Tomographic PIV investigation of vortex shedding topology for a cantilevered circular cylinder

2021 ◽  
Vol 931 ◽  
Author(s):  
R.J. Crane ◽  
A.R. Popinhak ◽  
R.J. Martinuzzi ◽  
C. Morton
Keyword(s):  
Circular Cylinder ◽  
Mean Field ◽  
Three Dimensional ◽  
Base Region ◽  
Aspect Ratios ◽  
Topological Features ◽  
Image Velocimetry ◽  
Side Walls ◽  
Order Representation ◽  
The Mean

The wake of a finite wall-mounted circular cylinder of diameter $D$ and height $H$ is investigated for aspect ratios $3\leq H/D \leq 7$ and boundary layer thickness of $\delta /D \approx 0.98$ using tomographic particle image velocimetry. The Reynolds number based on $D$ is $Re = 750$ . The mean wake topology is related to the evolution of the periodically shed vortices, educed from a low-order representation based on proper orthogonal decomposition of the three-dimensional velocity field. The main topological features are an arch vortex, defining the recirculating base region, and a quadrupole structure consisting of two pairs of opposite-sign vorticity concentrations extending downstream behind the obstacle-free end and wall junction. The quadrupole is the time-averaged signature of shed vortices. Vortex-tilting terms in the base region act to reorient flow-normal vorticity components streamwise, resulting in the reorientation of the ends of vortices initially shed parallel to the cylinder side walls. Through the action of the vortex-stretching terms, the bent ends connect successive vortices in a continuous chain. The influence of $H/D$ on the development of the quadrupole is characterized. The results demonstrate that the quadrupole in the mean field emerges as an imprint of the shed full-loop structures. This work reconciles mean and instantaneous interpretations satisfying the solenoidal condition on the vorticity field.

Three-dimensional instabilities in oscillatory flow past elliptic cylinders

2016 ◽  
Vol 798 ◽  
pp. 371-397 ◽  
Author(s):  
José P. Gallardo ◽  
Helge I. Andersson ◽  
Bjørnar Pettersen
Keyword(s):  
Circular Cylinder ◽  
Flow Direction ◽  
Three Dimensional ◽  
Circular Cylinders ◽  
Flow Structures ◽  
Three Dimensional Flow ◽  
Elliptical Cross ◽  
Dimensional Flow ◽  
Aspect Ratios ◽  
Flow Past

We investigate the early development of instabilities in the oscillatory viscous flow past cylinders with elliptic cross-sections using three-dimensional direct numerical simulations. This is a classical hydrodynamic problem for circular cylinders, but other configurations have received only marginal attention. Computed results for some different aspect ratios ${\it\Lambda}$ from 1 : 1 to 1 : 3, all with the major axis of the ellipse aligned in the main flow direction, show good qualitative agreement with Hall’s stability theory (J. Fluid Mech., vol. 146, 1984, pp. 347–367), which predicts a cusp-shaped curve for the onset of the primary instability. The three-dimensional flow structures for aspect ratios larger than 2 : 3 resemble those of a circular cylinder, whereas the elliptical cross-section with the lowest aspect ratio of 1 : 3 exhibits oblate rather than tubular three-dimensional flow structures as well as a pair of counter-rotating spanwise vortices which emerges near the tips of the ellipse. Contrary to a circular cylinder, instabilities for an elliptic cylinder with sufficiently high eccentricity emerge from four rather than two different locations in accordance with the Hall theory.

scholarly journals Direct Numerical Simulation of Flow around a Circular Cylinder Controlled Using Plasma Actuators

2014 ◽  
Vol 2014 ◽  
pp. 1-13 ◽  
Author(s):  
Taichi Igarashi ◽  
Hiroshi Naito ◽  
Koji Fukagata
Keyword(s):  
Numerical Simulation ◽  
Circular Cylinder ◽  
Direct Numerical Simulation ◽  
Drag Reduction ◽  
Three Dimensional ◽  
Reduction Rate ◽  
Plasma Actuators ◽  
Two Dimensional ◽  
Freestream Velocity ◽  
The Mean

Flow around a circular cylinder controlled using plasma actuators is investigated by means of direct numerical simulation (DNS). The Reynolds number based on the freestream velocity and the cylinder diameter is set atReD=1000. The plasma actuators are placed at±90° from the front stagnation point. Two types of forcing, that is, two-dimensional forcing and three-dimensional forcing, are examined and the effects of the forcing amplitude and the arrangement of plasma actuators are studied. The simulation results suggest that the two-dimensional forcing is primarily effective in drag reduction. When the forcing amplitude is higher, the mean drag and the lift fluctuations are suppressed more significantly. In contrast, the three-dimensional forcing is found to be quite effective in reduction of the lift fluctuations too. This is mainly due to a desynchronization of vortex shedding. Although the drag reduction rate of the three-dimensional forcing is slightly lower than that of the two-dimensional forcing, considering the power required for the forcing, the three-dimensional forcing is about twice more efficient.

