Modeling of atmospheric “cyclone” and “tornado” in laboratory conditions

An experiment on natural modeling of vortex structures of “cyclones” and “tornadoes” on a room-size laboratory setup.

Previously, I wrote several articles about the supposed mechanisms of cyclones and tornadoes in the atmosphere of planet Earth.

https://habr.com/ru/articles/832582/

https://habr.com/ru/articles/834254/

https://habr.com/ru/articles/839624/

After writing these articles I had a question:

Is it possible to build a small-scale working model of a cyclone and tornado in order to test theoretical assumptions in practice?

Having dug around the Internet on the topic of natural experiments with tornadoes, I found out that in all the current “models” of tornadoes, the main attention is paid to twisting the tornado cord.

In my model of a “tornado”, the role of the rotation of the “tornado cord” is of secondary importance, and the main importance is the compression of the axial cord by oncoming air flows directed towards the axis.

It was precisely this model of counter-current air flows to a common center on a plane that I decided to build.

This requires a high-pressure fan and the flat ring air distribution device itself.

I assembled all of this into a single installation using available materials and affordable household devices (see Fig. 1.)

Fig. 1. General diagram of the setup for simulating axisymmetric vortex flows of the “tornado” type converging towards the center.

High pressure fan

First I tried to find the fan I needed in the “ventilation equipment” sections.

But there were no high-pressure, low-performance fans there, and the prices were very high.

Here I remembered the blowing function of household vacuum cleaners, with the help of which ceilings were previously whitewashed in the USSR through a sprayer with a shaped lid that was put on an ordinary glass jar – this was called a “sprayer”.

As a result, I used a regular construction vacuum cleaner with an air blowing function as a high-pressure fan. The vacuum cleaner looks approximately like the one in the picture in appearance and price. (See Fig. 2-3.)

Fig. 2. General view of the vacuum cleaner that I used as a high-pressure fan.

Fig. 3. Brief technical characteristics of the vacuum cleaner adopted as an air blower.

That is, for only 4 thousand rubles I received a very powerful fan with a low flow rate of about 5.3*3600/1000=19 m3/h, but with a very high maximum pressure of 17 kPa = 1.7 m.water column.

True, this maximum suction pressure occurs with a flow rate of about zero, that is, when working with a plugged hole.

In the maximum flow mode of the vacuum cleaner through the hose without attachments, the jet pressure was more than 2 kPa (200 mm H2O) – I couldn't find a deeper jug, which corresponds to a flow speed of more than 58 m/s (= more than 208 km/h).

The air flow through the outlet pipe with a diameter of Ф27mm in the vacuum cleaner hose was about 33 l/s or 119 m3/h:

Q=(0.27/2)^2*3.14*10*58=33l/s

Q=(0.27/2)^2*3.14*10*58*3600/1000=119m3/hour

Flat ring air distributor

I made the air distributor from almost free materials at hand, namely a 1-liter plastic bucket from sauerkraut from Pyaterochka, and a metal screw cap from some pickles from the same store. (See Fig. 4.)

Fig. 4. An example of a plastic bucket from store-bought pickles, which was used in the experiment.

It was easy to cut round holes in the thin plastic of the bucket and in its lid using an ordinary stationery knife.

The joints were sealed using transparent office tape and plastic bags (see Fig. 5-6)

Fig. 5. General view of the assembled flat flow distributor.

Fig. 6. General view of the flat flow distributor with the cover removed.

Result of system purge

Visualization of a “tornado”

The very first launch of the resulting assembly gave a positive result: a complex air flow with obvious turning points could be felt with a simple touch of the fingers.

To visualize air flows, we had to additionally purchase a “smoke machine”, which is used at concerts for smoke special effects.

It turned out that such smoke machines can be very tiny for home indoor discos, and their price turned out to be very small, that is, even less than a vacuum cleaner. (See Fig. 7.)

Fig. 7. Approximate view of a smoke machine for visualizing air flows in an experimental tornado.

When blowing smoky air through a disc air distributor, a bright picture was obtained, which was very similar to the appearance of a natural tornado.

Moreover, if you blow a direct stream of air through the bucket, you get a narrow vertical column of smoke, gradually expanding in height, that is, almost like a “tornado”. (See Fig. 8-11)

Fig. 8. Smoke column of a “tornado”.

Fig. 9. The smoke column of the “tornado”. The deviation to the right is due to the high pressure of the stream in the bucket after hitting the far wall and its flight upward to the outlet slit. The smoke above the can hardly curls due to the high flow rate at full power of the vacuum cleaner.

Fig.10. The smoke column of the “tornado”. The density of the smoke increased with a decrease in the air flow from the vacuum cleaner, the smoke in the column became more noticeable, curling at the outer edges due to the lower air speed in the “tornado” flow.

Fig. 11. The smoke column of the “tornado”. The smoke above the can hardly curls up due to the high flow rate at full power of the vacuum cleaner.

Detecting the “tornado heel”

A hole was made in the center of the disc air distributor, through which a thin hose was led through the volume of the bucket, needed to measure the pressure on the outer surface of the disc.

The pressure was measured by the height of the water column displaced or sucked in when the end of the hose was immersed in a glass jar of water.

For the “tornado” in the turning zone of the jets in the center of the disk, an excess pressure of about 100 mm H2O = 1 kPa was obtained.

Approximately the same pressure was obtained by measuring the air flow velocity at the exit from the annular gap of the air distributor.

Geometry of jets in a “tornado” column

The movement of jets in the air distributor in the “tornado” mode is shown in the diagram (see Fig. 12-13)

Fig. 12. Formation of a “tornado” smoke column with a direct radial entry of the pipe into the air distributor.

Fig. 13. A table with a support made of bent pipes, the shape of which almost perfectly illustrates the shape of air flows in the imitation of a “tornado” in the “heel” zone.

