow fields surrounding an oscillating piezoelectric fan

International Nuclear Information System (INIS)

Jeffers, Nicholas; Nolan, Kevin; Stafford, Jason; Donnelly, Brian

2014-01-01

Piezoelectric fans have been studied extensively and are seen as a promising technology for thermal management due to their ability to provide quiet, reliable cooling with low power consumption. The fluid mechanics of an unconfined piezoelectric fan are complex which is why the majority of the literature to date confines the fan in an attempt to simplify the flow field. This paper investigates the fluid mechanics of an unconfined fan operating in its first vibration frequency mode. The piezoelectric fan used in this study measures 12.7 mm × 70 mm and resonates at 92.5 Hz in air. A custom built experimental facility was developed to capture the fan's flow field using phase locked Particle Image Velocimetry (PIV). The phase locked PIV results are presented in terms of vorticity and show the formation of a horse shoe vortex. A three dimensional A2 criterion constructed from interpolated PIV measurements was used to identify the vortex core in the vicinity of the fan. This analysis was used to clearly identify the formation of a horse shoe vortex that turns into a hairpin vortex before it breaks up due to a combination of vortex shedding and flow along the fan blade. The results presented in this paper contribute to both the fluid dynamics and heat transfer literature concerning first mode fan oscillation.

PIV Validation of 3D Multicomponent Model for Cold Spray Within Nitrogen and Helium Supersonic Flow Field

Science.gov (United States)

Faizan-Ur-Rab, M.; Zahiri, S. H.; Masood, S. H.; Jahedi, M.; Nagarajah, R.

2017-06-01

This study presents the validation of a developed three-dimensional multicomponent model for cold spray process using two particle image velocimetry (PIV) experiments. The k- ɛ type 3D model developed for spherical titanium particles was validated with the measured titanium particle velocity within a nitrogen and helium supersonic jet. The 3D model predicted lower values of particle velocity than the PIV experimental study that used irregularly shaped titanium particles. The results of the 3D model were consistent with the PIV experiment that used spherical titanium powder. The 3D model simulation of particle velocity within the helium and nitrogen jet was coupled with an estimation of titanium particle temperature. This was achieved with the consideration of the fact that cold spray particle temperature is difficult and expensive to measure due to considerably lower temperature of particles than thermal spray. The model predicted an interesting pattern of particle size distribution with respect to the location of impact with a concentration of finer particles close to the jet center. It is believed that the 3D model outcomes for particle velocity, temperature and location could be a useful tool to optimize system design, deposition process and mechanical properties of the additively manufactured cold spray structures.

Measurement of gas-liquid two-phase flow in bubble columns using ensemble correlation PIV

NARCIS (Netherlands)

Delnoij, E.; Kuipers, J.A.M.; van Swaaij, Willibrordus Petrus Maria; Westerweel, J.

2000-01-01

This paper highlights the development of a new ensemble correlation, multiphase flow PIV technique. The particular approach discussed in this paper is a straightforward extension of single-phase PIV and one of the major advantages of the technique is that it employs a single CCD camera. This

Volume reconstruction optimization for tomo-PIV algorithms applied to experimental data

Science.gov (United States)

Martins, Fabio J. W. A.; Foucaut, Jean-Marc; Thomas, Lionel; Azevedo, Luis F. A.; Stanislas, Michel

2015-08-01

Tomographic PIV is a three-component volumetric velocity measurement technique based on the tomographic reconstruction of a particle distribution imaged by multiple camera views. In essence, the performance and accuracy of this technique is highly dependent on the parametric adjustment and the reconstruction algorithm used. Although synthetic data have been widely employed to optimize experiments, the resulting reconstructed volumes might not have optimal quality. The purpose of the present study is to offer quality indicators that can be applied to data samples in order to improve the quality of velocity results obtained by the tomo-PIV technique. The methodology proposed can potentially lead to significantly reduction in the time required to optimize a tomo-PIV reconstruction, also leading to better quality velocity results. Tomo-PIV data provided by a six-camera turbulent boundary-layer experiment were used to optimize the reconstruction algorithms according to this methodology. Velocity statistics measurements obtained by optimized BIMART, SMART and MART algorithms were compared with hot-wire anemometer data and velocity measurement uncertainties were computed. Results indicated that BIMART and SMART algorithms produced reconstructed volumes with equivalent quality as the standard MART with the benefit of reduced computational time.

Volume reconstruction optimization for tomo-PIV algorithms applied to experimental data

International Nuclear Information System (INIS)

Martins, Fabio J W A; Foucaut, Jean-Marc; Stanislas, Michel; Thomas, Lionel; Azevedo, Luis F A

2015-01-01

Tomographic PIV is a three-component volumetric velocity measurement technique based on the tomographic reconstruction of a particle distribution imaged by multiple camera views. In essence, the performance and accuracy of this technique is highly dependent on the parametric adjustment and the reconstruction algorithm used. Although synthetic data have been widely employed to optimize experiments, the resulting reconstructed volumes might not have optimal quality. The purpose of the present study is to offer quality indicators that can be applied to data samples in order to improve the quality of velocity results obtained by the tomo-PIV technique. The methodology proposed can potentially lead to significantly reduction in the time required to optimize a tomo-PIV reconstruction, also leading to better quality velocity results. Tomo-PIV data provided by a six-camera turbulent boundary-layer experiment were used to optimize the reconstruction algorithms according to this methodology. Velocity statistics measurements obtained by optimized BIMART, SMART and MART algorithms were compared with hot-wire anemometer data and velocity measurement uncertainties were computed. Results indicated that BIMART and SMART algorithms produced reconstructed volumes with equivalent quality as the standard MART with the benefit of reduced computational time. (paper)

Fabrication of artificial arteriovenous fistula and analysis of flow field and shear stress by using μ-PIV technology

Energy Technology Data Exchange (ETDEWEB)

Park, Sun Cheol; Kim, Hyun Kyu [Div. of Vascular Surgery, Dept. of Surgery, College of Medicine, The Catholic University of Korea, Seoul (Korea, Republic of); Song, Ryun Geun; Kim, Sun Ho; Lee, Jin Kee [School of Mechanical Engineering, Sungkyunkwan University, Suwon (Korea, Republic of); Kim, Seung Hyun [School of Engineering, Brown University, Providence (United States)

2016-12-15

Radio-cephalic arteriovenous fistula (RC-AVF) is an operation performed to achieve vascular access for hemodialysis. Although RC-AVF is a reliable and well-known method, this technique presents high rates of early failure depending on the vessel condition. These failures are due to blood shear stress around the anastomosis site and the vascular access failure caused by thrombosis secondary to stenosis formation, as well as vascular access reocclusion after percutaneous interventions. In this work, we fabricate in vitro 3D RC-AVF by using polydimethylsiloxane and 3D printing technology to understand the underlying mechanism and predict AVF failure. Micro- Particle image velocimetry (μ-PIV) focusing on the cardiac pulse cycle is used to measure the velocity field within the artificial blood vessel. Results are confirmed by numerical simulation. Accordingly, the in vitro AVF model agrees well with the simulations. Overall, this research would provide the future possibility of using the proposed method to reduce in vivo AVF failure for various conditions.

Estimation of uncertainty bounds for individual particle image velocimetry measurements from cross-correlation peak ratio

International Nuclear Information System (INIS)

Charonko, John J; Vlachos, Pavlos P

2013-01-01

Numerous studies have established firmly that particle image velocimetry (PIV) is a robust method for non-invasive, quantitative measurements of fluid velocity, and that when carefully conducted, typical measurements can accurately detect displacements in digital images with a resolution well below a single pixel (in some cases well below a hundredth of a pixel). However, to date, these estimates have only been able to provide guidance on the expected error for an average measurement under specific image quality and flow conditions. This paper demonstrates a new method for estimating the uncertainty bounds to within a given confidence interval for a specific, individual measurement. Here, cross-correlation peak ratio, the ratio of primary to secondary peak height, is shown to correlate strongly with the range of observed error values for a given measurement, regardless of flow condition or image quality. This relationship is significantly stronger for phase-only generalized cross-correlation PIV processing, while the standard correlation approach showed weaker performance. Using an analytical model of the relationship derived from synthetic data sets, the uncertainty bounds at a 95% confidence interval are then computed for several artificial and experimental flow fields, and the resulting errors are shown to match closely to the predicted uncertainties. While this method stops short of being able to predict the true error for a given measurement, knowledge of the uncertainty level for a PIV experiment should provide great benefits when applying the results of PIV analysis to engineering design studies and computational fluid dynamics validation efforts. Moreover, this approach is exceptionally simple to implement and requires negligible additional computational cost. (paper)

Three Dimensional Plenoptic PIV Measurements of a Turbulent Boundary Layer Overlying a Hemispherical Roughness Element

Science.gov (United States)

Johnson, Kyle; Thurow, Brian; Kim, Taehoon; Blois, Gianluca; Christensen, Kenneth

2016-11-01

Three-dimensional, three-component (3D-3C) measurements were made using a plenoptic camera on the flow around a roughness element immersed in a turbulent boundary layer. A refractive index matched approach allowed whole-field optical access from a single camera to a measurement volume that includes transparent solid geometries. In particular, this experiment measures the flow over a single hemispherical roughness element made of acrylic and immersed in a working fluid consisting of Sodium Iodide solution. Our results demonstrate that plenoptic particle image velocimetry (PIV) is a viable technique to obtaining statistically-significant volumetric velocity measurements even in a complex separated flow. The boundary layer to roughness height-ratio of the flow was 4.97 and the Reynolds number (based on roughness height) was 4.57×103. Our measurements reveal key flow features such as spiraling legs of the shear layer, a recirculation region, and shed arch vortices. Proper orthogonal decomposition (POD) analysis was applied to the instantaneous velocity and vorticity data to extract these features. Supported by the National Science Foundation Grant No. 1235726.

PIV Measurements of Atmospheric Turbulence and Pollen Dispersal Above a Corn Canopy

Science.gov (United States)

Zhu, W.; van Hout, R.; Luznik, L.; Katz, J.

2003-12-01

Dispersal of pollen grains by wind and gravity (Anemophilous) is one of the oldest means of plant fertilization available in nature. Recently, the growth of genetically modified foods has raised questions on the range of pollen dispersal in order to limit cross-fertilization between organically grown and transgenic crops. The distance that a pollen grain can travel once released from the anther is determined, among others, by the aerodynamic parameters of the pollen and the characteristics of turbulence in the atmosphere in which it is released. Turbulence characteristics of the flow above a pollinating corn field were measured using Particle Image Velocimetry (PIV). The measurements were performed on the eastern shore of the Chesapeake Bay, in Maryland, during July 2003. Two PIV systems were used simultaneously, each with an overall sample area of 18x18 cm. The spacing between samples was about equal to the field of view. The PIV instrumentation, including CCD cameras, power supply and laser sheets forming optics were mounted on a measurement platform, consisting of a hydraulic telescopic arm that could be extended up to 10m. The whole system could be rotated in order to align it with the flow. The flow was seeded with smoke generated about 30m upstream of the sample areas. Measurements were carried out at several elevations, from just below canopy height up to 1m above canopy. The local meteorological conditions around the test site were monitored by other sensors including sonic anemometers, Rotorod pollen counters and temperature sensors. Each processed PIV image provides an instantaneous velocity distribution containing 64x64 vectors with a vector spacing of ~3mm. The pollen grains (~100mm) can be clearly distinguished from the smoke particles (~1mm) based on their size difference. The acquired PIV data enables calculation of the mean flow and turbulence characteristics including Reynolds stresses, spectra, turbulent kinetic energy and dissipation rate. Data

Sequential least-square reconstruction of instantaneous pressure field around a body from TR-PIV

Science.gov (United States)

Jeon, Young Jin; Gomit, G.; Earl, T.; Chatellier, L.; David, L.

2018-02-01

A procedure is introduced to obtain an instantaneous pressure field around a wing from time-resolved particle image velocimetry (TR-PIV) and particle image accelerometry (PIA). The instantaneous fields of velocity and material acceleration are provided by the recently introduced multi-frame PIV method, fluid trajectory evaluation based on ensemble-averaged cross-correlation (FTEE). The integration domain is divided into several subdomains in accordance with the local reliability. The near-edge and near-body regions are determined based on the recorded image of the wing. The instantaneous wake region is assigned by a combination of a self-defined criterion and binary morphological processes. The pressure is reconstructed from a minimization process of the difference between measured and reconstructed pressure gradients in a least-square sense. This is solved sequentially according to a decreasing order of reliability of each subdomain to prevent a propagation of error from the less reliable near-body region to the free-stream. The present procedure is numerically assessed by synthetically generated 2D particle images based on a numerical simulation. Volumetric pressure fields are then evaluated from tomographic TR-PIV of a flow around a 30-degree-inclined NACA0015 airfoil. A possibility of using a different scheme to evaluate material acceleration for a specific subdomain is presented. Moreover, this 3D application allows the investigation of the effect of the third component of the pressure gradient by which the wake region seems to be affected.

PIV-validated numerical modeling of pulsatile flows in distal coronary end-to-side anastomoses.

Science.gov (United States)

Xiong, F L; Chong, C K

2007-01-01

This study employed particle image velocimetry (PIV) to validate a numerical model in a complementary approach to quantify hemodynamic factors in distal coronary anastomoses and to gain more insights on their relationship with anastomotic geometry. Instantaneous flow fields and wall shear stresses (WSS) were obtained from PIV measurement in a modified life-size silastic anastomosis model adapted from a conventional geometry by incorporating a smooth graft-artery transition. The results were compared with those predicted by a concurrent numerical model. The numerical method was then used to calculate cycle-averaged WSS (WSS(cyc)) and spatial wall shear stress gradient (SWSSG), two critical hemodynamic factors in the pathogenesis of intimal thickening (IT), to compare the conventional and modified geometries. Excellent qualitative agreement and satisfactory quantitative agreement with averaged normalized error in WSS between 0.8% and 8.9% were achieved between the PIV experiment and numerical model. Compared to the conventional geometry, the modified geometry produces a more uniform WSS(cyc) distribution eliminating both high and low WSS(cyc) around the toe, critical in avoiding IT. Peak SWSSG on the artery floor of the modified model is less than one-half that in the conventional case, and high SWSSG at the toe is eliminated. The validated numerical model is useful for modeling unsteady coronary anastomotic flows and elucidating the significance of geometry regulated hemodynamics. The results suggest the clinical relevance of constructing smooth graft-artery transition in distal coronary anastomoses to improve their hemodynamic performance.

PIV, radiotracers and CFD for flow anomalies

International Nuclear Information System (INIS)

Houdek, P.; Reitspiesova, I.; Zitny, R.; Thyn, J.

2004-01-01

Experimental investigation of flow asymmetries in continuous direct ohmic heater by using PIV and stimulus response technique (radioisotope 99 Tc) is presented together with CFD modelling by using finite element code FEMINA. (author)

PIV Measurements of Chevrons on F400 Tactical Aircraft Nozzle Model

Science.gov (United States)

Bridges, James; Wernet, Mark; Frate, Franco

2010-01-01

Previous talks at this meeting have covered our collaborative work on high-energy jets such as present in tactical aircraft (those with supersonic plumes). The emphasis of this work is improving our understanding of flow physics and our prediction tools. In this presentation we will discuss recent flow diagnostics acquired using Particle Image Velocimetry (PIV) made on an underexpanded shocked jet plume from a tactical aircraft nozzle. In this presentation we show cross-sectional and streamwise cuts of both mean and turbulent velocities of an F404 engine nozzle with various chevron designs applied. The impact of chevron penetration, length, and width are documented. The impact of the parameters is generally nonlinear in measures considered here, a surprising result given the relatively smooth behavior of the noise to variations in these chevron parameters.

Particle image velocimetry measurements of Mach 3 turbulent boundary layers at low Reynolds numbers

Science.gov (United States)

Brooks, J. M.; Gupta, A. K.; Smith, M. S.; Marineau, E. C.

2018-05-01

Particle image velocimetry (PIV) measurements of Mach 3 turbulent boundary layers (TBL) have been performed under low Reynolds number conditions, Re_τ =200{-}1000, typical of direct numerical simulations (DNS). Three reservoir pressures and three measurement locations create an overlap in parameter space at one research facility. This allows us to assess the effects of Reynolds number, particle response and boundary layer thickness separate from facility specific experimental apparatus or methods. The Morkovin-scaled streamwise fluctuating velocity profiles agree well with published experimental and numerical data and show a small standard deviation among the nine test conditions. The wall-normal fluctuating velocity profiles show larger variations which appears to be due to particle lag. Prior to the current study, no detailed experimental study characterizing the effect of Stokes number on attenuating wall-normal fluctuating velocities has been performed. A linear variation is found between the Stokes number ( St) and the relative error in wall-normal fluctuating velocity magnitude (compared to hot wire anemometry data from Klebanoff, Characteristics of Turbulence in a Boundary Layer with Zero Pressure Gradient. Tech. Rep. NACA-TR-1247, National Advisory Committee for Aeronautics, Springfield, Virginia, 1955). The relative error ranges from about 10% for St=0.26 to over 50% for St=1.06. Particle lag and spatial resolution are shown to act as low-pass filters on the fluctuating velocity power spectral densities which limit the measurable energy content. The wall-normal component appears more susceptible to these effects due to the flatter spectrum profile which indicates that there is additional energy at higher wave numbers not measured by PIV. The upstream inclination and spatial correlation extent of coherent turbulent structures agree well with published data including those using krypton tagging velocimetry (KTV) performed at the same facility.

Identification of hydrodynamic forces around 3D surrogates using particle image velocimetry in a microfluidic channel

Science.gov (United States)

Afshar, Sepideh; Nath, Shubhankar; Demirci, Utkan; Hasan, Tayyaba; Scarcelli, Giuliano; Rizvi, Imran; Franco, Walfre

2018-02-01

Previous studies have demonstrated that flow-induced shear stress induces a motile and aggressive tumor phenotype in a microfluidic model of 3D ovarian cancer. However, the magnitude and distribution of the hydrodynamic forces that influence this biological modulation on the 3D cancer nodules are not known. We have developed a series of numerical and experimental tools to identify these forces within a 3D microchannel. In this work, we used particle image velocimetry (PIV) to find the velocity profile using fluorescent micro-spheres as surrogates and nano-particles as tracers, from which hydrodynamic forces can be derived. The fluid velocity is obtained by imaging the trajectory of a range of florescence nano-particles (500-800 μm) via confocal microscopy. Imaging was done at different horizontal planes and with a 50 μm bead as the surrogate. For an inlet current rate of 2 μl/s, the maximum velocity at the center of the channel was 51 μm/s. The velocity profile around the sphere was symmetric which is expected since the flow is dominated by viscous forces as opposed to inertial forces. The confocal PIV was successfully employed in finding the velocity profile in a microchannel with a nodule surrogate; therefore, it seems feasible to use PIV to investigate the hydrodynamic forces around 3D biological models.

Novel Atlantic bottlenose dolphin parainfluenza virus TtPIV-1 clusters with bovine PIV-3 genotype B strains.

Science.gov (United States)

Eberle, Kirsten C; Neill, John D; Venn-Watson, Stephanie K; McGill, Jodi L; Sacco, Randy E

2015-10-01

Parainfluenza virus 3 (PIV-3) is a common viral infection not only in humans, but also in many other species. Serological evidence suggests that nearly 100 % of children in the United States have been infected with PIV-3 by 5 years of age. Similarly, in cattle, PIV-3 is commonly associated with bovine respiratory disease complex. A novel dolphin PIV-3 (TtPIV-1) was described by Nollens et al. in 2008 from a dolphin that was diagnosed with an unknown respiratory illness. At that time, TtPIV-1 was found to be most similar to, but distinct from, bovine PIV-3 (BPIV-3). In the present study, similar viral growth kinetics and pro-inflammatory cytokine (IL-1β, IL-6, and CXCL8) production were seen between BPIV-3 and TtPIV-1 in BEAS-2B, MDBK, and Vero cell lines. Initial nomenclature of TtPIV-1 was based on partial sequence of the fusion and RNA polymerase genes. Based on the similarities we saw with the in vitro work, it was important to examine the TtPIV-1 genome in more detail. Full genome sequencing and subsequent phylogenetic analysis revealed that all six viral genes of TtPIV-1 clustered within the recently described BPIV-3 genotype B strains, and it is proposed that TtPIV-1 be re-classified with BPIV-3 genotype B strains.

