ANTHONY SPRANNGER ASTUHUAMAN RUIZ - Academia.edu (original) (raw)

Papers by ANTHONY SPRANNGER ASTUHUAMAN RUIZ

47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2011

SSRN Electronic Journal, 2013

In the wake of the Supreme Court's 2009 decision in Arizona v. Gant, lower courts continue to deb... more In the wake of the Supreme Court's 2009 decision in Arizona v. Gant, lower courts continue to debate whether Gant represents an overhaul of the search incident to arrest doctrine or is instead a minor tweak. This Note argues that the answer lies somewhere in the middle. It proposes that courts conduct a more searching inquiry into whether an arrestee has a reasonable possibility of access to the area searched at the time of the search, rather than apply the more lenient standard that some courts have adopted. This middle ground is more faithful to the policy considerations underpinning the search incident to arrest doctrine, while additionally providing the proper balance between officer safety and defendants' rights.

Progress in Propulsion Physics, 2011

In rocket engines, dense oxygen is injected in a high-pressure environment, above its critical pr... more In rocket engines, dense oxygen is injected in a high-pressure environment, above its critical pressure. Oxygen temperature varies from a subcritical value at injection to an SC value in burnt gases. Both the Vulcain 2 engine and Space

(2004). A turbulent jet at a Reynolds Number of 5,000 is injected into a laminar cross flow, with... more (2004). A turbulent jet at a Reynolds Number of 5,000 is injected into a laminar cross flow, with a jet to cross-flow velocity ratio of 5.7. Resolutions are varied from typical engineering spatial and temporal resolutions to near-DNS resolution. The near-DNS resolution has been extensively validated against experimental results in a previous study [Ruiz et al., Phys. Fluid (2014)], which also focused on the evolution of the major scales of turbulence. The grid resolution is coarsened to investigate the impact on the topology of coherent structures and mixing. Fourier analysis is conducted at all resolutions to observe the impact of filtering on the turbulent energy cascade, identify the main hydrodynamic frequencies, and determine the degree to which these are grid-dependent. Once hydrodynamics modes are known, phase-locked analysis of the flow field shows the spatial structure of these modes as a function of resolution. This enables a clear understanding of the impact of resolution on the flow.

Submitted for the DFD14 Meeting of The American Physical Society Destabilization of a liquid-gas ... more Submitted for the DFD14 Meeting of The American Physical Society Destabilization of a liquid-gas interface at supercritical pressure 1 GUILHEM LACAZE, ANTHONY RUIZ, JOSEPH OEFELEIN, Sandia National Laboratories-To improve efficiency, advanced propulsion systems are operated at high pressure. In many cases the pressure exceeds the critical pressure of the fuel and oxidizer, which leads to radical changes in mixing. Even though this transition is understood theoretically, many important questions remain. One is the impact of the strong interfacial density-gradient on destabilization of the shear layer. At these conditions, experimental imaging techniques fail to provide the resolution required for detailed analysis of the flow structures. In this work, we use Large Eddy Simulation to study these structures in a three-dimensional turbulent mixing layer at a Reynolds number of 500,000. A splitter separates streams of liquid oxygen and gaseous hydrogen. In the last decade, similar conditions have been studied using two-dimensional computational domains. This work is the first attempt to simulate a three-dimensional flow at these conditions with this level of resolution. Simulation results provide new insights on the destabilization processes of the liquid interface. Dynamic instabilities leading to turbulence are enhanced by inhomogeneities in density through baroclinic effects and high shear in the interfacial region.

