Pierre Vidal - Academia.edu (original) (raw)

Papers by Pierre Vidal

Research paper thumbnail of Parametric study of a moderate pressure nanosecond discharge to reduce detonation cell width

In a former work, the effect of a volumetric nanosecond discharge at decreasing the detonation ce... more In a former work, the effect of a volumetric nanosecond discharge at decreasing the detonation cell size was demonstrated experimentally. The experiments were performed under non-optimal conditions for plasma homogeneity. The present work is a paremetric study that aims at optimizing these experimental conditions. An electrode system was installed in a tube to produce a double-pulse discharge with high deposited energy ahead of the detonation front. The amplitude of the high-voltage pulses, the gas mixture and pressure were optimized so that the plasma filled the entire interelectrode space. The analysis of the detonation cell size with and without plasma generation was performed via the sooted-plate technique. Production of atoms and radicals in the discharge triggered combustion chemistry and decreased the ignition delay time. At these optimal conditions, the detonation cell size was thus reduced by a factor of 2, while passing through the region of the discharge.

Research paper thumbnail of Modeling detonation in liquid explosives: The effect of the inter-component transfer hypothesis on chemical lengths and critical diameters

Combustion and Flame, 2012

This work discusses the two-component model of reactive fluid-reactants and products-widely imple... more This work discusses the two-component model of reactive fluid-reactants and products-widely implemented for simulating detonation dynamics in condensed explosives. This study analyzes the sensitivity of detonation characteristic lengths to the inter-component heat-transfer hypothesis required to obtain a closed set of governing equations. The slowest and the fastest transfers-isentropic reactants and thermal equilibrium, resp.-are investigated. Earlier studies were restricted to the thermodynamic phase plane and have found a weak effect of the transfer hypothesis on state variables. On the contrary, this analysis considers the chemical kinetic process. A state-sensitive Arrhenius reaction rate and two sets of constitutive parameters are used to generate three types of reaction profiles suited to most one-step energy releases in liquid explosives-specifically, long, balanced or short induction, relative to reaction. The chemical lengths and critical diameters of one-or two-dimensional detonations thus prove to be very sensitive to the transfer hypothesis-specifically much larger with the fastest-as well as to small variations of constitutive parameters. Importantly, the profile type is independent of transfer but not of parameters. Therefore, a pertinent response to a transfer change is to recalibrate the rate time-factor so as to keep constant some reference length, according to the profile type. For inductive or balanced profiles, any length can be used such as the CJ reaction length or the critical diameter. Asymptotic profiles require special attention because their length ratios depend on transfer. Constitutive parameters cannot be used with a transfer hypothesis different from that they were calibrated with. Too large experimental errors or numerically under-resolved calibrations may lead to skewed reaction profiles, and hence erroneous simulations of detonation dynamics. Thus, more accurate constitutive relations and information on steady reaction profiles in detonating liquid explosives are necessary.

Research paper thumbnail of On the possibility of non-dimensionalizing DDT limits and distances

HAL (Le Centre pour la Communication Scientifique Directe), Nov 10, 2021

Research paper thumbnail of Experimental investigation of detonation quenching in non-uniform compositions

Combustion and Flame, Oct 1, 2016

This paper presents an experimental investigation into the dynamical behavior of detonation in no... more This paper presents an experimental investigation into the dynamical behavior of detonation in nonuniform mixtures of propane and oxygen at initial pressure and temperature of 200 mbar and 290 K, respectively, with gradients of initial composition parallel to the direction of detonation propagation. The experiments were carried out in a 50 × 50-mm 2-square section, 665-mm-long, vertical chamber. Filling was made from the chamber top-end by means of a planar, separate injection of the mixture components. The non-uniform distributions in the chamber were then controlled by molecular diffusion with diffusion time defining the composition gradient. A Chapman-Jouguet detonation was smoothly transmitted at the chamber bottom-end from a 3.6-m-long driver tube connected to the chamber. Injection and diffusion were monitored in such a way that the mixture composition at the chamber bottom-end was the same as the uniform composition in the driver tube at ignition time. Fast pressure transducers, sooted plates, Schlieren and CH * chemiluminescence visualizations were used to characterize the longitudinal velocities and cell widths, the front structure, the propagation modes and the quenching mechanisms of detonation. Detonation dynamics was found to depend on the steepness of the composition distribution and on the local and initial values of the equivalence ratio. In particular, a sudden one-dimensional detonation quenching of the multicellular detonation was observed in a lean to leaner distribution with a large gradient, whereas a progressive quenching through marginal propagation was obtained with a small gradient and a lower local equivalence ratio. The quenching mechanisms appear to be controlled by the rates of variation of composition and of detonation characteristic lengths: the faster the rate of change, the more sudden the quenching.