Three-dimensional, three-component wall-PIV

Science.gov (United States)

Berthe, André; Kondermann, Daniel; Christensen, Carolyn; Goubergrits, Leonid; Garbe, Christoph; Affeld, Klaus; Kertzscher, Ulrich

2010-06-01

This paper describes a new time-resolved three-dimensional, three-component (3D-3C) measurement technique called wall-PIV. It was developed to assess near wall flow fields and shear rates near non-planar surfaces. The method is based on light absorption according to Beer-Lambert’s law. The fluid containing a molecular dye and seeded with buoyant particles is illuminated by a monochromatic, diffuse light. Due to the dye, the depth of view is limited to the near wall layer. The three-dimensional particle positions can be reconstructed by the intensities of the particle’s projection on an image sensor. The flow estimation is performed by a new algorithm, based on learned particle trajectories. Possible sources of measurement errors related to the wall-PIV technique are analyzed. The accuracy analysis was based on single particle experiments and a three-dimensional artificial data set simulating a rotating sphere.

Increasing the Performance of a Sliding Discharge Actuator Through the Application of Multiple Potentials

Science.gov (United States)

2011-09-01

particle image velocimetry (PIV). In probe measurement techniques a probe, either a pitot static probe or a CTA hot wire probe, is inserted into the flow...and pitot probes and noted the differences that resulted between the probe results and the PIV results by seeding material type [20]. The PIV setup...Barrier Discharge Aerodynamic Actuator,” AIAA Paper 2009–4285, 2009. 188 41. Humble, R., Henry , G., and Larson, W., Space Propulsion Analysis and Design

Optical Flow-Field Techniques Used for Measurements in High-Speed Centrifugal Compressors

Science.gov (United States)

Skoch, Gary J.

1999-01-01

The overall performance of a centrifugal compressor depends on the performance of the impeller and diffuser as well as on the interactions occurring between these components. Accurate measurements of the flow fields in each component are needed to develop computational models that can be used in compressor design codes. These measurements must be made simultaneously over an area that covers both components so that researchers can understand the interactions occurring between the two components. Optical measurement techniques are being used at the NASA Lewis Research Center to measure the velocity fields present in both the impeller and diffuser of a 4:1 pressure ratio centrifugal compressor operating at several conditions ranging from design flow to surge. Laser Doppler Velocimetry (LDV) was used to measure the intrablade flows present in the impeller, and the results were compared with analyses obtained from two three-dimensional viscous codes. The development of a region of low throughflow velocity fluid within this high-speed impeller was examined and compared with a similar region first observed in a large low-speed centrifugal impeller at Lewis. Particle Image Velocimetry (PIV) is a relatively new technique that has been applied to measuring the diffuser flow fields. PIV can collect data rapidly in the diffuser while avoiding the light-reflection problems that are often encountered when LDV is used. The Particle Image Velocimeter employs a sheet of pulsed laser light that is introduced into the diffuser in a quasi-radial direction through an optical probe inserted near the diffuser discharge. The light sheet is positioned such that its centerline is parallel to the hub and shroud surfaces and such that it is parallel to the diffuser vane, thereby avoiding reflections from the solid surfaces. Seed particles small enough to follow the diffuser flow are introduced into the compressor at an upstream location. A high-speed charge-coupled discharge (CCD) camera is

Comparisons of LES and RANS Computations with PIV Experiments on a Cylindrical Cavity Flow

Directory of Open Access Journals (Sweden)

Wen-Tao Su

2013-01-01

Full Text Available A comparison study on the numerical computations by large eddy simulation (LES and Reynolds-averaged Navier-Stokes (RANS methods with experiment on a cylindrical cavity flow was conducted in this paper. Numerical simulations and particle image velocimetry (PIV measurement were performed for two Reynolds numbers of the flow at a constant aspect ratio of H/R = 2.4 (R is the radius of the cylindrical cavity, and H is liquid level. The three components of velocity were extracted from 100 sequential PIV measured velocity frames with averaging, in order to illustrate the axial jet flow evolution and circulation distribution in the radial direction. The results show that LES can reproduce well the fine structure inside the swirling motions in both the meridional and the horizontal planes, as well as the distributions of velocity components and the circulation, in good agreement with experimental results, while the RANS method only provided a rough trend of inside vortex structure. Based on the analysis of velocity profiles at various locations, it indicates that LES is more suitable for predicting the complex flow characteristics inside complicated three-dimensional geometries.

Microfluidic rheometry of a polymer solution by micron resolution particle image velocimetry: a model validation study

International Nuclear Information System (INIS)

Hemaka Bandalusena, H C; Zimmerman, William B; Rees, Julia M

2009-01-01

The main purpose of this study is to model non-Newtonian fluid flows in microgeometries. Velocity fields of dilute xanthan gum solutions in a microfluidic T-junction have been measured for pressure-driven flow using micron resolution particle image velocimetry (µ-PIV). Xanthan gum at a fixed concentration is a power-law fluid. Varying the concentration changes the rheology, effectively altering the power-law parameters reflecting the changes in the fluid's shear response since viscoelasticity and extensional viscosity are negligible for dilute solutions of this substance. As the flow is forced to turn the corner of the T-junction, a range of shear rates, and hence viscosities, is produced. If this feature could be incorporated into a viscometer, then potentially the constitutive parameters of a complex fluid could be ascertained from a single experiment. A mathematical model based on a finite element technique has been developed to simulate the fluid flow in the experimental system. Model predictions of the velocity field are found to agree well (less than 5% error) with observations, thus validating the model

Flow visualization over a thick blunt trailing-edge airfoil with base cavity at low Reynolds numbers using PIV technique.

Science.gov (United States)

Taherian, Gholamhossein; Nili-Ahmadabadi, Mahdi; Karimi, Mohammad Hassan; Tavakoli, Mohammad Reza

2017-01-01

In this study, the effect of cutting the end of a thick airfoil and adding a cavity on its flow pattern is studied experimentally using PIV technique. First, by cutting 30% chord length of the Riso airfoil, a thick blunt trialing-edge airfoil is generated. The velocity field around the original airfoil and the new airfoil is measured by PIV technique and compared with each other. Then, adding two parallel plates to the end of the new airfoil forms the desired cavity. Continuous measurement of unsteady flow velocity over the Riso airfoil with thick blunt trailing edge and base cavity is the most important innovation of this research. The results show that cutting off the end of the airfoil decreases the wake region behind the airfoil, when separation occurs. Moreover, adding a cavity to the end of the thickened airfoil causes an increase in momentum and a further decrease in the wake behind the trailing edge that leads to a drag reduction in comparison with the thickened airfoil without cavity. Furthermore, using cavity decreases the Strouhal number and vortex shedding frequency.

On the estimation of wall pressure coherence using time-resolved tomographic PIV

Science.gov (United States)

Pröbsting, Stefan; Scarano, Fulvio; Bernardini, Matteo; Pirozzoli, Sergio

2013-07-01

Three-dimensional time-resolved velocity field measurements are obtained using a high-speed tomographic Particle Image Velocimetry (PIV) system on a fully developed flat plate turbulent boundary layer for the estimation of wall pressure fluctuations. The work focuses on the applicability of tomographic PIV to compute the coherence of pressure fluctuations, with attention to the estimation of the stream and spanwise coherence length. The latter is required for estimations of aeroacoustic noise radiation by boundary layers and trailing edge flows, but is also of interest for vibro-structural problems. The pressure field is obtained by solving the Poisson equation for incompressible flows, where the source terms are provided by time-resolved velocity field measurements. Measured 3D velocity data is compared to results obtained from planar PIV, and a Direct Numerical Simulation (DNS) at similar Reynolds number. An improved method for the estimation of the material based on a least squares estimator of the velocity derivative along a particle trajectory is proposed and applied. Computed surface pressure fluctuations are further verified by means of simultaneous measurements by a pinhole microphone and compared to the DNS results and a semi-empirical model available from literature. The correlation coefficient for the reconstructed pressure time series with respect to pinhole microphone measurements attains approximately 0.5 for the band-pass filtered signal over the range of frequencies resolved by the velocity field measurements. Scaled power spectra of the pressure at a single point compare favorably to the DNS results and those available from literature. Finally, the coherence of surface pressure fluctuations and the resulting span- and streamwise coherence lengths are estimated and compared to semi-empirical models and DNS results.

Measurement of real pulsatile blood flow using X-ray PIV technique with CO2 microbubbles.

Science.gov (United States)

Park, Hanwook; Yeom, Eunseop; Seo, Seung-Jun; Lim, Jae-Hong; Lee, Sang-Joon

2015-03-06

Synchrotron X-ray imaging technique has been used to investigate biofluid flows in a non-destructive manner. This study aims to investigate the feasibility of the X-ray PIV technique with CO2 microbubbles as flow tracer for measurement of pulsatile blood flows under in vivo conditions. The traceability of CO2 microbubbles in a pulsatile flow was demonstrated through in vitro experiment. A rat extracorporeal bypass loop was used by connecting a tube between the abdominal aorta and jugular vein of a rat to obtain hemodynamic information of actual pulsatile blood flows without changing the hemorheological properties. The decrease in image contrast of the surrounding tissue was also investigated for in vivo applications of the proposed technique. This technique could be used to accurately measure whole velocity field information of real pulsatile blood flows and has strong potential for hemodynamic diagnosis of cardiovascular diseases.

Measurement of real pulsatile blood flow using X-ray PIV technique with CO2 microbubbles

Science.gov (United States)

Park, Hanwook; Yeom, Eunseop; Seo, Seung-Jun; Lim, Jae-Hong; Lee, Sang-Joon

2015-01-01

Synchrotron X-ray imaging technique has been used to investigate biofluid flows in a non-destructive manner. This study aims to investigate the feasibility of the X-ray PIV technique with CO2 microbubbles as flow tracer for measurement of pulsatile blood flows under in vivo conditions. The traceability of CO2 microbubbles in a pulsatile flow was demonstrated through in vitro experiment. A rat extracorporeal bypass loop was used by connecting a tube between the abdominal aorta and jugular vein of a rat to obtain hemodynamic information of actual pulsatile blood flows without changing the hemorheological properties. The decrease in image contrast of the surrounding tissue was also investigated for in vivo applications of the proposed technique. This technique could be used to accurately measure whole velocity field information of real pulsatile blood flows and has strong potential for hemodynamic diagnosis of cardiovascular diseases. PMID:25744850

Application of Time-resolved PIV to Supersonic Hot Jets

Science.gov (United States)

Bridges, James; Wernet, Mark P.

2007-01-01

This presentation lays out the ground-breaking work at bringing high-speed (25kHz) particle image velocimetry (PIV) to bear on measurements of noise-producing turbulence in hot jets. The work is still in progress in that the tremendous amount of data obtained are still be analyzed, but the method has been validated and initial results of interest to jet noise modeling have been obtained. After a brief demonstration of the validation process used on the data, results are shown for hot jets at different temperatures and Mach numbers. Comparisons of first order statistics show the relative indifference of the turbulence to the presence of shocks and independence to jet temperature. What does come out is that when the shock-containing jets are in a screech mode the turbulence is highly elevated, showing the importance of removing screech phenomena from model-scale jets before applying findings to full-scale aircraft which typically do not contain shocks.

Flow mapping by PIV in microstructures with three-dimensional flow behavior

DEFF Research Database (Denmark)

Westergaard, C.; Klank, Henning; Kutter, Jörg Peter

2003-01-01

fortement tridimensionnels. Ceci offre un challenge à la technique de la PIV appliquée à la micro-fluidique (souvent appelée Micro PIV). Le papier donne un exemple de mesures réalisées dans un micro-système pour illustrer les possibilités et discuter l'application du principe de stéréoscopie, permettant...

Comparison of PIV and Hot-Wire statistics of turbulent boundary layer

International Nuclear Information System (INIS)

Dróżdż, A; Uruba, V

2014-01-01

The paper shows a cross checking of turbulent boundary layer measurements using large field of view PIV and hot-wire anemometry techniques. The time-resolved PIV method was used for the experiments. The measuring plane was oriented perpendicularly to the wall and parallel to the mean flow. Hot wire measurement has been performed using the special probe with perpendicular hot wire. The HW point measurements were performed in the same place as PIV experiments. The hot-wire probe has the wire length of l + < 20 in considered range of Reynolds numbers. Various evaluation methods were applied on PIV data. The profiles of statistical characteristics of streamwise velocity components were evaluated from the data. Mean values, standard deviations as well as skewness and kurtosis coefficients were compared for a few values of Re θ . Reynolds number ranges from 1000 to 5500. The result shows that with the increasing Reynolds number the attenuation of fluctuations maximum in PIV measurements occurs with respect to Hot-Wire measurements, however representation of velocity fluctuations using the PIV method is satisfactory. The influence of wall-normal fluctuation component on Hot-Wire near wall peak was also investigated.

Flow field characteristics of impinging sweeping jets: TR-PIV measurement

Science.gov (United States)

Wen, Xin; Peng, Di; Liu, Yingzheng; Tang, Hui

2017-11-01

Influence of Reynolds number of sweeping jets on its impinging flow fields was extensively investigated in a water tank. Toward this end, a fluidic oscillator was specially designed to produce spatially sweeping jets which imping on a flat plate. Six Reynolds numbers were tested by controlling the supply flow rate of the fluidic oscillator. Impinging flow fields were captured by time-resolved Particle Image Velocimetry (TR-PIV) measurement. Reference signals were extracted from the flow fields for phase reconstruction. The oscillating flow fields with super-harmonic frequency at different regions were discussed in term of the phase-averaged velocity, vorticity and turbulent velocity. Dynamic mode decomposition (DMD) was used to capture the most-energetic flow patterns with distinct frequencies. By projecting the phase-averaged flow fields onto a reduced basis of DMD modes, the phase correlation between the distinct flow patterns were analyzed under different Reynolds numbers.

Displacement fields from point cloud data: Application of particle imaging velocimetry to landslide geodesy

Science.gov (United States)

Aryal, Arjun; Brooks, Benjamin A.; Reid, Mark E.; Bawden, Gerald W.; Pawlak, Geno

2012-01-01

Acquiring spatially continuous ground-surface displacement fields from Terrestrial Laser Scanners (TLS) will allow better understanding of the physical processes governing landslide motion at detailed spatial and temporal scales. Problems arise, however, when estimating continuous displacement fields from TLS point-clouds because reflecting points from sequential scans of moving ground are not defined uniquely, thus repeat TLS surveys typically do not track individual reflectors. Here, we implemented the cross-correlation-based Particle Image Velocimetry (PIV) method to derive a surface deformation field using TLS point-cloud data. We estimated associated errors using the shape of the cross-correlation function and tested the method's performance with synthetic displacements applied to a TLS point cloud. We applied the method to the toe of the episodically active Cleveland Corral Landslide in northern California using TLS data acquired in June 2005–January 2007 and January–May 2010. Estimated displacements ranged from decimeters to several meters and they agreed well with independent measurements at better than 9% root mean squared (RMS) error. For each of the time periods, the method provided a smooth, nearly continuous displacement field that coincides with independently mapped boundaries of the slide and permits further kinematic and mechanical inference. For the 2010 data set, for instance, the PIV-derived displacement field identified a diffuse zone of displacement that preceded by over a month the development of a new lateral shear zone. Additionally, the upslope and downslope displacement gradients delineated by the dense PIV field elucidated the non-rigid behavior of the slide.

Visualization investigation of acoustic and flow-induced vibration in main stream lines using a high-time-resolved PIV technique

International Nuclear Information System (INIS)

Li, Yanrong; Someya, Satoshi; Okamoto, Koji

2009-01-01

Systems with closed side-branches are liable to an excitation of sound, as called cavity tone. It may occur in pipe branches leading to safety valves or to boiler relief valves. The outbreak mechanism of the cavity tone has been known by phase-averaged measurement in previous researches, while the relation between sound propagation and flow field is still unclear due to the difficulty of detecting instantaneous velocity field. High-time-resolved PIV has a possibility to analyze the velocity field and the relation mentioned above. In this study, flow-induced acoustic resonance of piping system containing closed side-branches was investigated experimentally. A high-time-resolved PIV technique was applied to measure a gas-flow in a cavity. Air flow containing oil mist as tracer particles was measured using a high frequency pulse laser and a high speed camera. The present investigation on the coaxial closed side-branches is the first rudimentary study to visualize the fluid flow two-dimensionally in the cross-section by using PIV and to measure the pressure at the downstream side opening of the cavity by microphone. The fluid flows at different points in the cavity interact with some phase differences and the relation was clarified. (author)

In vivo measurement of hemodynamic information in stenosed rat blood vessels using X-ray PIV.

Science.gov (United States)

Park, Hanwook; Park, Jun Hong; Lee, Sang Joon

2016-11-28

Measurements of the hemodynamic information of blood flows, especially wall shear stress (WSS), in animal models with circulatory vascular diseases (CVDs) are important to understand the pathological mechanism of CVDs. In this study, X-ray particle image velocimetry (PIV) with high spatial resolution was applied to obtain velocity field information in stenosed blood vessels with high WSS. 3D clips fabricated with a 3D printer were applied to the abdominal aorta of a rat cadaver to induce artificial stenosis in the real blood vessel of an animal model. The velocity and WSS information of blood flows in the stenosed vessel were obtained and compared at various stenosis severities. In vivo measurement was also conducted by fastening a stenotic clip on a live rat model through surgical intervention to reduce the flow rate to match the limited temporal resolution of the present X-ray PIV system. Further improvement of the temporal resolution of the system might be able to provide in vivo measurements of hemodynamic information from animal disease models under physiological conditions. The present results would be helpful for understanding the relation between hemodynamic characteristics and the pathological mechanism in animal CVD models.

PIV measurements of the turbulence integral length scale on cold combustion flow field of tangential firing boiler

Energy Technology Data Exchange (ETDEWEB)

Wu, Wen-fei; Xie, Jing-xing; Gong, Zhi-jun; Li, Bao-wei [Inner Mongolia Univ. of Science and Technology, Baotou (China). Inner Mongolia Key Lab. for Utilization of Bayan Obo Multi-Metallic Resources: Elected State Key Lab.

2013-07-01

The process of the pulverized coal combustion in tangential firing boiler has prominent significance on improving boiler operation efficiency and reducing NO{sub X} emission. This paper aims at researching complex turbulent vortex coherent structure formed by the four corners jets in the burner zone, a cold experimental model of tangential firing boiler has been built. And by employing spatial correlation analysis method and PIV (Particle Image Velocimetry) technique, the law of Vortex scale distribution on the three typical horizontal layers of the model based on the turbulent Integral Length Scale (ILS) has been researched. According to the correlation analysis of ILS and the temporal average velocity, it can be seen that the turbulent vortex scale distribution in the burner zone of the model is affected by both jet velocity and the position of wind layers, and is not linear with the variation of jet velocity. The vortex scale distribution of the upper primary air is significantly different from the others. Therefore, studying the ILS of turbulent vortex integral scale is instructive to high efficiency cleaning combustion of pulverized coal in theory.

Pressure spectra from single-snapshot tomographic PIV

NARCIS (Netherlands)

Schneiders, J.F.G.; Avallone, F.; Pröbsting, S.; Ragni, D.; Scarano, F.

2018-01-01

The power spectral density and coherence of temporal pressure fluctuations are obtained from low-repetition-rate tomographic PIV measurements. This is achieved by extension of recent single-snapshot pressure evaluation techniques based upon the Taylor’s hypothesis (TH) of frozen turbulence and

Influence of the velocity vector base relocation to the center of mass of the interrogation area on PIV accuracy

Directory of Open Access Journals (Sweden)

Kouba Jan

2014-03-01

Full Text Available This paper is aimed at modification of calculation algorithm used in data processing from PIV (Particle Image Velocimetry method. The modification of standard Multi-step correlation algorithm is based on imaging the centre of mass of the interrogation area to define the initial point of the respective vector, instead of the geometrical centre. This paper describes the principle of initial point-vector assignment, the corresponding data processing methodology including the test track analysis. Both approaches are compared within the framework of accuracy in the conclusion. The accuracy test is performed using synthetic and real data.

Numerical simulation and PIV experimental analysis of electrohydrodynamic plumes induced by a blade electrode

International Nuclear Information System (INIS)

Traore, Ph; Daaboul, M; Louste, Ch

2010-01-01

In this paper a comparative study between numerical and experimental results from particle image velocimetry (PIV) measurements is presented in the case of two-dimensional electrohydrodynamic plumes that arise when a sharp metallic blade, submerged in non-conducting liquids, supports a high electric potential. Experiments and numerical simulations have been conducted in order to compare both the approaches. Very good agreement has been found through velocity profiles and velocity fields which proves the relevance of our numerical model. For high potentials the jet flow issued forth from the blade becomes unsteady and starts to flap on the vertical wall. Some snapshots of the temporal evolution of the isocontours of charge density which is not accessible from experiment are presented thanks to the numerical simulation.

