New experiment provides insight into the chaotic behavior of flows on planets

(ORDO NEWS) — The flows on planets like Earth are characterized by many features, such as rotation and temperature differences between the hot core and the cold surface. These streams are very large and very difficult to study.

To study them, Dr. Matteo Madonia set up a unique experiment called TROCONVEX – a rotating cylinder with a temperature difference from below and above and a maximum height of 4 meters.

TROCONVEX allows researchers to explore new behaviors that can help us understand planetary currents. Madonia successfully defended his thesis on April 13, 2022.

Planetary flows, such as the Earth’s atmosphere or its outer shell, are quite difficult to study, not only because of their large size, but also because of their complexity.

In fact, they are influenced by many factors: the rotation of the planet, the temperature difference between the upper and lower surfaces, spherical geometry, and often many other factors such as magnetic fields or their “flatness”.

Matteo Madonia, a researcher at the Fluid and Flows Research Group in the Department of Applied Physics, decided to study a simplified planetary flow model that takes into account only large rotation and temperature differences. However, even such a huge reduction leads to the fact that the system cannot be fully understood.

Chaos

Flows under the influence of rapid rotation tend to organize themselves into beautiful vertical structures, while flows between a hot bottom and a cold top behave very chaotically. If you mix these two effects, you can get many different flow states that behave differently depending on the balance between the two forces.

In addition, to study planet-sized flows, very high rotational forces must be achieved, which is very difficult to do by numerical simulation of the flow, and this is possible only when using very high containers.

That is why Madonia designed the TROCONVEX, a very tall rotating cylinder filled with water that is heated from below and cooled from above. Using this setup, up to 4 meters high, he was able to analyze flow configurations that were previously unavailable.

Two Approaches

Mixing the effects of rotation and temperature difference essentially creates many different states of flow that need to be differentiated and described. The researcher did this using two different approaches: the first involved using temperature sensors and the second involved measuring speed.

Using temperature sensors, he was able to analyze the difference in heat transfer between the top and bottom for each state, as well as how the temperature changes at different cylinder heights.

To do this, he used a special configuration that allowed him to thermally insulate the cylinder to avoid heat escaping from the sides. With these measurements, he was able to identify a new condition never seen before: the so-called rotational-influenced turbulence (RIT).

Chambers

Velocity measurements were taken in a transparent configuration which was specially designed to allow two chambers to look inside the cylinder and follow the movement of the colored particles that we injected into the liquid. These two cameras could track the movement of the stream and provide speed information in three specific directions.

With these measurements, Madonia was able to better characterize various flow states, including the new RIT, which presents an interesting feature: a structure consisting of four vortices filling a section of a cylinder.

Further analysis of the velocity measurements could not establish exactly whether this structure is generated by the presence of side walls or by the self-organization of the flow, which is typical for rotating flows.

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