INVESTIGATION ON FLOW STRUCTURE BEHIND A RING BY IMPLEMENTING OPTICAL PARTICLE CHARACTERIZATIONS

2006 ◽  
Vol 20 (25n27) ◽  
pp. 4511-4516
Author(s):  
CHEOL WOO PARK
Keyword(s):  
Flow Structure ◽  
Bluff Body ◽  
Water Channel ◽  
Cross Flow ◽  
Circular Ring ◽  
Outer Side ◽  
Mean Velocity ◽  
Circulating Water ◽  
Image Velocimetry ◽  
Bluff Body Wake

The flow structure behind circular and elliptical type rings embedded in a cross-flow was investigated experimentally using a particle image velocimetry (PIV), implementing optical particle characterizations. The experiments were performed in a circulating water channel with a test section of 0.2m height × 0.3m width × 1.2m length. The Reynolds number based on the ring hoop cord length is about Re =1200. The velocity fields near the ring hoop were measured using the two-frame cross-correlation PIV method. As a result, the flow near the sharp-edged end of ring hoop ascends fast and showed a conventional vortical structure appeared in a bluff body wake. In the mean velocity field behind a circular ring, there were two large vortices rotating in different directions from each other in the near wake regime caused by the interaction between the central jet flow and the entrained ambient fluids from outer side of ring hoop.

A Comparative Study Between DNS, LES and PIV for a Marine Riser With Fairings

2015 ◽  
Author(s):  
Håkon Strandenes ◽  
José Patricio Gallardo Canabes ◽  
Jan Visscher ◽  
Bjørnar Pettersen ◽  
Helge I. Andersson ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Bluff Body ◽  
Mean Flow ◽  
Surface Integral ◽  
Circulating Water ◽  
Flow Parameters ◽  
Image Velocimetry ◽  
Drag And Lift ◽  
Recirculation Length ◽  
Bluff Body Wake

This paper present results from numerical simulations and laboratory experiments investigating the flow around a riser with fairings at Reynolds number of 5000. We present fully resolved direct numerical simulations (DNS), large eddy simulations (LES) and compare the results with flowfields obtained from particle image velocimetry (PIV) experiments in a circulating water tunnel. The DNS and LES results do agree very well on surface integral quantities such as drag and lift force, but there are discrepancies in first order statistical flow parameters such as recirculation length. This indicate that a comparison of force coefficients is not sufficient to validate this type of bluff body wake flows. Comparing the simulation data with the experimental PIV data, also reveals significant discrepancies in the mean flow field, although the Strouhal number agrees between DNS and PIV results.

Different Modes of Gas Entrainment Through Bottom Discharge Branch by Using Three Dimensional Particle Image Velocimetry System

2007 ◽  
Author(s):  
Wael Fairouz Saleh ◽  
Ibrahim Galal Hassan
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Structure ◽  
Particle Image ◽  
Three Dimensional ◽  
Industrial Applications ◽  
Particle Image Velocimetry System ◽  
Three Dimension ◽  
Two Phase ◽  
Mean Velocity ◽  
Image Velocimetry

The discharge of two-phase flow from a stratified region through single or multiple branches is an important process in many industrial applications including the pumping of fluid from storage tanks, shell-and-tube heat exchangers, and the fluid flow through small breaks in cooling channels of nuclear reactors during loss-of-coolant accidents (LOCA). Knowledge of the flow phenomena involved along with the quality and mass flow rate of the discharging stream(s) is necessary to adequately predict the different phenomena associated with the process. Particle Image Velocimetry (PIV) in three dimension was used to provide detailed measurements of the flow patterns involving distributions of mean velocity, vorticity field, and flow structure. The experimental investigation was carried out to simulate two phase discharge from a stratified region through branches located on a semi-circular wall configuration during LOCA scenarios. The semi-circular test section is in close dimensional resemblance with that of a CANDU header-feeder system, with branches mounted at orientation angles of zero, 45 and 90 degrees from the horizontal. The experimental data for the phase development (mean velocity, flow structure, etc.) was done during single discharge through the bottom branch from an air/water stratified region over a three selected Froude numbers. These measurements were used to describe the effect of outlet flow conditions on phase redistribution in headers and understand the entrainment phenomena.

The Flow Structure and Statistics of a Passive Mixing Tab

1993 ◽  
Vol 115 (2) ◽  
pp. 255-263 ◽  
Author(s):  
W. J. Gretta ◽  
C. R. Smith
Keyword(s):  
Boundary Layer ◽  
Flow Visualization ◽  
Flow Structure ◽  
Water Channel ◽  
Symmetry Plane ◽  
Streamwise Vortices ◽  
Hairpin Vortices ◽  
Mean Velocity ◽  
Velocity Statistics ◽  
Passive Mixing

