The disordered movements at the surface of a liquid are called wave turbulences, like the waves in the ocean. The statistical characteristics of those movements have been studied for the first time without the parasitic effects of gravity during parabolic flights. A best comprehension of the phenomena makes scientists able to describe more precisely the climate and the renewable energy contained in the surface waves of the oceans.
The movements at the surface of a liquid are due to various factors: external disturbances (the wind for the ocean) which catalyst the movement and spring forces which tend to bring the surface back to its initial position (either flat or spherical). There are two spring forces: the weight of liquid (due to gravity) and the surface tension (like a balloon or a trampoline).
For a given excitation, the wave turbulence is due to the competition between source of movement and spring forces.
For the oceans, spring forces are inseparable and it is impossible to eliminate gravity and surface tension. Before those experiments were carried out, we did not know the statistical characteristics of the movement at the surface of the oceans without the gravity spring force, i.e. only with the surface tension forces.
How is it possible to eliminate gravity?
Of course, gravity elimination is possible in lab in plane geometry by studying movements at the separation surface between two liquids which are the same weight for example. But then, it is impossible to eliminate the disruptive impact of the wave reflection from the vessel edges which contain both liquids.
The solution to simulate movements at the surface of the oceans without gravity has been provided by the possibility of experimenting during parabolic flights aboard Novespace A300 Zero-G aircraft. Under these conditions fluids are weightless and it is possible to eliminate the gravity spring force.
Microgravity allows scientists to study the wave turbulences at the surface of a liquid which covers the inner surface of a transparent sphere in a oscillatory movement (source of movement) (see right/left).
This configuration not only gives the opportunity to avoid the wave reflections on edges but also to study the phenomenon of pure capillary waves, without the gravity spring force. In the absence of gravity, the only force which contributes to the wave turbulence is the surface tension.
So this experiment provided a laboratory model of an ocean located at the surface of a planet without gravity. The information collected are general and this experiment will contribute to an increased comprehension of those phenomena in order to obtain more precise descriptions of the climate and the renewable energy contained in the surface waves of the ocean.
- Condensed-matter physics program scientist: Bernard Zappoli