Research paper thumbnail of The Velocity-Entropy invariance theorem: a supplemental property of the Chapman-Jouguet model of planar detonation

HAL (Le Centre pour la Communication Scientifique Directe), Apr 1, 2022

Research paper thumbnail of Detonability enhancement by use of a nanosecond plasma

HAL (Le Centre pour la Communication Scientifique Directe), Jun 19, 2022

Research paper thumbnail of Régimes basse-vitesse de détonations thermonucléaires dans les supernovae de type Ia

Comptes Rendus Mecanique, Dec 1, 2007

Nous étudions les influences du détail du réseau nucléaire et de la divergence de l'écoulement su... more Nous étudions les influences du détail du réseau nucléaire et de la divergence de l'écoulement sur la zone de réaction des détonations thermonucléaires dans le plasma Carbone-Oxygène 50%-50% de température et densité initiales 2 × 10 8 K et 5 × 10 6 g cm −3. Nous montrons que les longueurs idéales de combustion, totale ou intermédiaires, obtenues avec un réseau très détaillé peuvent être 200 fois plus petites qu'avec les réseaux réduits habituellement utilisés et nous identifions deux régimes basse-vitesse de détonations courbes à combustion incomplète.

Research paper thumbnail of Steady rotation of a Mach shock: experimental and numerical evidences

Experiments in Fluids, Mar 18, 2023

This experimental and numerical work reports on the dynamical behaviour of a shock in an inert ga... more This experimental and numerical work reports on the dynamical behaviour of a shock in an inert gas at the concave wall of a hollow circular chamber. The gas in the chamber was air or He + O 2 + 2 Ar at initial pressures p c0 ranging from 2 to 12 kPa and initial temperature T 0 = 288 K. The shock was generated using a detonation driven shock tube. The shock dynamics were characterized through high-speed shadowgraph recordings and high-resolution numerical simulations. For each gas and p c0 , the experiments evidenced the formation of a Mach reflection along the wall and identified a range of initial pressures for which this configuration rotates with constant stem heights and constant velocities larger than those at the chamber entry. The numerical simulations were capable of capturing the dynamics quantitatively. These results extend to inert gases our previous work with a reactive gas for which we reported on the possibility of a steadily rotating overdriven Mach detonation. The steadiness range is narrower with the inert gases, likely because of the smaller initial pressure ratios at the chamber entry and lower support from the subsonic flow behind the shock. The initial support in the reactive case was more efficient because the discontinuities at the chamber entry were self-sustained Chapman-Jouguet detonations. Further investigations of these Mach rotating regimes should rely only on specific experiments and numerical simulations, for example, on the effect of the chamber dimensions, because of the complex non-dimensional formulation of the problem.

Research paper thumbnail of On the relevance of detonation cell regularity and width

HAL (Le Centre pour la Communication Scientifique Directe), Apr 1, 2022

Research paper thumbnail of On non-dimensionalized DDT distances and limits

HAL (Le Centre pour la Communication Scientifique Directe), Nov 10, 2021

Understanding the transition from deflagration to detonation in tubes is one of the oldest motiva... more Understanding the transition from deflagration to detonation in tubes is one of the oldest motivations for studying quasisonic and supersonic combustion waves. The main phenomena that participate in the deflagration and detonation processes, and the transitions from the former to the latter, are qualitatively well understood today [1]. However, each remains a numerical challenge and predicting how they combine in complex reactive flows is currently out of reach. One possibility is to approach particular DDT configurations with simplified macroscopic analyses that aim at bringing out relevant non-dimensional parameters for predicting DDT distances and boundaries.