Water channel flow visualization and anemometry studies were conducted to examine the flow structure and velocity statistics in the wake of a passive mixing tab designed for enhancement of cross-stream mixing by generation of flow structures characteristic of turbulent boundary layers. Flow visualization reveals that the mixing tab generates a wake comprising a combination of counter rotating, streamwise vortices enveloped by distinct hairpin vortex structures. The counter rotating streamwise vortices are observed to stimulate a strong ejection of fluid along the symmetry plane, which results in very rapid cross-stream mixing. The hairpin vortices are found to undergo successive amalgamation and coalescence downstream of the device, which aids in the streamwise mixing and outward penetration of ejected fluid. After an initially intense mixing process, the mixing tab wake rapidly develops mean velocity, turbulence intensity, and boundary layer integral properties characteristic of a significantly thickened turbulent boundary layer.

scholarly journals Investigation of the dissipation in the wake of a wind turbine array

2021 ◽  
Author(s):  
Ingrid Neunaber ◽  
Joachim Peinke ◽  
Martin Obligado
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Bluff Body ◽  
Wind Farms ◽  
Energy Transition ◽  
Mean Velocity ◽  
Maintenance Time ◽  
Bluff Body Wake ◽  
Turbine Wake ◽  
Wind Turbine Wake

Abstract. Within the energy transition, more and more wind turbines are clustered in big wind farms, often offshore. Therefore, an optimal positioning of the wind turbines is crucial to optimize both the annual power production and the maintenance time. Good knowledge of the wind turbine wake and the turbulence within is thus important. However, although wind turbine wakes have been subject to various studies, they are still not fully understood. One possibility to improve the comprehension is to look into the modeling of bluff body wakes. These wakes have been the subject of intensive study for decades, and by means of the scaling behavior of the centerline mean velocity deficit, the nature of the turbulence inside a wake can be classified. In this paper, we introduce the models for equilibrium and non-equilibrium turbulence from classical wake theory as introduced by A. Townsend and W. George, and we test whether the requirements are fulfilled in the wake of a wind turbine. Finally, we apply the theory to characterize the wind turbine wake, and we compare the results to the Jensen and the Bastankhah-Porté-Agel model. We find that the insight into the classical bluff body wake can be used to further improve the wind turbine wake models. Particularly, the classical bluff body wake models perform better than the wind turbine wake models due to the presence of a virtual origin in the scalings, and we demonstrate the possibility of improving the wind turbine wake models by implementing this parameter. We also see how the dissipation changes across the wake which is important to model wakes within wind farms correctly.

Energy Concentration by Bluff Bodies—A Particle Image Velocimetry Investigation

2018 ◽  
Vol 141 (6) ◽  
Author(s):  
Eshodarar Manickam Sureshkumar ◽  
Maziar Arjomandi ◽  
Bassam B. Dally ◽  
Benjamin S. Cazzolato ◽  
Mergen H. Ghayesh
Keyword(s):  
Particle Image Velocimetry ◽  
Circular Cylinder ◽  
Bluff Body ◽  
Particle Image ◽  
Transverse Velocity ◽  
Water Channel ◽  
Energy Concentration ◽  
Backward Facing Step ◽  
Flow Energy ◽  
Image Velocimetry

Particle image velocimetry (PIV) of four cylinders with different cross sections were performed in a recirculating water channel at Reynolds numbers of 5000 and 10,000. The cylinders were split into two distinct categories; semicircular and convex-edged triangular (c-triangular) prisms which have a smooth diverging fore-face and a flat, backward facing step aft-face, and a trapezoid which has a flat fore face and a backward-facing step aft-face. The resulting streamwise and transverse velocity vectors (u and v, respectively) were analyzed to provide a qualitative comparison of the bluff body wakes to the circular cylinder, which is the standard upstream stationary body in wake-induced vibration (WIV) energy technology. The Reynolds stresses, turbulent kinetic energy (TKE), mean spanwise vorticity, and the energy in the fluctuating component of the wake were compared. The main findings are: (i) a convex fore-face and a backward-facing step aft face are more effective at converting the flow energy to temporal wake energy (+20%) compared to a circular cylinder, (ii) a trapezoid type shape is less effective at converting flow energy to temporal wake energy (−40%) compared to a circular cylinder, (iii) increasing Reynolds number reduces the efficiency of conversion of upstream flow energy to downstream transverse temporal energy. Utilizing stationary upstream bodies such as the semicircle and the c-triangle can result in concentrating more energy in the fluctuating components for the downstream transversely vibrating bluff body in a WIV system, and hence can realize in more efficient WIV technology.

