PIV study of small-scale flow structure around a Rushton turbine

AIChE Journal ◽  
2001 ◽  
Vol 47 (4) ◽  
pp. 766-778 ◽  
Author(s):  
K. V. Sharp ◽  
R. J. Adrian
Keyword(s):  
Flow Structure ◽  
Small Scale ◽  
Rushton Turbine

Numerical Investigation of Heat Transfer Enhancement on a Small Scale Vortex Generator

2009 ◽  
Author(s):  
Jiansheng Wang ◽  
Zhiqin Yang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Flow Structure ◽  
Rectangular Channel ◽  
Vortex Generator ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Vortex Generators ◽  
Small Scale ◽  
Transfer Enhancement

The heat transfer characteristic and flow structure of fluid in the rectangular channel with different height vortex generators in small scale are investigated with numerical simulation. Meantime, the properties of heat transfer and flow of fluid in the rectangular channel are compared with the channel which located small scale vortex generator. The variation law of local heat transfer and flow structure in channel is obtained. The mechanism of heat transfer enhancement of small scale vortex generators is discussed in detail. It is found that the influence of vortex generator on heat transfer is not in proportion to the size of vortex generator. What is more, turbulent flow structure near the wall, which influences the temperature distribution near the wall, induces the variety of local heat transfer. The fluid movement towards to the wall causes the heat transfer enhanced. On the contrary, the fluid movement away from the wall decreases the local heat transfer.

scholarly journals Does the Representation of Flow Structure and Turbulence at a Cold Front Converge on Multiscale Observations with Model Resolution?

2017 ◽  
Vol 145 (11) ◽  
pp. 4345-4363 ◽  
Author(s):  
Ben Harvey ◽  
John Methven ◽  
Chloe Eagle ◽  
Humphrey Lean
Keyword(s):  
Flow Structure ◽  
Cold Front ◽  
Spatial Scales ◽  
Weather Prediction ◽  
Turbulent Fluxes ◽  
Numerical Weather Prediction Model ◽  
Shear Instability ◽  
Small Scale ◽  
Convective Boundary ◽  
Direct Evaluation

In situ aircraft observations are used to interrogate the ability of a numerical weather prediction model to represent flow structure and turbulence at a narrow cold front. Simulations are performed at a range of nested resolutions with grid spacings of 12 km down to 100 m, and the convergence with resolution is investigated. The observations include the novel feature of a low-altitude circuit around the front that is closed in the frame of reference of the front, thus allowing the direct evaluation of area-average vorticity and divergence values from circuit integrals. As such, the observational strategy enables a comparison of flow structures over a broad range of spatial scales, from the size of the circuit itself ([Formula: see text]100 km) to small-scale turbulent fluctuations ([Formula: see text]10 m). It is found that many aspects of the resolved flow converge successfully toward the observations with resolution if sampling uncertainty is accounted for, including the area-average vorticity and divergence measures and the narrowest observed cross-frontal width. In addition, there is a gradual handover from parameterized to resolved turbulent fluxes of moisture and momentum as motions in the convective boundary layer behind the front become partially resolved in the highest-resolution simulations. In contrast, the parameterized turbulent fluxes associated with subgrid-scale shear-driven turbulence ahead of the front do not converge on the observations. The structure of frontal rainbands associated with a shear instability along the front also does not converge with resolution, indicating that the mechanism of the frontal instability may not be well represented in the simulations.

Response of supersonic turbulent boundary layers to local and global mechanical distortions

2009 ◽  
Vol 630 ◽  
pp. 225-265 ◽  
Author(s):  
ISAAC W. EKOTO ◽  
RODNEY D. W. BOWERSOX ◽  
THOMAS BEUTNER ◽  
LARRY GOSS
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Boundary Layers ◽  
Flow Structure ◽  
Small Scale ◽  
Pressure Gradients ◽  
Local Surface ◽  
Turbulence Flow ◽  
Turbulent Flow Structure ◽  
The Mean