Research paper thumbnail of Experimental analysis of cellular detonations: a discussion on regularity and three-dimensional patterns

HAL (Le Centre pour la Communication Scientifique Directe), Nov 10, 2021

Research paper thumbnail of Progress in understanding Rotating Detonation Modes

AIAA Scitech 2019 Forum, Jan 6, 2019

Research paper thumbnail of Detonation Generation and Propagation in Homogeneous Liquid Explosives

Journal de physique, May 1, 1995

Research paper thumbnail of Rotating Detonation Regimes in Annular and Hallow Chambers: Experimental Observations

Research paper thumbnail of Steadily-rotating overdriven detonation : experiments vs. GSD modeling

HAL (Le Centre pour la Communication Scientifique Directe), 2019

Research paper thumbnail of Previous and ongoing detonation studies applied to propulsion in Poitiers

HAL (Le Centre pour la Communication Scientifique Directe), 2018

Research paper thumbnail of Steadily-rotating, semi-confined detonation: schlieren, direct-light and chemo-luminescence characterizations

HAL (Le Centre pour la Communication Scientifique Directe), 2018

Research paper thumbnail of Instabilities and efficiencies of continuous rotating detonation in annular chambers with constant or linearly-increasing section

HAL (Le Centre pour la Communication Scientifique Directe), 2018

Research paper thumbnail of Detonation dynamics in a curved chamber for an argon diluted hydrogen-oxygen mixture

HAL (Le Centre pour la Communication Scientifique Directe), 2019

The dynamics of detonation transmission from a straight channel into a curved chamber was investi... more The dynamics of detonation transmission from a straight channel into a curved chamber was investigated as a function of initial pressure using a combined experimental and numerical study. Hi-speed Schlieren and *OH chemiluminescense were used for flow visualization; numerical simulations considered the two-dimensional reactive Euler equations with detailed chemistry. Results show the highly transient sequence of events (i.e. detonation diffraction, re-initiation attempts and wave reflections) that precede the formation of a steadily rotating Mach detonation along the outer wall of the chamber. An increase in pressure, from 15 kPa to 26 kPa, expectedly resulted in detonations that are less sensitive to diffraction. Local quenching of the initial detonation occurred for all pressures considered. The location where this decoupling occurred along the inner wall determined the location where transition from regular reflection to a rather complex wave structure occurred along the outer wall. This complex wave structure includes a steadily rotating Mach detonation (stem), an incident decoupled shock-reaction zone region, and a transverse detonation that propagates in pre-shocked mixture.

Research paper thumbnail of The Sensitivity of Chemical Kinetics with Two Characteristic Lengths of Detonation Dynamics in Homogeneous Gases

International Journal of Energetic Materials and Chemical Propulsion, 2015

Research paper thumbnail of Parametric study of a moderate pressure nanosecond discharge to reduce detonation cell width

In a former work, the effect of a volumetric nanosecond discharge at decreasing the detonation ce... more In a former work, the effect of a volumetric nanosecond discharge at decreasing the detonation cell size was demonstrated experimentally. The experiments were performed under non-optimal conditions for plasma homogeneity. The present work is a paremetric study that aims at optimizing these experimental conditions. An electrode system was installed in a tube to produce a double-pulse discharge with high deposited energy ahead of the detonation front. The amplitude of the high-voltage pulses, the gas mixture and pressure were optimized so that the plasma filled the entire interelectrode space. The analysis of the detonation cell size with and without plasma generation was performed via the sooted-plate technique. Production of atoms and radicals in the discharge triggered combustion chemistry and decreased the ignition delay time. At these optimal conditions, the detonation cell size was thus reduced by a factor of 2, while passing through the region of the discharge.

Research paper thumbnail of Modeling detonation in liquid explosives: The effect of the inter-component transfer hypothesis on chemical lengths and critical diameters

Combustion and Flame, 2012

This work discusses the two-component model of reactive fluid-reactants and products-widely imple... more This work discusses the two-component model of reactive fluid-reactants and products-widely implemented for simulating detonation dynamics in condensed explosives. This study analyzes the sensitivity of detonation characteristic lengths to the inter-component heat-transfer hypothesis required to obtain a closed set of governing equations. The slowest and the fastest transfers-isentropic reactants and thermal equilibrium, resp.-are investigated. Earlier studies were restricted to the thermodynamic phase plane and have found a weak effect of the transfer hypothesis on state variables. On the contrary, this analysis considers the chemical kinetic process. A state-sensitive Arrhenius reaction rate and two sets of constitutive parameters are used to generate three types of reaction profiles suited to most one-step energy releases in liquid explosives-specifically, long, balanced or short induction, relative to reaction. The chemical lengths and critical diameters of one-or two-dimensional detonations thus prove to be very sensitive to the transfer hypothesis-specifically much larger with the fastest-as well as to small variations of constitutive parameters. Importantly, the profile type is independent of transfer but not of parameters. Therefore, a pertinent response to a transfer change is to recalibrate the rate time-factor so as to keep constant some reference length, according to the profile type. For inductive or balanced profiles, any length can be used such as the CJ reaction length or the critical diameter. Asymptotic profiles require special attention because their length ratios depend on transfer. Constitutive parameters cannot be used with a transfer hypothesis different from that they were calibrated with. Too large experimental errors or numerically under-resolved calibrations may lead to skewed reaction profiles, and hence erroneous simulations of detonation dynamics. Thus, more accurate constitutive relations and information on steady reaction profiles in detonating liquid explosives are necessary.

