The flow around a pipeline with a spoiler

2009 ◽  
Vol 224 (1) ◽  
pp. 109-121 ◽  
Author(s):  
A A Oner
Keyword(s):  
Shear Stress ◽  
Velocity Vector ◽  
Particle Image ◽  
Reynolds Numbers ◽  
Two Dimensional ◽  
Velocity Vector Field ◽  
Smooth Wall ◽  
Particle Image Velocimetry Technique ◽  
Offshore Pipelines ◽  
Image Velocimetry

Offshore pipelines are buried in the seabed to be protected from the damage caused by hydrodynamic forces or by human activities. However, because of soil erosion and interaction of currents with the pipeline on the moveable seabed, the processes of local scouring and, sometimes, self-burial of pipelines take place. To increase the rate and extent of scouring, the technique of attaching a spoiler to the pipeline has been developed. In this study, two-dimensional, steady, turbulent flow around a horizontal pipeline with a spoiler near a smooth wall is investigated experimentally by using the particle image velocimetry technique. The effect of the spoiler was examined for the Reynolds numbers of ReD=840, 1500, 4150, and 9500 based on the pipe diameter. The effect of the spoiler on the process of scouring is investigated through the parameters of the measured instantaneous and time-averaged patterns of the velocity vector field and the streamline topology. The results indicated that the attachment of the spoiler to the pipeline increases the length of the upstream and downstream separation regions and it is also observed that the spoiler does not significantly increase the rate of the flow that passes through the gap and the shear stress acting on the seabed.

Abstract 14952: Volumetric Echocardiographic Particle Image Velocimetry (V-Echo-PIV)

Circulation ◽  
2014 ◽  
Vol 130 (suppl_2) ◽  
Author(s):  
Ahmad Falahatpisheh ◽  
Arash Kheradvar
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Contrast Echocardiography ◽  
Ultrasound Contrast Agent ◽  
Three Dimensions ◽  
Small Scale ◽  
High Temporal Resolution ◽  
Two Dimensional ◽  
Particle Image Velocimetry Technique ◽  
Image Velocimetry

Introduction: The two-dimensional (2D) echocardiographic particle image velocimetry technique that was introduced in 2010 received much attention in clinical cardiology. Cardiac flow visualization based on contrast echocardiography results in images with high temporal resolution that are obtainable at relatively low cost. This makes it an ideal diagnostic and follow-up tool for routine clinical use. However, cardiac flow in a cardiac cycle is multidirectional with a tendency to spin in three dimensions rather than two-dimensional curl. Here, for the first time, we introduce a volumetric echocardiographic particle image velocimetry technique that robustly acquires the flow in three spatial dimensions and in time: Volumetric Echocardiographic Particle Image Velocimetry (V-Echo-PIV). Methods: V-Echo-PIV technique utilizes matrix array 3D ultrasound probes to capture the flow seeded with an ultrasound contrast agent (Definity). For this feasibility study, we used a pulse duplicator with a silicone ventricular sac along with bioprosthetic heart valves at the inlet and outlet. GE Vivid E9 system with an Active Matrix 4D Volume Phased Array probe at 30 Hz was used to capture the flow data (Figure 1). Results: The 3D particle field was obtained with excellent spatial resolution without significant noise (Figure 1). 3D velocity field was successfully captured for multiple cardiac cycles. Flow features are shown in Figure 2 where the velocity vectors in two selected slices and some streamlines in 3D space are depicted. Conclusions: We report successful completion of the feasibility studies for volumetric echocardiographic PIV in an LV phantom. The small-scale features of flow in the LV phantom were revealed by this technique. Validation and human studies are currently in progress.

Analysis of Entrainment at the Turbulent/Non-Turbulent Interface of a Square Jet

2013 ◽  
Author(s):  
Abbas Ghasemi ◽  
Vesselina Roussinova ◽  
Ronald Barron ◽  
Ram Balachandar
Keyword(s):  
Velocity Vector ◽  
Particle Image ◽  
Central Plane ◽  
Axial Distance ◽  
Velocity Vector Field ◽  
Ambient Fluid ◽  
Round Jet ◽  
Image Velocimetry ◽  
Swirling Strength ◽  
Cover Up

Particle image velocimetry measurements are carried out to study the entrainment at the interface between the non-turbulent and turbulent regions in a square jet. Jet Reynolds number based on the hydraulic diameter of the jet is 50,000. Measurements cover up to 25 diameters downstream of the nozzle exit using five horizontal field-of-views in the central plane of the jet. The turbulent/non-turbulent interface is identified using a velocity criterion and a suitable thresholding method. Using vorticity and swirling strength it is shown that the turbulent/non-turbulent interface separates the rotational and irrotational regions of the flow. Instantaneous velocity vector field superimposed with the turbulent/non-turbulent interface are presented. The relation between the vortex cores in the vicinity of the turbulent/non-turbulent interface and the contractions and expansions noticed in the jet velocity field are explained. Entrainment into the jet is evaluated at each axial distance by identifying the points falling inside the turbulent region of the jet. Compared to a round jet, the square jet entrains more ambient fluid. In addition, normal volume fluxes going through the turbulent/non-turbulent interface of the square jet are found to be larger compared to that of a round jet.

