scholarly journals Transition from hydrodynamic turbulence to magnetohydrodynamic turbulence in von Kármán flows

2012 ◽  
Vol 693 ◽  
pp. 243-260 ◽  
Author(s):  
Gautier Verhille ◽  
Ruslan Khalilov ◽  
Nicolas Plihon ◽  
Peter Frick ◽  
Jean-François Pinton
Keyword(s):  
Magnetic Field ◽  
Reynolds Number ◽  
Interaction Parameter ◽  
Applied Magnetic Field ◽  
Strong Increase ◽  
Liquid Gallium ◽  
Induced Magnetic Field ◽  
Global Variables ◽  
Von Karman ◽  
Von Kármán

AbstractThe influence of an externally applied magnetic field on flow turbulence is investigated in liquid-gallium von-Kármán (VK) swirling flows. Time-resolved measurements of global variables (such as the flow power consumption) and local recordings of the induced magnetic field are made. From these measurements, an effective Reynolds number is introduced as ${\mathit{Rm}}_{\mathit{eff}} = \mathit{Rm}(1\ensuremath{-} \ensuremath{\alpha} \sqrt{N} )$, so as to take into account the influence of the interaction parameter $N$. This effective magnetic Reynolds number leads to unified scalings for both global variables and the locally induced magnetic field. In addition, when the flow rotation axis is perpendicular to the direction of the applied magnetic field, significant flow and induced magnetic field fluctuations are observed at low interaction parameter values, but corresponding to an Alfvèn speed ${v}_{A} $ of the order of the fluid velocity fluctuations ${u}_{\mathit{rms}} $. This strong increase in the flow fluctuations is attributed to chaotic changes between hydrodynamic and magnetohydrodynamic velocity profiles.

scholarly journals Supercritical transition to turbulence in an inertially driven von Kármán closed flow

2008 ◽  
Vol 601 ◽  
pp. 339-364 ◽  
Author(s):  
FLORENT RAVELET ◽  
ARNAUD CHIFFAUDEL ◽  
FRANÇOIS DAVIAUD
Keyword(s):  
Reynolds Number ◽  
Time Dependence ◽  
Transition To Turbulence ◽  
Velocity Fluctuations ◽  
Fully Developed Turbulence ◽  
Developed Turbulence ◽  
Von Karman ◽  
Applied Torque ◽  
Local Quantity ◽  
Von Kármán

We study the transition from laminar flow to fully developed turbulence for an inertially driven von Kármán flow between two counter-rotating large impellers fitted with curved blades over a wide range of Reynolds number (102–106). The transition is driven by the destabilization of the azimuthal shear layer, i.e. Kelvin–Helmholtz instability, which exhibits travelling/drifting waves, modulated travelling waves and chaos before the emergence of a turbulent spectrum. A local quantity – the energy of the velocity fluctuations at a given point – and a global quantity – the applied torque – are used to monitor the dynamics. The local quantity defines a critical Reynolds number Rec for the onset of time-dependence in the flow, and an upper threshold/crossover Ret for the saturation of the energy cascade. The dimensionless drag coefficient, i.e. the turbulent dissipation, reaches a plateau above this finite Ret, as expected for ‘Kolmogorov’-like turbulence for Re→∞. Our observations suggest that the transition to turbulence in this closed flow is globally supercritical: the energy of the velocity fluctuations can be considered as an order parameter characterizing the dynamics from the first laminar time-dependence to the fully developed turbulence. Spectral analysis in the temporal domain, moreover, reveals that almost all of the fluctuation energy is stored in time scales one or two orders of magnitude slower than the time scale based on impeller frequency.

The Influence of Electroosmotic Flow on the Von Kármán Vortex Street in the Wake of a Cylinder Located in a Microchannel

2015 ◽  
Author(s):  
Mathias Scholz ◽  
Dominik P. J. Barz
Keyword(s):  
Reynolds Number ◽  
Vortex Street ◽  
Cylinder Surface ◽  
Flow Topology ◽  
Karman Vortex Street ◽  
Von Karman ◽  
Von Karman Vortex Street ◽  
Kármán Vortex Street ◽  
Karman Vortex ◽  
Von Kármán