Research paper thumbnail of On the possibility of non-dimensionalizing DDT limits and distances

HAL (Le Centre pour la Communication Scientifique Directe), Nov 10, 2021

Research paper thumbnail of Experimental investigation of detonation quenching in non-uniform compositions

Combustion and Flame, Oct 1, 2016

This paper presents an experimental investigation into the dynamical behavior of detonation in no... more This paper presents an experimental investigation into the dynamical behavior of detonation in nonuniform mixtures of propane and oxygen at initial pressure and temperature of 200 mbar and 290 K, respectively, with gradients of initial composition parallel to the direction of detonation propagation. The experiments were carried out in a 50 × 50-mm 2-square section, 665-mm-long, vertical chamber. Filling was made from the chamber top-end by means of a planar, separate injection of the mixture components. The non-uniform distributions in the chamber were then controlled by molecular diffusion with diffusion time defining the composition gradient. A Chapman-Jouguet detonation was smoothly transmitted at the chamber bottom-end from a 3.6-m-long driver tube connected to the chamber. Injection and diffusion were monitored in such a way that the mixture composition at the chamber bottom-end was the same as the uniform composition in the driver tube at ignition time. Fast pressure transducers, sooted plates, Schlieren and CH * chemiluminescence visualizations were used to characterize the longitudinal velocities and cell widths, the front structure, the propagation modes and the quenching mechanisms of detonation. Detonation dynamics was found to depend on the steepness of the composition distribution and on the local and initial values of the equivalence ratio. In particular, a sudden one-dimensional detonation quenching of the multicellular detonation was observed in a lean to leaner distribution with a large gradient, whereas a progressive quenching through marginal propagation was obtained with a small gradient and a lower local equivalence ratio. The quenching mechanisms appear to be controlled by the rates of variation of composition and of detonation characteristic lengths: the faster the rate of change, the more sudden the quenching.

Research paper thumbnail of The Velocity-Entropy invariance theorem: a supplemental property of the Chapman-Jouguet model of planar detonation

HAL (Le Centre pour la Communication Scientifique Directe), Apr 1, 2022

Research paper thumbnail of Detonability enhancement by use of a nanosecond plasma

HAL (Le Centre pour la Communication Scientifique Directe), Jun 19, 2022

Research paper thumbnail of Régimes basse-vitesse de détonations thermonucléaires dans les supernovae de type Ia

Comptes Rendus Mecanique, Dec 1, 2007

Nous étudions les influences du détail du réseau nucléaire et de la divergence de l'écoulement su... more Nous étudions les influences du détail du réseau nucléaire et de la divergence de l'écoulement sur la zone de réaction des détonations thermonucléaires dans le plasma Carbone-Oxygène 50%-50% de température et densité initiales 2 × 10 8 K et 5 × 10 6 g cm −3. Nous montrons que les longueurs idéales de combustion, totale ou intermédiaires, obtenues avec un réseau très détaillé peuvent être 200 fois plus petites qu'avec les réseaux réduits habituellement utilisés et nous identifions deux régimes basse-vitesse de détonations courbes à combustion incomplète.

Research paper thumbnail of Steady rotation of a Mach shock: experimental and numerical evidences