The response of the mean and turbulent flow structure of a supersonic high-Reynolds-number turbulent boundary layer flow subjected to local and global mechanical distortions was experimentally examined. Local disturbances were introduced via small-scale wall patterns, and global distortions were induced through streamline curvature-driven pressure gradients. Local surface topologies included k-type diamond and d-type square elements; a smooth wall was examined for comparison purposes. Three global distortions were studied with each of the three surface topologies. Measurements included planar contours of the mean and fluctuating velocity via particle image velocimetry, Pitot pressure profiles, pressure sensitive paint and Schlieren photography. The velocity data were acquired with sufficient resolution to characterize the mean and turbulent flow structure and to examine interactions between the local surface roughness distortions and the imposed pressure gradients on the turbulence production. A strong response to both the local and global distortions was observed with the diamond elements, where the effect of the elements extended into the outer regions of the boundary layer. It was shown that the primary cause for the observed response was the result of local shock and expansion waves modifying the turbulence structure and production. By contrast, the square elements showed a less pronounced response to local flow distortions as the waves were significantly weaker. However, the frictional losses were higher for the blunter square roughness elements. Detailed quantitative characterizations of the turbulence flow structure and the associated production mechanisms are described herein. These experiments demonstrate fundamental differences between supersonic and subsonic rough-wall flows, and the new understanding of the underlying mechanisms provides a scientific basis to systematically modify the mean and turbulence flow structure all the way across supersonic boundary layers.

scholarly journals CFD study of the effect of Baffles on the energy consumption and the flow structure in a vessel stirred by a Rushton turbine

Mechanika ◽  
2016 ◽  
Vol 22 (3) ◽  
Author(s):  
Kamla Youcef ◽  
M. Bouzit ◽  
A. Hadjeb ◽  
I.M. Arab ◽  
M. Beloudane
Keyword(s):  
Energy Consumption ◽  
Flow Structure ◽  
Rushton Turbine

Flow Structure Identification in Unsteady Flow in Porous Media

2012 ◽  
Author(s):  
Vishal A. Patil ◽  
James A. Liburdy
Keyword(s):  
Reynolds Number ◽  
Flow Structure ◽  
Rotation Rate ◽  
Flow In Porous Media ◽  
Structure Identification ◽  
Small Scale ◽  
Strength Analysis ◽  
Average Pore ◽  
Number Range ◽  
Vortical Structures

This study is an experimental investigation of the turbulent flow structure in randomly packed porous bed made with uniform sized spheres. Results are based on time resolved, two component PIV measurements in individual pore spaces of the bed. Data are presented for pore Reynolds number range of 54–3964. Three different flow regimes are identified, steady laminar, and unsteady transitional and turbulent flows. Small scale coherent vortical structures are visualized, by performing large eddy scale decomposition, for pore Reynolds number of greater than 1000. Quantative analysis of vortical coherent structures was performed using swirl strength analysis. The number density of vortical structures is found to monotonically increase gradually with pore Reynolds number. The rotation rate of these vortical structures is found to increase linearly with pore Reynolds number. The stretching rate (linear deformation) of the eddies were calculated using continuity to determine the out of plane stretching. The ratio of stretching rate to swirl strength (rotation rate) shows a normal distribution which collapsed onto a single curve. The convective velocities of the structures show a symmetric distribution with a peak value close to 0.8 times the average pore velocity.

Analysis of Crank Angle-Resolved Vortex Characteristics Under High Swirl Condition in a Spark-Ignition Direct-Injection Engine

2017 ◽  
Author(s):  
Fengnian Zhao ◽  
Penghui Ge ◽  
Hanyang Zhuang ◽  
David L. S. Hung
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
High Speed ◽  
Large Scale ◽  
Early Stage ◽  
Direct Injection ◽  
Spark Ignition ◽  
Small Scale ◽  
Vortex Center ◽  
Intake Stroke