Simulations Numériques Instationnaires de la combustion turbulente et transcritique dans les mote... more Simulations Numériques Instationnaires de la combustion turbulente et transcritique dans les moteurs cryotechniques Ces 50 dernières années, la majorité des paramètres de conception des moteurs cryotechniques ont été ajustés en l'absence d'une compréhension détaillée de la dynamique de flamme, en raison des limites des diagnostiques expérimentaux et des capacités de calcul. L'objectif de cette thèse est de réaliser des simulations numériques instationnaires d'écoulements réactifs transcritiques de haute fidélité, pour permettre une meilleure compréhension de la dynamique de flamme dans les moteurs cryotechniques et finalement guider leur amélioration. Dans un premier temps, la thermodynamique gaz-réel et son impact sur les schémas numériques sont présentés. Comme la Simulation aux Grandes Echelles (SGE) comporte des équations filtrées, les effets de filtrages induits par la thermodynamique gaz-réel sont ensuite mis en évidence dans une configuration transcritique type et un opérateur de diffusion artificiel, spécifique au gaz réel, est proposé pour lisser les gradients transcritiques en SGE. Dans un deuxième temps, une étude fondamentale du mélange turbulent et de la combustion dans la zone proche-injecteur des moteurs cryotechniques est menée grâce à la Simulation Numérique Directe (SND). Dans le cas non-réactif, les lâchers tourbillonnaires dans le sillage de la lèvre de l'injecteur jouent un rôle majeur dans le mélange turbulent et provoquent la formation de structures en peigne déjà observées expérimentalement dans des conditions similaires. Dans le cas réactif, la flamme reste attachée à la lèvre de l'injecteur, sans extinction locale, et les structures en peigne disparaissent. La structure de flamme est analysée et différents modes de combustion sont identifiés. Enfin, une étude de flamme-jet transcritique H 2 /O 2 , accrochée à un injecteur coaxial avec et sans retrait interne, est menée. Les résultats numériques sont d'abord validés par des données expérimentales pour l'injecteur sans retrait. Ensuite, la configuration avec retrait est comparée à la solution de référence sans retrait et à des données experimentales pour observer les effets de ce paramètre de conception sur l'efficacité de combustion.

The numerical simulation of fluid dynamics and combustion in cryogenic rocket engines is addresse... more The numerical simulation of fluid dynamics and combustion in cryogenic rocket engines is addressed in this paper, with the intent to elucidate flame stabilization mechanisms. A model configuration is devised to allow a fully resolved simulation, both for the dynamics and the flame structure: a two-dimensional splitter plate represents the lip of an injector and the operating point is typical of a real engine. The non-reacting flow field is first scrutinized to evaluate the impact of the large density gradients between the fuel (hydrogen) and oxidizer (oxygen) streams. It is found that the turbulence generated by the splitter is very intense and strongly distorts the high-densitygradient front at both small and large scales. Under reacting conditions, the flame stabilizes right at the lip of the injector, which is a common feature of hydrogen / oxygen flames under these conditions. A particularly complex flame structure is evidenced at the anchoring point, with turbulent transport playing an important role.

Proceedings of the Combustion Institute, 2015

ABSTRACT Abstract This article describes a numerical investigation that explores the dynamics of ... more ABSTRACT Abstract This article describes a numerical investigation that explores the dynamics of multiple cryogenic jet flames interacting with high frequency transverse acoustic modes. This research is motivated by the numerous issues associated with high-frequency instabilities in liquid rocket engines. Large eddy simulations are carried out in a complex flow configuration which is turbulent, reactive, transcritical and in the absence or presence of a large-amplitude acoustic motion. The geometry is that of a model scale experimental configuration. Results obtained by exploiting high end computational resources demonstrate the feasibility of such calculations, provide insight in the coupling process, exhibit features which are found in experiments and complement the experimental data. Depending on the acoustic environment (dominated by velocity or pressure oscillations), selective responses of the cryogenic jets and flames can be observed and analyzed. It is found that the flames are more compact when they are made to interact with the transverse acoustic motion and that the dense core length is notably reduced. In the span-wise direction, the flames and dense cores are flattened, a feature which is also found in experiments. The unsteady motion observed experimentally is well retrieved numerically. The simulations highlight the mechanisms that can feed energy in the transverse mode and suggest possible descriptions of the instability driving process. The light methane jet is shaken by the acoustic motion and impacts the dense oxygen stream alternatively on its top and bottom sides. The unsteady heat release rate and the corresponding acoustic Rayleigh term produced by the flames prove to be different according to the flame position regarding the acoustic environment.

