Projet de recherche PX/7/LP/41 (Action de recherche PX)
The BAMBI (Bifurcation Anomalies in Marangoni-Bénard Instability) experiment was proposed to ESA and accepted in April 1991, as one of the reference experiments planned for the FSL (Fluid Structure Facility), which later evolved into the FLUIDPAC facility. Most of the effort accomplished on the design of the BAMBI cell took place in parallel with the development of the FLUIDPAC-1 facility (both were both ready for flight in 1999).
The BAMBI experiment was first flown onboard the FOTON-12 satellite, in September 1999. Unfortunately, the solenoid valve selected by the industrial contractor failed at activation of BAMBI, which resulted in complete failure of the experiment, as no liquid was injected in the cell. The BAMBI experiment was then attributed a re-flight onboard the unfortunate FOTON-M1 satellite (destroyed following the explosion of the Soyuz launcher shortly after lift-off), in October 2002. The BAMBI experiment is now foreseen for the FOTON-M2 flight, planned for May 2005.
Its main goal is to determine the anomalous bifurcation structure (i.e. exhibiting hysteresis) from the rest state to the convective hexagonal structure, when a silicon oil layer is progressively heated from below. The focus will also be on the secondary transition from a hexagonal to a square pattern, when the heat flux crossing the layer is sufficiently increased. Finally, particular attention will be paid to the development and evolution of defects in hexagonal and square structures, as recently analyzed theoretically.
Due to the two failures of the BAMBI-FOTON experiment and the fact that the experiment was technically ready since 1999, it has been necessary to adapt its scientific goals and identify new challenging features, in order to guarantee the interest of the results, as well as to ensure the future publication of results obtained in microgravity. Therefore, most of the effort since 2000 has been on theoretical, numerical and experimental ground studies necessary to understand the fundamental aspects of the non-linear regimes of the Marangoni-Bénard instability. This fundamental research activity has been quite prolific, as attested by the number of publications of the MRC, related to Marangoni-Bénard instabilities. In particular, several books have been recently published, which summarize the progress accomplished into this fascinating and still promising field (see Refs [1], [2], [3]). Comparing these results with results obtained during the FOTON flight is therefore our main objective, in order to validate the theoretical and numerical approaches.
Despite the unusually long delay between the original proposal and the foreseen date for flight, we believe that some of the results expected from the BAMBI experiment can still be considered as up-to-date, even though several teams in Europe and in the world have studied surface-tension-driven instabilities during this last decade. Several experimental studies were indeed performed using very thin liquid films for which the effect of buoyancy may be neglected, at least in theory. In this way, the selection between “perfect” (i.e. defect-free) patterns has been studied in details, showing in particular the transition between hexagonal and square symmetries occurring at high constraint.
However, even though the development of “perfect patterns” can now be considered as well understood, it remains to understand the role of defects (both intrinsic and extrinsic) on the selection between patterns. Some discrepancies between interpretations of ground experiments indeed remain, as far as the role of pentagon-heptagon pairs in the transition between hexagons and squares is concerned. Other discrepancies still exist about the tendency of the wavelength of convective structures to increase (or decrease) with the distance from the primary threshold. As some of these differences have been attributed to the role of buoyancy, always present especially at increasing constraint, we hope that the BAMBI experiment will completely answer such fundamental questions, by providing a purely surface-tension-driven reference case at all values of the thermal flux crossing the layer.
Moreover, it is well known that using amplitude equations, it is possible to predict that the lateral walls (and more generally, the defects) are able to select the wavelength of the convective structures appearing above convection threshold. More recently, it has been shown that for hexagonal patterns, the wavelength selected by the walls is not necessarily the critical wavelength, because of the non-variational terms appearing in amplitude equations (see the books [1,2]), which have maximal impact in the purely surface-tension-driven case. Further 3D numerical simulations are planned to confirm this effect, whose results should be thoroughly compared to the experiment performed during the FOTON-M2 flight.
If successful, this would be an important advance in the theory of pattern formation, which should lead to several high-level publications due to its interest in several branches of Science. Indeed, weakly non-linear theories based on amplitude equations are well known to be universal, and in this context, it has been realized in last years that Marangoni-Bénard convection appears as a rather “pure” and rich test case in order to validate theoretical models.
Satellite(s) or flight opportunity(ies):
- FLUIDPAC on FOTON-M2
Field of research:
Physical Science: Structure and Dynamics of Fluids and Multiphase Systems
