The ESA/JAXA JEREMI (Japanese European Research Experiments on Marangoni Instabilities) Project

JEREMI是“日本欧洲马兰戈尼不稳定性研究实验”（Japanese European Research Experiments on Marangoni Instabilities）的缩写。这个雄心勃勃的项目是欧洲航天局（ESA）和日本航天局（JAXA）之间协议的一部分。该卫星于2001年启动，目前正进入最后准备阶段，目前已获准在国际空间站上飞行。这些实验将利用日本宇宙航空研究开发机构的FPEF（流体物理实验设施）进行，这是一个研究微重力下流体的多用途设施。这类研究是非常相关和有用的，因为它们使人们有可能观察在正常重力条件下交织或被掩盖的一些物理力（主要是流体表面张力及其梯度）如何对液体的行为产生关键影响（导致所谓的“马兰戈尼”或热毛细效应）。特别是，在没有地球上重力驱动对流的复杂情况下，英国科学家希望在空间测试由这些力产生的三维层流、振荡流和湍流的基本理论，这些理论原则上也可以应用于各种“地球”情况。更具体地说，JEREMI系列实验是基于所谓的“液体桥”，即在不同温度下保持在两个圆盘之间的具有圆柱形自由液-气界面的液滴。在太空中，由于没有重力，可能形成相对较大的液体桥，否则这将倾向于使液体-空气界面变形并破坏漂浮液体的柱。在微重力条件下，施加于漂浮液体的温差产生无浮力（纯粹由表面张力驱动，即马兰戈尼）对流。这种类型的流动最初是非常规则的，但是如果施加的温差增加到超过给定的阈值，则它变成振荡的和三维的。该项目的目标是更好地了解这种不稳定性，并制定可能的手段，通过改变液体-空气界面的条件来控制它。另一个目标涉及在所谓的“颗粒堆积结构”（PAS）的根源上的因果关系的识别。最近已经发现，在马兰戈尼流的作用下，最初均匀分布在液体桥中的固体颗粒可以自发地从周围的流体中分层并形成三维聚集体。由粒子形成的结果簇或图案看起来像空间延伸的“闭合线”或“电路”（具有带有几个叶片的风车的形状）。这个迷人的结构被观察到漂浮在液体中，并以恒定的角速度在空间中旋转，从而给人一种自由漂浮的“旋转固体”的错觉。一个国际科学家小组（来自联合王国、比利时、奥地利、西班牙和日本）具有不同的互补背景、专门知识和观点，已经合作了15年多，以精确确定为解决上述专题而将要进行的一系列空间实验。由于该项目目前已进入最后阶段，将进一步努力开发更先进的数学和数字工具，用于微调实验“输入参数”和解释飞行结果。该项目的目标是对仍然知之甚少的基本物理原理进行实验研究和建模（理论和数字），从而产生可能适用于各种领域的“新知识”，这些领域从机械、化学和热工程到材料科学，从小规模系统中微小粒子的操纵到天体物理规模的问题。该项目与英国空间环境和载人航天国家战略中列出的研究优先事项保持一致。

The acronym JEREMI stands for "Japanese European Research Experiments on Marangoni Instabilities". This ambitious project is part of an agreement between the European Space Agency (ESA) and the Japanese Space Agency (JAXA). Started in 2001, it is now entering its final stage of preparation and is currently endorsed to fly on the International Space Station (ISS). These experiments will be executed using the FPEF (Fluid Physics Experiment Facility) of JAXA, a multipurpose facility for the investigation of fluids in microgravity. Studies of such a kind are very relevant and useful as they make it possible to observe how some physical forces, interwoven or overshadowed in normal gravity conditions (essentially the fluid surface tension and its gradients), can have a crucial impact on the behaviour of liquids (leading to the so-called "Marangoni" or thermocapillary effect). Without the complications of gravity-driven convection flows on Earth, in particular, UK scientists want to test in space fundamental theories of three-dimensional laminar, oscillatory and turbulent flows generated by these forces, which can be applied, in principle, also in a variety of "terrestrial" circumstances. More specifically, the JEREMI series of experiments is based on the so-called "liquid bridge", a drop of liquid with cylindrical free liquid-air interface held between two disks at different temperature. In space it is possible to form relatively large liquid bridges due to the absence of gravity, which would otherwise tend to deform the liquid-air interface and break the column of floating liquid. In microgravity conditions, the difference of temperature applied to the floating liquid produces buoyancy-free (purely surface-tension driven, i.e. Marangoni) convection. This type of flow is initially very regular, but it becomes oscillatory and three-dimensional if the applied temperature difference is increased beyond a given threshold. The project targets an improved understanding of this instability and the elaboration of possible means to control it by modifying the conditions at the liquid-air interface. Another objective relates to the identification of the cause-and-effect relationships at the root of the so-called "Particle Accumulation Structures" (PAS). Very recently it has been discovered that, under the effect of Marangoni flow, solid particles initially distributed uniformly in a liquid bridge can demix spontaneously from the surrounding fluid and form three-dimensional aggregates. The resulting cluster or pattern formed by particles looks like a spatially extended "closed wire" or "circuit" (having the shape of a windmill with several blades). This fascinating structure has been observed to float inside the liquid and rotate in space with constant angular velocity, thereby giving the illusion of a freely-floating "rotating solid body". An international team of scientists (from UK, Belgium, Austria, Spain and Japan) with different complementary backgrounds, expertise and perspectives, has been collaborating for more than 15 years to define precisely the set of space experiments to be executed to address the above topics. As the project is now entering its final stage, additional effort will be devoted to the elaboration of even more advanced mathematical and numerical tools to be used for the fine tuning of the experiment "input parameters" and for the interpretation of the flight results. The objective of this project is to examine experimentally and model (theoretically and numerically) fundamental physical principles still poorly known, thereby generating "new knowledge" potentially applicable in a variety of fields, which range from mechanical, chemical and thermal engineering to materials science and from the manipulation of tiny particles in small-scale systems to problems with astrophysical scale. The project aligns with the research priorities listed in the UK National Strategy on Space Environments and Human Spaceflight.