Use of the μPIV technique for an indirect determination of the microchannel cross-section passage geometry

International Nuclear Information System (INIS)

Puccetti, G; Pulvirenti, B; Morini, G L

2014-01-01

In this work the possible use of the μPIV technique for the experimental determination of the microchannel cross-section geometry has been investigated by means of a blind test in which a series of experimental measurements obtained using glass microchannels having a declared rectangular cross-section with a depth of 100 μm and width of 300 μm and a square microchannel with a 300 μm side have been compared with the direct SEM visualisation of the real cross section of the microchannels. For the (oPIV measurements water is used as working fluid. The laminar fully developed 2D velocity profile has been reconstructed by moving the focal plane of the microscope objective from the bottom to the top of the microchannel. The results shown in this paper demonstrate that the real cross section geometry of the microchannel can be predicted by minimizing the difference between the theoretical and the experimental 2D velocity profiles. When the right passage geometry is determined, the average difference between the theoretical and the experimental velocity is within 4-6%.

Isothermal flow measurement using planar PIV in the 1/4 scaled model of CANDU reactor

Energy Technology Data Exchange (ETDEWEB)

Im, Sunghyuk; Sung, Hyung Jin [KAIST, Daejeon (Korea, Republic of); Seo, Han; Bang, In Cheol [UNIST, Ulsan (Korea, Republic of); Kim, Hyoung Tae [KAERI, Daejeon (Korea, Republic of)

2015-05-15

The local temperature of the moderator is a key parameter in determining the available subcooling. To predict the flow field and local temperature distribution in the calandria, Korea Atomic Energy Research Institute (KAERI) started the experimental research on moderator circulation as one of a national R and D research programs from 2012. This research program includes the construction of the Moderator Circulation Test (MCT) facility, production of the validation data for self-reliant CFD tools, and development of optical measurement system using the Particle Image Velocimetry (PIV) and Laser Induced Fluorescence (LIF) techniques. Small-scale 1/40 and 1/8 small-scale model tests were performed prior to installation of the main MCT facility to identify the potential problems of the flow visualization and measurement expected in the 1/4 scale MCT facility. In the 1/40 scale test, a flow field was measured with a PIV measurement technique under an iso-thermal state, and the temperature field was visualized using a LIF technique. In this experiment, the key point was to illuminate the region of interest as uniformly as possible since the velocity and temperature fields in the shadow regions were distorted and unphysical. In the 1/8 scale test, the flow patterns from the inlet nozzles to the top region of the tank were investigated using PIV measurement at two different positions of the inlet nozzle. For each position of laser beam exposure the measurement sections were divided to 7 groups to overcome the limitation of the laser power to cover the relatively large test section. The MCT facility is the large-scale facility designed to reproduce the important characteristics of moderator circulation in a CANDU6 calandria under a range of operating conditions. It is reduced in a 1/4 scale and a moderator test vessel is built to the specifications of the CANDU6 reactor design, where a working fluid is sub-cooled water with atmospheric pressure. Previous studies were

Isothermal flow measurement using planar PIV in the 1/4 scaled model of CANDU reactor

International Nuclear Information System (INIS)

Im, Sunghyuk; Sung, Hyung Jin; Seo, Han; Bang, In Cheol; Kim, Hyoung Tae

2015-01-01

The local temperature of the moderator is a key parameter in determining the available subcooling. To predict the flow field and local temperature distribution in the calandria, Korea Atomic Energy Research Institute (KAERI) started the experimental research on moderator circulation as one of a national R and D research programs from 2012. This research program includes the construction of the Moderator Circulation Test (MCT) facility, production of the validation data for self-reliant CFD tools, and development of optical measurement system using the Particle Image Velocimetry (PIV) and Laser Induced Fluorescence (LIF) techniques. Small-scale 1/40 and 1/8 small-scale model tests were performed prior to installation of the main MCT facility to identify the potential problems of the flow visualization and measurement expected in the 1/4 scale MCT facility. In the 1/40 scale test, a flow field was measured with a PIV measurement technique under an iso-thermal state, and the temperature field was visualized using a LIF technique. In this experiment, the key point was to illuminate the region of interest as uniformly as possible since the velocity and temperature fields in the shadow regions were distorted and unphysical. In the 1/8 scale test, the flow patterns from the inlet nozzles to the top region of the tank were investigated using PIV measurement at two different positions of the inlet nozzle. For each position of laser beam exposure the measurement sections were divided to 7 groups to overcome the limitation of the laser power to cover the relatively large test section. The MCT facility is the large-scale facility designed to reproduce the important characteristics of moderator circulation in a CANDU6 calandria under a range of operating conditions. It is reduced in a 1/4 scale and a moderator test vessel is built to the specifications of the CANDU6 reactor design, where a working fluid is sub-cooled water with atmospheric pressure. Previous studies were

Deriving a blood-mimicking fluid for particle image velocimetry in Sylgard-184 vascular models.

Science.gov (United States)

Yousif, Majid Y; Holdsworth, David W; Poepping, Tamie L

2009-01-01

A new blood-mimicking fluid (BMF) has been developed for particle image velocimetry (PIV), which enables flow studies in vascular models (phantoms). A major difficulty in PIV that affects measurement accuracy is the refraction and distortion of light passing through the interface between the model and the fluid, due to the difference in refractive index (n) between the two materials. The problem can be eliminated by using a fluid with a refractive index matching that of the model. Such fluids are not commonly available, especially for vascular research where the fluid should also have a viscosity similar to human blood. In this work, a blood-mimicking fluid, composed of water (47.38% by weight), glycerol (36.94% by weight) and sodium iodide salt (15.68% by weight), was developed for compatibility with our silicone (Sylgard 184; n = 1.414) phantoms. The fluid exhibits a dynamic viscosity of 4.31+/-0.03 cP which lies within the range of human blood viscosity (4.4+/-0.6 cP). Both refractive index and viscosity were attained at 22.2+/-0.2 degrees C, which is a feasible room temperature, thus eliminating the need for a temperature-control system. The fluid will be used to study hemodynamics in vascular flow models fabricated from Sylgard 184.

3D scanning particle tracking velocimetry

Energy Technology Data Exchange (ETDEWEB)

Hoyer, Klaus; Holzner, Markus; Guala, Michele; Liberzon, Alexander; Kinzelbach, Wolfgang [Swiss Federal Institut of Technology Zurich, Institut fuer Hydromechanik und Wasserwirtschaft, Zuerich (Switzerland); Luethi, Beat [Risoe National Laboratory, Roskilde (Denmark)

2005-11-01

In this article, we present an experimental setup and data processing schemes for 3D scanning particle tracking velocimetry (SPTV), which expands on the classical 3D particle tracking velocimetry (PTV) through changes in the illumination, image acquisition and analysis. 3D PTV is a flexible flow measurement technique based on the processing of stereoscopic images of flow tracer particles. The technique allows obtaining Lagrangian flow information directly from measured 3D trajectories of individual particles. While for a classical PTV the entire region of interest is simultaneously illuminated and recorded, in SPTV the flow field is recorded by sequential tomographic high-speed imaging of the region of interest. The advantage of the presented method is a considerable increase in maximum feasible seeding density. Results are shown for an experiment in homogenous turbulence and compared with PTV. SPTV yielded an average 3,500 tracked particles per time step, which implies a significant enhancement of the spatial resolution for Lagrangian flow measurements. (orig.)

PIV measurements of velocities and accelerations under breaking waves on a slope

DEFF Research Database (Denmark)

Vested, Malene Hovgaard; Carstensen, Stefan; Christensen, Erik Damgaard

2017-01-01

waves. In this study, we have investigated the wave kinematics under steep and breaking waves on a laboratory beach with a slope of 1/25. The velocity field was measured by use of Particle Image Velocimetry (PIV) at a sample rate of 96Hz. The high sample rate allowed for the accelerations...... to be determined directly from the sampled velocities. It was found that both velocities and accelerations differ from the ones predicted from common wave theories such as streamfunction theory. This was especially evident at the top part of the wave close to the surface. This was not surprising, since...... the breaking event is a highly non-linear process. The results presented here may facilitate computations of the impact force on offshore structures and furthermore be used for validation of CFD models while altogether shedding light on the mechanisms behind breaking waves....

PIV study of large-scale flow organisation in slot jets

International Nuclear Information System (INIS)

Shestakov, Maxim V.; Dulin, Vladimir M.; Tokarev, Mikhail P.; Sikovsky, Dmitrii Ph.; Markovich, Dmitriy M.

2015-01-01

Highlights: • Volumetric velocity measurements are perfumed by PIV to analyse 3D flow organisation in a slot jet. • Proper orthogonal decomposition is used to extract coherent flow motion. • Movement of quasi-two-dimensional large-scale vortices is associated with jet meandering. • Amplitude of jet meandering is found to be aperiodically modulated. • Secondary longitudinal vortex rolls are important for cross-stream mixing and momentum transfer. - Abstract: The paper reports on particle image velocimetry (PIV) measurements in turbulent slot jets bounded by two solid walls with the separation distance smaller than the jet width (5–40%). In the far-field such jets are known to manifest features of quasi-two dimensional, two component turbulence. Stereoscopic and tomographic PIV systems were used to analyse local flows. Proper orthogonal decomposition (POD) was applied to extract coherent modes of the velocity fluctuations. The measurements were performed both in the initial region close to the nozzle exit and in the far fields of the developed turbulent slot jets for Re ⩾ 10,000. A POD analysis in the initial region indicates a correlation between quasi-2D vortices rolled-up in the shear layer and local flows in cross-stream planes. While the near-field turbulence shows full 3D features, the wall-normal velocity fluctuations day out gradually due to strong wall-damping resulting in an almost two-component turbulence. On the other hand, the longitudinal vortex rolls take over to act as the main agents in wall-normal and spanwise mixing and momentum transfer. The quantitative analysis indicates that the jet meandering amplitude was aperiodically modulated when arrangement of the large-scale quasi-2D vortices changed between asymmetric and symmetric pattern relatively to the jet axis. The paper shows that the dynamics of turbulent slot jets are more complex than those of 2D, plane and rectangular 3D jets. In particular, the detected secondary longitudinal

Flow in a Low Specific Speed Centrifugal Pump Using PIV

Directory of Open Access Journals (Sweden)

Cui Dai

2013-01-01

Full Text Available The interflow plays important roles in centrifugal pump design. In order to study the effect of rotation and z-axis on internal flow, two-dimensional particle image velocimetry (PIV measurements have been performed to measure the steady velocity field on three planes in all impeller passages of a low specific-speed centrifugal pump. The results show that the relative velocity flows in blade passages are obviously different in terms of the positions of the blade relative to the tongue. The interaction between the impeller and tongue changes the occurrence and development of low velocity region with time. From shroud to hub, the relative velocity gradually increases, and the minimum value moves toward the suction surface. On the midplane, the magnitude increases with increased flow rate from pressure surface to suction surface, while at the shroud and hub, the measured velocity first increases with decreased flow rate from the blade pressure surface to nearly ζ = 0.5 to 0.6.

PIV Measurements of the CEV Hot Abort Motor Plume for CFD Validation

Science.gov (United States)

Wernet, Mark; Wolter, John D.; Locke, Randy; Wroblewski, Adam; Childs, Robert; Nelson, Andrea

2010-01-01

NASA s next manned launch platform for missions to the moon and Mars are the Orion and Ares systems. Many critical aspects of the launch system performance are being verified using computational fluid dynamics (CFD) predictions. The Orion Launch Abort Vehicle (LAV) consists of a tower mounted tractor rocket tasked with carrying the Crew Module (CM) safely away from the launch vehicle in the event of a catastrophic failure during the vehicle s ascent. Some of the predictions involving the launch abort system flow fields produced conflicting results, which required further investigation through ground test experiments. Ground tests were performed to acquire data from a hot supersonic jet in cross-flow for the purpose of validating CFD turbulence modeling relevant to the Orion Launch Abort Vehicle (LAV). Both 2-component axial plane Particle Image Velocimetry (PIV) and 3-component cross-stream Stereo Particle Image Velocimetry (SPIV) measurements were obtained on a model of an Abort Motor (AM). Actual flight conditions could not be simulated on the ground, so the highest temperature and pressure conditions that could be safely used in the test facility (nozzle pressure ratio 28.5 and a nozzle temperature ratio of 3) were used for the validation tests. These conditions are significantly different from those of the flight vehicle, but were sufficiently high enough to begin addressing turbulence modeling issues that predicated the need for the validation tests.

Calculation of the weighting function and determination of the depth of correlation in micro-PIV from experimental particle images

International Nuclear Information System (INIS)

Hein, M; Seemann, R; Wieneke, B

2014-01-01

Micro-particle image velocimetry (µPIV) uses volume-illumination and imaging of particles through a single microscope objective. Displacement fields are obtained by image correlation and depend on all imaged particles, including defocused particles. The measured in-plane displacement is a weighted spatial average of the true displacement, with a weighting function W(z) that depends on the optical system and flow-gradients. The characteristic width of the weighting function W(z) is also referred to as depth of correlation (DOC) and is a measure up to which distance from the focal plane particles influence the measurement, which is crucial for the interpretation of measured flow fields. We present procedures to determine the W(z) from which the DOC can be derived and to directly determine the DOC from PIV double images, generated from experimentally recorded particle images. Both procedures provide comparable DOC results. Our approach allows determination of the DOC and W(z)as a function of out of plane gradients, optical setup parameters and PIV-analysis parameters. Experimental results for different objectives and particle sizes are discussed, revealing substantial deviations from theoretical predictions for high NA air-objectives. Moreover, using the determined weighting function W(z), the correction of measured flow profiles for errors introduced by the spatial averaging is demonstrated. (paper)

In vitro confocal micro-PIV measurements of blood flow in a square microchannel: the effect of the haematocrit on instantaneous velocity profiles.

Science.gov (United States)

Lima, Rui; Wada, Shigeo; Takeda, Motohiro; Tsubota, Ken-ichi; Yamaguchi, Takami

2007-01-01

A confocal microparticle image velocimetry (micro-PIV) system was used to obtain detailed information on the velocity profiles for the flow of pure water (PW) and in vitro blood (haematocrit up to 17%) in a 100-microm-square microchannel. All the measurements were made in the middle plane of the microchannel at a constant flow rate and low Reynolds number (Re=0.025). The averaged ensemble velocity profiles were found to be markedly parabolic for all the working fluids studied. When comparing the instantaneous velocity profiles of the three fluids, our results indicated that the profile shape depended on the haematocrit. Our confocal micro-PIV measurements demonstrate that the root mean square (RMS) values increase with the haematocrit implying that it is important to consider the information provided by the instantaneous velocity fields, even at low Re. The present study also examines the potential effect of the RBCs on the accuracy of the instantaneous velocity measurements.

Rheometry-PIV of shear-thickening wormlike micelles.

Science.gov (United States)

Marín-Santibañez, Benjamín M; Pérez-Gonzalez, José; de Vargas, Lourdes; Rodríguez-Gonzalez, Francisco; Huelsz, Guadalupe

2006-04-25

The shear-thickening behavior of an equimolar semidilute aqueous solution of 40 mM/L cetylpyridinium chloride and sodium salicylate was studied in this work by using a combined method of rheometry and particle image velocimetry (PIV). Experiments were conducted at 27.5 degrees C with Couette, vane-bob, and capillary rheometers in order to explore a wide shear stress range as well as the effect of boundary conditions and time of flow on the creation and destruction of shear-induced structures (SIS). The use of the combined method of capillary rheometry with PIV allowed the detection of fast spatial and temporal variations in the flow kinematics, which are related to the shear-thickening behavior and the dynamics of the SIS but are not distinguished by pure rheometrical measurements. A rich-in-details flow curve was found for this solution, which includes five different regimes. Namely, at very low shear rates a Newtonian behavior was found, followed by a shear thinning one in the second regime. In the third, shear banding was observed, which served as a precursor of the SIS and shear-thickening. The fourth and fifth regimes in the flow curve were separated by a spurtlike behavior, and they clearly evidenced the existence of shear-thickening accompanied by stick-slip oscillations at the wall of the rheometer, which subsequently produced variations in the shear rate under shear stress controlled flow. Such a stick-slip phenomenon prevailed up to the highest shear stresses used in this work and was reflected in asymmetric velocity profiles with spatial and temporal variations linked to the dynamics of creation and breakage of the SIS. The presence of apparent slip at the wall of the rheometer provides an energy release mechanism which leads to breakage of the SIS, followed by their further reformation during the stick part of the cycles. In addition, PIV measurements allowed the detection of apparent slip at the wall, as well as mechanical failures in the bulk of the

Three-dimensional investigation of the two-phase flow structure in a bubbly pipe flow

International Nuclear Information System (INIS)

Schmidl, W.; Hassan, Y.A.; Ortiz-Villafuerte, J.

1996-01-01

Particle image velocimetry (PIV) is a nonintrusive measurement technique that can be used to study the structure of various fluid flows. PIV is used to measure the time-varying, full-field velocity data of a particle-seeded flow field within either a two-dimensional plane or three-dimensional volume. PIV is a very efficient measurement technique since it can obtain both qualitative and quantitative spatial information about the flow field being studied. The quantitative spatial velocity information can be further processed into information of flow parameters such as vorticity and turbulence over extended areas. The objective of this study was to apply recent advances and improvements in the PIV flow measurement technique to the full-field, nonintrusive analysis of a three-dimensional, two-phase fluid flow system in such a manner that both components of the two-phase system could be experimentally quantified

PIV measurements of turbulent jet and pool mixing produced by a steam jet discharge in a subcooled water pool

International Nuclear Information System (INIS)

Choo, Yeon Jun; Song, Chul-Hwa

2010-01-01

This experimental research is on the fluid-dynamic features produced by a steam injection into a subcooled water pool. The relevant phenomena could often be encountered in water cooled nuclear power plants. Two major topics, a turbulent jet and the internal circulation produced by a steam injection, were investigated separately using a particle image velocimetry (PIV) as a non-intrusive optical measurement technique. Physical domains of both experiments have a two-dimensional axi-symmetric geometry of which the boundary and initial conditions can be readily and well defined. The turbulent jet experiments with the upward discharging configuration provide the parametric values for quantitatively describing a turbulent jet such as the self-similar velocity profile, central velocity decay, spreading rate, etc. And in the internal circulation experiments with the downward discharging configuration, typical flow patterns in a whole pool region are measured in detail, which reveals both the local and macroscopic characteristics of the mixing behavior in a pool. This quantitative data on the condensing jet-induced mixing behavior in a pool could be utilized as benchmarking for a CFD simulation of relevant phenomena.

Characterization of Unsteady Flow Structures Near Leading-Edge Slat. Part 1; PIV Measurements

Science.gov (United States)

Jenkins, Luther N.; Khorrami, Mehdi R.; Choudhari, Meelan

2004-01-01

A comprehensive computational and experimental study has been performed at the NASA Langley Research Center as part of the Quiet Aircraft Technology (QAT) Program to investigate the unsteady flow near a leading-edge slat of a two-dimensional, high-lift system. This paper focuses on the experimental effort conducted in the NASA Langley Basic Aerodynamics Research Tunnel (BART) where Particle Image Velocimetry (PIV) data was acquired in the slat cove and at the slat trailing edge of a three-element, high-lift model at 4, 6, and 8 degrees angle of attack and a freestream Mach Number of 0.17. Instantaneous velocities obtained from PIV images are used to obtain mean and fluctuating components of velocity and vorticity. The data show the recirculation in the cove, reattachment of the shear layer on the slat lower surface, and discrete vortical structures within the shear layer emanating from the slat cusp and slat trailing edge. Detailed measurements are used to examine the shear layer formation at the slat cusp, vortex shedding at the slat trailing edge, and convection of vortical structures through the slat gap. Selected results are discussed and compared with unsteady, Reynolds-Averaged Navier-Stokes (URANS) computations for the same configuration in a companion paper by Khorrami, Choudhari, and Jenkins (2004). The experimental dataset provides essential flow-field information for the validation of near-field inputs to noise prediction tools.

