Tomsk State University. Physical Department.
Laboratory of training physics experiment
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Self - Organization   Обратно   Далее  

DEMONSTRATIONS ON SELF-ORGANIZATION IN THE PHYSICS COURSE 

Interest in demonstration production of Bernard Cells and Taylor Vortices aroused in connection with the idea dissemination of self-organization in physics. Among the popular physics demonstrations there are experiments where the approach to their explanation now is more interesting from the point of view of self-organization. For instance, in hydrodynamics the demonstration of Karman Vortex Street is very obvious, which we earlier showed only as an illustration of turbulent flow in two pairs of vortices behind the barrier in the physics course. If this phenomenon would be considered from a position of self-organization, it should be necessary to demonstrate the extensive vortex street emphasizing the stability of vortex structure.

BERNARD CELLS 

If there is no lack of time, it is desirable to give the observers an opportunity to notice the fact of simultaneous cells occurrence and their self-organization over the whole volume at the optimal conditions. The cooperative formation is demonstrated in this way as common characteristic of self-organization processes.

Next important demonstration result is concluded in formation of hexahedral cells family of the same (equal) size and that produces the greatest impression. One can change the cell size by sloping down the vessel because the cell sizes depend on the thickness of the liquid layer.

Teylor_rotors

TAYLOR VORTICES 

In a lecture room Taylor Vortices demonstration is performed in vertical projection. We made a transpiration vessel from organic glass in a parallelepiped form for it not focusing the light like a cylindrical lens. We obtained a contrasting pattern of vortices only when we added a layer of heated oil, which has the other refractive index. Since the liquid is not actually mixed before vortices appearing by laminar flow, the layer existence with different refractive indexes in liquid leads to formation of schlieren pattern. This method enables to observe the initial process of simultaneous vortices formation at critical value of Taylor number. This figure shows the photo of the pair of neighboring vortices one second later after the formation began. The neighboring vortices are twisting in opposite directions.

air rings

THE RINGS ON THE ROTATING ROD (new structure of self-organization)

For the demonstration performing on a large scale we attempted to obtain only one pair of great vortices in the vessel. We noticed a new structure in the result of our experiments with such unusual large space between the cylinders. In liquid on the rotating rod an ordered system of air rings were being occurring. First, at the rotation frequency of about 1000 rpm on the vortices boundary on the rotating rod in the liquid an air ring is being formed about 2 mm in width. Its appearance is connected with air bubbles transportation through the created cavity above. With increasing of rotation frequency up to 1100 rpm a single ring is increasing in volume and then divides in two. The upper ring divides into two rings again and all the system is moving down

In the result an ordered system consisting of 5-9 air rings has been formed on the rotating ring. The ring system forms a stable structure which continues if the rotation frequency would not be changed.

We mention these experimental protocols about the formation of air ring system on the rotating rod according to two reasons. Firstly, so unusual results have been obtained due to seemingly ordinary work on elaboration of lecture demonstrations. Secondly, the given protocols could be interesting to the experts in hydrodynamics in order to their continuation.


A.R. Arjanik, Y.P. Mikhaylichenko., G.N. Sotiriady. Production of demonstrations of Benar cells and Teylor vortex.

Physics in Higher Education. Journal of the Moscow Physical Siciety Series B. V. 6, #4, 2000, 60-67. (in russian)

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