Proceedings of the Combustion Institute, 2015

Imaging has long shown that under some high-pressure conditions, the presence of discrete two-pha... more Imaging has long shown that under some high-pressure conditions, the presence of discrete two-phase flow processes becomes diminished. Instead, liquid injection processes transition from classical sprays to dense-fluid jets with no drops present. When and how this transition occurs, however, was not well understood until recently. In this paper, we summarized a new theoretical description that quantifies the effects of real fluid thermodynamics on liquid fuel injection processes as a function of pressure at typical Diesel engine operating conditions. We then apply the Large Eddy Simulation (LES) technique coupled with real-fluid thermodynamics and transport to analyze the flow at conditions when cylinder pressures exceed the thermodynamic critical pressure of the injected fuel. To facilitate the analysis, we use the experimental data posted as part of the Engine Combustion Network (see www.sandia.gov/ECN); namely the "Spray-A" case. Calculations are performed by rigorously treating the experimental operating conditions. Numerical results are in good agreement with available experimental measurements. The high-fidelity simulation is then used to analyze the details of transient mixing and understand the processes leading to auto-ignition. The analysis reveals the profound effect of supercritical fluid phenomena on the instantaneous threedimensional mixing processes. The large density ratio between the supercritical fuel and the ambient gas leads to significant penetration of the jet with enhanced turbulent mixing at the tip and strong entrainment effects. Using detailed chemistry, a map of the auto-ignition delay time was calculated in simulation results. This map shows that a large flammable region with low velocity and mixture gradients is generated 250 diameters downstream of the injector. In the experiment, the first ignition site is observed at this location. This correspondence seems to indicate that the ignition location is piloted by the efficient mixing operating at the extremity of the jet coupled with long residence times, low strain rates and low scalar gradients. Published by Elsevier Inc. on behalf of The Combustion Institute.

SAE International Journal of Engines, 2014

ABSTRACT This paper first summarizes a new theoretical description that quantifies the effects of... more ABSTRACT This paper first summarizes a new theoretical description that quantifies the effects of real-fluid thermodynamics on liquid fuel injection processes as a function of pressure at typical engine operating conditions. It then focuses on the implications this has on modeling such flows with emphasis on application of the Large Eddy Simulation (LES) technique. The theory explains and quantifies the major differences that occur in the jet dynamics compared to that described by classical spray theory in a manner consistent with experimental observations. In particular, the classical view of spray atomization as an appropriate model at some engine operating conditions is questionable. Instead, non-ideal real-fluid behavior must be taken into account using a multicomponent formulation that applies to hydrocarbon mixtures at high-pressure supercritical conditions. To highlight the implications and needs related to modeling, we present a series of studies using LES that focus on experiments being conducted in the high-pressure combustion vessel at Sandia National Laboratories. We extend LES studies performed previously to the Engine Combustion Network (www.sandia.gov/ECN) Spray-H and Spray-A injectors using n-heptane and n-dodecane as the respective fuels. The accompanying analysis reveals the structural characteristics associated with the inherent scalar mixing processes at conditions directly relevant to advanced Diesel engines.

Tetrahedron Letters, 1997

Rou~BP 08,76131 Mont-Saint-Aignancedex(France)Y A6atract:A newN-demethylationreactionof N-methyla... more Rou~BP 08,76131 Mont-Saint-Aignancedex(France)Y A6atract:A newN-demethylationreactionof N-methylaziniumderivativesby using boiling pyidinium chlorideis described.The reactionis quite clean,fast andyieldsare almostquantitative.

Physical Review Letters, 2012

A search for direct pair production of supersymmetric top squarks (t 1) is presented, assuming th... more A search for direct pair production of supersymmetric top squarks (t 1) is presented, assuming thet 1 decays into a top quark and the lightest supersymmetric particle, 0 1 , and that both top quarks decay to purely hadronic final states. A total of 16 (4) events are observed compared to a predicted standard model background of 13:5 þ3:7 À3:6 ð4:4 þ1:7 À1:3 Þ events in two signal regions based on R Ldt ¼ 4:7 fb À1 of pp collision data taken at ffiffi ffi s p ¼ 7 TeV with the ATLAS detector at the LHC. An exclusion region in thet 1 versus 0 1 mass plane is evaluated: 370 < mt 1 < 465 GeV is excluded for m0 1 $ 0 GeV while mt 1 ¼ 445 GeV is excluded for m0 1 50 GeV.

