scholarly journals Evolution of vortical structures behind an inclined flat plate

2018 ◽  
Vol 168 ◽  
pp. 05003 ◽  
Author(s):  
Pavel Procházka ◽  
Václav Uruba ◽  
Vladislav Skála
Keyword(s):  
Flat Plate ◽  
High Velocity ◽  
Velocity Vector ◽  
Vector Fields ◽  
Vortical Structures ◽  
Piv Technique ◽  
Streamwise Structures ◽  
New Hypothesis ◽  
Instantaneous Velocity Vector ◽  
Good Agreement

2D3C TR-PIV technique was utilized to investigate streamwise-oriented vortical structures behind an inclined flat plate. The angle of attack was set to 7 deg, several fields of view in the wake were investigated. The instantaneous velocity vector fields were captured, dynamics of the flow was studied using POD method. The streamwise structures are determined by vorticity and low- and high-velocity streaks are defined. The acquired results are in a good agreement with the new hypothesis of a principle of flight.

Direct numerical simulations of riblets to constrain the growth of turbulent spots

2011 ◽  
Vol 668 ◽  
pp. 267-292 ◽  
Author(s):  
JAMES S. STRAND ◽  
DAVID B. GOLDSTEIN
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Immersed Boundary ◽  
Ensemble Averaging ◽  
Hairpin Vortices ◽  
Turbulent Spots ◽  
Vortical Structures ◽  
Flat Wall ◽  
Self Similar ◽  
Good Agreement

A spectral direct numerical simulation (DNS) code was used to study the growth and spreading of turbulent spots in a nominally laminar, zero-pressure-gradient boundary layer. In addition to the flat-plate case, the interaction of these spots with riblets was investigated. The flat plate, riblets and initial spot perturbation were simulated via an immersed boundary method, and a ‘suction wall’ allowed the available channel code to model a boundary layer. In both flat-wall and riblet cases, self-similar arrowhead-shaped spots formed. The λ2 variable of Jeong & Hussain (1995) was used to visualize the vortical structures within a spot, and a spot was seen to consist primarily of a multitude of entwined hairpin vortices. The range of scales of the hairpin vortices was found to increase as the spot matures. Ensemble averaging was used to obtain more accurate results for the spot spreading angle, both for the flat-wall case and the riblet case. The spreading angle for the flat-wall spot was 6.3°, in reasonably good agreement with prior DNS work. The spreading angle for the spot over riblets was 5.4°, a decrease of 14% compared with the flat-wall.

An Effect of Fractal Baffles and Impellers with Double Stage 4-Blade Rushton Turbine to Fluid Flow Behaviour in Stirred Tank

2014 ◽  
Vol 660 ◽  
pp. 816-822 ◽  
Author(s):  
Bukhari Manshoor ◽  
Afifah Yusof ◽  
Suraya Laily ◽  
Izzuddin Zaman ◽  
Amir Khalid
Keyword(s):  
Flow Field ◽  
High Velocity ◽  
Velocity Vector ◽  
Fluid Mixing ◽  
Stirred Tank ◽  
Mixing Efficiency ◽  
Rushton Turbine ◽  
Fractal Pattern ◽  
Piv Technique ◽  
Piv Measurement

The stirred tank is widely used in many industries to obtain the desired type of fluid mixing. In the context of mixing process, two different fluids and have a different properties will mix in a single equipment to produce another fluid with a new property. In this research, a new approach of stirred tank which is containing a new design of baffles and impellers was proposed for fluid mixing. The new design of baffles and impellers that proposed here are used a fractal pattern for both parts in the stirred tank. Implementing a fractal pattern for baffles and impellers in stirred tank believe will influence the flow characteristic inside the stirred tank, hence will improve a mixing performance. In order to investigate the kinds of flow properties, a Particle Image Velocimetry (PIV) technique with 1 μm seeding particle was used. Four configurations were tested which are normal baffles and normal impellers, normal baffles and fractal impellers, fractal baffles and normal impellers, and the last configuration is fractal baffles and fractal impellers. In this study, dual Rushton impellers with 4 blades were used with the configurations mentioned. The result shows the significant flow field capture by PIV measurement on each configuration. By using fractal impeller some vortex are shown in the tank and high velocity vector on flow field compare with normal impeller while normal baffles gives high velocity vector depends on the configuration were used. From the results, it was showed that the fractal design can give a certain level of mixing efficiency in stirred tank. The PIV technique also gives good flow visualization in order to determine the flow pattern in stirred tank with a new concept of baffles and impellers.

