Experiment turbulence Post-Doctoral Researcher (M/F)

About this position

It is known that turbulent flows, in nature or in the laboratory, are subject to random bifurcations, during which the flow spontaneously switches from one behavior to another over a random period of time. Von Kármán flows, where a large-scale bifurcation has already been observed, are a very good example. However, a precise understanding of the origin of these bifurcations still eludes us, thus preventing the prediction of such events.

One hypothesis is that they are triggered by extreme, small-scale singular events that propagate to a large scale. A detailed verification of this hypothesis therefore requires multiscale tools and dedicated experimental setups, as well as the development of an experimental database. In this context, one of the objectives of the ALEAS project is to utilize two existing experimental setups at SPEC and instrument them accordingly: a 10 cm radius Von Kármán flow will be instrumented using an array of 1D pressure sensors and event cameras to recreate a particle imaging velocimetry (PIV) system capable of recording large-scale flow field variations.

Event-driven vision is relatively new in the field of computer vision. The neuromorphic design allows for a much higher acquisition frequency, but above all, much longer acquisition times. This makes it ideal for recording bifurcations whose timing is unknown.

Finally, in a large-scale Von Kármán (GVK) flow at SPEC, high-resolution 3D-PIV/PTV velocity measurements have been and will be performed in the boundary layer-turbine interaction zone, as well as at the center. This should shed new light on the dissipative structures and extreme events potentially responsible for large-scale flow evolution. This project is part of a larger project aimed at developing a strategy for identifying precursor signals of rare events and/or bifurcations in turbulent flows.

The first step, therefore, is to create a database of such events (through numerical and experimental simulation).

To experimentally study turbulent flows, the SPHYNX team at SPEC draws on decades of experience and possesses in-depth expertise in Von Kármán vortex flows with fluids ranging from water to superfluids. Measurement techniques have been developed over the years, and research is conducted using state-of-the-art 3D optical diagnostic tools. Activities would include the development of a specific 3D PTV tool for very high density, laser manipulation, data post-processing, and physical analysis of turbulent flows, in order to improve the measurement and understanding of small scales.

ALEAS Project :

It is known that turbulent flows, in nature or in the laboratory, are subject to random bifurcations, during which the flow spontaneously switches from one behavior to another over a random period of time. Von Kármán flows, where a large-scale bifurcation has already been observed, are a very good example. However, a precise understanding of the origin of these bifurcations still eludes us, thus preventing the prediction of such events.

One hypothesis is that they are triggered by extreme, small-scale singular events that propagate to a large scale.