... Acknowledgements This work is generously supported by Snecma, which is the prime contractor f... more ... Acknowledgements This work is generously supported by Snecma, which is the prime contractor for the European launcher Ariane 5 cryogenic propulsion systems and CNES (Centre National d'Etudes Spatiales), which is the ... [14] T. Schmitt, Y. Méry, M. Boileau, and S. Candel ...

The numerical simulation of fluid dynamics and combustion in cryogenic rocket engines is addresse... more The numerical simulation of fluid dynamics and combustion in cryogenic rocket engines is addressed in this paper, with the intent to elucidate flame stabilization mechanisms. A model configuration is devised to allow a fully resolved simulation, both for the dynamics and the flame structure: a twodimensional splitter plate represents the lip of an injector and the operating point is typical of a real engine. The non-reacting flow field is first scrutinized to evaluate the impact of the large density gradients between the fuel (hydrogen) and oxidizer (oxygen) streams. It is found that the turbulence generated by the splitter is very intense and strongly distorts the high-density-gradient front at both small and large scales. Under reacting conditions, the flame stabilizes right at the lip of the injector, which is a common feature of hydrogen / oxygen flames under these conditions. A particularly complex flame structure is evidenced at the anchoring point, with turbulent transport playing an important role.

AIAA Journal, 2010

ABSTRACT This paper presents the numerical computation of a turbulent jet of nitrogen into nitrog... more ABSTRACT This paper presents the numerical computation of a turbulent jet of nitrogen into nitrogen under supercritical pressure. The large-eddy simulation framework for turbulence modeling is used and real-gas effects are accounted for through a cubic equation of state and appropriate viscosity and conductivity coefficients. The purpose of this paper is to evaluate how low-pressure large-eddy simulation equations coupled with real-gas thermodynamics and transport compare with experiments. Although this approach does not take into account the impact of high density gradients and nonlinear thermodynamics on turbulence modeling, the results show reasonable agreement with available experimental data and reveal the importance of numerics for such computations. The simulations indicate a limited influence of the density ratio and the thermodynamic conditions on the jets spreading rate and pseudosimilarity behavior.

47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &amp; Exhibit, 2011

SSRN Electronic Journal, 2013

In the wake of the Supreme Court's 2009 decision in Arizona v. Gant, lower courts continue to deb... more In the wake of the Supreme Court's 2009 decision in Arizona v. Gant, lower courts continue to debate whether Gant represents an overhaul of the search incident to arrest doctrine or is instead a minor tweak. This Note argues that the answer lies somewhere in the middle. It proposes that courts conduct a more searching inquiry into whether an arrestee has a reasonable possibility of access to the area searched at the time of the search, rather than apply the more lenient standard that some courts have adopted. This middle ground is more faithful to the policy considerations underpinning the search incident to arrest doctrine, while additionally providing the proper balance between officer safety and defendants' rights.

Progress in Propulsion Physics, 2011

In rocket engines, dense oxygen is injected in a high-pressure environment, above its critical pr... more In rocket engines, dense oxygen is injected in a high-pressure environment, above its critical pressure. Oxygen temperature varies from a subcritical value at injection to an SC value in burnt gases. Both the Vulcain 2 engine and Space

(2004). A turbulent jet at a Reynolds Number of 5,000 is injected into a laminar cross flow, with... more (2004). A turbulent jet at a Reynolds Number of 5,000 is injected into a laminar cross flow, with a jet to cross-flow velocity ratio of 5.7. Resolutions are varied from typical engineering spatial and temporal resolutions to near-DNS resolution. The near-DNS resolution has been extensively validated against experimental results in a previous study [Ruiz et al., Phys. Fluid (2014)], which also focused on the evolution of the major scales of turbulence. The grid resolution is coarsened to investigate the impact on the topology of coherent structures and mixing. Fourier analysis is conducted at all resolutions to observe the impact of filtering on the turbulent energy cascade, identify the main hydrodynamic frequencies, and determine the degree to which these are grid-dependent. Once hydrodynamics modes are known, phase-locked analysis of the flow field shows the spatial structure of these modes as a function of resolution. This enables a clear understanding of the impact of resolution on the flow.