Scaling for turbulent viscosity of buoyant plumes in stratified fluids: PIV measurement with implications for submarine hydrothermal plume turbulence

Science.gov (United States)

Zhang, Wei; He, Zhiguo; Jiang, Houshuo

2017-11-01

Time-resolved particle image velocimetry (PIV) has been used to measure instantaneous two-dimensional velocity vector fields of laboratory-generated turbulent buoyant plumes in linearly stratified saltwater over extended periods of time. From PIV-measured time-series flow data, characteristics of plume mean flow and turbulence have been quantified. To be specific, maximum plume penetration scaling and entrainment coefficient determined from the mean flow agree well with the theory based on the entrainment hypothesis for buoyant plumes in stratified fluids. Besides the well-known persistent entrainment along the plume stem (i.e., the 'plume-stem' entrainment), the mean plume velocity field shows persistent entrainment along the outer edge of the plume cap (i.e., the 'plume-cap' entrainment), thereby confirming predictions from previous numerical simulation studies. To our knowledge, the present PIV investigation provides the first measured flow field data in the plume cap region. As to measured plume turbulence, both the turbulent kinetic energy field and the turbulence dissipation rate field attain their maximum close to the source, while the turbulent viscosity field reaches its maximum within the plume cap region; the results also show that maximum turbulent viscosity scales as νt,max = 0.030(B/N)1/2, where B is source buoyancy flux and N is ambient buoyancy frequency. These PIV data combined with previously published numerical simulation results have implications for understanding the roles of hydrothermal plume turbulence, i.e. plume turbulence within the cap region causes the 'plume-cap' entrainment that plays an equally important role as the 'plume-stem' entrainment in supplying the final volume flux at the plume spreading level.

Extraction of the wake induction and angle of attack on rotating wind turbine blades from PIV and CFD results

Directory of Open Access Journals (Sweden)

I. Herráez

2018-01-01

Full Text Available The analysis of wind turbine aerodynamics requires accurate information about the axial and tangential wake induction as well as the local angle of attack along the blades. In this work we present a new method for obtaining them conveniently from the velocity field. We apply the method to the New Mexico particle image velocimetry (PIV data set and to computational fluid dynamics (CFD simulations of the same turbine. This allows the comparison of experimental and numerical results of the mentioned quantities on a rotating wind turbine. The presented results open up new possibilities for the validation of numerical rotor models.

PIV and Rotational Raman-Based Temperature Measurements for CFD Validation in a Single Injector Cooling Flow

Science.gov (United States)

Wernet, Mark P.; Georgiadis, Nicholas J.; Locke, Randy J.

2018-01-01

Film cooling is used in a wide variety of engineering applications for protection of surfaces from hot or combusting gases. The design of more efficient thin film cooling geometries/configurations could be facilitated by an ability to accurately model and predict the effectiveness of current designs using computational fluid dynamics (CFD) code predictions. Hence, a benchmark set of flow field property data were obtained for use in assessing current CFD capabilities and for development of better turbulence models. Both Particle Image Velocimetry (PIV) and spontaneous rotational Raman scattering (SRS) spectroscopy were used to acquire high quality, spatially-resolved measurements of the mean velocity, turbulence intensity and also the mean temperature and normalized root mean square (rms) temperatures in a single injector cooling flow arrangement. In addition to flowfield measurements, thermocouple measurements on the plate surface enabled estimates of the film effectiveness. Raman spectra in air were obtained across a matrix of radial and axial locations downstream from a 68.07 mm square nozzle blowing heated air over a range of temperatures and Mach numbers, across a 30.48cm long plate equipped with a single injector cooling hole. In addition, both centerline streamwise 2-component PIV and cross-stream 3-component Stereo PIV data at 15 axial stations were collected in the same flows. The velocity and temperature data were then compared against Wind-US CFD code predictions for the same flow conditions. The results of this and planned follow-on studies will support NASA's development and assessment of turbulence models for heated flows.

Dynamic PIV measurement of the effect of sound waves in the upper plenum of the boiling water reactor

International Nuclear Information System (INIS)

Kumagai, Kosuke; Someya, Satoshi; Okamoto, Koji

2008-01-01

In recent years, power uprating of boiling power reactors has been conducted at several existing power plants in order to improve plant economy. In one power uprated plant (117.8% uprate) in the United States, steam dryer breakages due to fatigue fracture occurred. It is conceivable that the increased steam flow passing through the branches caused a self-induced vibration with the propagation of sound waves into the steam-dome. The resonance among the structure, the flow, and the pressure fluctuation resulted in the breakages. In order to clarify the basic mechanism of the resonance, previous studies were performed by conducting a point measurement of the pressure and a phase averaged measurement of the flow, although detecting the interaction among the structure, the flow, and the pressure fluctuation by the conventional method was difficult. In a preliminary study, a dynamic Particle Image Velocimetry (PIV) system was used to investigate the effect of sound on the flow. A dynamic PIV system is the newest entrant to the field of fluid flow measurement. Its paramount advantage is the instantaneous global evaluation of conditions over a plane extended across the entire velocity field. Using the dynamic PIV system, the influence of sound waves on the flow field was measured. As a result, when two speakers were placed diagonally and sound waves were presented in the same phase, vertical motion was strongly observed compared to horizontal motion. (author)

Cross-correlation Doppler global velocimetry (CC-DGV)

Science.gov (United States)

Cadel, Daniel R.; Lowe, K. Todd

2015-08-01

A flow velocimetry method, cross-correlation Doppler global velocimetry (CC-DGV), is presented as a robust, simplified, and high dynamic range implementation of the Doppler global/planar Doppler velocimetry technique. A sweep of several gigahertz of the vapor absorption spectrum is used for each velocity sample, with signals acquired from both Doppler-shifted scattered light within the flow and a non-Doppler shifted reference beam. Cross-correlation of these signals yields the Doppler shift between them, averaged over the duration of the scan. With presently available equipment, velocities from 0 ms-1 to over 3000 ms-1 can notionally be measured simultaneously, making the technique ideal for high speed flows. The processing routine is shown to be robust against large changes in the vapor pressure of the iodine cell, benefiting performance of the system in facilities where ambient conditions cannot be easily regulated. Validation of the system was performed with measurements of a model wind turbine blade boundary layer made in a 1.83 m by 1.83 m subsonic wind tunnel for which laser Doppler velocimetry (LDV) measurements were acquired alongside the CC-DGV results. CC-DGV uncertainties of ±1.30 ms-1, ±0.64 ms-1, and ±1.11 ms-1 were determined for the orthogonal stream-wise, transverse-horizontal, and transverse-vertical velocity components, and root-mean-square deviations of 2.77 ms-1 and 1.34 ms-1 from the LDV validation results were observed for Reynolds numbers of 1.5 million and 2 million, respectively. Volumetric mean velocity measurements are also presented for a supersonic jet, with velocity uncertainties of ±4.48 ms-1, ±16.93 ms-1, and ±0.50 ms-1 for the orthogonal components, and self-validation done by collapsing the data with a physical scaling.

Simulating Dynamic Stall in a 2D VAWT: Modeling strategy, verification and validation with Particle Image Velocimetry data

International Nuclear Information System (INIS)

Ferreira, C J Simao; Bijl, H; Bussel, G van; Kuik, G van

2007-01-01

The implementation of wind energy conversion systems in the built environment renewed the interest and the research on Vertical Axis Wind Turbines (VAWT), which in this application present several advantages over Horizontal Axis Wind Turbines (HAWT). The VAWT has an inherent unsteady aerodynamic behavior due to the variation of angle of attack with the angle of rotation, perceived velocity and consequentially Reynolds number. The phenomenon of dynamic stall is then an intrinsic effect of the operation of a Vertical Axis Wind Turbine at low tip speed ratios, having a significant impact in both loads and power. The complexity of the unsteady aerodynamics of the VAWT makes it extremely attractive to be analyzed using Computational Fluid Dynamics (CFD) models, where an approximation of the continuity and momentum equations of the Navier-Stokes equations set is solved. The complexity of the problem and the need for new design approaches for VAWT for the built environment has driven the authors of this work to focus the research of CFD modeling of VAWT on: .comparing the results between commonly used turbulence models: URANS (Spalart-Allmaras and k-ε) and large eddy models (Large Eddy Simulation and Detached Eddy Simulation) .verifying the sensitivity of the model to its grid refinement (space and time), .evaluating the suitability of using Particle Image Velocimetry (PIV) experimental data for model validation. The 2D model created represents the middle section of a single bladed VAWT with infinite aspect ratio. The model simulates the experimental work of flow field measurement using Particle Image Velocimetry by Simao Ferreira et al for a single bladed VAWT. The results show the suitability of the PIV data for the validation of the model, the need for accurate simulation of the large eddies and the sensitivity of the model to grid refinement

Novel Atlantic bottlenose dolphin parainfluenza virus TtPIV-1 clusters with bovine PIV-3 genotype B strains

Science.gov (United States)

Parainfluenza virus 3 (PIV-3) is a common viral infection not only in humans, but many other species. Serological evidence suggests that nearly 100% of children in the United States have been infected with PIV-3 by five years of age. Similarly, in cattle PIV-3 is commonly associated with bovine re...

μ-PIV measurements of the ensemble flow fields surrounding a migrating semi-infinite bubble.

Science.gov (United States)

Yamaguchi, Eiichiro; Smith, Bradford J; Gaver, Donald P

2009-08-01

Microscale particle image velocimetry (μ-PIV) measurements of ensemble flow fields surrounding a steadily-migrating semi-infinite bubble through the novel adaptation of a computer controlled linear motor flow control system. The system was programmed to generate a square wave velocity input in order to produce accurate constant bubble propagation repeatedly and effectively through a fused glass capillary tube. We present a novel technique for re-positioning of the coordinate axis to the bubble tip frame of reference in each instantaneous field through the analysis of the sudden change of standard deviation of centerline velocity profiles across the bubble interface. Ensemble averages were then computed in this bubble tip frame of reference. Combined fluid systems of water/air, glycerol/air, and glycerol/Si-oil were used to investigate flows comparable to computational simulations described in Smith and Gaver (2008) and to past experimental observations of interfacial shape. Fluorescent particle images were also analyzed to measure the residual film thickness trailing behind the bubble. The flow fields and film thickness agree very well with the computational simulations as well as existing experimental and analytical results. Particle accumulation and migration associated with the flow patterns near the bubble tip after long experimental durations are discussed as potential sources of error in the experimental method.

μ-PIV measurements of the ensemble flow fields surrounding a migrating semi-infinite bubble

Science.gov (United States)

Yamaguchi, Eiichiro; Smith, Bradford J.; Gaver, Donald P.

2012-01-01

Microscale particle image velocimetry (μ-PIV) measurements of ensemble flow fields surrounding a steadily-migrating semi-infinite bubble through the novel adaptation of a computer controlled linear motor flow control system. The system was programmed to generate a square wave velocity input in order to produce accurate constant bubble propagation repeatedly and effectively through a fused glass capillary tube. We present a novel technique for re-positioning of the coordinate axis to the bubble tip frame of reference in each instantaneous field through the analysis of the sudden change of standard deviation of centerline velocity profiles across the bubble interface. Ensemble averages were then computed in this bubble tip frame of reference. Combined fluid systems of water/air, glycerol/air, and glycerol/Si-oil were used to investigate flows comparable to computational simulations described in Smith and Gaver (2008) and to past experimental observations of interfacial shape. Fluorescent particle images were also analyzed to measure the residual film thickness trailing behind the bubble. The flow fields and film thickness agree very well with the computational simulations as well as existing experimental and analytical results. Particle accumulation and migration associated with the flow patterns near the bubble tip after long experimental durations are discussed as potential sources of error in the experimental method. PMID:23049158

Investigation of a transonic separating/reattaching shear layer by means of PIV

Directory of Open Access Journals (Sweden)

S. Scharnowski

2015-01-01

Full Text Available The separating/reattaching flow over an axisymmetric backward-facing step is analyzed experimentally by means of particle image velocimetry (PIV. The main purpose of the measurements is the investigation of the mean flow field as well as of the Reynolds stress distributions at a Mach number of 0.7 and at a Reynolds number of 3.3×105 based on the step height. Due to the strong progress of optical flow measurements in the last years it was possible to resolve all flow scales down to 180μm (≈1% of the step height with high precision. Thanks to the high spatial resolution it was found for the first time that the Reynolds stress distribution features a local minimum between the first part of the shear layer and a region inside the recirculation region. This implies a more complex wake dynamics than assumed before.

Comparison of Stereo-PIV and Plenoptic-PIV Measurements on the Wake of a Cylinder in NASA Ground Test Facilities.

Science.gov (United States)

Fahringer, Timothy W.; Thurow, Brian S.; Humphreys, William M., Jr.; Bartram, Scott M.

2017-01-01

A series of comparison experiments have been performed using a single-camera plenoptic PIV measurement system to ascertain the systems performance capabilities in terms of suitability for use in NASA ground test facilities. A proof-of-concept demonstration was performed in the Langley Advanced Measurements and Data Systems Branch 13-inch (33- cm) Subsonic Tunnel to examine the wake of a series of cylinders at a Reynolds number of 2500. Accompanying the plenoptic-PIV measurements were an ensemble of complementary stereo-PIV measurements. The stereo-PIV measurements were used as a truth measurement to assess the ability of the plenoptic-PIV system to capture relevant 3D/3C flow field features in the cylinder wake. Six individual tests were conducted as part of the test campaign using three different cylinder diameters mounted in two orientations in the tunnel test section. This work presents a comparison of measurements with the cylinders mounted horizontally (generating a 2D flow field in the x-y plane). Results show that in general the plenoptic-PIV measurements match those produced by the stereo-PIV system. However, discrepancies were observed in extracted pro les of the fuctuating velocity components. It is speculated that spatial smoothing of the vector fields in the stereo-PIV system could account for the observed differences. Nevertheless, the plenoptic-PIV system performed extremely well at capturing the flow field features of interest and can be considered a viable alternative to traditional PIV systems in smaller NASA ground test facilities with limited optical access.

A PIV Study of Slotted Air Injection for Jet Noise Reduction

Science.gov (United States)

Henderson, Brenda S.; Wernet, Mark P.

2012-01-01

Results from acoustic and Particle Image Velocimetry (PIV) measurements are presented for single and dual-stream jets with fluidic injection on the core stream. The fluidic injection nozzles delivered air to the jet through slots on the interior of the nozzle at the nozzle trailing edge. The investigations include subsonic and supersonic jet conditions. Reductions in broadband shock noise and low frequency mixing noise were obtained with the introduction of fluidic injection on single stream jets. Fluidic injection was found to eliminate shock cells, increase jet mixing, and reduce turbulent kinetic energy levels near the end of the potential core. For dual-stream subsonic jets, the introduction of fluidic injection reduced low frequency noise in the peak jet noise direction and enhanced jet mixing. For dual-stream jets with supersonic fan streams and subsonic core streams, the introduction of fluidic injection in the core stream impacted the jet shock cell structure but had little effect on mixing between the core and fan streams.

Tomographic Particle Image Velocimetry using Smartphones and Colored Shadows

KAUST Repository

Aguirre-Pablo, Andres A.

2017-06-12

We demonstrate the viability of using four low-cost smartphone cameras to perform Tomographic PIV. We use colored shadows to imprint two or three different time-steps on the same image. The back-lighting is accomplished with three sets of differently-colored pulsed LEDs. Each set of Red, Green & Blue LEDs is shone on a diffuser screen facing each of the cameras. We thereby record the RGB-colored shadows of opaque suspended particles, rather than the conventionally used scattered light. We subsequently separate the RGB color channels, to represent the separate times, with preprocessing to minimize noise and cross-talk. We use commercially available Tomo-PIV software for the calibration, 3-D particle reconstruction and particle-field correlations, to obtain all three velocity components in a volume. Acceleration estimations can be done thanks to the triple pulse illumination. Our test flow is a vortex ring produced by forcing flow through a circular orifice, using a flexible membrane, which is driven by a pressurized air pulse. Our system is compared to a commercial stereoscopic PIV system for error estimations. We believe this proof of concept experiment will make this technique available for education, industry and scientists for a fraction of the hardware cost needed for traditional Tomo-PIV.

Dynamic PIV measurement on the effect of sound wave in upper plenum of boiling water reactor

International Nuclear Information System (INIS)

Kumagai, Kosuke; Someya, Satoshi; Okamoto, Koji

2008-01-01

In one of the power uprated plants in the United States, the steam dryer breakages due to fatigue fracture occurred. It is conceivable that the increased steam flow passing through the branches caused a self-induced vibration with the propagation of sound wave into the steam-dome. The resonance among the structure, flow and the pressure fluctuation resulted in the breakages. To understand the basic mechanism of the resonance, previous researches were done by a point measurement of the pressure and by a phase averaged measurement of the flow, while it was difficult to detect the interaction among them by the conventional method. In the preliminary study, Dynamic Particle Image Velocimetry (PIV) System was applied to investigate the effect of sound on the flow. (author)

Planar measurements of velocity and concentration of turbulent mixing in a T-junction

DEFF Research Database (Denmark)

Ingvorsen, Kristian Mark; Meyer, Knud Erik; Nielsen, N. F.

Turbulent mixing of two isothermal air streams in a T-junction of square ducts are investigated. Three dimensional velocity fields and turbulent kinetic energy are measured with stereoscopic Particle Image Velocimetry (PIV). The concentration field is obtained with a planar Mie scattering technique...

Laboratory modelling of the wind-wave interaction with modified PIV-method

Directory of Open Access Journals (Sweden)

Sergeev Daniil

2017-01-01

Full Text Available Laboratory experiments on studying the structure of the turbulent air boundary layer over waves were carried out at the Wind-Wave Flume of the Large Thermostratified Tank of the Institute of Applied Physics, Russian Academy of Sciences (IAP RAS, in conditions modeling the near water boundary layer of the atmosphere under strong and hurricane winds and the equivalent wind velocities from 10 to 48 m/s at the standard height of 10 m. A modified technique of Particle Image Velocimetry (PIV was used to obtain turbulent pulsation averaged velocity fields of the air flow over the water surface curved by a wave and average profiles of the wind velocity. The main modifications are: 1 the use of high-speed video recording (1000-10000 frames/sec with continuous laser illumination helps to obtain ensemble of the velocity fields in all phases of the wavy surface for subsequent statistical processing; 2 the development and application of special algorithms for obtaining form of the curvilinear wavy surface of the images for the conditions of parasitic images of the particles and the droplets in the air side close to the surface; 3 adaptive cross-correlation image processing to finding the velocity fields on a curved grid, caused by wave boarder; 4 using Hilbert transform to detect the phase of the wave in which the measured velocity field for subsequent appropriate binning within procedure obtaining the average characteristics.

Laboratory modelling of the wind-wave interaction with modified PIV-method

Science.gov (United States)

Sergeev, Daniil; Kandaurov, Alexander; Troitskaya, Yuliya; Caulliez, Guillemette; Bopp, Maximilian; Jaehne, Bernd

Laboratory experiments on studying the structure of the turbulent air boundary layer over waves were carried out at the Wind-Wave Flume of the Large Thermostratified Tank of the Institute of Applied Physics, Russian Academy of Sciences (IAP RAS), in conditions modeling the near water boundary layer of the atmosphere under strong and hurricane winds and the equivalent wind velocities from 10 to 48 m/s at the standard height of 10 m. A modified technique of Particle Image Velocimetry (PIV) was used to obtain turbulent pulsation averaged velocity fields of the air flow over the water surface curved by a wave and average profiles of the wind velocity. The main modifications are: 1) the use of high-speed video recording (1000-10000 frames/sec) with continuous laser illumination helps to obtain ensemble of the velocity fields in all phases of the wavy surface for subsequent statistical processing; 2) the development and application of special algorithms for obtaining form of the curvilinear wavy surface of the images for the conditions of parasitic images of the particles and the droplets in the air side close to the surface; 3) adaptive cross-correlation image processing to finding the velocity fields on a curved grid, caused by wave boarder; 4) using Hilbert transform to detect the phase of the wave in which the measured velocity field for subsequent appropriate binning within procedure obtaining the average characteristics.