In-cylinder air flow structure makes significant impacts on fuel spray dispersion, fuel mixture formation, and flame propagation in spark ignition direct injection (SIDI) engines. While flow vortices can be observed during the early stage of intake stroke, it is very difficult to clearly identify their transient characteristics because these vortices are of multiple length scales with very different swirl motion strength. In this study, a high-speed time-resolved 2D particle image velocimetry (PIV) is applied to record the flow structure of in-cylinder flow field along a swirl plane at 30 mm below the injector tip. First, a discretized method using flow field velocity vectors is presented to identify the location, strength, and rotating direction of vortices at different crank angles. The transients of vortex formation and dissipation processes are revealed by tracing the location and motion of the vortex center during the intake and compression strokes. In addition, an analysis method known as the wind-rose diagram, which is implemented for meteorological application, has been adopted to show the velocity direction distributions of 100 consecutive cycles. Results show that there exists more than one vortex center during early intake stroke and their fluctuations between each cycle can be clearly visualized. In summary, this approach provides an effective way to identify the vortex structure and to track the motion of vortex center for both large-scale and small-scale vortices.

Interaction of a deep-water wave with a vertical cylinder: effect of self-excited vibrations on quantitative flow patterns

2007 ◽  
Vol 572 ◽  
pp. 189-217 ◽  
Author(s):  
M. OZGOREN ◽  
D. ROCKWELL
Keyword(s):  
Flow Structure ◽  
Deep Water ◽  
Water Wave ◽  
Large Scale ◽  
Wave Motion ◽  
Vertical Cylinder ◽  
Small Scale ◽  
Cylinder Surface ◽  
Deep Water Wave ◽  
Quantitative Flow

Interaction of a deep-water wave with a cylinder gives rise to ordered patterns of the flow structure, which are quantitatively characterized using a technique of high-image-density particle image velocimetry. When the cylinder is stationary, the patterns of instantaneous flow structure take on increasingly complex forms for increasing Keulegan--Carpenter number KC. These patterns involve stacking of small-scale vorticity concentrations, as well as large-scale vortex shedding. The time-averaged consequence of these patterns involves, at sufficiently high KC, an array of vorticity concentrations about the cylinder.When the lightly damped cylinder is allowed to undergo bidirectional oscillations, the trajectories can be classified according to ranges of KC. At low values of KC, the trajectory is elliptical, and further increases of KC allow, first of all, both elliptical and in-line trajectories as possibilities, followed by predominantly in-line and figure-of-eight oscillations at the largest value of KC.Representations of the quantitative flow structure, in relation to the instantaneous cylinder position on its oscillation trajectory, show basic classes of patterns. When the trajectory is elliptical, layers of vorticity rotate about the cylinder surface, in accordance with rotation of the relative velocity vector of the wave motion with respect to the oscillating cylinder. Simultaneously, the patterns of streamline topology take the form of large-scale bubbles, which also rotate about the cylinder. When the cylinder trajectory is predominantly in-line with the wave motion, generic classes of vortex formation and shedding can be identified; they include sweeping of previously shed vorticity concentrations past the cylinder to the opposite side. Certain of these patterns are directly analogous to those from the stationary cylinder.

Research on Flow Field of a Fixed Duct in a Rotary Energy Recovery Device

2017 ◽  
Author(s):  
K. Liu ◽  
J. Q. Deng ◽  
B. Yang
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
Energy Recovery ◽  
Flow Instability ◽  
Structural Parameters ◽  
Operating Conditions ◽  
Small Scale ◽  
Mixing Rate ◽  
Piv Measurement ◽  
Turbulent Flow Structure

An experimental study was carried out to investigate flow structures in the duct of a rotary energy recovery device (RERD). In order to visualize the flow field, a new type structure of the RERD was proposed in this experiment, which had a fixed duct and two rotating ports. A two-dimensional particle image velocimetry (PIV) measurement was performed to visualize the flow structure in the duct of the RERD. The turbulent flow structure in the duct was analyzed. The instantaneous vorticity contours and associated vectors showed the generation of vorticities in the duct. Moreover, the formation of the small-scale-vortex would significantly increase the flow instability and the fluid mixing rate. These results may be beneficial to researchers in better understanding the flow dynamic in the duct of a RERD and optimize the operating conditions and structural parameters of it.

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