Submitted for the DFD14 Meeting of The American Physical Society Destabilization of a liquid-gas ... more Submitted for the DFD14 Meeting of The American Physical Society Destabilization of a liquid-gas interface at supercritical pressure 1 GUILHEM LACAZE, ANTHONY RUIZ, JOSEPH OEFELEIN, Sandia National Laboratories-To improve efficiency, advanced propulsion systems are operated at high pressure. In many cases the pressure exceeds the critical pressure of the fuel and oxidizer, which leads to radical changes in mixing. Even though this transition is understood theoretically, many important questions remain. One is the impact of the strong interfacial density-gradient on destabilization of the shear layer. At these conditions, experimental imaging techniques fail to provide the resolution required for detailed analysis of the flow structures. In this work, we use Large Eddy Simulation to study these structures in a three-dimensional turbulent mixing layer at a Reynolds number of 500,000. A splitter separates streams of liquid oxygen and gaseous hydrogen. In the last decade, similar conditions have been studied using two-dimensional computational domains. This work is the first attempt to simulate a three-dimensional flow at these conditions with this level of resolution. Simulation results provide new insights on the destabilization processes of the liquid interface. Dynamic instabilities leading to turbulence are enhanced by inhomogeneities in density through baroclinic effects and high shear in the interfacial region.

Simulations Numériques Instationnaires de la combustion turbulente et transcritique dans les mote... more Simulations Numériques Instationnaires de la combustion turbulente et transcritique dans les moteurs cryotechniques Ces 50 dernières années, la majorité des paramètres de conception des moteurs cryotechniques ont été ajustés en l'absence d'une compréhension détaillée de la dynamique de flamme, en raison des limites des diagnostiques expérimentaux et des capacités de calcul. L'objectif de cette thèse est de réaliser des simulations numériques instationnaires d'écoulements réactifs transcritiques de haute fidélité, pour permettre une meilleure compréhension de la dynamique de flamme dans les moteurs cryotechniques et finalement guider leur amélioration. Dans un premier temps, la thermodynamique gaz-réel et son impact sur les schémas numériques sont présentés. Comme la Simulation aux Grandes Echelles (SGE) comporte des équations filtrées, les effets de filtrages induits par la thermodynamique gaz-réel sont ensuite mis en évidence dans une configuration transcritique type et un opérateur de diffusion artificiel, spécifique au gaz réel, est proposé pour lisser les gradients transcritiques en SGE. Dans un deuxième temps, une étude fondamentale du mélange turbulent et de la combustion dans la zone proche-injecteur des moteurs cryotechniques est menée grâce à la Simulation Numérique Directe (SND). Dans le cas non-réactif, les lâchers tourbillonnaires dans le sillage de la lèvre de l'injecteur jouent un rôle majeur dans le mélange turbulent et provoquent la formation de structures en peigne déjà observées expérimentalement dans des conditions similaires. Dans le cas réactif, la flamme reste attachée à la lèvre de l'injecteur, sans extinction locale, et les structures en peigne disparaissent. La structure de flamme est analysée et différents modes de combustion sont identifiés. Enfin, une étude de flamme-jet transcritique H 2 /O 2 , accrochée à un injecteur coaxial avec et sans retrait interne, est menée. Les résultats numériques sont d'abord validés par des données expérimentales pour l'injecteur sans retrait. Ensuite, la configuration avec retrait est comparée à la solution de référence sans retrait et à des données experimentales pour observer les effets de ce paramètre de conception sur l'efficacité de combustion.