Pressure spectra from single-snapshot tomographic PIV

Science.gov (United States)

Schneiders, Jan F. G.; Avallone, Francesco; Pröbsting, Stefan; Ragni, Daniele; Scarano, Fulvio

2018-03-01

The power spectral density and coherence of temporal pressure fluctuations are obtained from low-repetition-rate tomographic PIV measurements. This is achieved by extension of recent single-snapshot pressure evaluation techniques based upon the Taylor's hypothesis (TH) of frozen turbulence and vortex-in-cell (VIC) simulation. Finite time marching of the measured instantaneous velocity fields is performed using TH and VIC. Pressure is calculated from the resulting velocity time series. Because of the theoretical limitations, the finite time marching can be performed until the measured flow structures are convected out of the measurement volume. This provides a lower limit of resolvable frequency range. An upper limit is given by the spatial resolution of the measurements. Finite time-marching approaches are applied to low-repetition-rate tomographic PIV data of the flow past a straight trailing edge at 10 m/s. Reference results of the power spectral density and coherence are obtained from surface pressure transducers. In addition, the results are compared to state-of-the-art experimental data obtained from time-resolved tomographic PIV performed at 10 kHz. The time-resolved approach suffers from low spatial resolution and limited maximum acquisition frequency because of hardware limitations. Additionally, these approaches strongly depend upon the time kernel length chosen for pressure evaluation. On the other hand, the finite time-marching approaches make use of low-repetition-rate tomographic PIV measurements that offer higher spatial resolution. Consequently, increased accuracy of the power spectral density and coherence of pressure fluctuations are obtained in the high-frequency range, in comparison to the time-resolved measurements. The approaches based on TH and VIC are found to perform similarly in the high-frequency range. At lower frequencies, TH is found to underestimate coherence and intensity of the pressure fluctuations in comparison to time-resolved PIV

A regular Strouhal number for large-scale instability in the far wake of a rotor

DEFF Research Database (Denmark)

Okulov, Valery; Naumov, Igor V.; Mikkelsen, Robert Flemming

2014-01-01

The flow behind a model of a wind turbine rotor is investigated experimentally in a water flume using particle image velocimetry (PIV) and laser Doppler anemometry (LDA). The study performed involves a three-bladed wind turbine rotor designed using the optimization technique of Glauert (Aerodynamic...... visualizations and a reconstruction of the flow field using LDA and PIV measurements it is found that the wake dynamics is associated with a precession (rotation) of the helical vortex core....

A 3D velocimetry study of the flow through prosthetic heart valves

Science.gov (United States)

Ledesma, R.; Zenit, R.; Pulos, G.; Sanchez, E.; Juarez, A.

2006-11-01

Blood damage commonly appears in medical valve prothesis. It is a mayor concern for the designers and surgeons. It is well known that this damage and other complications result from the modified fluid dynamics through the replacement valve. To evaluate the performance of prosthetic heart valves, it is necessary to study the flow through them. To conduct this study , we have built a flow channel that emulates cardiac conditions and allows optical access such that a 3D-PIV velocimetry system could be used. The experiments are aimed to reconstruct the downstream structure of the flow through a mechanical and a bio-material tricuspid heart valve prothesis. Preliminary results show that the observed coherent structures can be related with haemolysis and trombosis, illnesses commonly found in valve prothesis recipients. The mean flow, the levels of strain rate and the turbulence intensity generated by the valves can also be directly related to blood damage. In general, bio-material made valves tend to reduce these complications.

PIV investigation of the flow induced by a passive surge control method in a radial compressor

Energy Technology Data Exchange (ETDEWEB)

Guillou, Erwann; Gancedo, Matthieu; Gutmark, Ephraim [University of Cincinnati, Department of Aerospace Engineering, Cincinnati, OH (United States); Mohamed, Ashraf [Honeywell Turbo Technologies, Greater Los Angeles, CA (United States)

2012-09-15

Due to recent emission regulations, the use of turbochargers for force induction of internal combustion engines has increased. Actually, the trend in diesel engines is to downsize the engine by use of turbochargers that operate at higher pressure ratios. Unfortunately, increasing the impeller rotational speed of turbocharger radial compressors tends to reduce their range of operation, which is limited at low mass flow rate by the occurrence of surge. In order to extend the operability of turbochargers, compressor housings can be equipped with a passive surge control device such as a ''ported shroud.'' This specific casing treatment has been demonstrated to enhance the surge margin with minor negative impact on the compressor efficiency. However, the actual working mechanisms of the system remain not well understood. Hence, in order to optimize the design of the ported shroud, it is crucial to identify the dynamic flow changes induced by the implementation of the device to control instabilities. From the full dynamic survey of the compressor performance characteristics obtained with and without ported shroud, specific points of operation were selected to carry out planar flow visualization. At normal working, both standard and stereoscopic particle imaging velocimetry (PIV) measurements were performed to evaluate instantaneous and mean velocity flow fields at the inlet of the compressor. At incipient and full surge, phase-locked PIV measurements were added. As a result, satisfying characterization of the compressor instabilities was provided at different operational speeds. Combining transient pressure data and PIV measurements, the time evolution of the complex flow patterns occurring at surge was reconstructed and a better insight into the bypass mechanism was achieved. (orig.)

PIV investigation of the flow induced by a passive surge control method in a radial compressor

Science.gov (United States)

Guillou, Erwann; Gancedo, Matthieu; Gutmark, Ephraim; Mohamed, Ashraf

2012-09-01

Due to recent emission regulations, the use of turbochargers for force induction of internal combustion engines has increased. Actually, the trend in diesel engines is to downsize the engine by use of turbochargers that operate at higher pressure ratios. Unfortunately, increasing the impeller rotational speed of turbocharger radial compressors tends to reduce their range of operation, which is limited at low mass flow rate by the occurrence of surge. In order to extend the operability of turbochargers, compressor housings can be equipped with a passive surge control device such as a "ported shroud." This specific casing treatment has been demonstrated to enhance the surge margin with minor negative impact on the compressor efficiency. However, the actual working mechanisms of the system remain not well understood. Hence, in order to optimize the design of the ported shroud, it is crucial to identify the dynamic flow changes induced by the implementation of the device to control instabilities. From the full dynamic survey of the compressor performance characteristics obtained with and without ported shroud, specific points of operation were selected to carry out planar flow visualization. At normal working, both standard and stereoscopic particle imaging velocimetry (PIV) measurements were performed to evaluate instantaneous and mean velocity flow fields at the inlet of the compressor. At incipient and full surge, phase-locked PIV measurements were added. As a result, satisfying characterization of the compressor instabilities was provided at different operational speeds. Combining transient pressure data and PIV measurements, the time evolution of the complex flow patterns occurring at surge was reconstructed and a better insight into the bypass mechanism was achieved.

PIV Analysis Comparing Aerodynamic Downforce Devices on Race Car in Water Tunnel

Science.gov (United States)

Hellman, Sam; Tkacik, Peter; Uddin, Mesbah; Kelly, Scott

2010-11-01

There have been claims that the rear wing on the NASCAR Car of Tomorrow (COT) race car causes lift in the condition where the car spins during a crash and is traveling backwards down the track at a high rate of speed. When enough lift is generated, the race car can lose control and even fly off of the track surface completely. To address this concern, a new rear spoiler was designed by NASCAR to replace the wing and prevent this dangerous condition. Flow characteristics of both the rear wing and the new spoiler are qualitatively analyzed using particle image velocimetry (PIV). The experiment is done in a continuous flow water tunnel using a simplified 10% scale model COT. Flow structures are identified and compared for both the wing and spoiler. The same conditions are also reviewed when the car is traveling backwards as it might during a crash. The cause of the lift generated by the rear wing when in reverse is shown.

Laser speckle velocimetry applied to Rayleigh-Benard convection

International Nuclear Information System (INIS)

Arroyo, M.P.; Yonte, T.; Quintanilla, M.; Saviron, J.M.

1986-01-01

An application of speckle velocimetry technique to Rayleigh-Benard convection is presented. A 5-mW He-Ne laser allows precise determination of the two-dimensional velocity flow field, up to several mm/sec. The digital techniques used to analyze automatically the multiexposed photographs and to generate velocity and vorticity fields are described. The obtained results are in good agreement with previously reported data. The ability of the technique to cover other experimental conditions is discussed. 14 references

Investigation of a turbulent spot and a tripped turbulent boundary layer flow using time-resolved tomographic PIV

NARCIS (Netherlands)

Schröder, A.; Geisler, R.; Elsinga, G.E.; Scarano, F.; Dierksheide, U.

2007-01-01

In this feasibility study the tomographic PIV technique has been applied to time resolved PIV recordings for the study of the growth of a turbulent spot in a laminar flat plate boundary layer and to visualize the topology of coherent flow structures within a tripped turbulent flat plate boundary

Improvement in the independence of relaxation method-based particle tracking velocimetry

International Nuclear Information System (INIS)

Jia, P; Wang, Y; Zhang, Y

2013-01-01

New techniques are developed to improve the independence of relaxation method-based particle tracking velocimetry (RM-PTV). Firstly, Delaunay tessellation (DT) is employed to form clusters of neighboring particles with similar motion in the same frame; and then a bidirectional calculation concept is adopted to improve the way of particle pairing. These new techniques are tested with both self-defined particle images and the particle image velocimetry standard synthetic particle images. The results indicate that the DT method performs well and efficiently in determining the particle clusters, and the particle pairing process is well optimized by the bidirectional calculation concept. With these methods, three computation parameters are eliminated, which makes RM-PTV more autonomous in applications. (paper)

μ-PIV/Shadowgraphy measurements to elucidate dynamic physicochemical interactions in a multiphase model of pulmonary airway reopening

Science.gov (United States)

Yamaguchi, Eiichiro

2010-10-01

We employ micro-particle image velocimetry (μ-PIV) and shadowgraphy to measure the ensemble-averaged fluid-phase velocity field and interfacial geometry during pulsatile bubble propagation that includes a reverse-flow phase under influence of exogenous lung surfactant (Infasurf). Disease states such as respiratory distress syndrome (RDS) are characterized by insufficient pulmonary surfactant concentrations that enhance airway occlusion and collapse. Subsequent airway reopening, driven by mechanical ventilation, may generate damaging stresses that cause ventilator-induced lung injury (VILI). It is hypothesized that reverse flow may enhance surfactant uptake and protect the lung from VILI. The microscale observations conducted in this study will provide us with a significant understanding of dynamic physicochemical interactions that can be manipulated to reduce the magnitude of this damaging mechanical stimulus during airway reopening. Bubble propagation through a liquid-occluded fused glass capillary tube is controlled by linear-motor-driven syringe pumps that provide mean and sinusoidal velocity components. A translating microscope stage mechanically subtracts the mean velocity of the bubble tip in order to hold the progressing bubble tip in the microscope field of view. To optimize the signal-to-noise ratio near the bubble tip, μ-PIV and shadow images are recorded in separate trials then combined during post-processing with help of a custom-designed micro scale marker. Non-specific binding of Infasurf proteins to the channel wall is controlled by oxidation and chemical treatment of the glass surface. The colloidal stability and dynamic/static surface properties of the Infasurf-PIV particle solution are carefully adjusted based on Langmuir trough measurements. The Finite Time Lyapunov Exponent (FTLE) is computed to provide a Lagrangian perspective for comparison with our boundary element predictions.

Broadband phase difference method for ultrasonic velocimetry in molten glass

International Nuclear Information System (INIS)

Kikura, Hiroshige; Ihara, Tomonori

2016-01-01

This study aims to develop ultrasonic Doppler velocimetry in molten glass. Realization of such a technique has two difficulties: ultrasonic transmission into molten salt and Doppler signal processing. Buffer rod technique was developed in our research to transmit ultrasound into high temperature molten glass. This article discusses newly developed signal processing technique named broadband phase difference method. (J.P.N.)

Study on Natural Convection around a vertical heated rod using PIV/LIF technique,

International Nuclear Information System (INIS)

Szijarto, R.; Yamaji, B.; Aszodi, A.

2010-01-01

The Nuclear Training Reactor of the Institute of Nuclear Techniques (Budapest University of Technology and Economics, Hungary) is a pool-type reactor with light water moderator and with a maximum thermal power of 100 kW. The fuel elements are cooled by natural convection. An experimental setup was built to analyse the nature of the natural convection around a heated rod. The flow field was investigated using an electrically heated rod, which models the geometry of a fuel pin in the training reactor. The electric power of the model rod is variable between 0-500 W. The rod was placed in a square-based glass tank. Particle Image Velocimetry and Laser Induced Fluorescence measurement techniques were used to study the velocity and temperature field in a two-dimensional area. The thermal and the hydraulic boundary layers were detected near a rod in a lower section of the aquarium. The laminar-turbulent transition of the flow regime was observed, the maximum velocity of the up-flow was 0.025-0.05 m/s. From the temperature measurements the local heat transfer coefficient was estimated. (Authors)

Visualization of nasal airflow patterns in a patient affected with atrophic rhinitis using particle image velocimetry

Energy Technology Data Exchange (ETDEWEB)

Garcia, G J M [Hamner Institutes for Health Sciences, NC (United States); Mitchell, G [The Queens University of Belfast, Belfast (United Kingdom); Bailie, N [The Queens University of Belfast, Belfast (United Kingdom); Thornhill, D [The Queens University of Belfast, Belfast (United Kingdom); Watterson, J [The Queens University of Belfast, Belfast (United Kingdom); Kimbell, J S [Hamner Institutes for Health Sciences, NC (United States)

2007-10-15

The relationship between airflow patterns in the nasal cavity and nasal function is poorly understood. This paper reports an experimental study of the interplay between symptoms and airflow patterns in a patient affected with atrophic rhinitis. This pathology is characterized by mucosal dryness, fetor, progressive atrophy of anatomical structures, a spacious nasal cavity, and a paradoxical sensation of nasal congestion. A physical replica of the patient's nasal geometry was made and particle image velocimetry (PIV) was used to visualize and measure the flow field. The nasal replica was based on computed tomography (CT) scans of the patient and was built in three steps: three-dimensional reconstruction of the CT scans; rapid prototyping of a cast; and sacrificial use of the cast to form a model of the nasal passage in clear silicone. Flow patterns were measured by running a water-glycerol mixture through the replica and evaluating the displacement of particles dispersed in the liquid using PIV. The water-glycerol flow rate used corresponded to an air flow rate representative of a human breathing at rest. The trajectory of the flow observed in the left passage of the nose (more affected by atrophic rhinitis) differed markedly from what is considered normal, and was consistent with patterns of epithelial damage observed in cases of the condition. The data are also useful for validation of computational fluid dynamics predictions.

Visual Observations of Bubbly Flow in a Subchannel by using Optical Measurement Methods

International Nuclear Information System (INIS)

Chang, Seok Kyu; Choo, Yeon Jun; Kim, B. D.; Song, Chul Hwa

2008-01-01

PIV (Particle Image Velocimetry) measurement technique is widely used in the experimental study on the fluid flow in many industrial fields. In the study of the subchannel mixing in a nuclear reactor, there have been many works by using optical measurement techniques and almost of these were limited to the single phase flow. But many occasions of safety issues in a nuclear power plant are in a condition of two phase flow. In an application of two phase flow in subchannels, intrusive probes i.e., a conductivity sensor or an optical sensor were generally used. But these probes cause breaks or distortions of bubbles when contact. PIV technique is one of the non-intrusive measurement methods which can avoid the problem of intrusive probes. This study presents an applicability of the PIV technique on an experimental study of a bubbly flow in the subchannel geometry. The bubble peaking in a subchannel according to the bubble sizes was demonstrated. The HSC (high speed camera) was also used to confirm the PIV measurement results

The Use of Tactile Sensors and PIV Analysis for Understanding the Bearing Mechanism of Pile Groups.

Science.gov (United States)

You, Zhijia; Chen, Yulong

2018-02-06

Model tests were carried out in dry silica sand under pile loading and visualizing observation to investigate the behavior of a pile group. The pile group consisted of nine cylindrical model piles of 40 mm in diameter in most tests or three rectangular parallelepiped model piles in the visualizing observation. Pile spacings of 200 mm and 100 mm between pile centers were used in the models. Tactile sensors were installed to measure the pressure distribution in the ground and colored sand layer with particle image velocimetry (PIV) analysis to reveal the ground deformation in addition to strain gauges inside the model piles to investigate the interaction among group piles. The tests results showed that a narrower spacing between piles resulted in a wider affected area of the ground and the interaction was more significant below the tips.

Motion tracking-enhanced MART for tomographic PIV

International Nuclear Information System (INIS)

Novara, Matteo; Scarano, Fulvio; Batenburg, Kees Joost

2010-01-01

A novel technique to increase the accuracy of multiplicative algebraic reconstruction technique (MART) reconstruction from tomographic particle image velocimetry (PIV) recordings at higher seeding density than currently possible is presented. The motion tracking enhancement (MTE) method is based on the combined utilization of images from two or more exposures to enhance the reconstruction of individual intensity fields. The working principle is first introduced qualitatively, and the mathematical background is given that explains how the MART reconstruction can be improved on the basis of an improved first guess object obtained from the combination of non-simultaneous views reduced to the same time instant deforming the 3D objects by an estimate of the particle motion field. The performances of MTE are quantitatively evaluated by numerical simulation of the imaging, reconstruction and image correlation processes. The cases of two or more exposures obtained from time-resolved experiments are considered. The iterative application of MTE appears to significantly improve the reconstruction quality, first by decreasing the intensity of the ghost images and second, by increasing the intensity and the reconstruction precision for the actual particles. Based on computer simulations, the maximum imaged seeding density that can be dealt with is tripled with respect to the MART analysis applied to a single exposure. The analysis also illustrates that the maximum effect of the MTE method is comparable to that of doubling the number of cameras in the tomographic system. Experiments performed on a transitional jet at Re = 5000 apply the MTE method to double-frame recordings. The velocity measurement precision is increased for a system with fewer views (two or three cameras compared with four cameras). The ghost particles' intensity is also visibly reduced although to a lesser extent with respect to the computer simulations. The velocity and vorticity field obtained from a three

Remote measurement of surface-water velocity using infrared videography and PIV: a proof-of-concept for Alaskan rivers

Science.gov (United States)

Kinzel, Paul J.; Legleiter, Carl; Nelson, Jonathan M.; Conaway, Jeffrey S.

2017-01-01

Thermal cameras with high sensitivity to medium and long wavelengths can resolve features at the surface of flowing water arising from turbulent mixing. Images acquired by these cameras can be processed with particle image velocimetry (PIV) to compute surface velocities based on the displacement of thermal features as they advect with the flow. We conducted a series of field measurements to test this methodology for remote sensing of surface velocities in rivers. We positioned an infrared video camera at multiple stations across bridges that spanned five rivers in Alaska. Simultaneous non-contact measurements of surface velocity were collected with a radar gun. In situ velocity profiles were collected with Acoustic Doppler Current Profilers (ADCP). Infrared image time series were collected at a frequency of 10Hz for a one-minute duration at a number of stations spaced across each bridge. Commercial PIV software used a cross-correlation algorithm to calculate pixel displacements between successive frames, which were then scaled to produce surface velocities. A blanking distance below the ADCP prevents a direct measurement of the surface velocity. However, we estimated surface velocity from the ADCP measurements using a program that normalizes each ADCP transect and combines those normalized transects to compute a mean measurement profile. The program can fit a power law to the profile and in so doing provides a velocity index, the ratio between the depth-averaged and surface velocity. For the rivers in this study, the velocity index ranged from 0.82 – 0.92. Average radar and extrapolated ADCP surface velocities were in good agreement with average infrared PIV calculations.

Measurement and Image Processing Techniques for Particle Image Velocimetry Using Solid-Phase Carbon Dioxide

Science.gov (United States)

2014-03-27

stereoscopic PIV: the angular displacement configuration and the translation configuration. The angular displacement configuration is most commonly used today...images were processed using ImageJ, an open-source, Java -based image processing software available from the National Institute of Health (NIH). The

Single calibration multiplane stereo-PIV: the effect of mitral valve orientation on three-dimensional flow in a left ventricle model

Science.gov (United States)

Saaid, Hicham; Segers, Patrick; Novara, Matteo; Claessens, Tom; Verdonck, Pascal

2018-03-01

The characterization of flow patterns in the left ventricle may help the development and interpretation of flow-based parameters of cardiac function and (patho-)physiology. Yet, in vivo visualization of highly dynamic three-dimensional flow patterns in an opaque and moving chamber is a challenging task. This has been shown in several recent multidisciplinary studies where in vivo imaging methods are often complemented by in silico solutions, or by in vitro methods. Because of its distinctive features, particle image velocimetry (PIV) has been extensively used to investigate flow dynamics in the cardiovascular field. However, full volumetric PIV data in a dynamically changing geometry such as the left ventricle remain extremely scarce, which justifies the present study. An investigation of the left ventricle flow making use of a customized cardiovascular simulator is presented; a multiplane scanning-stereoscopic PIV setup is used, which allows for the measurement of independent planes across the measurement volume. Due to the accuracy in traversing the illumination and imaging systems, the present setup allows to reconstruct the flow in a 3D volume performing only one single calibration. The effects of the orientation of a prosthetic mitral valve in anatomical and anti-anatomical configurations have been investigated during the diastolic filling time. The measurement is performed in a phase-locked manner; the mean velocity components are presented together with the vorticity and turbulent kinetic energy maps. The reconstructed 3D flow structures downstream the bileaflet mitral valve are shown, which provides additional insight of the highly three-dimensional flow.

Digital PIV (DPIV) Software Analysis System

Science.gov (United States)

Blackshire, James L.

