After about two years of work, countless virtual meetings, innumerable exchanges of graphs, equations, models, scripts, files, etc. my long-range collaborators Chao and Linfeng (Tsinghua, Beijing) and I have been able to combine experimental measurements, numerical simulations and theoretical modelling, in a single (hopefully) enjoyable paper.
What do we learn from this work? Aside from the specificities of the tumbling of particles in the complex flow machine that is the turbulent convective cell, we learn that in the bulk of a RB system we find just exactly the same type of flow fluctuations as in any other developed turbulent flow. Of course, since Richardson in the ’20 and Kolmogorov in the ’40 this was already suspected and later known, but here we prove it in a new way and with unprecedented precision. How we do it? We look at how aspherical particles tumble in such a flow. Because the rotation dynamics of small neutrally buoyant particles is highly sensitive to the flow velocity gradient evolution, small differences in the latter quantity as compared to other turbulent flows should lead to sensibly different particle tumbling dynamics. However, that seems not to occur, and this irrespectively of the shape of the particle used as a probe. The take home message: regardless of the particular stirring mechanism the core of turbulent flow system is pretty much universal. Hence, the title of this post “be careful it’s universal inside“.
The full paper here : http://dx.doi.org/10.1017/jfm.2020.539
The last preprint here: https://arxiv.org/abs/1912.00229