The numerical simulation of fluid dynamics and combustion in cryogenic rocket engines is addresse... more The numerical simulation of fluid dynamics and combustion in cryogenic rocket engines is addressed in this paper, with the intent to elucidate flame stabilization mechanisms. A model configuration is devised to allow a fully resolved simulation, both for the dynamics and the flame structure: a two-dimensional splitter plate represents the lip of an injector and the operating point is typical of a real engine. The non-reacting flow field is first scrutinized to evaluate the impact of the large density gradients between the fuel (hydrogen) and oxidizer (oxygen) streams. It is found that the turbulence generated by the splitter is very intense and strongly distorts the high-densitygradient front at both small and large scales. Under reacting conditions, the flame stabilizes right at the lip of the injector, which is a common feature of hydrogen / oxygen flames under these conditions. A particularly complex flame structure is evidenced at the anchoring point, with turbulent transport playing an important role.

Proceedings of the Combustion Institute, 2015

ABSTRACT Abstract This article describes a numerical investigation that explores the dynamics of ... more ABSTRACT Abstract This article describes a numerical investigation that explores the dynamics of multiple cryogenic jet flames interacting with high frequency transverse acoustic modes. This research is motivated by the numerous issues associated with high-frequency instabilities in liquid rocket engines. Large eddy simulations are carried out in a complex flow configuration which is turbulent, reactive, transcritical and in the absence or presence of a large-amplitude acoustic motion. The geometry is that of a model scale experimental configuration. Results obtained by exploiting high end computational resources demonstrate the feasibility of such calculations, provide insight in the coupling process, exhibit features which are found in experiments and complement the experimental data. Depending on the acoustic environment (dominated by velocity or pressure oscillations), selective responses of the cryogenic jets and flames can be observed and analyzed. It is found that the flames are more compact when they are made to interact with the transverse acoustic motion and that the dense core length is notably reduced. In the span-wise direction, the flames and dense cores are flattened, a feature which is also found in experiments. The unsteady motion observed experimentally is well retrieved numerically. The simulations highlight the mechanisms that can feed energy in the transverse mode and suggest possible descriptions of the instability driving process. The light methane jet is shaken by the acoustic motion and impacts the dense oxygen stream alternatively on its top and bottom sides. The unsteady heat release rate and the corresponding acoustic Rayleigh term produced by the flames prove to be different according to the flame position regarding the acoustic environment.

Proceedings of the Combustion Institute, 2015

Imaging has long shown that under some high-pressure conditions, the presence of discrete two-pha... more Imaging has long shown that under some high-pressure conditions, the presence of discrete two-phase flow processes becomes diminished. Instead, liquid injection processes transition from classical sprays to dense-fluid jets with no drops present. When and how this transition occurs, however, was not well understood until recently. In this paper, we summarized a new theoretical description that quantifies the effects of real fluid thermodynamics on liquid fuel injection processes as a function of pressure at typical Diesel engine operating conditions. We then apply the Large Eddy Simulation (LES) technique coupled with real-fluid thermodynamics and transport to analyze the flow at conditions when cylinder pressures exceed the thermodynamic critical pressure of the injected fuel. To facilitate the analysis, we use the experimental data posted as part of the Engine Combustion Network (see www.sandia.gov/ECN); namely the "Spray-A" case. Calculations are performed by rigorously treating the experimental operating conditions. Numerical results are in good agreement with available experimental measurements. The high-fidelity simulation is then used to analyze the details of transient mixing and understand the processes leading to auto-ignition. The analysis reveals the profound effect of supercritical fluid phenomena on the instantaneous threedimensional mixing processes. The large density ratio between the supercritical fuel and the ambient gas leads to significant penetration of the jet with enhanced turbulent mixing at the tip and strong entrainment effects. Using detailed chemistry, a map of the auto-ignition delay time was calculated in simulation results. This map shows that a large flammable region with low velocity and mixture gradients is generated 250 diameters downstream of the injector. In the experiment, the first ignition site is observed at this location. This correspondence seems to indicate that the ignition location is piloted by the efficient mixing operating at the extremity of the jet coupled with long residence times, low strain rates and low scalar gradients. Published by Elsevier Inc. on behalf of The Combustion Institute.