1997-01-01

A software package was developed to provide a Digital PIV (DPIV) capability for NASA LaRC. The system provides an automated image capture, test correlation, and autocorrelation analysis capability for the Kodak Megaplus 1.4 digital camera system for PIV measurements. The package includes three separate programs that, when used together with the PIV data validation algorithm, constitutes a complete DPIV analysis capability. The programs are run on an IBM PC/AT host computer running either Microsoft Windows 3.1 or Windows 95 using a 'quickwin' format that allows simple user interface and output capabilities to the windows environment.

PIV and PTV measurements in hydro-sciences with focus on turbulent open-channel flows

OpenAIRE

Nezu, Iehisa; Sanjou, Michio

2011-01-01

PIV is one of the most popular measurement techniques in hydraulic engineering as well as in fluid sciences. It has been applied to study various turbulent phenomena in laboratory experiments related to natural rivers, e.g., bursting phenomena near the bed, mixing layers observed at confluences, wake turbulence around dikes and piers, and so on. In these studies, PIV plays important roles in revealing the space-time structure of velocity fluctuations and coherent vortices. This review article...

Stereo particle image velocimetry set up for measurements in the wake of scaled wind turbines

Science.gov (United States)

Campanardi, Gabriele; Grassi, Donato; Zanotti, Alex; Nanos, Emmanouil M.; Campagnolo, Filippo; Croce, Alessandro; Bottasso, Carlo L.

2017-08-01

Stereo particle image velocimetry measurements were carried out in the boundary layer test section of Politecnico di Milano large wind tunnel to survey the wake of a scaled wind turbine model designed and developed by Technische Universität München. The stereo PIV instrumentation was set up to survey the three velocity components on cross-flow planes at different longitudinal locations. The area of investigation covered the entire extent of the wind turbines wake that was scanned by the use of two separate traversing systems for both the laser and the cameras. Such instrumentation set up enabled to gain rapidly high quality results suitable to characterise the behaviour of the flow field in the wake of the scaled wind turbine. This would be very useful for the evaluation of the performance of wind farm control methodologies based on wake redirection and for the validation of CFD tools.

PIV-based estimation of unsteady loads on a flat plate at high angle of attack using momentum equation approaches

Science.gov (United States)

Guissart, A.; Bernal, L. P.; Dimitriadis, G.; Terrapon, V. E.

2017-05-01

This work presents, compares and discusses results obtained with two indirect methods for the calculation of aerodynamic forces and pitching moment from 2D Particle Image Velocimetry (PIV) measurements. Both methodologies are based on the formulations of the momentum balance: the integral Navier-Stokes equations and the "flux equation" proposed by Noca et al. (J Fluids Struct 13(5):551-578, 1999), which has been extended to the computation of moments. The indirect methods are applied to spatio-temporal data for different separated flows around a plate with a 16:1 chord-to-thickness ratio. Experimental data are obtained in a water channel for both a plate undergoing a large amplitude imposed pitching motion and a static plate at high angle of attack. In addition to PIV data, direct measurements of aerodynamic loads are carried out to assess the quality of the indirect calculations. It is found that indirect methods are able to compute the mean and the temporal evolution of the loads for two-dimensional flows with a reasonable accuracy. Nonetheless, both methodologies are noise sensitive, and the parameters impacting the computation should thus be chosen carefully. It is also shown that results can be improved through the use of dynamic mode decomposition (DMD) as a pre-processing step.

Creating a benchmark of vertical axis wind turbines in dynamic stall for validating numerical models

DEFF Research Database (Denmark)

Castelein, D.; Ragni, D.; Tescione, G.

2015-01-01

An experimental campaign using Particle Image Velocimetry (2C-PIV) technique has been conducted on a H-type Vertical Axis Wind Turbine (VAWT) to create a benchmark for validating and comparing numerical models. The turbine is operated at tip speed ratios (TSR) of 4.5 and 2, at an average chord...

Assembling filamentous phage occlude pIV channels.

Science.gov (United States)

Marciano, D K; Russel, M; Simon, S M

2001-07-31

Filamentous phage f1 is exported from its Escherichia coli host without killing the bacterial cell. Phage-encoded protein pIV, which is required for phage assembly and secretion, forms large highly conductive channels in the outer membrane of E. coli. It has been proposed that the phage are extruded across the bacterial outer membrane through pIV channels. To test this prediction, we developed an in vivo assay by using a mutant pIV that functions in phage export but whose channel opens in the absence of phage extrusion. In E. coli lacking its native maltooligosacharride transporter LamB, this pIV variant allowed oligosaccharide transport across the outer membrane. This entry of oligosaccharide was decreased by phage production and still further decreased by production of phage that cannot be released from the cell surface. Thus, exiting phage block the pIV-dependent entry of oligosaccharide, suggesting that phage occupy the lumen of pIV channels. This study provides the first evidence, to our knowledge, for viral exit through a large aqueous channel.

HFSB-seeding for large-scale tomographic PIV in wind tunnels

Science.gov (United States)

Caridi, Giuseppe Carlo Alp; Ragni, Daniele; Sciacchitano, Andrea; Scarano, Fulvio

2016-12-01

A new system for large-scale tomographic particle image velocimetry in low-speed wind tunnels is presented. The system relies upon the use of sub-millimetre helium-filled soap bubbles as flow tracers, which scatter light with intensity several orders of magnitude higher than micron-sized droplets. With respect to a single bubble generator, the system increases the rate of bubbles emission by means of transient accumulation and rapid release. The governing parameters of the system are identified and discussed, namely the bubbles production rate, the accumulation and release times, the size of the bubble injector and its location with respect to the wind tunnel contraction. The relations between the above parameters, the resulting spatial concentration of tracers and measurement of dynamic spatial range are obtained and discussed. Large-scale experiments are carried out in a large low-speed wind tunnel with 2.85 × 2.85 m2 test section, where a vertical axis wind turbine of 1 m diameter is operated. Time-resolved tomographic PIV measurements are taken over a measurement volume of 40 × 20 × 15 cm3, allowing the quantitative analysis of the tip-vortex structure and dynamical evolution.

Conserved amino acid motifs from the novel Piv/MooV family of transposases and site-specific recombinases are required for catalysis of DNA inversion by Piv.

Science.gov (United States)

Tobiason, D M; Buchner, J M; Thiel, W H; Gernert, K M; Karls, A C

2001-02-01

Piv, a site-specific invertase from Moraxella lacunata, exhibits amino acid homology with the transposases of the IS110/IS492 family of insertion elements. The functions of conserved amino acid motifs that define this novel family of both transposases and site-specific recombinases (Piv/MooV family) were examined by mutagenesis of fully conserved amino acids within each motif in Piv. All Piv mutants altered in conserved residues were defective for in vivo inversion of the M. lacunata invertible DNA segment, but competent for in vivo binding to Piv DNA recognition sequences. Although the primary amino acid sequences of the Piv/MooV recombinases do not contain a conserved DDE motif, which defines the retroviral integrase/transposase (IN/Tnps) family, the predicted secondary structural elements of Piv align well with those of the IN/Tnps for which crystal structures have been determined. Molecular modelling of Piv based on these alignments predicts that E59, conserved as either E or D in the Piv/MooV family, forms a catalytic pocket with the conserved D9 and D101 residues. Analysis of Piv E59G confirms a role for E59 in catalysis of inversion. These results suggest that Piv and the related IS110/IS492 transposases mediate DNA recombination by a common mechanism involving a catalytic DED or DDD motif.

Measurements of the velocity fields by PIV method round about titling gate

Directory of Open Access Journals (Sweden)

Mistrová Ivana

2012-04-01

Full Text Available The article deals with problems of using of measurement method Particle Image Velocimetry (PIV to measure velocity fields in the flowing water in front, above and behind drowned titling weir gate. The aim was to obtain information about the distribution of speed in the area of interest for the verification or calibration of the numerical model. Experiments were carried out in inclinable channel connected to the hydraulic circuit with a pump and storage tank at the Water Management Research Laboratory (LVV of Institute of Water Structures at the Faculty of Civil Engineering in Brno University of Technology. Hydraulic inclinable channel has cross-section with dimensions of 0.4×0.4m and length of 12.5m. The measured area has cross-section approximately 0.2m wide and 0.4m high and its length is 1m. The results of physical modelling allowed a comparison of experimental data with numerical simulation results of this type of flow in the commercial software ANSYS CFX-12.0.

Velocimetry Overview for visitors from the DOD

Energy Technology Data Exchange (ETDEWEB)

Briggs, Matthew E. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Physics Division; Holtkamp, David Bruce [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Physics Division

2016-08-19

We are in the midst of a transformative period in which technological advances are making fundamental changes in the measurement techniques that form the backbone of nuclear weapon certification. Optical velocimetry has replaced electrical shorting pins in “Hydrotests,” which measure the dynamic implosion process. This advance has revolutionized nuclear weapons certification during the last 5 years. We can now measure the implosion process that drives a nuclear detonation with many orders of magnitude more resolution in both space and time than was possible just 10 years ago. It has been compared to going from Morse Code to HDTV, resulting in a dozen or more improvements in models of these weapons. These Hydrotests are carried out at LANL, LLNL and the NNSS, with the later holding the important role of allowing us to test with nuclear materials, in sub-critical configurations (i.e., no yield.) Each of these institutions has largely replaced pins with hundreds of channels of optical velocimetry. Velocimetry is non-contact and is used simultaneously with the X-ray capability of these facilities. The U1-a facility at NNSS pioneered this approach in the Gemini series in 2012, and continues to lead, both in channel count and technological advances. Close cooperation among LANL, LLNL and NSTec in these advances serves the complex by leveraging capabilities across sites and accelerating the pace of technical improvements.

Potential profiles obtained from applied dust cloud perturbations

International Nuclear Information System (INIS)

Thomas, Edward Jr.

2002-01-01

This paper details an experimental investigation of the local potential structure within a cloud of suspended microparticles - a 'dusty' or 'complex' plasma - using particle image velocimetry (PIV) techniques. Applied perturbations, synchronized to the PIV measurements, are used to force a cloud of suspended microparticles to become unconfined. From the free-streaming motion of the particles during the loss of confinement and subsequent reformation of the dust cloud, an analysis of the potential is performed. Furthermore, a new method of analyzing the potential structure from the motion of free-streaming microparticles in the plasma is presented

Adaptive interrogation for 3D-PIV

International Nuclear Information System (INIS)

Novara, Matteo; Scarano, Fulvio; Ianiro, Andrea

2013-01-01

A method to adapt the shape and orientation of interrogation volumes for 3D-PIV motion analysis is introduced, aimed to increase the local spatial resolution. The main application of this approach is the detailed analysis of complex 3D and vortex-dominated flows that exhibit high vorticity in confined regions like shear layers and vortex filaments. The adaptive criterion is based on the analysis of the components of the local velocity gradient tensor, which returns the level of anisotropy of velocity spatial fluctuations. The principle to increase the local spatial resolution is based on the deformation of spherical isotropic interrogation regions, obtained by means of Gaussian weighting, into ellipsoids, with free choice of the principal axes and their directions. The interrogation region is contracted in the direction of the maximum velocity variation and elongated in the minimum one in order to maintain a constant interrogation volume. The adaptivity technique for three-dimensional PIV data takes advantage of the 3D topology of the flow, allowing increasing the spatial resolution not only in the case of shear layers, but also for vortex filaments, which is not possible for two-dimensional measurement in the plane normal to the vortex axis. The definition of the ellipsoidal interrogation region semi-axes is based on the singular values and singular directions of the local velocity gradient tensor as obtained by the singular values decomposition technique (SVD). The working principle is verified making use of numerical simulations of a shear layer and of a vortex filament. The application of the technique to data from a Tomo-PIV experiment conducted on a round jet, shows that the resolution of the shear layer at the jet exit can be considerably improved and an increase of about 25% in the vorticity peak is attained when the adaptive approach is applied. On the other hand, the peak vorticity description in the core of vortex rings is only slightly improved with

A PIV Study of Drop-interface Coalescence with Surfactants

Science.gov (United States)

Weheliye, Weheliye Hashi; Dong, Teng; Angeli, Panagiota

2017-11-01

In this work, the coalescence of a drop with an aqueous-organic interface was studied by Particle Image Velocimetry (PIV). The effect of surfactants on the drop surface evolution, the vorticity field and the kinetic energy distribution in the drop during coalescence were investigated. The coalescence took place in an acrylic rectangular box with 79% glycerol solution at the bottom and Exxsol D80 oil above. The glycerol solution drop was generated through a nozzle fixed at 2cm above the aqueous/oil interface and was seeded with Rhodamine particles. The whole process was captured by a high-speed camera. Different mass ratios of non-ionic surfactant Span80 to oil were studied. The increase of surfactant concentration promoted deformation of the interface before the rupture of the trapped oil film. At the early stages after film rupture, two counter-rotating vortices appeared at the bottom of the drop which then travelled to the upper part. The propagation rates, as well as the intensities of the vortices decreased at high surfactant concentrations. At early stages, the kinetic energy was mainly distributed near the bottom part of the droplet, while at later stages it was distributed near the upper part of the droplet. Programme Grant MEMPHIS, Chinese Scholarship Council (CSC).

Validation of a numerical 3-D fluid-structure interaction model for a prosthetic valve based on experimental PIV measurements.

Science.gov (United States)

Guivier-Curien, Carine; Deplano, Valérie; Bertrand, Eric

2009-10-01

A numerical 3-D fluid-structure interaction (FSI) model of a prosthetic aortic valve was developed, based on a commercial computational fluid dynamics (CFD) software program using an Arbitrary Eulerian Lagrangian (ALE) formulation. To make sure of the validity of this numerical model, an equivalent experimental model accounting for both the geometrical features and the hydrodynamic conditions was also developed. The leaflet and the flow behaviours around the bileaflet valve were investigated numerically and experimentally by performing particle image velocimetry (PIV) measurements. Through quantitative and qualitative comparisons, it was shown that the leaflet behaviour and the velocity fields were similar in both models. The present study allows the validation of a fully coupled 3-D FSI numerical model. The promising numerical tool could be therefore used to investigate clinical issues involving the aortic valve.

Volumetric velocimetry for fluid flows

Science.gov (United States)

Discetti, Stefano; Coletti, Filippo

2018-04-01

In recent years, several techniques have been introduced that are capable of extracting 3D three-component velocity fields in fluid flows. Fast-paced developments in both hardware and processing algorithms have generated a diverse set of methods, with a growing range of applications in flow diagnostics. This has been further enriched by the increasingly marked trend of hybridization, in which the differences between techniques are fading. In this review, we carry out a survey of the prominent methods, including optical techniques and approaches based on medical imaging. An overview of each is given with an example of an application from the literature, while focusing on their respective strengths and challenges. A framework for the evaluation of velocimetry performance in terms of dynamic spatial range is discussed, along with technological trends and emerging strategies to exploit 3D data. While critical challenges still exist, these observations highlight how volumetric techniques are transforming experimental fluid mechanics, and that the possibilities they offer have just begun to be explored.

A synchronized particle image velocimetry and infrared thermography technique applied to convective mass transfer in champagne glasses

Science.gov (United States)

Beaumont, Fabien; Liger-Belair, Gérard; Bailly, Yannick; Polidori, Guillaume

2016-05-01

In champagne glasses, it was recently suggested that ascending bubble-driven flow patterns should be involved in the release of gaseous carbon dioxide (CO2) and volatile organic compounds. A key assumption was that the higher the velocity of the upward bubble-driven flow patterns in the liquid phase, the higher the volume fluxes of gaseous CO2 desorbing from the supersaturated liquid phase. In the present work, simultaneous monitoring of bubble-driven flow patterns within champagne glasses and gaseous CO2 escaping above the champagne surface was performed, through particle image velocimetry and infrared thermography techniques. Two quite emblematic types of champagne drinking vessels were investigated, namely a long-stemmed flute and a wide coupe. The synchronized use of both techniques proved that the cloud of gaseous CO2 escaping above champagne glasses strongly depends on the mixing flow patterns found in the liquid phase below.

Experimental characterization of solid particle transport by slug flow using Particle Image Velocimetry

International Nuclear Information System (INIS)

Goharzadeh, A; Rodgers, P

2009-01-01

This paper presents an experimental study of gas-liquid slug flow on solid particle transport inside a horizontal pipe with two types of experiments conducted. The influence of slug length on solid particle transportation is characterized using high speed photography. Using combined Particle Image Velocimetry (PIV) with Refractive Index Matching (RIM) and fluorescent tracers (two-phase oil-air loop) the velocity distribution inside the slug body is measured. Combining these experimental analyses, an insight is provided into the physical mechanism of solid particle transportation due to slug flow. It was observed that the slug body significantly influences solid particle mobility. The physical mechanism of solid particle transportation was found to be discontinuous. The inactive region (in terms of solid particle transport) upstream of the slug nose was quantified as a function of gas-liquid composition and solid particle size. Measured velocity distributions showed a significant drop in velocity magnitude immediately upstream of the slug nose and therefore the critical velocity for solid particle lifting is reached further upstream.

Investigation of LPP combustors under elevated pressure conditions; Untersuchungen zu LPP-Flugtriebwerksbrennkammern unter erhoehtem Druck

Energy Technology Data Exchange (ETDEWEB)

Fink, R.

2001-05-01

The development of new combustor concepts for aero engines to meet future emissions regulations in based on a detailed knowledge of the combustion process and the velocity field. In the presented thesis, non intrusive measurements were performed in a model combustion chamber under almost realistic pressure and temperature conditions. The species OH, NO, unburned hydrocarbons and fuel droplets were detected in 2 dimensions with the Laser Induced Fluorescence (LIF). The velocity field was measured with the Particle Image Velocimetry technique (PIV). [German] Die Weiterentwicklung neuer Brennkammerkonzepte zur Erfuellung zukuenftiger Schadstoffemissionsrichtlinien erfordert genaue Kenntnisse der ablaufenden Verbrennungs- und Stroemungsvorgaenge in der Brennkammer. Bei den in der Arbeit vorgestellten Untersuchungen wurden in einer LPP-Modellbrennkammer unter annaehernd realistischen Eintrittsbedingungen die Spezies OH, NO, unverbrannte Kohlenwasserstoffe sowie noch fluessiger Brennstoff zweidimensional anhand der Laserinduzierten Fluoreszenz (LIF) nachgewiesen. Das Stroemungsfeld wurde mit Hilfe der Particle Image Velocimetry (PIV) gemessen.

PIV quantification of the flow induced by an ultrasonic horn and numerical modeling of the flow and related processing times.

Science.gov (United States)

Schenker, M C; Pourquié, M J B M; Eskin, D G; Boersma, B J

2013-01-01

The flow in a confined container induced by an ultrasonic horn is measured by Particle Image Velocimetry (PIV). This flow is caused by acoustic streaming and highly influenced by the presence of cavitation. The jet-like experimentally observed flow is compared with the available theoretical solution for a turbulent free round jet. The similarity between both flows enables a simplified numerical model to be made, whilst the phenomenon is very difficult to simulate otherwise. The numerical model requires only two parameters, i.e. the flow momentum and turbulent kinetic energy at the position of the horn tip. The simulated flow is used as a basis for the calculation of the time required for the entire liquid volume to pass through the active cavitation region. Copyright © 2012 Elsevier B.V. All rights reserved.

PIV and LDA measurements of the wake behind a wind turbine model

Science.gov (United States)

Naumov, I. V.; Mikkelsen, R. F.; Okulov, V. L.; Sørensen, J. N.

2014-06-01

In the present work we review the results of a series of measurements of the flow behind a model scale of a horizontal axis wind turbine rotor carried out at the water flume at Technical University of Denmark (DTU). The rotor is three-bladed and designed using Glauert theory for tip speed ratio λ =5 with a constant design lift coefficient along the span, CLdesign= 0.8. The measurements include dye visualization, Particle Image Velocimetry and Laser Doppler Anemometry. The wake instability has been studied in the range λ =3 - 9 at different cross-sections from the very near wake up to 10 rotor diameters downstream from the rotor. The initial flume flow was subject to a very low turbulence level with a uniform velocity profile, limiting the influence of external disturbances on the development of the inherent vortex instability. Using PIV measurements and visualizations, special attention was paid to detect and categorize different types of wake instabilities and the development of the flow in the near and the far wake. In parallel to PIV, LDA measurements provided data for various rotor regimes, revealing the existence of three main regular frequencies governing the development of different processes and instabilities in the rotor wake. In the far wake a constant frequency corresponding to the Strouhal number was found for the long-scale instabilities. This Strouhal number is in good agreement with the well-known constant that usually characterizes the oscillation in wakes behind bluff bodies. From associated visualizations and reconstructions of the flow field, it was found that the dynamics of the far wake is associated with the precession (rotation) of a helical vortex core. The data indicate that Strouhal number of this precession is independent of the rotor angular speed.

