Experimental and numerical study of weak shock wave transmissions through minitubes

International audienceThe aim of this paper is to present an original experimental technique to study weak shock wave in a mini-tube. Thus, we have designed an apparatus, which can be connected to any classical shock tube, in order to characterise high speed flows induced by the shock wave transmission in mini-tubes. We have proposed appropriated measurements based on high speed strioscopy coupled with pressure sensors. Two mini-tube diameters are considered: 1.020 ±0.010 mm and 0.480 ±0.010 mm. We have realized preliminary experimental and numerical campaigns with an incident shock wave Mach number at 1.12 ±0.01. The generation of a micro-shock wave was observable in the two mini-tubes. For the smallest mini-tube, we have found an attenuation of the strength of the shock wave with a decrease of 1.8% of the Mach number

Special Issue on Aerodynamics and Environment Introduction

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Dynamics of UV short pulse laser-induced plasmas from a ceramic material “titanium carbide”: a hydrodynamical out of equilibrium investigation

International audienceThe present work is motivated by the numerous applications of short lasers–ceramics interaction. It aims at applying a newly developed model to investigate the dynamic of laser-induced plasmas from a ceramic material into a helium gas under atmospheric pressure. To have a better understanding of the link between the material properties, the plume characteristics and its interaction with the laser beam, a thorough examination of the entire ablation processes is conducted. Comparison with the behavior of laser-induced plumes under the same conditions from a pure material is shown to have a key role in shedding the light on what monitors the plume expansion in the background environment. Plume temperatures, velocities, ionization rates as well as elemental composition have been presented and compared under carefully chosen relevant conditions. This study is of interest for laser matter applications depending on the induced plasmas dynamics and composition

Modification of the shock wave shape of a supersonic low Reynolds number flow field around a cylinder by a glow discharge in air

Oral presentationInternational audienceThis paper describes investigations focused on the shock wave modification induced by a plasma actuator flush mounted on a cylinder in rarefied flow regime. The experimental measurements were carried out in a supersonic low-density wind tunnel and the numerical investigation used a 2D fully compressible Navier Stokes simulation. Experimental observations showed the modification of the shock wave when the discharge was switched on. The numerical simulations show that this modification cannot be reproduced correctly by thermal effects. A theoretical approach was then proposed, in which the shock stand-off distance is written as a function of the ionization degree of the plasma. This approach was confirmed experimentally by measuring electronic properties of the plasma

Numerical study of an original device to generate compressible flow in microchannels

International audienceThis study is devoted to the design of an experimental device to generate shock waves in a micropipe. Indeed, the recent advances in the microfluidics of gas lead the scientific community to the question of scaling law in supersonic regime. Thus, in this paper, we simulate the flow induced by the opening of a small solenoid valve to know if it is able to generate a minishock wave. This shock wave moving in an intermediate pipe could be transmitted into a micro one. In this work, we focus on the flow in the intermediate pipe and on the properties of the transmitted wave into the microchannel. Three geometry of convergent between intermediate and micropipe are investigated. We have compared the results of our simulation to the classical analytical models dealing with shock tubes. After presenting the geometries of the study case, we give the characteristics of our numerical approach, and then we describe our main results. In a last section, the flow generated by the valve used in free jet regime is described

Quantification of the effect of surface heating on shock wave modification by a plasma actuator in a low-density supersonic flow over a flat plate

International audienceThis paper describes experimental and numerical investigations focused on the shock wave modification induced by a dc glow discharge. The model is a flat plate in a Mach 2 air flow, equipped with a plasma actuator composed of two electrodes. A weakly ionized plasma was created above the plate by generating a glow discharge with a negative dc potential applied to the upstream electrode. The natural flow exhibited a shock wave with a hyperbolic shape. Pitot measurements and ICCD images of the modified flow revealed that when the discharge was ignited, the shock wave angle increased with the discharge current. The spatial distribution of the surface temperature was measured with an IR camera. The surface temperature increased with the current and decreased along the model. The temperature distribution was reproduced experimentally by placing a heating element instead of the active electrode, and numerically by modifying the boundary condition at the model surface. For the same surface temperature, experimental investigations showed that the shock wave angle was lower with the heating element than for the case with the discharge switched on. The results show that surface heating is responsible for roughly 50 % of the shock wave angle increase, meaning that purely plasma effects must also be considered to fully explain the flow modifications observed

Efficiency of plasma actuator ionization in shock wave modification in a rarefied supersonic flow over a flat plate

International audienceThis paper describes experimental and numerical investigations focused on the shock wave modification, induced by a dc glow discharge, of a Mach 2 flow under rarefied regime. The model under investigation is a flat plate equipped with a plasma actuator composed of two electrodes. The glow discharge is generated by applying a negative potential to the upstream electrode, enabling the creation of a weakly ionized plasma. The natural flow (i.e. without the plasma) exhibits a thick laminar boundary layer and a shock wave with a hyperbolic shape. Images of the flow obtained with an ICCD camera revealed that the plasma discharge induces an increase in the shock wave angle. Thermal effects (volumetric, and at the surface) and plasma effects (ionization, and thermal non-equilibrium) are the most relevant processes explaining the observed modifications. The effect induced by the heating of the flat plate surface is studied experimentally by replacing the upstream electrode by a heating element, and numerically by modifying the thermal boundary condition of the model surface. The results show that for a similar temperature distribution over the plate surface, modifications induced by the heating element are lower than those produced by the plasma. This difference shows that other effects than purely thermal effects are involved with the plasma actuator. Measurements of the electron density with a Langmuir probe highlight the fact that the ionization degree plays an important role into the modification of the flow. The gas properties, especially the isentropic exponent, are indeed modified by the plasma above the actuator and upstream the flat plate. This leads to a local modification of the flow conditions, inducing an increase in the shock wave angle

Mach 2 rarefied airflow over a plate submitted to a DC discharge: surface temperature gradient investigation

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Non-equilibrium modeling of UV laser induced plasma on a copper target in the presence of Cu2+

International audienceThis work is a contribution to the understanding of UV laser ablation of a copper sample in the presence of Cu2+ species as well as electronic non-equilibrium in the laser induced plasma. This particular study extends a previous paper and develops a 1D hydrodynamic model to describe the behavior of the laser induced plume, including the thermal non-equilibrium between electrons and heavy particles. Incorporating the formation of doubly charged ions (Cu2+) in such an approach has not been considered previously. We evaluate the effect of the presence of doubly ionized species on the characteristics of the plume, i.e., temperature, pressure, and expansion velocity, and on the material itself by evaluating the ablation depth and plasma shielding effects. This study evaluates the effects of the doubly charged species using a non-equilibrium hydrodynamic approach which comprises a contribution to the understanding of the governing processes of the interaction of ultraviolet nanosecond laser pulses with metals and the parameter optimization depending on the intended application. (C) 2016 AIP Publishing LLC

Laser-Induced Plasma on a Titanium Target, a Non-equilibrium Model

International audienceWe use a comprehensive model to investigate the interaction of ultraviolet nanosecond laser pulses with a titanium material. We calculate plasma ignition thresholds and study the effect of the laser-plasma interaction and the importance of the electronic non-equilibrium in the laser-induced plume and its expansion in the background gas. Our calculations of plasma ignition thresholds on titanium targets are validated and compared with experimental and theoretical results. A comparison with experimental data indicates that our results agree well with those reported in the literature. Results for titanium and copper are also compared under the same conditions. The inclusion of electronic non-equilibrium in our work indicates that this important process must be included in laser ablation and plasma plume formation models