Experiments in Fluids, Mar 18, 2023

This experimental and numerical work reports on the dynamical behaviour of a shock in an inert ga... more This experimental and numerical work reports on the dynamical behaviour of a shock in an inert gas at the concave wall of a hollow circular chamber. The gas in the chamber was air or He + O 2 + 2 Ar at initial pressures p c0 ranging from 2 to 12 kPa and initial temperature T 0 = 288 K. The shock was generated using a detonation driven shock tube. The shock dynamics were characterized through high-speed shadowgraph recordings and high-resolution numerical simulations. For each gas and p c0 , the experiments evidenced the formation of a Mach reflection along the wall and identified a range of initial pressures for which this configuration rotates with constant stem heights and constant velocities larger than those at the chamber entry. The numerical simulations were capable of capturing the dynamics quantitatively. These results extend to inert gases our previous work with a reactive gas for which we reported on the possibility of a steadily rotating overdriven Mach detonation. The steadiness range is narrower with the inert gases, likely because of the smaller initial pressure ratios at the chamber entry and lower support from the subsonic flow behind the shock. The initial support in the reactive case was more efficient because the discontinuities at the chamber entry were self-sustained Chapman-Jouguet detonations. Further investigations of these Mach rotating regimes should rely only on specific experiments and numerical simulations, for example, on the effect of the chamber dimensions, because of the complex non-dimensional formulation of the problem.

Research paper thumbnail of On the relevance of detonation cell regularity and width

HAL (Le Centre pour la Communication Scientifique Directe), Apr 1, 2022

Research paper thumbnail of On non-dimensionalized DDT distances and limits

HAL (Le Centre pour la Communication Scientifique Directe), Nov 10, 2021

Understanding the transition from deflagration to detonation in tubes is one of the oldest motiva... more Understanding the transition from deflagration to detonation in tubes is one of the oldest motivations for studying quasisonic and supersonic combustion waves. The main phenomena that participate in the deflagration and detonation processes, and the transitions from the former to the latter, are qualitatively well understood today [1]. However, each remains a numerical challenge and predicting how they combine in complex reactive flows is currently out of reach. One possibility is to approach particular DDT configurations with simplified macroscopic analyses that aim at bringing out relevant non-dimensional parameters for predicting DDT distances and boundaries.

Research paper thumbnail of Experimental analysis of cellular detonations: a discussion on regularity and three-dimensional patterns

HAL (Le Centre pour la Communication Scientifique Directe), Nov 10, 2021

Research paper thumbnail of Progress in understanding Rotating Detonation Modes

AIAA Scitech 2019 Forum, Jan 6, 2019

Research paper thumbnail of Detonation Generation and Propagation in Homogeneous Liquid Explosives

Journal de physique, May 1, 1995

Research paper thumbnail of Rotating Detonation Regimes in Annular and Hallow Chambers: Experimental Observations

Research paper thumbnail of Steadily-rotating overdriven detonation : experiments vs. GSD modeling

HAL (Le Centre pour la Communication Scientifique Directe), 2019

Research paper thumbnail of Previous and ongoing detonation studies applied to propulsion in Poitiers

HAL (Le Centre pour la Communication Scientifique Directe), 2018

Research paper thumbnail of Steadily-rotating, semi-confined detonation: schlieren, direct-light and chemo-luminescence characterizations

HAL (Le Centre pour la Communication Scientifique Directe), 2018

Research paper thumbnail of Instabilities and efficiencies of continuous rotating detonation in annular chambers with constant or linearly-increasing section

HAL (Le Centre pour la Communication Scientifique Directe), 2018

Research paper thumbnail of Detonation dynamics in a curved chamber for an argon diluted hydrogen-oxygen mixture

HAL (Le Centre pour la Communication Scientifique Directe), 2019

The dynamics of detonation transmission from a straight channel into a curved chamber was investi... more The dynamics of detonation transmission from a straight channel into a curved chamber was investigated as a function of initial pressure using a combined experimental and numerical study. Hi-speed Schlieren and *OH chemiluminescense were used for flow visualization; numerical simulations considered the two-dimensional reactive Euler equations with detailed chemistry. Results show the highly transient sequence of events (i.e. detonation diffraction, re-initiation attempts and wave reflections) that precede the formation of a steadily rotating Mach detonation along the outer wall of the chamber. An increase in pressure, from 15 kPa to 26 kPa, expectedly resulted in detonations that are less sensitive to diffraction. Local quenching of the initial detonation occurred for all pressures considered. The location where this decoupling occurred along the inner wall determined the location where transition from regular reflection to a rather complex wave structure occurred along the outer wall. This complex wave structure includes a steadily rotating Mach detonation (stem), an incident decoupled shock-reaction zone region, and a transverse detonation that propagates in pre-shocked mixture.

Research paper thumbnail of The Sensitivity of Chemical Kinetics with Two Characteristic Lengths of Detonation Dynamics in Homogeneous Gases

International Journal of Energetic Materials and Chemical Propulsion, 2015