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Topic supervisors:
Eric Moreau (eric.moreau@univ-poitiers.fr / +33 5 49 49 69 33 )
David Babonneau (david.babonneau@univ-poitiers.fr / +33 5 49 49 67 25 )
When a fluid is in contact with a solid wall, a space charge develops due to two different mechanisms:
These two mechanisms have been widely studied in the past, but they are not well understood due to the complexity of the multi-scale physical and chemical phenomena involved which depend on the properties of the two materials in contact. In addition, when the fluid is air, an electrical surface discharge is required to produce an EHD force at the solid interface. These plasma actuators have already demonstrated their capabilities in effectively controlling air flow in real time and improving heat transfer, but they are actually limited to applications of low speed subsonic air flows in simple geometries, on a centimeter to millimeter scale. Their efficiency could be improved by modifying the properties of the solid material and by imagining new control strategies.
This subject, which includes parts of themes 3, 5 and 6 of Labex I, pursues three main objectives. The first aims to better understand the electrical phenomena occurring at solid-fluid interfaces. For this, a strong collaboration between researchers in electro-hydrodynamics, tribology and physics of materials is necessary to explain the electrical phenomena generally observed at the millimeter scale, by mechanisms occurring at micro and / or nanoscales (in collaboration with subjects 1 and 2). The second objective is to use these electrical phenomena, which originate on a very small scale, for large-scale industrial applications in the fields of engineering and energy science. Finally, the last objective is to improve the performance of multi-physical systems at interfaces (mass and heat transfers, aerodynamic or hydrodynamic performance, reduction of noise pollution) by using passive and / or active flow control strategies. Thus, the skills of researchers working on electrical, mechanical, thermal and combustion applications will be put to use.
To achieve these objectives, the first part of our research could be devoted to the space charge developing at a liquid-solid interface, focusing on three themes:
In addition, the application of an external electric field in a liquid at rest can cause its movement, research on such EHD actuators could be extended on a small scale to develop microfluidic systems. The last application should relate to combustion assisted by EHD with electrically charged sprays.
The second part will deal with plasma actuators for the control of subsonic flows and potentially for hypersonic flows. Thus, since the fluxes close to the walls can be controlled with very little energy if they are precisely directed to the right place and at the right time, one can imagine new designs of plasma actuators, such as micro arrays – surface plasmas which could deposit energy anywhere on the wall, at any time. This requires new research on high-voltage power supplies and a significant effort in terms of reducing the size of the actuator using new manufacturing processes, such as photolithography and / or the FIB technique (theme 2). In addition, the influence of the properties of the solid material (such as its morphology, its surface structure, its electrical properties) should be studied more precisely because they play a key role in the propagation of the discharge on the surface of the dielectric and in the resulting HDE phenomena. In addition, research on improving combustion using the plasma network actuator should be extended and scientific collaboration with researchers from the Labex CAPRYSSES (University of Orléans) could be expected.
The last part will deal with the interactions between a fluid and the solid wall along which it flows. First, the influence of the wall morphology (roughness, micro-structuring) on the characteristics of the flow and / or the associated sound field could be analyzed. More particularly, the modifications of the flow in the vicinity of the wall could be identified (laminar to turbulent transition, turbulence, topology of the streaks, friction of the skin, acoustic field) and the capacities of the different active or passive approaches to control the turbulence and / or or handling separate flows should be studied. In addition, to better understand the underlying physics of the phenomena studied, several scientific fields ranging from the physical analysis of data to numerical modeling, including the practical implementation of advanced control techniques, could be used.
Overall, a better understanding of the electrical phenomena occurring at a solid-liquid interface could allow new techniques making it possible to reduce industrial electrostatic risks by using new materials, to increase the reliability of the membranes in fuel cells and electrolysers, in order to achieve active lubrication using EHD forces or to electrostatically separate tribocharged granular plastic waste. In addition, this research could lead to new designs of micro-pumps for dielectric liquids and a new generation of plasma actuators based on micro-dielectric surface barrier discharges. Finally, studies on the influence of wall characteristics on flow, whether or not associated with advanced active control strategies, should have many applications in aerodynamics and aeroacoustics.