scholarly journals Streamwise and spanwise vortical structure merging inside the wake of an inclined flat plate

2019 ◽  
Vol 20 (7) ◽  
pp. 705 ◽  
Author(s):  
Pavel Procházka ◽  
Václav Uruba
Keyword(s):  
Flat Plate ◽  
Physical Mechanism ◽  
Flow Instability ◽  
Adverse Pressure Gradient ◽  
Streamwise Vorticity ◽  
Time Resolved ◽  
Vortical Structures ◽  
High Dynamic ◽  
Change Position ◽  
New Hypothesis

The aim of this paper is to study the physics related to lift generation on an airfoil. A new hypothesis [1] of physical mechanism of flight relies on existence of streamwise vortical structures above the wing and inside the wake. The vortices origin as a consequence of flow instability inside the boundary layer developed under adverse pressure gradient. These structures are highly dynamical in nature, they change position and size very rapidly. A simple airfoil in the form of a flat plate with moderate angle of attack is considered in the presented research that generates suitable flow at rather low Reynolds number. Stereo PIV time resolved measurement technique is used to capture high-dynamic data in several planes which are located in the wake and are perpendicular to freestream or parallel to the airfoil. The overall image of the flow field dynamics will be created using POD decomposition. Distinct flow patterns with associated kinetic energy are to be described as well as their role in the studied case. Existence of streamwise vorticity is proved, topology and other parameters are estimated in the paper; however related pressures and forces are not evaluated.

Echo-PIV Measurement Around the Pump System in the Nuclear Reactor

2011 ◽  
Author(s):  
Xin-Cheng Tu ◽  
Jae-Eun Cha ◽  
Hyoung-Bum Kim
Keyword(s):  
Flow Rate ◽  
Velocity Vector ◽  
Vector Fields ◽  
Nuclear Reactor ◽  
Velocity Fields ◽  
Fluid Machinery ◽  
Reactor Model ◽  
Pump System ◽  
Piv Measurement ◽  
Instantaneous Velocity Vector

Echo-PIV system was applied to measure the velocity fields of a pump system inside the nuclear reactor model. The scale-downed model of pump system driven by a motor was built for this study. 2D instantaneous velocity vector fields of the downstream region of impeller were obtained. The flow rate was calculated and compared with the result from the flow meter. From this study, the feasibility of echo-PIV for studying the opaque flow in the fluid machinery was shown.

Galactic orbits of stars

1966 ◽  
Vol 25 ◽  
pp. 93-97
Author(s):  
Richard Woolley
Keyword(s):  
Globular Cluster ◽  
Potential Field ◽  
High Velocity ◽  
Velocity Vector ◽  
Variable Stars ◽  
The Sun ◽  
Proper Motions ◽  
Rr Lyrae ◽  
The Galaxy

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.

Development of an Instantaneous Velocity-Vector-Profile Method Using Conventional Ultrasonic Transducers

2021 ◽  
Author(s):  
Dongik Yoon ◽  
Hyun Jin Park ◽  
Tomonori Ihara
Keyword(s):  
Velocity Vector ◽  
Ultrasound Velocity ◽  
Ultrasonic Transducers ◽  
New Method ◽  
Ultrasound Transducers ◽  
Accuracy And Precision ◽  
Conventional Ultrasound ◽  
Measurable Distance ◽  
Profile Technique ◽  
Good Agreement

Abstract The velocity vector profile technique based on an ultrasound pulsed Doppler method can enrich the information of a flow field, however, it has shown a low availability because a new design of special transducers is required for each measurement case. This study proposes a new method of profiling the velocity vectors using conventional ultrasound transducers that are widely supplied to UVP (Ultrasound velocity profile) users. We constructed a configuration of the transducers to minimize the uncertainty of the detection points at the receivers, and a measurable distance was theoretically determined by the configuration. Two feasibility tests were carried out. One was a test for the assessment of the measurable distance, which agreed well with the theoretical distance. The other was the evaluation of the measurement of two-dimensional velocity vectors by the new method and it was performed in a towing tank facility without the velocity fluctuation. From the evaluation, it was confirmed that the measured vectors showed good agreement to the reference values, and their accuracy and precision were competitive compared to previous studies. The developed method was applied to two unsteady flows for demonstrations. The results clarified that the proposed method guarantees high availability and accuracy for the velocity vector profiles.