Visualization of a “cyclone”

If air is supplied to the bucket tangentially along the wall, then the result is an air analogue of a vortex nozzle for liquid rocket fuel, which creates an intense dispersion of the sprayed medium in the radial direction (see Fig. 14.)

Fig. 14. Two versions of a vortex atomizing nozzle for liquid fuel: a – swirling occurs in a cylindrical volume (2) when a jet of fuel is supplied tangentially to the outer cylinder of the nozzle through an opening (1); b – swirling of the flow occurs in spiral grooves (3).

The air stream directed tangentially to the wall continues to move in a circle along the wall of the can, creating a moment of rotation of the entire mass of air passing through the can to the outlet annular gap.

When entering the distributor annular gap, such circular rotation of the flow did not stop, which led to the preservation of the tangential velocity of the air flow even after exiting the annular gap.

As a result, at the outlet of the disk distributor, the air jets have not only a radial velocity vector obtained from the excess pressure in the can, but also a very high tangential velocity component from the circular rotation created in the can.

It is the tangential component of the overall speed of the air streams that causes the air flows to fly away from the center of the disk (see Fig. 15).

Fig. 15. Formation of a smoke cone “cyclone” with the emergence of the “eye of the cyclone” of a tornado with an oblique tangential entry of the pipe into the air distributor.

Thus, in the experiment a conical diverging flow similar to a “cyclone” was obtained, equipped with an “eye” of neutral space in the center.

The presence of a “cyclone eye” is determined both by finger sensations and by instrumental pressure measurement using a pulse tube from the center of the disk.

The pressure in the center of the “eye of the cyclone” dropped to atmospheric pressure, while in the center of the “heel of the tornado” the pressure was greatly excessive: plus 1 kPa (100 mm H2O).

The Pitot tube was also used to measure the flow velocity pressure at the outlet of the annular distributor, which was about 1 kPa, i.e. almost equal to the velocity pressure of the direct, untwisted “wind” from the slot gap of the air distributor.

Below are photos of smoke conical vortices of “cyclones” (see Fig. 16-18.)

Fig. 16. The smoke cone of the “cyclone”. The smoke above the can hardly curls up due to the high flow rate at full power of the vacuum cleaner.

Fig. 17. The smoke cone of the “cyclone”. The smoke above the can hardly curls up due to the high flow rate at full power of the vacuum cleaner.

Fig. 18. The smoke cone of the “cyclone”. The smoke above the can is denser and noticeably billows due to the reduced flow rate at a reduced vacuum cleaner flow rate (the vacuum cleaner suction flow rate is stifled).

Geometry of jets in the “cyclone” cone

Geometrically, the shape of the “cyclone” flows is a set of straight lines located in a circle at some equal angle to the generating circle at the base.

Such a figure in geometry is called a “hyperboloid of revolution” (see Fig. 19-21.)

Fig.19. Help for the query “hyperboloid of revolution” in Yandex.

Fig.20. Rod structures in the form of hyperboloids of revolution. The left one-sided twisted structure very accurately shows the shape of the “cyclone” flows at the outlet of the annular air distributor in this experiment.

Fig. 21. Table support in the form of a rod hyperboloid of revolution with unidirectional straight rods.

Application of “hyperboloids of rotation” in architecture and engineering

Many tower-type engineering structures are made in the form of a “hyperboloid of revolution”, for example the Shukhov Tower in Moscow and many others. (See Fig. 22-24.)

Fig.22. Radio broadcasting “Shukhov Tower” in the form of a hyperboloid of revolution in Moscow on Shablovka Street.

Fig.23. Water tower support in the form of a rod hyperboloid of revolution. All rods in the structure are straight pipes. The curvature of the rods in the hyperboloid is an optical illusion.

Fig. 24. Table support in the form of a rod hyperboloid of revolution with two sets of rods in opposite directions.

Visualization of vortex flow cross-sections

The next stage of the experiment was the visualization of the transverse structure of smoke vortices, a picture of which is obtained when the smoke is cut by a flat beam from a construction laser “level” (see Fig. 25.)

Fig. 25. View of a hand-held laser level used to visualize the cross-sectional structure of smoke vortices.

This cheap hand level turned out to have a rather weak beam, and the plane was created by splitting the beam on some kind of divider, which gave a series of dots instead of a continuous line of light at a great distance.

Nevertheless, at a short distance from the source of the rays, the strength of the rays and their frequency in the fractional “fan” were quite sufficient to obtain a quite noticeable light image in the sections of the foggy vortices.

Unfortunately, no clearly visible internal structure could be detected at the roots of the vortices, since all the internal volumes of the vortices in the stagnant zones of the “tornado heel” or “cyclone eye” turned out to be filled with smoke with air with practically the same concentration of smoke as the main stream.

Conclusion

This experiment quite clearly demonstrated the plausibility of the models I had previously expressed for both a fairly small atmospheric phenomenon – a “tornado” – and for a much larger atmospheric vortex formation – a “cyclone”.

Thus, the experiment showed that the transition from the “tornado” mode to the “cyclone” mode occurred in the installation only when one parameter was changed, namely the angle of entry of the jet into the volume of the cylindrical static pressure chamber in front of the air distributor.

In this case, the angle of entry of the jet into the cylindrical volume of the chamber is responsible for the intensity of rotation of the flow at the exit from the slit gap.

The emergence of a tornado air column without strong swirling of the flow confirmed the low significance of the component of the tornado rotation around the axis, compared to the influence of the ground air flows converging towards a common center.

Also, the intensive swirling of the flow in front of the slot distributor made it possible to create a characteristic “cyclone eye” with a practically calm regime, which is a very significant structural element of the “cyclone” as a vortex atmospheric phenomenon.