Study of the Origin of Three Dimensional Structures in Shear Flows through External Forcing

1990 ◽  
Author(s):  
M. Gharib ◽  
K. Williams
Keyword(s):  
Shear Flows ◽  
Three Dimensional ◽  
External Forcing

On Some Transition Processes in Three-Dimensional Shear Flows

1985 ◽  
pp. 479-486
Author(s):  
S. Y. Gertsenstein ◽  
V. A. Zheligowsky ◽  
N. V. Nikitin ◽  
A. Y. Rudnitsky ◽  
A. N. Sukhorukov ◽  
...  
Keyword(s):  
Shear Flows ◽  
Three Dimensional ◽  
Transition Processes

Three-dimensional vortex formation from an oscillating, non-uniform cylinder

1992 ◽  
Vol 238 ◽  
pp. 31-54 ◽  
Author(s):  
F. Nuzzi ◽  
C. Magness ◽  
D. Rockwell
Keyword(s):  
Flow Structure ◽  
Phase Plane ◽  
Shear Flows ◽  
Vortex Formation ◽  
Excitation Frequency ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Near Wake ◽  
Shedding Frequency

A cylinder having mild variations in diameter along its span is subjected to controlled excitation at frequencies above and below the inherent shedding frequency from the corresponding two-dimensional cylinder. The response of the near wake is characterized in terms of timeline visualization and velocity traces, spectra, and phase plane representations. It is possible to generate several types of vortex formation, depending upon the excitation frequency. Globally locked-in, three-dimensional vortex formation can occur along the entire span of the flow. Regions of locally locked-in and period-doubled vortex formation can exist along different portions of the span provided the excitation frequency is properly tuned. Unlike the classical subharmonic instability in free shear flows, the occurrence of period-doubled vortex formation does not involve vortex coalescence; instead, the flow structure alternates between two different states.

Instability of Three Dimensional Waves in Shear Flows

1989 ◽  
Vol 81 (1) ◽  
pp. 41-55 ◽  
Author(s):  
D. J. Benney ◽  
Y. F Zhou
Keyword(s):  
Shear Flows ◽  
Three Dimensional

On the structure of three-dimensional shear flows

1993 ◽  
Vol 16 (1-2) ◽  
pp. 179-187 ◽  
Author(s):  
M.A. Hopkins ◽  
J.T. Jenkins ◽  
M.Y. Louge
Keyword(s):  
Shear Flows ◽  
Three Dimensional

Climate Response Using a Three-Dimensional Operator Based on the Fluctuation–Dissipation Theorem

2007 ◽  
Vol 64 (7) ◽  
pp. 2558-2575 ◽  
Author(s):  
Andrey Gritsun ◽  
Grant Branstator
Keyword(s):  
Influence Function ◽  
General Circulation ◽  
Three Dimensional ◽  
Circulation Model ◽  
Tropical Indian Ocean ◽  
The Arctic ◽  
External Forcing ◽  
Fluctuation Dissipation ◽  
Fluctuation Dissipation Theorem ◽  
Reduced Space

Abstract The fluctuation–dissipation theorem (FDT) states that for systems with certain properties it is possible to generate a linear operator that gives the response of the system to weak external forcing simply by using covariances and lag-covariances of fluctuations of the undisturbed system. This paper points out that the theorem can be shown to hold for systems with properties very close to the properties of the earth’s atmosphere. As a test of the theorem’s applicability to the atmosphere, a three-dimensional operator for steady responses to external forcing is constructed for data from an atmospheric general circulation model (AGCM). The response of this operator is then compared to the response of the AGCM for various heating functions. In most cases, the FDT-based operator gives three-dimensional responses that are very similar in structure and amplitude to the corresponding GCM responses. The operator is also able to give accurate estimates for the inverse problem in which one derives the forcing that will produce a given response in the AGCM. In the few cases where the operator is not accurate, it appears that the fact that the operator was constructed in a reduced space is at least partly responsible. As an example of the potential utility of a response operator with the accuracy found here, the FDT-based operator is applied to a problem that is difficult to solve with an AGCM. It is used to generate an influence function that shows how well heating at each point on the globe excites the AGCM’s Northern Hemisphere annular mode (NAM). Most of the regions highlighted by this influence function, including the Arctic and tropical Indian Ocean, are verified by AGCM solutions as being effective locations for stimulating the NAM.