Particle Image Velocimetry Measurements Near the Onset of Cavitation in a Converging-Diverging Glass Nozzle

2016 ◽  
Author(s):  
Aaron Schmidt ◽  
B. Terry Beck ◽  
Mohammad H. Hosni
Keyword(s):  
Velocity Vector ◽  
Particle Image ◽  
Time Interval ◽  
Seed Density ◽  
Velocity Vector Field ◽  
Nozzle Throat ◽  
Piv Measurements ◽  
Seed Particles ◽  
Image Velocimetry ◽  
Onset Of Cavitation

Water flow through a converging-diverging glass nozzle experiences a pressure drop and its velocity increases as it flows through the converging section. For an inviscid fluid, the pressure minimum occurs at the nozzle throat, where the cross-sectional area is minimum. If the minimum pressure is below the water vapor pressure, cavitation may occur. The actual minimum pressure through a converging-diverging nozzle depends on many factors and may not occur at the nozzle throat. Additionally, fluid through the nozzle may be driven into the metastable region and subsequently cavitate at a lower pressure than the vapor pressure. All of these factors combine to create a complex and unsteady flow pattern. The precise conditions leading to the onset of cavitation in water flowing in a converging-diverging nozzle are not well understood. Utilization of a clear glass converging-diverging nozzle enabled Particle Image Velocimetry (PIV) measurements of the velocity vector field inside the nozzle without significantly promoting premature cavitation formation. Glass spheres of 10 μm diameter were selected as seed particles for use in the PIV measurements. These seed particles did not significantly affect the formation (or onset) of cavitation in the nozzle; however, larger seed particles (120 μm diameter) provided nucleation sights and promoted cavitation prematurely. The seed particles were injected into the flow significantly upstream from the nozzle to prevent disrupting the flow entering the nozzle. High seed density was needed to supply enough seed particles to interrogate small regions near the nozzle wall; however, high seed density could also cause speckling and reduce the ability to produce meaningful PIV measurements. A Nd:YAG laser provided illumination of the seed particles in the nozzle. Laser reflections off of the nozzle exterior had to be minimized to avoid saturating the PIV camera. A polarizing filter was installed on the camera to reduce reflections. An enclosure that surrounded the nozzle was also designed and utilized. The enclosure was filled with water to reduce laser reflections off of the nozzle exterior wall. The time elapsed between frames had to be adjusted for each section of the nozzle interrogated with PIV. For accurate velocity measurements, particles needed to travel at least two particles diameters but less than 25% of each interrogation cell. The large variation in velocities present in the nozzle prevented one time interval from satisfying the seed particles displacement requirements. The time interval between frames had to be tailored to each section of the nozzle, depending upon the range of velocities seen in that section. Detailed measurement of the velocity profile near the nozzle throat required precise control over all timing parameters and pushed the available hardware to its smallest possible time interval. Detailed PIV measurements near the wall in regions of recirculation and at the cavitation front required the use of a long-distance microscope. This limited the field of view and necessitated a high seed particle density, which presented problems due to the lack of control over the flow of the seed particles in the near wall region. PIV allowed for the measurement of the velocity vector field inside a converging-diverging nozzle without disrupting the flow. These measurements provided detailed velocity and flow pattern information throughout the nozzle, particularly in the regions near the cavitation front where boundary layer separation was observed along with regions of recirculating flow. These detailed velocity profiles were compiled to present a complete PIV analysis of the converging-diverging glass nozzle. Measurements of the velocity field near cavitation onset allowed for a better understanding of the conditions triggering cavitation and the degree to which the water flow was able to be driven into the metastable region.

Experimental Study of Jet Flow Impingement Within a Rod Bundle Using PIV Technique

2008 ◽  
Author(s):  
Noushin Amini ◽  
Yassin A. Hassan
Keyword(s):  
Particle Image ◽  
Rectangular Channel ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Reynolds Stresses ◽  
Particle Image Velocimetry Technique ◽  
Time Resolved ◽  
Rod Bundle ◽  
Piv Technique ◽  
Image Velocimetry

In this investigation Particle Image Velocimetry technique was implemented to a matched refractive index facility which was placed in a rectangular channel of L:1016 mm×W:76.2 mm×H:76.2 mm. Water was pumped into either one or both of the inlet jets which were entering the channel’s top wall with several different Reynolds numbers. The instantaneous and time-resolved velocity fields were successfully obtained from which several flow characteristics such as vorticity, turbulence instabilities and Reynolds stresses can be calculated.

