Jean-Denis Parisse

Comparison between Mach 2 rarefied airflow modification by an electrical discharge and numerical simulation of airflow modification by surface heating

This study is devoted to numerical and experimental investigations about the influence of an electrical discharge over a flat plate immersed in a rarefied Mach 2 airflow. Regarding the experimental work, a negative dc discharge is created by applying a potential difference gap between two spanwise aluminum electrodes flush mounted on the plate. The electrode placed close to the leading edge is connected to the negative dc voltage, the second one is grounded. The influence due to the presence of the electric discharge is investigated with a glass Pitot tube by measuring the pressure proles above the flat plate. These experimental results are compared to the numerical work, where the effect of a surface temperature increase is simulated. Different effects can be attributed to the electrical discharge: the ionization of the gas above the plate with the creation of charged species, the acceleration of the positive charged species, the heat of the gas volume above the flat plate, and the heating of the surface...

Laser induced plasma on copper target, a non-equilibrium model

The aim of this work is to present a comprehensive numerical model for the UV laser ablation of metal targets, it focuses mainly on the prediction of laser induced plasma thresholds, 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. This paper describes a set of numerical models for laser-matter interaction between 193-248 and 355 nm lasers and a copper target. Along with the thermal effects inside the material resulting from the irradiation of the latter with the pulsed laser, the laser-evaporated matter interaction and the plasma formation are thoroughly modelled. In the laser induced plume, the electronic nonequilibrium and the laser beam absorption have been investigated. Our calculations of the plasmas ignition thresholds on copper targets have been validated and compared to experimental as well as theoretical results. Comparison with experiment data indicates that our results are in goo...

Modeling and numerical simulation of laser matter interaction and ablation with a 193 nanometer laser for nanosecond pulse

Purpose – The aim of this paper is to develop and validate a model and a numerical code describing the laser matter interaction and also laser ablation. The laser wavelength is 193 nm and the pulse duration is several nanoseconds.Design/methodology/approach – The developed model is based on strong theoretical background (cf. references). The electronic nonequilibrium aspect is always taken into account. The electronic nonequilibrium is one of the key aspect the UV laser matter interaction and must be treated carefully and that is not always the case. The numerical code was developed using efficient and versatile numerical methods. The model and simulations are always compared to experiments in order to validate them and also to find their limitations.Findings – This work has greatly improved the code accuracy. The key role of the electronic nonequilibrium is also demonstrated. From experimental comparisons it is obvious that photo‐ablation should be taken into account for the lower fluences, but to do so,...

Theoretical and numerical study of the interaction of a nanosecond laser pulse with a copper target for laser-induced breakdown spectroscopy applications

This work is a presentation of a modeling approach aimed at describing laser–matter interaction under laser-induced breakdown spectroscopy operating conditions. In order to set up a simple numerical tool to compute our model, only the most relevant processes appearing during the interaction were considered. This allowed us to develop a quick and rather accurate idea about how some physical parameters evolve during the interaction, so that the optimization of the laser beam parameters for better analytical results would be possible. For a basic understanding we used for our numerical computation a nanosecond laser pulse with an ideal Gaussian temporal profile and a pure Cu target. In order to optimize the interaction parameters, this study was focused on the effect of some of the laser parameters such as the wavelength (UV, Vis, IR), the pulse duration, and the irradiation on the results of the interaction. An investigation of the influence of some processes such as the vaporization effects and the plasma shielding was also included. The processes occuring on the material surface were closely examined as well. A comparison between the use of temperature-dependent and temperature-independent optical parameters was conducted, and their influence on the results was investigated. The use of variable optical parameters is revealed to be a means to correct the values of the temperature distribution inside the material and convert them into more realistic ones. Our code was first validated when operating under the same conditions used by other authors, and then it was used to present our proper contributions, as previously stated.

Influence of a plasma actuator on aerodynamic forces over a flat plate interacting with a rarefied Mach 2 flow

Purpose The purpose of this paper is to describe experimental and numerical investigations focussed on the shock wave modification induced by a dc glow discharge. The model is a flat plate in a rarefied Mach 2 air flow, equipped with a plasma actuator composed of two electrodes. The natural flow without actuation exhibits a shock wave with a hyperbolic shape. When the discharge is on, the shock wave shape remains hyperbolic but the shock wave is pushed forward, leading to an increase in the shock wave angle. In order to discriminate thermal effects from purely plasma ones, the plasma actuator is then replaced by an heating element. Design/methodology/approach The experimental study is carried out with the super/hypersonic wind tunnel MARHy located at the ICARE Laboratory in Orleans. The experimental configuration with the heating element is simulated with a code using the 2D full compressible Navier-Stokes equations adapted for the rarefied conditions. Findings For heating element temperatures equal to the flat plate wall surface ones with the discharge on, experimental and numerical investigations showed that the shock wave angle was lower with the heating element, only 50 percent of the values got with the plasma actuator, meaning that purely plasma effects must also be considered to fully explain the flow modifications observed. The results obtained with the numerical simulations are then used to calculate the aerodynamic forces, i.e. the drag and the lift. These numerical results are then extrapolated to the plasma actuator case and it was found that the drag coefficient rises up to 13 percent when the plasma actuator is used, compared to only 5 percent with the heating element. Originality/value This paper matters in the topic of atmospheric entries where flow control, heat management and aerodynamic forces are of huge importance.

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

This 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.

Numerical simulation of air/H2 combustion processes in a scramjet turbulent flow

The aim of this work is to develop a numerical approach, based on the Favres averaged Navier-Stokes equations coupled with a turbulence model and with a complex finite rate Air/Hydrogen combustion kinetic model to simulate the unsteady axisymetric supersonic hydrogen-air mixing processes. The main application is dedicated to the scramjet hypersonic air-breathing propulsion engine. To achieve this goal the Spalart-Allmaras turbulence model (SA) with correction terms to model the compressibility effects and the complete finite rate chemistry model of Jachimowsky involving 13 species and 153 reactions have been implemented in a finite volume code.

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

This 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.

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

AbstractWe 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.

Shock modification induced by a DC discharge: numerical and experimental study

The present work is devoted to the study of the influence of an electrical DC discharge applied over a flat plate subjected to a supersonic and rarefied air flow. The main topic of this paper concerns the 2D Navier-Stokes numerical simulation of the flow developed around the model and submitted to the effects induced by the presence of glow plasma created above the flat plate. Different effects like, surface plate temperature, gas volume temperature and plate geometry, were considered in the numerical simulation and compared with the experimental results obtained in a wind tunnel producing a laminar Mach 2 air flow at ambient pressure equivalent to the 80 km altitude atmospheric pressure.