scholarly journals Global bifurcations to subcritical magnetorotational dynamo action in Keplerian shear flow

2013 ◽  
Vol 731 ◽  
pp. 1-45 ◽  
Author(s):  
A. Riols ◽  
F. Rincon ◽  
C. Cossu ◽  
G. Lesur ◽  
P.-Y. Longaretti ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Shear Flow ◽  
Shear Flows ◽  
Three Dimensional ◽  
Transition To Turbulence ◽  
Global Bifurcations ◽  
Magnetic Field Generation ◽  
Dynamo Action ◽  
Systems Research ◽  
Hydrodynamic Shear

AbstractMagnetorotational dynamo action in Keplerian shear flow is a three-dimensional nonlinear magnetohydrodynamic process, the study of which is relevant to the understanding of accretion processes and magnetic field generation in astrophysics. Transition to this form of dynamo action is subcritical and shares many characteristics with transition to turbulence in non-rotating hydrodynamic shear flows. This suggests that these different fluid systems become active through similar generic bifurcation mechanisms, which in both cases have eluded detailed understanding so far. In this paper, we build on recent work on the two problems to investigate numerically the bifurcation mechanisms at work in the incompressible Keplerian magnetorotational dynamo problem in the shearing box framework. Using numerical techniques imported from dynamical systems research, we show that the onset of chaotic dynamo action at magnetic Prandtl numbers larger than unity is primarily associated with global homoclinic and heteroclinic bifurcations of nonlinear magnetorotational dynamo cycles born out of saddle-node bifurcations. These global bifurcations are found to be supplemented by local bifurcations of cycles marking the beginning of period-doubling cascades. The results suggest that nonlinear magnetorotational dynamo cycles provide the pathway to injection of both kinetic and magnetic energy for the problem of transition to turbulence and dynamo action in incompressible magnetohydrodynamic Keplerian shear flow in the absence of an externally imposed magnetic field. Studying the nonlinear physics and bifurcations of these cycles in different regimes and configurations may subsequently help to understand better the physical conditions of excitation of magnetohydrodynamic turbulence and instability-driven dynamos in a variety of astrophysical systems and laboratory experiments. The detailed characterization of global bifurcations provided for this three-dimensional subcritical fluid dynamics problem may also prove useful for the problem of transition to turbulence in hydrodynamic shear flows.

The evolution of a localized vortex disturbance in external shear flows. Part 1. Theoretical considerations and preliminary experimental results

1995 ◽  
Vol 289 ◽  
pp. 159-177 ◽  
Author(s):  
Vladimir Levinski ◽  
Jacob Cohen
Keyword(s):  
Boundary Layers ◽  
Shear Flows ◽  
Flow Direction ◽  
Linear Equations ◽  
Three Dimensional ◽  
Finite Amplitude ◽  
Experimental Results ◽  
Instability Criterion ◽  
Hairpin Vortices ◽  
Plane Normal

The evolution of a finite-amplitude three-dimensional localized disturbance embedded in external shear flows is addressed. Using the fluid impulse integral as a characteristic of such a disturbance, the Euler vorticity equation is integrated analytically, and a system of linear equations describing the temporal evolution of the three components of the fluid impulse is obtained. Analysis of this system of equations shows that inviscid plane parallel flows as well as high Reynolds number two-dimensional boundary layers are always unstable to small localized disturbances, a typical dimension of which is much smaller than a dimensional length scale corresponding to an O(1) change of the external velocity. Since the integral character of the fluid impulse is insensitive to the details of the flow, universal properties are obtained. The analysis predicts that the growing vortex disturbance will be inclined at 45° to the external flow direction, in a plane normal to the transverse axis. This prediction agrees with previous experimental observations concerning the growth of hairpin vortices in laminar and turbulent boundary layers. In order to demonstrate the potential of this approach, it is applied to Taylor-Couette flow, which has additional dynamical effects owing to rotation. Accordingly, a new instability criterion associated with three-dimensional localized disturbances is found. The validity of this criterion is supported by our experimental results.

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