An Experimental Investigation of the Separation Points on a Circular Rotating Cylinder in Cross Flow

2007 ◽  
Vol 129 (9) ◽  
pp. 1203-1211 ◽  
Author(s):  
L. Labraga ◽  
G. Kahissim ◽  
L. Keirsbulck ◽  
F. Beaubert
Keyword(s):  
Experimental Investigation ◽  
Laser Doppler Anemometry ◽  
Water Channel ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Rotating Cylinder ◽  
Stream Velocity ◽  
Sufficient Information ◽  
Image Velocimetry ◽  
Two Dimensional Flow

The flow past a rotating cylinder placed within a uniform stream is investigated at Reynolds numbers ranging from 8500 to 17,000 to 34,000. The dimensionless rotation rate α (ratio of the cylinder peripheral speed to the free-stream velocity) varies from 0 to 7. The experimental investigation is based on laser-Doppler anemometry measurements and particle-image velocimetry (PIV) within a water channel. The analysis of the experimental results mainly concerns the location of the separation points as defined by various criteria. It is found that the criterion suggested by Moore, Rott and Sears (MRS) is met in the case of the downstream-moving walls. Moreover, this study shows that sufficient information was obtained to confirm that the MRS criterion is still valid even in the case of the upstream-moving walls. This is confirmed by the behavior of the vertical velocity component educed from the averaged two-dimensional flow field obtained by PIV measurements.

The Passive Control of Unsteady Flow Structure Downstream of a Circular Cylinder in Shallow Water

2013 ◽  
Author(s):  
Tahir Durhasan ◽  
Engin Pınar ◽  
Muhammed M. Aksoy ◽  
Göktürk M. Özkan ◽  
Hüseyin Akıllı ◽  
...  
Keyword(s):  
Circular Cylinder ◽  
Shallow Water ◽  
Flow Structure ◽  
Vortex Shedding ◽  
Passive Control ◽  
Outer Cylinder ◽  
Water Channel ◽  
Stream Velocity ◽  
Image Velocimetry ◽  
Perforated Cylinder

In the present study, it was aimed to suppress the vortex shedding occurred in the near wake of a circular cylinder (inner cylinder) by perforated cylinder (outer cylinder) in shallow water flow. The inner cylinder (Di) and outer cylinder (Do) have fixed diameters, such as Di = 50 mm and Do = 100 mm, respectively. The effect of porosity, β, was examined using four different porosity ratios, 0.3, 0.5, 0.6 and 0.8. In order to investigate the effect of arc angle of outer cylinder, α, four different arc angles, α = 360°, 180°, 150° and 120° were used. The experiments were implemented in a recirculating water channel using the particle image velocimetry, PIV technique. The depth-averaged free-stream velocity was kept constant as U∞ = 100 mm/s which corresponded to a Reynolds number of Re = 5000 based on the inner cylinder diameter. The results demonstrated that the suppression of vortex shedding is substantially achieved by perforated outer cylinder for arc angle of α = 360° at β = 0.6. Turbulence Kinetic Energy statistics show that porosity, β, is highly effective on the flow structure. In comparison with the values obtained from the case of the bare cylinder, at porosity β = 0.6, turbulence characteristics are reduced by %80. Also, the point, which the values of maximum TKE, shift to a farther downstream compared to the case of bare cylinder.

A Versatile Fully Submersible Stereo-PIV Probe for Tow Tank Applications

2003 ◽  
Author(s):  
Francisco Pereira ◽  
Tiziano Costa ◽  
Mario Felli ◽  
Guido Calcagno ◽  
Fabio Di Felice
Keyword(s):  
Particle Image ◽  
Water Channel ◽  
Three Dimensional ◽  
Stereoscopic Particle Image Velocimetry ◽  
Velocity Measurements ◽  
Piv Measurements ◽  
Circulating Water ◽  
Image Velocimetry ◽  
Out Of Plane ◽  
Yaw Angle

A unique, highly modular and flexible underwater system for stereoscopic particle image velocimetry (PIV) measurements has been designed, manufactured and tested. The instrument is intended for planar three-dimensional velocity measurements in large facilities such as water tow tanks and tunnels. The performance of the system is assessed in four major stereoscopic configurations. Errors under 2% for the in-plane components and 4% for the out-of-plane components are found. The system is tested in the INSEAN large circulating water channel where the measurement of the flow around a model ship oriented at a moderate yaw angle is performed and puts into evidence the main features of the flow.

Analysis of Wake Interaction of Oscillating Platform With Four Columns

2019 ◽  
Author(s):  
Shinichiro Hirabayashi ◽  
Murilo M. Cicolin ◽  
Rodolfo T. Gonçalves ◽  
Gustavo R. S. Assi ◽  
Hideyuki Suzuki
Keyword(s):  
Particle Image Velocimetry ◽  
Constant Velocity ◽  
Particle Image ◽  
Hydrodynamic Force ◽  
Water Channel ◽  
Circulating Water ◽  
Image Velocimetry ◽  
Wake Interaction ◽  
The Difference ◽  
A Current

Abstract The effect of wake interaction on the hydrodynamic force was experimentally investigated. A scaled platform model with four columns was subjected to a current in the circulating water channel with constant velocity. The diameter of each column was 75 mm, and the aspect ratio (defined by the ratio between the column draft and diameter) was 1.5. The spacing ratios, (defined by the ratio between the distance of column centers and diameter) were 3 and 4. The platform was forced to oscillate with different frequencies and amplitudes. Flow around columns was measured by using Particle Image Velocimetry (PIV). The difference of hydrodynamic forces on each column was discussed concerning the effect of wake interaction among columns.

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