Characteristics of 3D Turbulent Wall Jets and Offset Jets With Small Offset Ratios

2009 ◽  
Author(s):  
M. Agelinchaab ◽  
M. F. Tachie
Keyword(s):  
Three Dimensional ◽  
Symmetry Plane ◽  
Shear Stresses ◽  
Wall Jets ◽  
Particle Image Velocimetry Technique ◽  
Image Velocimetry ◽  
Turbulent Wall Jets ◽  
The Mean ◽  
Turbulent Wall ◽  
Proper Orthogonal

This paper reports an experimental study of turbulent three-dimensional generic wall jets and offset jets. The jets were created from a long circular pipe. A particle image velocimetry technique was used to conduct velocity measurements in the symmetry plane of the jet. From these measurements, the salient features of the flows are reported in terms of the mean velocities, turbulence intensities and Reynolds shear stresses. The energy spectra and profiles of reconstructed turbulence intensities and Reynolds shear stresses from low order proper orthogonal decomposition modes are also reported.

Influence of a Magnetic Obstacle on Forced Convection in a Three-Dimensional Duct With a Circular Cylinder

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Xidong Zhang ◽  
Hulin Huang ◽  
Yin Zhang ◽  
Hongyan Wang
Keyword(s):  
Pressure Drop ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Three Dimensional ◽  
Separated Flow ◽  
Optimum Conditions ◽  
Nusselt Numbers ◽  
Maximum Value ◽  
Wide Range ◽  
The Mean

The predictions of flow structure, vortex shedding, and drag force around a circular cylinder are promoted by both academic interest and a wide range of practical situations. To control the flow around a circular cylinder, a magnetic obstacle is set upstream of the circular cylinder in this study for active controlling the separated flow behind bluff obstacle. Moreover, the changing of position, size, and intensity of magnetic obstacle is easy. The governing parameters are the magnetic obstacle width (d/D = 0.0333, 0.1, and 0.333) selected on cylinder diameter, D, and position (L/D) ranging from 2 to 11.667 at fixed Reynolds number Rel (based on the half-height of the duct) of 300 and the relative magnetic effect given by the Hartmann number Ha of 52. Results are presented in terms of instantaneous contours of vorticity, streamlines, drag coefficient, Strouhal number, pressure drop penalty, and local and average Nusselt numbers for various magnetic obstacle widths and positions. The computed results show that there are two flow patterns, one with vortex shedding from the magnetic obstacle and one without vortex shedding. The optimum conditions for drag reduction are L/D = 2 and d/D = 0.0333–0.333, and under these conditions, the pressure drop penalty is acceptable. However, the maximum value of the mean Nusselt number of the downstream cylinder is about 93% of that for a single cylinder.

Effect of Aspect Ratio on the Flow Field Above the Free End of a Finite Circular Cylinder

2014 ◽  
Author(s):  
Noorallah Rostamy ◽  
David Sumner ◽  
Donald J. Bergstrom ◽  
James D. Bugg
Keyword(s):  
Wind Tunnel ◽  
Circular Cylinder ◽  
Recirculation Zone ◽  
Ground Plane ◽  
Symmetry Plane ◽  
Leading Edge ◽  
Velocity Measurements ◽  
Reattachment Point ◽  
Aspect Ratios ◽  
The Mean

The flow above the free end of a surface-mounted finite-height circular cylinder was studied in a low-speed wind tunnel using particle image velocimetry (PIV). The cylinder was mounted vertically in the wind tunnel, normal to a ground plane. The approaching flow was in the x-direction and the cylinder axis was aligned in the z-direction. Velocity measurements were made above the free-end surface in several vertical (x-z) planes and several horizontal (x-y) planes, for finite circular cylinders of aspect ratios AR = 9, 7, 5 and 3, at a Reynolds number of Re = 4.2×104. The relative thickness of the boundary layer on the ground plane was δ/D = 1.7. In the vertical symmetry plane, the mean velocity measurements show the prominent separation from the circumferential leading edge, the mean recirculation zone above the free-end surface, the arch vortex inside the recirculation zone, and reattachment of the flow onto the free-end surface. Experimental evidence is found for a leading-edge separation bubble, a flow structure which has been reported in some numerical simulations in the literature. As AR decreases, the reattachment point and the centre of the arch vortex move downstream, the recirculation zone becomes thicker, and the centre of the arch vortex moves higher above the free end. Away from the symmetry plane, the recirculation zone becomes thinner, the arch vortex centre moves upstream and closer to the free-end surface, and the reattachment point moves upstream. In the horizontal planes, measurements made very close to the surface can approximate the mean surface streamline topology, revealing the pair of foci representing the termination points of the arch vortex, the prominent curved reattachment line, reverse flow beneath the mean recirculation zone, and the reattachment and separation saddle points on the free-end centerline.