PIV and LDA measurements of the wake behind a wind turbine model

International Nuclear Information System (INIS)

Naumov, I V; Okulov, V L; Mikkelsen, R F; Sørensen, J N

2014-01-01

In the present work we review the results of a series of measurements of the flow behind a model scale of a horizontal axis wind turbine rotor carried out at the water flume at Technical University of Denmark (DTU). The rotor is three-bladed and designed using Glauert theory for tip speed ratio λ =5 with a constant design lift coefficient along the span, C Ldesign = 0.8. The measurements include dye visualization, Particle Image Velocimetry and Laser Doppler Anemometry. The wake instability has been studied in the range λ =3 – 9 at different cross-sections from the very near wake up to 10 rotor diameters downstream from the rotor. The initial flume flow was subject to a very low turbulence level with a uniform velocity profile, limiting the influence of external disturbances on the development of the inherent vortex instability. Using PIV measurements and visualizations, special attention was paid to detect and categorize different types of wake instabilities and the development of the flow in the near and the far wake. In parallel to PIV, LDA measurements provided data for various rotor regimes, revealing the existence of three main regular frequencies governing the development of different processes and instabilities in the rotor wake. In the far wake a constant frequency corresponding to the Strouhal number was found for the long-scale instabilities. This Strouhal number is in good agreement with the well-known constant that usually characterizes the oscillation in wakes behind bluff bodies. From associated visualizations and reconstructions of the flow field, it was found that the dynamics of the far wake is associated with the precession (rotation) of a helical vortex core. The data indicate that Strouhal number of this precession is independent of the rotor angular speed

Near-ground tornado-like vortex structure resolved by particle image velocimetry (PIV)

Energy Technology Data Exchange (ETDEWEB)

Zhang, Wei [Iowa State University, Aerospace Engineering Department, Ames, IA (United States); University of Minnesota, Saint Anthony Falls Laboratory, Minneapolis, MN (United States); Sarkar, Partha P. [Iowa State University, Aerospace Engineering Department, Ames, IA (United States)

2012-02-15

The near-ground flow structure of tornadoes is of utmost interest because it determines how and to what extent civil structures could get damaged in tornado events. We simulated tornado-like vortex flow at the swirl ratios of S = 0.03-0.3 (vane angle {theta}{sub v} = 15 -60 ), using a laboratory tornado simulator and investigated the near-ground-vortex structure by particle imaging velocimetry. Complicated near-ground flow was measured in two orthogonal views: horizontal planes at various elevations (z = 11, 26 and 53 mm above the ground) and the meridian plane. We observed two distinct vortex structures: a single-celled vortex at the lowest swirl ratio (S = 0.03, {theta}{sub v} = 15 ) and multiple suction vortices rotating around the primary vortex (two-celled vortex) at higher swirl ratios (S = 0.1-0.3, {theta}{sub v} = 30 -60 ). We quantified the effects of vortex wandering on the mean flow and found that vortex wandering was important and should be taken into account in the low swirl ratio case. The tangential velocity, as the dominant velocity component, has the peak value about three times that of the maximum radial velocity regardless of the swirl ratio. The maximum velocity variance is about twice at the high swirl ratio ({theta}{sub v} = 45 ) that at the low swirl ratio ({theta}{sub v} = 15 ), which is contributed significantly by the multiple small-scale secondary vortices. Here, the results show that not only the intensified mean flow but greatly enhanced turbulence occurs near the surface in the tornado-like vortex flow. The intensified mean flow and enhanced turbulence at the ground level, correlated with the ground-vortex interaction, may cause dramatic damage of the civil structures in tornadoes. This work provides detailed characterization of the tornado-like vortex structure, which has not been fully revealed in previous field studies and laboratory simulations. It would be helpful in improving the understanding of the interaction between the

Investigation of an IC Engine Intake Flow Based on Highly Resolved LES and PIV

Directory of Open Access Journals (Sweden)

Buhl Stefan

2017-05-01

Full Text Available To reduce emissions and fuel consumption, the current generation of gasoline engines uses technologies such as direct injection, downsizing and supercharging. All of them require a strong vortical in-cylinder charge motion, usually described as “tumble”, to improve fuel-air mixing and enhance flame propagation. The tumble development strongly depends on the flow field during the intake stroke. This flow field is dominated by the intake jet, which has to be captured well in the simulation. This work investigates the intake jet on a steady-state flow bench, especially in the vicinity of the intake valve. At first, the general flow dynamics of the intake jet for three different valve lifts and three different mass flows were investigated experimentally. For the smallest valve lift (3 mm, flow-field measurements using Particle Image Velocimetry (PIV show that the orientation of the intake jet significantly depends on the air flow rate, attaching to the pent roof for low flow rates. This phenomenon is less pronounced for higher valve lifts. An intermediate valve lift and flow rate were chosen for further investigations by scale-resolving simulations. Three different meshes (coarse, medium and fine and two turbulence models (Sigma and Detached Eddy Simulation-Shear Stress Transport (DES-SST are applied to consider their effect on the numerical results. An ad-hoc post-processing methodology based on the ensemble-averaged velocity field is presented capturing the jet centerline’s mean velocity and velocity fluctuations as well as its orientation, curvature and penetration depth. The simulation results are compared to each other as well as to measurements by PIV.

EXPERIMENTAL STUDY ON THE GAS-LIQUID FLOW IN THE MEMBRANE MICROPORE AERATION BIOREACTOR

Directory of Open Access Journals (Sweden)

DONG LIU

2008-12-01

Full Text Available Particle Image Velocimetry (PIV has been developed to measure the typical two-phase flow of various work conditions in Membrane Micropore Aeration Bioreactor (MMAB. The fluid phase is separated out using image processing techniques, which provides accurate measurements for the Bioreactor’s flow field, and makes it possible for quantitative analysis of the momentum exchange, heat exchange and the process of micro-admixture. The experimental method PIV used in this paper can preferably measure the complex flow in the reactor and initiates a new approach for the bioreactor design which mainly depends on experience at present.

Visualization of air flow around soccer ball using a particle image velocimetry

Science.gov (United States)

Hong, Sungchan; Asai, Takeshi; Seo, Kazuya

2015-10-01

A traditional soccer ball is constructed using 32 pentagonal and hexagonal panels. In recent years, however, the likes of the Teamgeist and Jabulani balls, constructed from 14 and 8 panels, respectively, have entered the field, marking a significant departure from conventionality in terms of shape and design. Moreover, the recently introduced Brazuca ball features a new 6-panel design and has already been adopted by many soccer leagues. However, the shapes of the constituent panels of these balls differ substantially from those of conventional balls. Therefore, this study set out to investigate the flight and aerodynamic characteristics of different orientations of the soccer ball, which is constructed from panels of different shapes. A wind tunnel test showed substantial differences in the aerodynamic forces acting on the ball, depending on its orientation. Substantial differences were also observed in the aerodynamic forces acting on the ball in different directions, corresponding to its orientation and rotation. Moreover, two-dimensional particle image velocimetry (2D-PIV) measurements showed that the boundary separation varies depending on the orientation of the ball. Based on these results, we can conclude that the shape of the panels of a soccer ball substantially affects its flight trajectory.

Experimental investigation of helicity in turbulent swirling jet using dual-plane dye laser PIV technique

Czech Academy of Sciences Publication Activity Database

Regunath, G.; Zimmerman, W. B.; Tesař, Václav; Hewakandamby, B.N.

2008-01-01

Roč. 45, č. 6 (2008), s. 973-986 ISSN 0723-4864 R&D Projects: GA AV ČR IAA200760705 Institutional research plan: CEZ:AV0Z20760514 Keywords : jet * swirling jet * helicity * PIV Subject RIV: BK - Fluid Dynamics Impact factor: 1.854, year: 2008 http://www.springerlink.com/

Time-resolved particle image velocimetry and laser doppler anemometry study of the turbulent flow field of bileaflet mechanical mitral prostheses.

Science.gov (United States)

Akutsu, Toshinosuke; Fukuda, Takamasa

2005-01-01

Dynamic particle image velocimetry (PIV) was applied to the study of the flow field associated with prosthetic heart valves. The results were compared with those of laser Doppler anemometry (LDA). Anatomically and antianatomically oriented Jyros (JR) and St. Jude Medical (SJM) valves were compared in the mitral position to study the effects of valve design on the downstream flow field. The experimental program used a dynamic PIV system utilizing high-speed, high-resolution video to map the true time-resolved velocity field inside the simulated ventricle. This system was complemented by a study using the more traditional LDA system for comparison. Based on the experimental data, the following general conclusions can be made. High-resolution dynamic PIV can capture true chronological changes in the velocity and turbulence fields. It also produces very detailed velocity and turbulence information comparable to the LDA results. In the vertical measuring plane that passes both the center of the aortic and mitral valves (A-A section), the two valves (the SJM and the JR) show distinct circulatory flow patterns when the valve is installed in the antianatomical orientation. Small differences in valve design can generate noticeable differences, particularly during the accelerating flow phase. The SJM valve maintains a relatively high velocity through the central orifice; the curved leaflets of the JR valve generate higher velocities with a divergent flow during the accelerating and peak flow phases. In the velocity field directly below the mitral valve and normal to the previous measuring plane (B-B section), where characteristic differences in valve design will be visible, symmetrical twin circulations were observed because of the divergent nature of the flow generated by the two inclined half-disks installed in the antianatomical orientation. The SJM valve, with a central downward flow near the valve, is contrasted with the JR valve, which has a peripheral downward

In vitro 2D PIV measurements and related aperture areas of tricuspid bioprosthetic mitral valves at the beginning of diastole.

Science.gov (United States)

Bazan, Ovandir; Ortiz, Jayme Pinto; Fukumasu, Newton Kiyoshi; Pacifico, Antonio Luiz; Yanagihara, Jurandir Itizo

2016-07-04

Besides ventricular parameters, the design and angular orientation of a prosthetic heart valve induce a specific flow field. The aim of this study was to know the inflow characteristics of a left ventricular model (LVM), investigating the behavior of tricuspid bioprosthetic mitral valves in terms of velocity profiles and related valve aperture areas at the beginning of diastole, under different conditions. 3 heart rates (HRs) were established in the LVM and each mitral bioprosthesis (27 and 31 mm diameter) was installed in 2 orientations, rotated by 180° . For each experimental setup, 2-dimensional particle image velocimetry (2D PIV) measurements and simultaneous mitral valve (MV) area detection were obtained from 50 samples. The results from the velocity profiles immediately downstream of mitral bioprostheses showed the influence of valve orientation for moderate HRs, although for a similar magnitude of mean velocity vectors. The geometries of MV open areas for each HR were similar regardless of valve orientation, except for the 27-mm valve at 90 beats per minute (bpm), and for the 31-mm valve at 60 bpm. Moreover, for each HR, similar percentages of valve open area were obtained regardless of MV nominal diameters. In conclusion, the experimental setup for the 2D PIV measurements synchronized with the MV area detection was a useful tool for knowing the inflow characteristics of the LVM.

Droplet morphometry and velocimetry (DMV): a video processing software for time-resolved, label-free tracking of droplet parameters.

Science.gov (United States)

Basu, Amar S

2013-05-21

Emerging assays in droplet microfluidics require the measurement of parameters such as drop size, velocity, trajectory, shape deformation, fluorescence intensity, and others. While micro particle image velocimetry (μPIV) and related techniques are suitable for measuring flow using tracer particles, no tool exists for tracking droplets at the granularity of a single entity. This paper presents droplet morphometry and velocimetry (DMV), a digital video processing software for time-resolved droplet analysis. Droplets are identified through a series of image processing steps which operate on transparent, translucent, fluorescent, or opaque droplets. The steps include background image generation, background subtraction, edge detection, small object removal, morphological close and fill, and shape discrimination. A frame correlation step then links droplets spanning multiple frames via a nearest neighbor search with user-defined matching criteria. Each step can be individually tuned for maximum compatibility. For each droplet found, DMV provides a time-history of 20 different parameters, including trajectory, velocity, area, dimensions, shape deformation, orientation, nearest neighbour spacing, and pixel statistics. The data can be reported via scatter plots, histograms, and tables at the granularity of individual droplets or by statistics accrued over the population. We present several case studies from industry and academic labs, including the measurement of 1) size distributions and flow perturbations in a drop generator, 2) size distributions and mixing rates in drop splitting/merging devices, 3) efficiency of single cell encapsulation devices, 4) position tracking in electrowetting operations, 5) chemical concentrations in a serial drop dilutor, 6) drop sorting efficiency of a tensiophoresis device, 7) plug length and orientation of nonspherical plugs in a serpentine channel, and 8) high throughput tracking of >250 drops in a reinjection system. Performance metrics

CFD Simulation and Experimental Validation of Fluid Flow and Particle Transport in a Model of Alveolated Airways.

Science.gov (United States)

Ma, Baoshun; Ruwet, Vincent; Corieri, Patricia; Theunissen, Raf; Riethmuller, Michel; Darquenne, Chantal

2009-05-01

Accurate modeling of air flow and aerosol transport in the alveolated airways is essential for quantitative predictions of pulmonary aerosol deposition. However, experimental validation of such modeling studies has been scarce. The objective of this study is to validate CFD predictions of flow field and particle trajectory with experiments within a scaled-up model of alveolated airways. Steady flow (Re = 0.13) of silicone oil was captured by particle image velocimetry (PIV), and the trajectories of 0.5 mm and 1.2 mm spherical iron beads (representing 0.7 to 14.6 mum aerosol in vivo) were obtained by particle tracking velocimetry (PTV). At twelve selected cross sections, the velocity profiles obtained by CFD matched well with those by PIV (within 1.7% on average). The CFD predicted trajectories also matched well with PTV experiments. These results showed that air flow and aerosol transport in models of human alveolated airways can be simulated by CFD techniques with reasonable accuracy.

The interaction between liquid motion and mass transfer induced by single rising bubble via PIV/LIE

International Nuclear Information System (INIS)

Yoshimoto, Kenjo; Yamamoto, Manabu; Sone, Daiji; Saito, Takayuki

2009-01-01

Deep understanding of gas-liquid two phase flows is essential for safe operation and high efficiency of nuclear reactors, chemical reactors and so on. In this study, we focus on the process of mass transfer induced by a single rising bubble. The mass transfer process of a zigzag ascending single bubble is investigated via LIF (Laser Induced Fluorescence) and PIV (Particle Image Velocimetry). From these results, we discuss the relationship between the mass transfer and the surrounding liquid motion of the single bubble. We examined single CO 2 -bubbles of 2-3 mm in equivalent diameter, which shows zigzagging motion in rest water. To directly visualize the dynamic mass transfer of CO 2 from the bubble surface to the surrounding liquid, HPTS (8-hydroxypyrene-1, 3, 6-trisulfonic acid) was used as a fluorescent substance for LIF. From LIF results, it was observed that the CO 2 -rich regions were spread by advective flow in the rest water as horseshoe-like vortices. From LIF results combined with the PIV results, it was observed that the horseshoe-like vortices were transported by the fast upward flow (buoyancy driven flow). Especially, in the case of a larger-diameter bubble with large shape oscillations, the high turbulence intensity (in a strict sense, fluctuation intensity of the liquid-phase velocity) was observed. The CO 2 -rich regions spread over a wide range by the strong flow. As a result, it is considered that the high turbulence intensity which was caused by the shape oscillations enhances the mass transportation from the bubble to the surrounding liquid. (author)

PIV Measurements of Flows around the Wind Turbines with a Flanged-Diffuser Shroud

Institute of Scientific and Technical Information of China (English)

Kazuhiko Toshimitsu; Koutarou Nishikawa; Wataru Haruki; Shinichi Oono; Manabu Takao; Yuji Ohya

2008-01-01

The wind turbines with a flanged-diffuser shroud -so called "wind lens turbine"- are developed as one of high performance wind turbines by Ohya et al. In order to investigate the flow characteristics and flow acceleration, the paper presents the flow velocity measurements of a long-type and a compact-type wind turbines with a flanged-diffuser shroud by particle image velocimetry. In the case of the long type wind turbine, the velocity vec-tors of the inner flow field of the diffuser for turbine blades rotating and no blades rotating are presented at Rey-nolds number, 0.9x105. Furthermore the flow fields between with and without rotating are compared. Through the PIV measurement results, one can realize that the turbine blades rotating affects as suppress the disturbance and the flow separation near the inner wall of the diffuser. The time average velocity vectors are made on the av-erage of the instantaneous velocity data. There are two large vortices in downstream region of the diffuser. One vortex behind the flange acts as suck in wind to the diffuser and raise the inlet flow velocity. Another large vortex appears in downstream. It might be act as blockage vortex of main flow. The large blockage vortex is not clear in the instantaneous velocity vectors, however it exists clearly in the time average flow field. The flow field around the wind turbine with a compact-type flanged-diffuser shroud is also investigated. The flow pattern behind the flange of the compact-type turbine is the same as the long-type one. It means that the effect of flow acceleration is caused by the unsteady vortices behind the flange. The comparison with CFD and PIV results of meridional time-average streamlines after the compact-type diffuser is also presented.

Three-dimensional particle tracking in concave structures made by ultraviolet nanoimprint via total internal reflection fluorescence microscopy and refractive-index-matching method

Science.gov (United States)

Fujinami, Taku; Kigami, Hiroshi; Unno, Noriyuki; Taniguchi, Jun; Satake, Shin-ichi

2018-03-01

Total internal reflection fluorescence microscopy (TIRFM) is a promising method for measuring fluid flow close to a wall with nanoscale resolution in a process that is termed "multilayer nanoparticle image velocimetry" (MnPIV). TIRFM uses evanescent light that is generated on a substrate (typically a glass slide) by total internal reflection of light. Many researchers have previously studied x-y-z (3D) flows of water close to flat glass slides using MnPIV. On the other hand, a fluid flow close to a structured surface is also important. To measure flows of water near micro-patterns, we previously developed an MnPIV technique that uses a refractive-index-matching method. In previous study, the micropattern is made of a thermoplastic material with a refractive index that closely matches that of water. In this study, ultraviolet nanoimprint lithography was used for fabricating the appropriate micro-patterns because this technique can fabricate a pattern with a high resolution. As a result, we succeeded in performing MnPIV in water with a circular hole array pattern made by ultraviolet nanoimprint using a refractive-index-matching method. We believe that this technique will be helpful in elucidating fluid flows around microstructures.

Turbulent Non-Premixed Flames Stabilized on Double-Slit Curved Wall-Jet Burner with Simultaneous OH-Planar Laser-Induced Fluorescence and Particle Image Velocimetry Measurements

KAUST Repository

Mansour, Morkous S.

2015-04-29

A double-slit curved wall-jet (CWJ) burner utilizing a Coanda effect by supplying fuel and air as annular-inward jets over a curved surface was employed to investigate the stabilization characteristics and structure of propane/air turbulent non-premixed flames with varying global equivalence ratio and Reynolds number. Simultaneous time-resolved measurements of particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) of OH radicals were conducted. The burner showed a potential of stable and non-sooting operation for relatively large fuel loading and overall rich conditions. Mixing characteristics in cold flow were first examined using an acetone fluorescence technique, indicating substantial transport between the fuel and air by exhibiting appreciable premixing conditions. PIV measurements revealed that the flow field consisted of a wall-jet region leading to a recirculation zone through flow separation, an interaction jet region resulting from the collision of annular-inward jets, followed by a merged-jet region. The flames were stabilized in the recirculation zone and, in extreme cases, only a small flame seed remained in the recirculation zone. Together with the collision of the slit jets in the interaction jet region, the velocity gradients in the shear layers at the boundaries of the annular jets generate the turbulence. Turbulent mean and rms velocities were influenced by the presence of the flame, particularly in the recirculation zone. Flames with a high equivalence ratio were found to be more resistant to local extinction and exhibited a more corrugated and folded nature, particularly at high Reynolds numbers. For flames with a low equivalence ratio, local quenching and re-ignition processes maintained flames in the merged jet region, revealing a strong intermittency, which was substantiated by the increased principal strain rates for these flames. © 2015 Taylor & Francis Group, LLC.

Thermal hydraulics-I. 1. Phasic Discrimination in Two-Phase-Flow Measurements Using Particle Image Velocimetry

International Nuclear Information System (INIS)

Todd, D.R.; Ortiz-Villafuerte, J.; Schmidl, W.D.; Hassan, Y.A.; Sanchez-Silva, F.