The von Kármán vortex street is a flow instability that is observed in the wake of a blunt body if a certain (cylinder) Reynolds number is exceeded. It is one of the classical problems in fluid mechanics and a vast amount of research has been dedicated to the investigation of the fundamentals of this phenomenon. The present study is concerned with the numerical simulation of the flow in a microchannel having a cylinder located in its channel center. A pressure driven flow is induced in the channel described by the channel Reynolds number. The cylinder is subjected to an externally-applied electric field that causes electroosmosis in the electrical double layer which is present around the cylinder surface. In this setup, two distinctions to the classical von Kármán vortex street can be noted. On the one hand, the presence of the microchannel walls confines the flow field in lateral direction. On the other hand, the electroosmotic slip velocity impacts the flow topology in the vicinity of the cylinder and, thus, may have an impact on the formation and the periodic nature of the von Kármán vortex street. Various numerical simulations are performed to investigate the influence of the cylinder-diameter-to-channel-width ratio and the direction of the electrical field.

scholarly journals Ultrasonic Study of Thermal hysteresis in Helical antiferromagnetic Dy

2018 ◽  
Vol 57 (2) ◽  
pp. 241-245 ◽  
Author(s):  
Iu. Liubimova ◽  
K. Sapozhnikov ◽  
V. Nikolaev ◽  
M.-Li Corró ◽  
S. Kustov
Keyword(s):  
Magnetic Field ◽  
Heating Rate ◽  
Applied Magnetic Field ◽  
Domain Walls ◽  
Thermal Hysteresis ◽  
Lattice Defects ◽  
Ferromagnetic Phase ◽  
Strong Increase ◽  
Ultrasonic Absorption ◽  
Thermal Cycles

Abstract High-resolution ultrasonic mechanical spectroscopy technique has been used to study the nature and dynamics of lattice defects and magnetic domain walls in the helical-type antiferromagnetic phase during thermal cycling of polycrystalline Dy samples between 80 and 210K. Effects of the lowest temperature of thermal cycles, applied magnetic field and cooling/ heating rate on the ultrasonic absorption and Young´s modulus have been investigated. A strong influence of cooling/heating rate on the ultrasonic absorption is found over the temperature range between the Néel temperature, ca. 178K, and approximately 145K, confirming the existence of a new category of magnetomechanical damping - transitory ultrasonic absorption related to translational motion of domain walls. A strong increase of the ultrasonic absorption below approximately 140K is attributed to the formation of nuclei of ferromagnetic phase, presumably stabilized by such lattice defects as dislocations. The effect of applied magnetic field on ultrasonic absorption also emerges below 140K and is ascribed to the appearance of the net magnetization due to ferromagnetic nuclei. We argue that these nuclei are responsible for the controversial thermal hysteresis of elastic and anelastic properties, which is strongly promoted by decreasing the temperature of thermal cycles.

Influence of Heat and Mass Transfer on the Peristaltic Transport of a Phan-Thien–Tanner Fluid

2013 ◽  
Vol 68 (12) ◽  
pp. 751-758 ◽  
Author(s):  
Tasawar Hayat ◽  
Saima Noreen ◽  
Muhammad Qasim
Keyword(s):  
Magnetic Field ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Heat And Mass Transfer ◽  
Series Solution ◽  
Flow System ◽  
Peristaltic Flow ◽  
Weissenberg Number ◽  
Induced Magnetic Field ◽  
Long Wavelength

In this paper, we discuss the effects of heat and mass transfer on the peristaltic flow in the presence of an induced magnetic field. Constitutive equations of a Phan-Thien-Tanner fluid are utilized in the mathematical description. Mathematical modelling is based upon the laws of mass, linear momentum, energy, and concentration. Relevant equations are simplified using long wavelength and low Reynolds number assumptions. A series solution is presented for small Weissenberg number. Variations of emerging parameters embedded in the flow system are discussed.

Consequence of induced magnetic field on peristaltic motion of a Carreau nanofluid in a tapered asymmetric channel

2017 ◽  
Vol 27 (9) ◽  
pp. 1986-2014 ◽  
Author(s):  
M. Kothandapani ◽  
V. Pushparaj
Keyword(s):  
Magnetic Field ◽  
Reynolds Number ◽  
Magnetic Force ◽  
Force Function ◽  
Asymmetric Channel ◽  
Mean Flow ◽  
Induced Magnetic Field ◽  
Regular Perturbation ◽  
Content Type ◽  
Carreau Nanofluid

Purpose This paper aims to investigate the consequence of the combined impacts of an induced magnetic field and thermal radiation on peristaltic transport of a Carreau nanofluid in a vertical tapered asymmetric channel. The model applied for the nanofluid comprises the effects of Brownian motion and thermophoresis. Design/methodology/approach The governing equations have been simplified under the widespread assumption of long-wavelength and low-Reynolds number approximations. The reduced coupled nonlinear equations of momentum and magnetic force function have also been solved analytically using the regular perturbation method. Findings The physical features of emerging parameters have been discussed by drawing the graphs of velocity, temperature, nanoparticle concentration profile, magnetic force function, current density, heat transfer coefficient and stream function. It has been realized that the magnetic force function is increased with the increase of Hartmann number, magnetic Reynolds number and mean flow rate. Originality/value It may be first paper in which the effect of induced magnetic field on peristaltic flow of non-Newtonian nanofluid in a tapered asymmetric channel has been studied.