Flow Visualization, Transport Mechanism, and Temperature Distributions in an Enclosure With Two Side Walls Each Differentially Heated: Upper Half, Cold; Lower Half, Hot

2003 ◽  
Author(s):  
H. Li ◽  
M. J. Braun ◽  
E. Evans ◽  
G. Wang ◽  
G. Paudal ◽  
...  
Keyword(s):  
Numerical Models ◽  
Numerical Data ◽  
Growth Conditions ◽  
Lower Half ◽  
Quartz Crystals ◽  
Full Field ◽  
Aspect Ratios ◽  
Image Velocimetry ◽  
Growth Production ◽  
Side Walls

Due to the experimental difficulties brought about by the high pressure and temperature growth conditions flow and heat transport in a hydrothermal autoclave for the growth of single quartz crystals has been studied mostly numerically. To date, most of the numerical models and associated results are not validated, or only qualitatively validated through results derived from crystal growth production. In this study, the authors used a simulated model reactor represented by an enclosure with the two lower half sidewalls uniformly heated while the upper halves are uniformly cooled. Flow in the reactor is qualitatively visualized using a full field flow lighting and seeding technique and quantitatively evaluated using particle image velocimetry. Finally, based on the physical setup and experimentally determined boundary conditions, flow is numerically simulated and compared to the experimental results. The agreement between the experimental and the numerical data was used to validate the numerical model. The ensuing parametric study shows the changing of flow pattern and velocity magnitudes for two differential temperature cases: (ΔT = 10°C and ΔT = 1°C) and a variety of enclosure aspect ratios.

MEAN-FIELD THEORY FOR LAYERED HIGH-TEMPERATURE SUPERCONDUCTORS

1988 ◽  
Vol 02 (05) ◽  
pp. 1059-1065 ◽  
Author(s):  
D. Baeriswyl ◽  
T. Schneider
Keyword(s):  
High Temperature Superconductors ◽  
Mean Field Theory ◽  
Mean Field ◽  
Three Dimensional ◽  
Interlayer Coupling ◽  
Interlayer Spacing ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Pairing Mechanism ◽  
The Mean

Using the mean-field approximation we study a model for quasi-two-dimensional layered superconductors. The interlayer coupling, assumed to be mediated by a small electron hopping term, is found to leave Tc practically unaffected. Consequently, a three-dimensional pairing mechanism is required to explain the observed dependence of Tc on the average interlayer spacing in the Bi and Tl compounds.

scholarly journals Flow control with rotating cylinders

2017 ◽  
Vol 825 ◽  
pp. 743-763 ◽  
Author(s):  
James C. Schulmeister ◽  
J. M. Dahl ◽  
G. D. Weymouth ◽  
M. S. Triantafyllou
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Three Dimensional ◽  
Rotating Cylinders ◽  
Piv Measurements ◽  
Rotation Rates ◽  
Image Velocimetry ◽  
The Mean ◽  
Recirculation Length ◽  
Control Cylinder

We study the use of small counter-rotating cylinders to control the streaming flow past a larger main cylinder for drag reduction. In a water tunnel experiment at a Reynolds number of 47 000 with a three-dimensional and turbulent wake, particle image velocimetry (PIV) measurements show that rotating cylinders narrow the mean wake and shorten the recirculation length. The drag of the main cylinder was measured to reduce by up to 45 %. To examine the physical mechanism of the flow control in detail, a series of two-dimensional numerical simulations at a Reynolds number equal to 500 were conducted. These simulations investigated a range of control cylinder diameters in addition to rotation rates and gaps to the main cylinder. Effectively controlled simulated flows present a streamline that separates from the main cylinder, passes around the control cylinder, and reattaches to the main cylinder at a higher pressure. The computed pressure recovery from the separation to reattachment points collapses with respect to a new scaling, which indicates that the control mechanism is viscous.

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