scholarly journals Particle image velocimetry measurement of turbulent wake past circular cylinder at Reynolds numbers from 2.5·103 to 1.5·104

2021 ◽  
Vol 345 ◽  
pp. 00030
Author(s):  
Ondřej Sterly
Keyword(s):  
Particle Image Velocimetry ◽  
Circular Cylinder ◽  
Particle Image ◽  
Transverse Velocity ◽  
Reynolds Numbers ◽  
Particle Image Velocimetry Technique ◽  
Recirculation Bubble ◽  
Image Velocimetry ◽  
Ensemble Statistics ◽  
Vorticity Component

A canonical case of air flow past a circular cylinder is studied by using Particle Image Velocimetry technique. This contribution focus to the ensemble statistics (first and second moment) of the stream-wise and transverse velocity component as well as to the in-plane vorticity component. Although the range of explored Reynolds numbers is narrow, we observe a significant shortening of recirculation bubble within this range.

Experimental Investigation of Drag Reducing Fluid Flow in Annular Geometry Using Particle Image Velocimetry Technique

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Fabio E. Rodriguez Corredor ◽  
Majid Bizhani ◽  
Ergun Kuru
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Reynolds Numbers ◽  
Turbulent Kinetic Energy Budget ◽  
Flow Loop ◽  
Particle Image Velocimetry Technique ◽  
Mean Velocity ◽  
Image Velocimetry ◽  
Annular Geometry ◽  
Fully Developed Turbulent Flow

Fully developed turbulent flow of drag reducing fluids through a horizontal flow loop with concentric annular geometry was investigated using the particle image velocimetry (PIV) technique. Experiments were conducted at solvent Reynolds numbers ranged from 38,700 to 56,400. Axial mean velocity profile was found to be following the universal wall law close to the wall (i.e., y+ < 10), but it deviated from log law results with an increased slope in the logarithmic zone (i.e., y+ > 30). The study was also focused on turbulence statistics such as near wall Reynolds stress distribution, axial and radial velocity fluctuations, vorticity and turbulent kinetic energy budget.

Analysis of local velocity gradients in rapid mixer using particle image velocimetry technique

2002 ◽  
Vol 2 (5-6) ◽  
pp. 47-55
Author(s):  
N.-S. Park ◽  
H. Park
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Velocity Fields ◽  
Local Velocity ◽  
Mixing Condition ◽  
Particle Image Velocimetry Technique ◽  
Velocity Gradients ◽  
Image Velocimetry ◽  
Current Design ◽  
G Value

Recognizing the significance of factual velocity fields in a rapid mixer, this study focuses on analyzing local velocity gradients in various mixer geometries with particle image velocimetry (PIV) and comparing the results of the analysis with the conventional G-value, for reviewing the roles of G-value in the current design and operation practices. The results of this study clearly show that many arguments and doubts are possible about the scientific correctness of G-value, and its current use. This is because the G-value attempts to represent the turbulent and complicated factual velocity field in a jar. Also, the results suggest that it is still a good index for representing some aspects of mixing condition, at least, mixing intensity. However, it cannot represent the distribution of velocity gradients in a jar, which is an important factor for mixing. This study as a result suggests developing another index for representing the distribution to be used with the G-value.

A particle image velocimetry study on the pulsatile flow characteristics in straight tubes with an asymmetric bulge

2000 ◽  
Vol 214 (5) ◽  
pp. 655-671 ◽  
Author(s):  
S C M Yu ◽  
J B Zhao
Keyword(s):  
Particle Image Velocimetry ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Flow Condition ◽  
Particle Image ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Flow Conditions ◽  
Image Velocimetry

Flow characteristics in straight tubes with an asymmetric bulge have been investigated using particle image velocimetry (PIV) over a range of Reynolds numbers from 600 to 1200 and at a Womersley number of 22. A mixture of glycerine and water (approximately 40:60 by volume) was used as the working fluid. The study was carried out because of their relevance in some aspects of physiological flows, such as arterial flow through a sidewall aneurysm. Results for both steady and pulsatile flow conditions were obtained. It was found that at a steady flow condition, a weak recirculating vortex formed inside the bulge. The recirculation became stronger at higher Reynolds numbers but weaker at larger bulge sizes. The centre of the vortex was located close to the distal neck. At pulsatile flow conditions, the vortex appeared and disappeared at different phases of the cycle, and the sequence was only punctuated by strong forward flow behaviour (near the peak flow condition). In particular, strong flow interactions between the parent tube and the bulge were observed during the deceleration phase. Stents and springs were used to dampen the flow movement inside the bulge. It was found that the recirculation vortex could be eliminated completely in steady flow conditions using both devices. However, under pulsatile flow conditions, flow velocities inside the bulge could not be suppressed completely by both devices, but could be reduced by more than 80 per cent.

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