Cavitation Influence on von Kármán Vortex Shedding and Induced Hydrofoil Vibrations

2007 ◽  
Vol 129 (8) ◽  
pp. 966-973 ◽  
Author(s):  
Philippe Ausoni ◽  
Mohamed Farhat ◽  
Xavier Escaler ◽  
Eduard Egusquiza ◽  
François Avellan
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Trailing Edge ◽  
Cavitation Inception ◽  
Structure Interaction ◽  
New Correlation ◽  
Von Karman ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Von Kármán

The present study deals with the shedding process of the von Kármán vortices at the trailing edge of a 2D hydrofoil at high Reynolds number Reh=25×103–65×103. This research focuses mainly on the effects of cavitation and fluid-structure interaction on the mechanism of the vortex generation. The vortex shedding frequency, derived from the flow-induced vibration measurement, is found to follow the Strouhal law provided that no hydrofoil resonance frequencies are excited, i.e., lock-off. For such a regime, the von Kármán vortices exhibit strong spanwise 3D instabilities and the cavitation inception index is linearly dependent on the square root of the Reynolds number. In the case of resonance, the vortex shedding frequency is locked onto the hydrofoil eigenfrequency and the spatial coherence is enhanced with a quasi-2D shape. The measurements of the hydrofoil wall velocity amplitude and phase reveal the first torsion eigenmotion. In this case, the cavitation inception index is found to be significantly increased compared to lock-off conditions. It makes clear that the vortex roll-up is amplified by the phase locked vibrations of the trailing edge. For the cavitation inception index, a new correlation relationship that encompasses the entire range of Reynolds numbers, including both the lock-off and the lock-in cases, is proposed and validated. In contrast to the earlier models, the new correlation takes into account the trailing edge displacement velocity. In addition, it is found that the transverse velocity of the trailing edge increases the vortex strength linearly. This effect is important in the context of the fluid-structure interaction, since it implies that the velocity of the hydrofoil trailing edge increases the fluctuating forces on the body. It is also demonstrated that cavitation developing in the vortex street cannot be considered as a passive agent for the turbulent wake flow. In fact, for fully developed cavitation, the vortex shedding frequency increases up to 15%, which is accompanied by the increase of the vortex advection velocity and reduction of the streamwise vortex spacing. In addition, a significant increase of the vortex-induced vibration level is found at cavitation onset. These effects are addressed and thought to be a result of the increase of the vorticity by cavitation.

The Influence of Magnetization on Corrosion in Pipeline Steels

2006 ◽  
Author(s):  
Joshua E. Jackson ◽  
Angelique N. Lasseigne-Jackson ◽  
Francisco J. Sanchez ◽  
David L. Olson ◽  
Brajendra Mishra
Keyword(s):  
Magnetic Field ◽  
Hydrogen Content ◽  
Applied Magnetic Field ◽  
Cold Work ◽  
Strong Increase ◽  
Surface Layers ◽  
Electronic Spin ◽  
Thermodynamic Effect ◽  
Hydrogen Induced Cracking ◽  
Anodic Reactions

Laboratory measurements have shown a strong increase on the hydrogen content in steel after electrochemical hydrogen charging with a two Tesla applied magnetic field and a serious increase in hydrogen-induced cracking and pitting. Cold work combining with the effect of applied magnetic field creates a material more crack sensitive to increased hydrogen content. A derivation based on the use of the Helmholtz Free Energy is applied to examine the thermodynamic effect of magnetization on hydrogen content. The effect of magnetization on the electronic spin configurations, magnetostriction (directional strain induced in steel from an applied magnetic field), and interstitial solute-induced strain are considered. A possible kinetic model for enhanced hydrogen ion pickup and corrosion based on surface effects associated with the Gouy-Chapman Layer and the Helmholtz Double Layer is examined. Disturbance of these layers acts to enhance hydrogen transport to the surface. The high applied and remanent magnetic fields and large cathodic protection currents returning in the pipe simultaneously may disturb these surface layers, resulting in enhancement of both cathodic and anodic reactions.

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