Multi-scale flows controlled in the laboratory: toward turbulent like flows, their control and applications

This research project deals with the study of flows and their control at different scales with a focus on turbulence and mixing. Turbulence occurs in oceans, in the atmosphere, in industrial processes. It could be simply described as a fluid flow which appears random in space and time and is unpredictable. Mixing is how flows fuse or separate. The picture of a river flow is used to illustrate turbulence and mixing along with the project's approach. The surface of the water presents a lot of eddies of different scales. If two small pieces of wood are thrown in such a flow, they will separate. If some ink is thrown, the stain will expand. To study turbulence one can either observe the flow at one point and summarize its fluctuations using statistical measures or draw a sketch of the flow to measure it (topological approach). The complexity of turbulence is that in this sketch everything changes all the time, so space-time information must be extracted. In addition, the sketch drawn from the river side is not the sketch drawn from one of the moving pieces of wood. This is the difference between the Eulerian (from the river side) and the Lagrangian (from within the flow) approaches. The Lagrangian approach is essential in turbulent flow decryption and physical modelling. It has various applications: flow control of drag, mixing, lift, cloud formation, atmospheric transport and combustion systems.Many central properties of the turbulence such as its enhanced dissipation and transfer of momentum, energy and mass, require the answer to the following question for their physically accurate modelling: How to link the flow sketch with the velocity in one point ; and the way the pieces of wood move with how the ink stain expands?A target of this project is to define some key points/areas in the flow which hold the flow's key properties. As you can expect from the broad range of eddy sizes, the key points will have different scales. To analyze how those key points are distributed on different scales we use fractal tools (as a tree where a big branch is connected to many small branches which are themselves connected to smaller ones and so on).Once such key points are identified and analysed, we aim at controlling them so as to guide the flow toward a turbulent-like state (under control) with specific desired configurations. There are different approaches concerning these key points in turbulent flow; an ambitious multi-scale flow control should integrate the control of the flow topology, energy, momentum, vorticity and acceleration in its approach.The research project offers a combined statistical, topological, Eulerian and Lagrangian approach by means of experiments and simulations grounded on novel theory.The heart of this project is the idea of generating bespoke multi-scale flows by use of electromagnetic forcing for the purpose of efficient mixing and multi-scale flow control which offers unprecedented opportunities for the study of turbulence. For this, I will develop laboratory experiments and simulations where I can create the entire flow by controlling chosen key points used in the theory. I already have demonstrated that it is possible to generate such a multi-scale flow with electromagnetic forces within a shallow layer brine flow, and to control it at will in space and time. I am now going to develop to its full potential the existing laboratory experiment. Various measurements will be performed (Eulerian and Lagrangian velocities, accelerations, dye concentrations, etc) and completed by numerical simulations. This will lead to results where all the aspects of turbulence and mixing will be analysed. Their applications to mixing enhancement should be obvious, whilst they should also lead to a broad multi-scale flow control approach, with implications for drag, lift and heat transfer.Turbulence and mixing are in the heart of many engineering works and environment issues, so this project will have a broad impact.