scholarly journals Vortex Generation, Experimental Characterization, and Application in Turbulent Flows

2019 ◽  
Author(s):  
Guillermo Martin Capittini ◽  
Julio Marañon Di Leo ◽  
Juan Sebastian Delnero
Keyword(s):  
Turbulent Flows ◽  
Vortex Generation ◽  
Experimental Characterization

Influence of active control on STG-based generation of streamwise vortices in near-wall turbulence

2012 ◽  
Vol 710 ◽  
pp. 234-259 ◽  
Author(s):  
B.-Q. Deng ◽  
C.-X. Xu
Keyword(s):  
Drag Reduction ◽  
Turbulent Flows ◽  
Active Control ◽  
Phase Control ◽  
Transient Growth ◽  
Vortex Generation ◽  
Streamwise Vortices ◽  
Detection Plane ◽  
Near Wall ◽  
Opposition Control

AbstractNear-wall streamwise vortices are closely related to the generation of high skin friction in wall-bounded turbulent flows. A common feature of controlled, friction-reduced turbulent flows is weakened near-wall streamwise vortices. In the present study, the streak transient growth (STG) mechanism for generating near-wall streamwise vortices by Schoppa & Hussain (J. Fluid Mech., vol. 453, 2002, pp. 57–108) is employed, and the opposition control proposed by Choi, Moin & Kim (J. Fluid Mech., vol. 262, 1994, pp. 75–110) is imposed during the transient growth process of perturbations to determine how active control affects the generation of quasi-streamwise vortices. In the transient growth stage, when the detection plane is located near the wall (${ y}_{d}^{+ } = 15$), the control can suppress the production of streamwise vorticity by weakening the near-wall vertical velocity; when the detection plane moves away from the wall (${ y}_{d}^{+ } = 28$), the control has the opposite effect. In the vortex generation stage, the control cannot change the dominance of the stretching effect. Controls imposed at different stages reveal the importance of the STG stage in vortex generation. Strengthened out-of-phase control and lessened in-phase control are proposed as an extension of the original opposition-control scheme. Application in a fully developed turbulent channel flow shows that strengthened ${ y}_{d}^{+ } = 10$ control can yield an even higher drag reduction rate than the original ${ y}_{d}^{+ } = 15$ control. Moreover, lessened ${ y}_{d}^{+ } = 28$ control can also achieve drag reduction and turbulence suppression.

scholarly journals Experimental Characterization of VAWT Airfoils Under Turbulent Flows

2019 ◽  
pp. 21-38
Author(s):  
Andreu Carbó Molina ◽  
Sander Van de Maele ◽  
Gianni Bartoli ◽  
Tim De Troyer ◽  
Mark Runacres
Keyword(s):  
Turbulent Flows ◽  
Experimental Characterization

Experimental characterization of viscoelastic effects on two- and three-dimensional shear instabilities

2000 ◽  
Vol 416 ◽  
pp. 151-172 ◽  
Author(s):  
OLIVIER CADOT ◽  
SATISH KUMAR
Keyword(s):  
Turbulent Flows ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Experimental Characterization ◽  
Elastic Forces ◽  
Viscoelastic Effects ◽  
Karman Street ◽  
Dimensional Instability ◽  
Elasticity Number

Instabilities of a wake produced by a circular cylinder in a uniform water flow are studied experimentally when viscoelastic solutions are injected through holes pierced in the cylinder. It is shown that the viscoelastic solutions fill the shear regions and drastically modify the instabilities. The two-dimensional instability giving rise to the Kármán street is found to be inhibited: the roll-up process appears to be delayed and the wavelength of the street increases. The wavelength increase obeys an exponential law and depends on the elasticity number, which provides a ratio of elastic forces to inertial forces. The three-dimensional instability leading to the A mode is generally found to be suppressed. In the rare case where the A mode is observed, its wavelength is shown to be proportional to the wavelength of the Kármán street and the streamwise stretching appears to be inhibited. Injection of viscoelastic solutions also decreases the aspect ratio of the two-dimensional wake, and this is correlated with stabilization of the A mode and with changes in the shape of the Kármán vortices. The observations of this work are consistent with recent numerical simulations of viscoelastic mixing layers. The results suggest mechanisms through which polymers inhibit the formation of high-vorticity coherent structures and reduce drag in turbulent flows.

Numerical Analysis of Turbulent Flow in Fluid Couplings

1997 ◽  
Vol 119 (3) ◽  
pp. 569-576 ◽  
Author(s):  
L. Bai ◽  
M. Fiebig ◽  
N. K. Mitra
Keyword(s):  
Turbulent Flows ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Flow Structures ◽  
Finite Volume Scheme ◽  
Vortex Generation ◽  
Navier Stokes Equations ◽  
Torque Transmission ◽  
Basic Equations

Numerical simulation of three-dimensional unsteady turbulent flows in fluid couplings was carried out by numerically solving Navier-Stokes equations in a rotating coordinate system. The standard k-ε model was used to take turbulence into account. A finite volume scheme with colocated body-fitted grids was used to solve the basic equations. Computed flow structures show the vortex generation and its effect on the torque transmission. Computed local velocity and torque flow compare well with measurements.

Experimental characterization of a laminar diffusion flame in micro-gravity

1999 ◽  
Vol 96 (6) ◽  
pp. 1022-1030 ◽  
Author(s):  
T. Vietoris ◽  
P. Joulain ◽  
J. L. Torero
Keyword(s):  
Diffusion Flame ◽  
Experimental Characterization ◽  
Laminar Diffusion Flame ◽  
Laminar Diffusion ◽  
Micro Gravity

Experimental Characterization of the Reliability of 3-Terminal Dual-Damascene Copper Interconnect Trees

2002 ◽  
Vol 716 ◽  
Author(s):  
C. L. Gan ◽  
C. V. Thompson ◽  
K. L. Pey ◽  
W. K. Choi ◽  
F. Wei ◽  
...  
Keyword(s):  
Stress Conditions ◽  
Experimental Characterization ◽  
Contact Lines ◽  
Tree Structures ◽  
Similar Test ◽  
Dual Damascene ◽  
Copper Interconnect ◽  
Test Conditions

AbstractElectromigration experiments have been carried out on simple Cu dual-damascene interconnect tree structures consisting of straight via-to-via (or contact-to-contact) lines with an extra via in the middle of the line. As with Al-based interconnects, the reliability of a segment in this tree strongly depends on the stress conditions of the connected segment. Beyond this, there are important differences in the results obtained under similar test conditions for Al-based and Cu-based interconnect trees. These differences are thought to be associated with variations in the architectural schemes of the two metallizations. The absence of a conducting electromigrationresistant overlayer in Cu technology, and the possibility of liner rupture at stressed vias lead to significant differences in tree reliabilities in Cu compared to Al.

EXPERIMENTAL CHARACTERIZATION OF VVER-440 REACTOR CONTAINMENT TYPE SPRAY NOZZLE

2016 ◽  
Vol 26 (3) ◽  
pp. 235-255 ◽  
Author(s):  
Jeanne Malet ◽  
Z. Parduba
Keyword(s):  
Spray Nozzle ◽  
Experimental Characterization

Film Condensation and Aerosol Deposition in Turbulent Flows with Noncondensable Gases

1997 ◽  
Vol 28 (4-6) ◽  
pp. 277-288
Author(s):  
Leonid I. Zaichik ◽  
Bulat I. Nigmatulin ◽  
Vladimir M. Alipchenkov ◽  
V. A. Belov
Keyword(s):  
Turbulent Flows ◽  
Aerosol Deposition ◽  
Film Condensation ◽  
Noncondensable Gases
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