EXPLOIT

Viscous flows are ubiquitous in nature and impact many areas of physics, engineering sciences, astrophysics, geophysics or aeronautics. The minimal knowledge every scientist has about them is that if you stir strongly enough a viscous flow, it becomes turbulent and displays a power-law energy spectrum characteristic of scale to scale energy transfer, by which all the energy injected at large scales is transferred and dissipated at small scales. However, it was only understood in 1962 by Landau and Kolmogorov that the characterization of the properties of this dissipation is crucial, not only to understand fundamental issues such as intermittency corrections to the Kolmogorov spectrum, but also to tackle practical issues such as drag reduction or numerical modelisation of turbulent flows. The drag phenomenon is due to the dissipation induced by a moving object (like a car or a boat) in a fluid and is far more important in the turbulent regime than in the laminar one. With the end of an era of cheap, unlimited energy, it becomes of crucial importance to build efficient cars, ships, airplanes..., and try to lower their energy consumption. The present technological progresses on the drag have given interesting results but with neither real understanding of the origin of this phenomenon nor of its scaling laws. Recent advances in mathematical analysis of the equations governing viscous flow seem to indicate that there is a link between the scaling of dissipation in a turbulent fluid and the development of singularities. However very little is known about the dynamics and statistics of the corresponding dissipative structures, leaving a gap between the drag phenomenon and its theoretical explanation. The EXPLOIT project aims at filling this gap by providing a characterization of dissipation structures based on an experimental analysis of a model turbulent flow using multi-scale tools and advanced visualization techniques (3D Particle Tracking Velocimetry “Shake the Box” -STB- or Tomographic Particle Image Velocimetry -PIV- ) in a dedicated meter-size turbulent experiment. The EXPLOIT project is well included in Défi 2 : une énergie propre, sure et efficace, Axe 1 : recherche exploratoire et concepts en rupture. Within EXPLOIT project, we will: i) build a novel meter-size dedicated experiments instrumented with a high resolution space and time resolved 3D-PIV system; ii) detect the dissipation structures experimentally by following them in the scale space down to the dissipative scale to capture their dynamics and statistical properties; iii) explore their universality by systematic variation of the control parameters (Reynolds number) and of the forcing conditions. If successful, the project may lead to a breakthrough in the understanding of the drag origin, and provide new ideas for its substantial reduction, thereby contributing to energy savings and to the reduction of atmospheric pollution.