2001-01-01

Information about the dispersed phase parameters -such as location, displacement, and interfacial area -are very important in the analysis of two-phase flows. Local flow disturbances in the continuous phase can be quite significant when the dispersed phase (i.e., a particle, drop, or bubble) passes through the medium. Application of point-wise measurement methods such as hot wire anemometry and laser anemometry suffer significant limitations in two-phase-flow measurements when these local disturbances are strong. Also, these two methods typically lack the ability to quantify the dispersed phase. Previous work has shown that meaningful analysis of the instantaneous continuous phase velocity field requires knowledge of the dispersed phase parameters, especially location and trajectory. Continuous phase parameters such as the local instantaneous vorticity and local turbulence fluctuations are influenced by the passage of the dispersed phase. Thus, development of two-phase-flow models (such as a bubble wake model) requires knowledge of the relative location of a local continuous phase parameter to the dispersed flow object (i.e., directly behind or off the side of the object). Also, conditional sampling must be performed using a meaningful parameter as the sampling point, i.e., the passage of a specific size of bubble. A system has been developed at Texas A and M University to quantify the dispersed phase parameters for two-phase bubbly flow in a vertical pipe with co-current upward flow. This system uses an orthogonal shadow particle image velocimetry (SPIV) technique, which instantaneously measures three-dimensional bubble locations, volumes, and interfacial areas -while measuring the three-dimensional bubble velocities and accelerations over a sequence of discrete measurements. The SPIV system is capable of analyzing flows with a large number of bubbles in close proximity. A set of sample images has been collected as part of the preliminary testing and development

Improvements on digital inline holographic PTV for 3D wall-bounded turbulent flow measurements

International Nuclear Information System (INIS)

Toloui, Mostafa; Mallery, Kevin; Hong, Jiarong

2017-01-01

Three-dimensional (3D) particle image velocimetry (PIV) and particle tracking velocimetry (PTV) provide the most comprehensive flow information for unraveling the physical phenomena in a wide range of fluid problems, from microfluidics to wall-bounded turbulent flows. Compared with other 3D PIV techniques, such as tomographic PIV and defocusing PIV, the digital inline holographic PTV (DIH-PTV) provides 3D flow measurement solution with high spatial resolution, low cost optical setup, and easy alignment and calibration. Despite these advantages, DIH-PTV suffers from major limitations including poor longitudinal resolution, human intervention (i.e. requirement for manually determined tuning parameters during tracer field reconstruction and extraction), limited tracer concentration, small sampling volume and expensive computations, limiting its broad use for 3D flow measurements. In this study, we present our latest developments on minimizing these challenges, which enables high-fidelity DIH-PTV implementation to larger sampling volumes with significantly higher particle seeding densities suitable for wall-bounded turbulent flow measurements. The improvements include: (1) adjustable window thresholding; (2) multi-pass 3D tracking; (3) automatic wall localization; and (4) continuity-based out-of-plane velocity component computation. The accuracy of the proposed DIH-PTV method is validated with conventional 2D PIV and double-view holographic PTV measurements in smooth-wall turbulent channel flow experiments. The capability of the technique in characterization of wall-bounded turbulence is further demonstrated through its application to flow measurements for smooth- and rough-wall turbulent channel flows. In these experiments, 3D velocity fields are measured within sampling volumes of 14.7  ×  50.0  ×  14.4 mm 3 (covering the entire depth of the channel) with a velocity resolution of  <1.1 mm/vector. Overall, the presented DIH-PTV method and

Structure analysis of turbulent liquid phase by POD and LSE techniques

International Nuclear Information System (INIS)

Munir, S.; Muthuvalu, M. S.; Siddiqui, M. I.; Heikal, M. R.; Aziz, A. Rashid A.

2014-01-01

In this paper, vortical structures and turbulence characteristics of liquid phase in both single liquid phase and two-phase slug flow in pipes were studied. Two dimensional velocity vector fields of liquid phase were obtained by Particle image velocimetry (PIV). Two cases were considered one single phase liquid flow at 80 l/m and second slug flow by introducing gas at 60 l/m while keeping liquid flow rate same. Proper orthogonal decomposition (POD) and Linear stochastic estimation techniques were used for the extraction of coherent structures and analysis of turbulence in liquid phase for both cases. POD has successfully revealed large energy containing structures. The time dependent POD spatial mode coefficients oscillate with high frequency for high mode numbers. The energy distribution of spatial modes was also achieved. LSE has pointed out the coherent structured for both cases and the reconstructed velocity fields are in well agreement with the instantaneous velocity fields

Structure analysis of turbulent liquid phase by POD and LSE techniques

Energy Technology Data Exchange (ETDEWEB)

Munir, S., E-mail: shahzad-munir@comsats.edu.pk; Muthuvalu, M. S.; Siddiqui, M. I. [Department of Fundamental and Applied Science, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak Darul Ridzuan (Malaysia); Heikal, M. R., E-mail: morgan.heikal@petronas.com.my; Aziz, A. Rashid A., E-mail: morgan.heikal@petronas.com.my [Department of Mechanical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak Darul Ridzuan (Malaysia)

2014-10-24

In this paper, vortical structures and turbulence characteristics of liquid phase in both single liquid phase and two-phase slug flow in pipes were studied. Two dimensional velocity vector fields of liquid phase were obtained by Particle image velocimetry (PIV). Two cases were considered one single phase liquid flow at 80 l/m and second slug flow by introducing gas at 60 l/m while keeping liquid flow rate same. Proper orthogonal decomposition (POD) and Linear stochastic estimation techniques were used for the extraction of coherent structures and analysis of turbulence in liquid phase for both cases. POD has successfully revealed large energy containing structures. The time dependent POD spatial mode coefficients oscillate with high frequency for high mode numbers. The energy distribution of spatial modes was also achieved. LSE has pointed out the coherent structured for both cases and the reconstructed velocity fields are in well agreement with the instantaneous velocity fields.

Measurement of Ambient Air Motion of D. I. Gasoline Spray by LIF-PIV

Science.gov (United States)

Yamakawa, Masahisa; Isshiki, Seiji; Yoshizaki, Takuo; Nishida, Keiya

Ambient air velocity distributions in and around a D. I. gasoline spray were measured using a combination of LIF and PIV techniques. A rhodamine and water solution was injected into ambient air to disperse the fine fluorescent liquid particles used as tracers. A fuel spray was injected into the fluorescent tracer cloud and was illuminated by an Nd: YAG laser light sheet (532nm). The scattered light from the spray droplets and tracers was cut off by a high-pass filter (>560nm). As the fluorescence (>600nm) was transmitted through the high-pass filter, the tracer images were captured using a CCD camera and the ambient air velocity distribution could be obtained by PIV based on the images. This technique was applied to a D. I. gasoline spray. The ambient air flowed up around the spray and entered into the tail of the spray. Furthermore, the relative velocity between the spray and ambient air was investigated.

Measurement of mean rotation and strain-rate tensors by using stereoscopic PIV

DEFF Research Database (Denmark)

Özcan, Oktay; Meyer, Knud Erik; Larsen, Poul Scheel

2005-01-01

A technique is described for measuring the mean velocity gradient (rate-of-displacement) tensor by using a conventional stereoscopic particle image velocimetry (SPIV) system. Planar measurement of the mean vorticity vector, rate-of-rotation and rate-of-strain tensors and the production of turbule...

Main results of the third international PIV Challenge

NARCIS (Netherlands)

Stanislas, M.; Okamoto, K.; Kähler, C.J.; Westerweel, J.; Scarano, F.

2008-01-01

This paper presents the main results of the third international PIV Challenge which took place in Pasadena (USA) on the 19th and 20th of September 2005. This workshop was linked to the PIV05 International Symposium held at the same place the same week. The present contribution states the objectives

Multiparticle imaging technique for two-phase fluid flows using pulsed laser speckle velocimetry

Energy Technology Data Exchange (ETDEWEB)

Hassan, T.A.

1992-12-01

The practical use of Pulsed Laser Velocimetry (PLV) requires the use of fast, reliable computer-based methods for tracking numerous particles suspended in a fluid flow. Two methods for performing tracking are presented. One method tracks a particle through multiple sequential images (minimum of four required) by prediction and verification of particle displacement and direction. The other method, requiring only two sequential images uses a dynamic, binary, spatial, cross-correlation technique. The algorithms are tested on computer-generated synthetic data and experimental data which was obtained with traditional PLV methods. This allowed error analysis and testing of the algorithms on real engineering flows. A novel method is proposed which eliminates tedious, undersirable, manual, operator assistance in removing erroneous vectors. This method uses an iterative process involving an interpolated field produced from the most reliable vectors. Methods are developed to allow fast analysis and presentation of sets of PLV image data. Experimental investigation of a two-phase, horizontal, stratified, flow regime was performed to determine the interface drag force, and correspondingly, the drag coefficient. A horizontal, stratified flow test facility using water and air was constructed to allow interface shear measurements with PLV techniques. The experimentally obtained local drag measurements were compared with theoretical results given by conventional interfacial drag theory. Close agreement was shown when local conditions near the interface were similar to space-averaged conditions. However, theory based on macroscopic, space-averaged flow behavior was shown to give incorrect results if the local gas velocity near the interface as unstable, transient, and dissimilar from the average gas velocity through the test facility.

Krypton tagging velocimetry of an underexpanded jet.

Science.gov (United States)

Parziale, N J; Smith, M S; Marineau, E C

2015-06-01

In this work, we present the excitation/emission strategy, experimental setup, and results of an implementation of krypton tagging velocimetry (KTV). KTV is performed as follows: (i) seed a base flow with krypton; (ii) photosynthesize metastable krypton atoms with a frequency-doubled dye laser to form the tagged tracer; (iii) record the translation of the tagged metastable krypton by imaging the laser-induced fluorescence (LIF) that is produced with an additional dye laser. The principle strength of KTV, relative to other tagging velocimetry techniques, is the use of a chemically inert tracer. KTV results are presented for an underexpanded jet of three mixtures of varying Kr/N2 concentration. It is demonstrated that KTV can be used in gas mixtures of relatively low krypton mole fraction (0.5% Kr/99.5% N2), and the KTV data from that experiment are found to be in good agreement with an empirical fit found in the literature. We find that KTV is useful to perform instantaneous velocity measurements with metastable krypton as a chemically inert, dilute, long-lifetime tracer in gas-phase flows.

An efficient and accurate approach to MTE-MART for time-resolved tomographic PIV

NARCIS (Netherlands)

Lynch, KP; Scarano, F.

2015-01-01

The motion-tracking-enhanced MART (MTE-MART; Novara et al. in Meas Sci Technol 21:035401, 2010) has demonstrated the potential to increase the accuracy of tomographic PIV by the combined use of a short sequence of non-simultaneous recordings. A clear bottleneck of the MTE-MART technique has been

An efficient and accurate approach to MTE-MART for time-resolved tomographic PIV

NARCIS (Netherlands)

Lynch, K.P.; Scarano, F.

2015-01-01

The motion-tracking-enhanced MART (MTE-MART; Novara et al. in Meas Sci Technol 21:035401, 2010) has demonstrated the potential to increase the accuracy of tomographic PIV by the combined use of a short sequence of non-simultaneous recordings. A clear bottleneck of the MTE-MART technique has been its

Preliminary Investigation on Turbulent Flow in Tight-lattice Rod Bundle with Twist-mixing Vane Spacer Grid

International Nuclear Information System (INIS)

Lee, Chiyoung; Kwack, Youngkyun; Park, Juyong; Shin, Changhwan; In, Wangkee

2013-01-01

Our research group has investigated the effect of P/D difference on the behavior of turbulent rod bundle flow without the mixing vane spacer grid, using PIV (Particle Image Velocimetry) and MIR (Matching Index of Refraction) techniques for tight lattice fuel rod bundle application. In this work, using the tight-lattice rod bundle with a twist-mixing vane spacer grid, the turbulent rod bundle flow is preliminarily examined to validate the PIV measurement and CFD (Computational Fluid Dynamics) simulation. The turbulent flow in the tight-lattice rod bundle with a twist-mixing vane spacer grid was preliminarily examined to validate the PIV measurement and CFD simulation. Both were in agreement with each other within a reasonable degree of accuracy. Using PIV measurement and CFD simulation tested in this work, the detailed investigations on the behavior of turbulent rod bundle flow with the twist-mixing vane spacer grid will be performed at various conditions, and reported in the near future

Non-intrusive load characterization of an airfoil using PIV

Energy Technology Data Exchange (ETDEWEB)

Oudheusden, B.W. van; Scarano, F.; Casimiri, E.W.F. [Dept. of Aerospace Engineering, Delft Univ. of Tech., Delft (Netherlands)

2006-06-15

An assessment is made of the feasibility of using PIV velocity data for the non-intrusive aerodynamic force characterization (lift, drag and pitching moment) of an airfoil. The method relies upon the application of control-volume approaches in combination with the deduction of the pressure from the PIV experimental data, by making use of the momentum equation. First, the consistency of the method is verified by means of synthetic data obtained from CFD. Subsequently, the procedure was applied in an experimental investigation, in which the PIV approach is validated against standard pressure-based methods (surface pressure distribution and wake rake). (orig.)

PIV and CFD studies on analyzing intragastric flow phenomena induced by peristalsis using a human gastric flow simulator.

Science.gov (United States)

Kozu, Hiroyuki; Kobayashi, Isao; Neves, Marcos A; Nakajima, Mitsutoshi; Uemura, Kunihiko; Sato, Seigo; Ichikawa, Sosaku

2014-08-01

This study quantitatively analyzed the flow phenomena in model gastric contents induced by peristalsis using a human gastric flow simulator (GFS). Major functions of the GFS include gastric peristalsis simulation by controlled deformation of rubber walls and direct observation of inner flow through parallel transparent windows. For liquid gastric contents (water and starch syrup solutions), retropulsive flow against the direction of peristalsis was observed using both particle image velocimetry (PIV) and computational fluid dynamics (CFD). The maximum flow velocity was obtained in the region occluded by peristalsis. The maximum value was 9 mm s(-1) when the standard value of peristalsis speed in healthy adults (UACW = 2.5 mm s(-1)) was applied. The intragastric flow-field was laminar with the maximum Reynolds number (Re = 125). The viscosity of liquid gastric contents hardly affected the maximum flow velocity in the applied range of this study (1 to 100 mPa s). These PIV results agreed well with the CFD results. The maximum shear rate in the liquid gastric contents was below 20 s(-1) at UACW = 2.5 mm s(-1). We also measured the flow-field in solid-liquid gastric contents containing model solid food particles (plastic beads). The direction of velocity vectors was influenced by the presence of the model solid food particle surface. The maximum flow velocity near the model solid food particles ranged from 8 to 10 mm s(-1) at UACW = 2.5 mm s(-1). The maximum shear rate around the model solid food particles was low, with a value of up to 20 s(-1).

Multilaboratory particle image velocimetry analysis of the FDA benchmark nozzle model to support validation of computational fluid dynamics simulations.

Science.gov (United States)

Hariharan, Prasanna; Giarra, Matthew; Reddy, Varun; Day, Steven W; Manning, Keefe B; Deutsch, Steven; Stewart, Sandy F C; Myers, Matthew R; Berman, Michael R; Burgreen, Greg W; Paterson, Eric G; Malinauskas, Richard A

2011-04-01

This study is part of a FDA-sponsored project to evaluate the use and limitations of computational fluid dynamics (CFD) in assessing blood flow parameters related to medical device safety. In an interlaboratory study, fluid velocities and pressures were measured in a nozzle model to provide experimental validation for a companion round-robin CFD study. The simple benchmark nozzle model, which mimicked the flow fields in several medical devices, consisted of a gradual flow constriction, a narrow throat region, and a sudden expansion region where a fluid jet exited the center of the nozzle with recirculation zones near the model walls. Measurements of mean velocity and turbulent flow quantities were made in the benchmark device at three independent laboratories using particle image velocimetry (PIV). Flow measurements were performed over a range of nozzle throat Reynolds numbers (Re(throat)) from 500 to 6500, covering the laminar, transitional, and turbulent flow regimes. A standard operating procedure was developed for performing experiments under controlled temperature and flow conditions and for minimizing systematic errors during PIV image acquisition and processing. For laminar (Re(throat)=500) and turbulent flow conditions (Re(throat)≥3500), the velocities measured by the three laboratories were similar with an interlaboratory uncertainty of ∼10% at most of the locations. However, for the transitional flow case (Re(throat)=2000), the uncertainty in the size and the velocity of the jet at the nozzle exit increased to ∼60% and was very sensitive to the flow conditions. An error analysis showed that by minimizing the variability in the experimental parameters such as flow rate and fluid viscosity to less than 5% and by matching the inlet turbulence level between the laboratories, the uncertainties in the velocities of the transitional flow case could be reduced to ∼15%. The experimental procedure and flow results from this interlaboratory study (available

Measurement of turbulent mixing in a confined wake flow using combined PIV and PLIF

NARCIS (Netherlands)

Hjertager, Lene K.; Hjertager, Bjorn H.; Deen, N.G.; Solberg, Tron; Kuipers, J.A.M.

2003-01-01

Turbulent mixing in a confined wake flow was studied by using the combined PIV/PLIF technique to measure instantaneous concentration and velocity fields. Measurements were performed at two slightly overlapping areas in the initial mixing zone and at an area at the end of the channel. The

Experimental study of the inverse diffusion flame using high repetition rate OH/acetone PLIF and PIV

KAUST Repository

Elbaz, Ayman M.; Roberts, William L.

2015-01-01

Most previous work on inverse diffusion flames (IDFs) has focused on laminar IDF emissions and the soot formation characteristics. Here, we investigate the characteristics and structure of methane IDFs using high speed planar laser-induced fluorescence (PLIF) images of OH, particle image velocimetry (PIV), and acetone PLIF imaging for non-reacting cases. First, the flame appearance was investigated with fixed methane loading (mass flux) but with varying airflow rates, yielding a central air jet Reynolds number (Re) of 1,000 to 6,000 (when blow-off occurs). Next, it was investigated a fixed central air jet Re of 4500, but with varied methane mass flux such that the global equivalence ratio spanned 0.5 to 4. It was observed that at Re smaller than 2000, the inner air jet promotes the establishment of an inverse diffusion flame surrounded by a normal diffusion flame. However, when the Re was increased to 2500, two distinct zones became apparent in the flame, a lower entrainment zone and an upper mixing and combustion zone. 10 kHz OH-PLIF images, and 2D PIV allow the identification of the fate and spatial flame structure. Many flame features were identified and further analyzed using simple but effective image processing methods, where three types of structure in all the flames investigated here: flame holes or breaks; closures; and growing kernels. Insights about the rate of evolution of these features, the dynamics of local extinction, and the sequence of events that lead to re-ignition are reported here. In the lower entrainment zone, the occurrence of the flame break events is counterbalanced by closure events, and the edge propagation appears to control the rate at which the flame holes and closures propagate. The rate of propagation of holes was found to be statistically faster than the rate of closure. As the flames approach blow-off, flame kernels become the main mechanism for flame re-ignition further downstream. The simultaneous OH-PLIF/Stereo PIV

Experimental study of the inverse diffusion flame using high repetition rate OH/acetone PLIF and PIV

KAUST Repository

Elbaz, Ayman M.

2015-10-29

Most previous work on inverse diffusion flames (IDFs) has focused on laminar IDF emissions and the soot formation characteristics. Here, we investigate the characteristics and structure of methane IDFs using high speed planar laser-induced fluorescence (PLIF) images of OH, particle image velocimetry (PIV), and acetone PLIF imaging for non-reacting cases. First, the flame appearance was investigated with fixed methane loading (mass flux) but with varying airflow rates, yielding a central air jet Reynolds number (Re) of 1,000 to 6,000 (when blow-off occurs). Next, it was investigated a fixed central air jet Re of 4500, but with varied methane mass flux such that the global equivalence ratio spanned 0.5 to 4. It was observed that at Re smaller than 2000, the inner air jet promotes the establishment of an inverse diffusion flame surrounded by a normal diffusion flame. However, when the Re was increased to 2500, two distinct zones became apparent in the flame, a lower entrainment zone and an upper mixing and combustion zone. 10 kHz OH-PLIF images, and 2D PIV allow the identification of the fate and spatial flame structure. Many flame features were identified and further analyzed using simple but effective image processing methods, where three types of structure in all the flames investigated here: flame holes or breaks; closures; and growing kernels. Insights about the rate of evolution of these features, the dynamics of local extinction, and the sequence of events that lead to re-ignition are reported here. In the lower entrainment zone, the occurrence of the flame break events is counterbalanced by closure events, and the edge propagation appears to control the rate at which the flame holes and closures propagate. The rate of propagation of holes was found to be statistically faster than the rate of closure. As the flames approach blow-off, flame kernels become the main mechanism for flame re-ignition further downstream. The simultaneous OH-PLIF/Stereo PIV