Coherent Structures in Turbulent Shear Flows

1990 ◽  
Vol 43 (5S) ◽  
pp. S203-S209 ◽  
Author(s):  
J. M. Wallace ◽  
F. Hussain
Keyword(s):  
Coherent Structures ◽  
Shear Flows ◽  
Turbulent Shear ◽  
Turbulent Shear Flows ◽  
Kinematic Properties

What is firmly known about the kinematic properties and dynamic importance of coherent structures in bounded and unbounded turbulent shear flows is briefly summarized. The nature of instabilities giving rise to these structures is discussed. Unanswered questions requiring further research are posed.

Streamwise vortices in shear flows: harbingers of transition and the skeleton of coherent structures

2010 ◽  
Vol 661 ◽  
pp. 178-205 ◽  
Author(s):  
PHILIP HALL ◽  
SPENCER SHERWIN
Keyword(s):  
Coherent Structures ◽  
Shear Flows ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Wave Interaction ◽  
Streamwise Vortex ◽  
Navier Stokes ◽  
Turbulent Shear ◽  
Turbulent Shear Flows ◽  
External Flows

The relationship between asymptotic descriptions of vortex–wave interactions and more recent work on ‘exact coherent structures’ is investigated. In recent years immense interest has been focused on so-called self-sustained processes in turbulent shear flows where the importance of waves interacting with streamwise vortex flows has been elucidated in a number of papers. In this paper, it is shown that the so-called ‘lower branch’ state which has been shown to play a crucial role in these self-sustained processes is a finite Reynolds number analogue of a Rayleigh vortex–wave interaction with scales appropriately modified from those for external flows to Couette flow, the flow of interest here. Remarkable agreement between the asymptotic theory and numerical solutions of the Navier–Stokes equations is found even down to relatively small Reynolds numbers, thereby suggesting the possible importance of vortex–wave interaction theory in turbulent shear flows. The relevance of the work to more general shear flows is also discussed.

Pattern-recognized structures in bounded turbulent shear flows

1977 ◽  
Vol 83 (4) ◽  
pp. 673-693 ◽  
Author(s):  
James M. Wallace ◽  
Robert S. Brodkey ◽  
Helmut Eckelmann
Keyword(s):  
Reynolds Stress ◽  
Coherent Structures ◽  
Shear Flows ◽  
Local Maximum ◽  
Total Sample ◽  
Turbulent Shear ◽  
Turbulence Structures ◽  
Signal Pattern ◽  
Turbulent Shear Flows ◽  
High Reynolds

It is now well established that coherent structures exist in turbulent shear flows. It should be possible to recognize these in the turbulence signals and to program a computer to extract and ensemble average the corresponding portions of the signals in order to obtain the characteristics of the structures. In this work only the u-signal patterns are recognized, using several simple criteria; simultaneously, however, the v or w signals as well as uv or uw are also processed. It is found that simple signal shapes describe the turbulence structures on the average. The u-signal pattern consists of a gradual deceleration from a local maximum followed by a strong acceleration. This pattern is found in over 65% of the total sample in the region of high Reynolds-stress production. The v signal is found to be approximately 180° out of phase with the u signal. These signal shapes can be easily associated with the coherent structures that have been observed visually. Their details have been enhanced by quadrant truncating. These results are compared with randomly generated signals processed by the same method.

Toward full-field measurements of instantaneous visualizations of coherent structures in turbulent shear flows

1990 ◽  
Vol 3 (1) ◽  
pp. 74-86 ◽  
Author(s):  
Laertis Economikos ◽  
Craig Shoemaker ◽  
Keith Russ ◽  
Robert S. Brodkey ◽  
Dave Jones
Keyword(s):  
Coherent Structures ◽  
Shear Flows ◽  
Field Measurements ◽  
Turbulent Shear ◽  
Full Field ◽  
Turbulent Shear Flows
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