Reconstructing Three-Dimensional Fluid Velocity Vector Fields from Acoustic Transmission Measurements

1977 ◽  
pp. 307-326 ◽  
Author(s):  
S. A. Johnson ◽  
J. F. Greenleaf ◽  
C. R. Hansen ◽  
W. F. Samayoa ◽  
M. Tanaka ◽  
...  
Keyword(s):  
Velocity Vector ◽  
Vector Fields ◽  
Fluid Velocity ◽  
Three Dimensional ◽  
Acoustic Transmission ◽  
Transmission Measurements

Morphing Continuum Theory: Incorporating the Physics of Microstructures to Capture the Transition to Turbulence Within a Boundary Layer

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Louis B. Wonnell ◽  
James Chen
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Ad Hoc ◽  
Constitutive Relations ◽  
Turbulence Models ◽  
Continuum Theory ◽  
Transition To Turbulence ◽  
Flow Turbulence ◽  
Good Agreement ◽  
Inherent Advantage

A boundary layer with Re = 106 is simulated numerically on a flat plate using morphing continuum theory. This theory introduces new terms related to microproperties of the fluid. These terms are added to a finite-volume fluid solver with appropriate boundary conditions. The success of capturing the initial disturbances leading to turbulence is shown to be a byproduct of the physical and mathematical rigor underlying the balance laws and constitutive relations introduced by morphing continuum theory (MCT). Dimensionless equations are introduced to produce the parameters driving the formation of disturbances leading to turbulence. Numerical results for the flat plate are compared with the experimental results determined by the European Research Community on Flow, Turbulence, and Combustion (ERCOFTAC) database. Experimental data show good agreement inside the boundary layer and in the bulk flow. Success in predicting conditions necessary for turbulent and transitional (T2) flows without ad hoc closure models demonstrates the theory's inherent advantage over traditional turbulence models.

Characterization of the Surface Curvature Effect Using LES for a Single Round Impinging Jet

2017 ◽  
Author(s):  
Pierre Aillaud ◽  
Florent Duchaine ◽  
Laurent Gicquel ◽  
Sheddia Didorally
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Temporal Distribution ◽  
Impinging Jet ◽  
Ambient Air ◽  
Surface Curvature ◽  
Flow Topology ◽  
Reference Case ◽  
Vortical Structures ◽  
Eddy Simulation

In this paper, wall resolved Large Eddy Simulation is used to study the effect of the surface curvature for two impinging jet configurations. The reference case is a single round jet impinging on a flat plate at a Reynolds number (based on the bulk velocity Ub and the pipe diameter D) Re = 23 000 and for a nozzle to plate distance H = 2D. The results on this configuration have been previously analyzed and validated against experimental results. This paper compares for the same operating point, the flat plate impingement to an impinging jet on a concave hemispherical surface with a relative curvature d/D = 0.089 where d is the concave surface diameter. Mean and Root Mean Square (RMS) quantities are compared to highlight differences and similarities between the two cases. In addition high order statistic such as Skewness of the temporal distribution of wall heat flux is analyzed. Probability density functions (PDF) are also built to further characterize the effect of surface curvature. It is shown that the surface curvature has a destabilizing effect on the vortical structures present in such a flow leading to a modification of the wall heat transfer compared to the flat plate case. The flow topology in the concave case is dominated by a large toroidal stationary vortex. This vortex generates a natural confinement that causes the increase of the mean temperature of the ambient air around the jet. The main effect is the reduction of the capacity of the vortical structures to enhance heat transfer. Finally, the confinement effect combined with the destabilization due to the concave curvature lead to an alleviation of the secondary peak in the Nusselt distribution and a reduction of the heat transfer at the wall.

scholarly journals Unsteady Boundary Layers on a Flat Plate Disturbed by Periodic Wakes: Part I — Measurement of Wake-Affected Heat Transfer and Wake-Induced Transition Model

1994 ◽  
Author(s):  
K. Funazaki
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Rotating Disk ◽  
Circular Cylinders ◽  
Transition Model ◽  
Time Diagram ◽  
Test Conditions ◽  
Intermittency Factor ◽  
Unsteady Boundary Layers ◽  
Good Agreement

Measurements of wake-affected heat transfer distributions on a flat plate are made by use of a wake generator that consists of a rotating disk and several types of circular cylinders. The main purpose of this study is to construct a wake-induced transition model in terms of an intermittency factor, considering the evolution of the wake-induced turbulent region, a so-called turbulent patch in a distance-time diagram. A comparison between the proposed transition model and the measured heat transfer data reveals that the transition model yields good agreement with the measured data of all test conditions in this study.

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