SAE International Journal of Engines, 2014

ABSTRACT This paper first summarizes a new theoretical description that quantifies the effects of... more ABSTRACT This paper first summarizes a new theoretical description that quantifies the effects of real-fluid thermodynamics on liquid fuel injection processes as a function of pressure at typical engine operating conditions. It then focuses on the implications this has on modeling such flows with emphasis on application of the Large Eddy Simulation (LES) technique. The theory explains and quantifies the major differences that occur in the jet dynamics compared to that described by classical spray theory in a manner consistent with experimental observations. In particular, the classical view of spray atomization as an appropriate model at some engine operating conditions is questionable. Instead, non-ideal real-fluid behavior must be taken into account using a multicomponent formulation that applies to hydrocarbon mixtures at high-pressure supercritical conditions. To highlight the implications and needs related to modeling, we present a series of studies using LES that focus on experiments being conducted in the high-pressure combustion vessel at Sandia National Laboratories. We extend LES studies performed previously to the Engine Combustion Network (www.sandia.gov/ECN) Spray-H and Spray-A injectors using n-heptane and n-dodecane as the respective fuels. The accompanying analysis reveals the structural characteristics associated with the inherent scalar mixing processes at conditions directly relevant to advanced Diesel engines.

Tetrahedron Letters, 1997

Rou~BP 08,76131 Mont-Saint-Aignancedex(France)Y A6atract:A newN-demethylationreactionof N-methyla... more Rou~BP 08,76131 Mont-Saint-Aignancedex(France)Y A6atract:A newN-demethylationreactionof N-methylaziniumderivativesby using boiling pyidinium chlorideis described.The reactionis quite clean,fast andyieldsare almostquantitative.

Physical Review Letters, 2012

A search for direct pair production of supersymmetric top squarks (t 1) is presented, assuming th... more A search for direct pair production of supersymmetric top squarks (t 1) is presented, assuming thet 1 decays into a top quark and the lightest supersymmetric particle, 0 1 , and that both top quarks decay to purely hadronic final states. A total of 16 (4) events are observed compared to a predicted standard model background of 13:5 þ3:7 À3:6 ð4:4 þ1:7 À1:3 Þ events in two signal regions based on R Ldt ¼ 4:7 fb À1 of pp collision data taken at ffiffi ffi s p ¼ 7 TeV with the ATLAS detector at the LHC. An exclusion region in thet 1 versus 0 1 mass plane is evaluated: 370 < mt 1 < 465 GeV is excluded for m0 1 $ 0 GeV while mt 1 ¼ 445 GeV is excluded for m0 1 50 GeV.

... Acknowledgements This work is generously supported by Snecma, which is the prime contractor f... more ... Acknowledgements This work is generously supported by Snecma, which is the prime contractor for the European launcher Ariane 5 cryogenic propulsion systems and CNES (Centre National d'Etudes Spatiales), which is the ... [14] T. Schmitt, Y. Méry, M. Boileau, and S. Candel ...

The numerical simulation of fluid dynamics and combustion in cryogenic rocket engines is addresse... more The numerical simulation of fluid dynamics and combustion in cryogenic rocket engines is addressed in this paper, with the intent to elucidate flame stabilization mechanisms. A model configuration is devised to allow a fully resolved simulation, both for the dynamics and the flame structure: a twodimensional splitter plate represents the lip of an injector and the operating point is typical of a real engine. The non-reacting flow field is first scrutinized to evaluate the impact of the large density gradients between the fuel (hydrogen) and oxidizer (oxygen) streams. It is found that the turbulence generated by the splitter is very intense and strongly distorts the high-density-gradient front at both small and large scales. Under reacting conditions, the flame stabilizes right at the lip of the injector, which is a common feature of hydrogen / oxygen flames under these conditions. A particularly complex flame structure is evidenced at the anchoring point, with turbulent transport playing an important role.

AIAA Journal, 2010

ABSTRACT This paper presents the numerical computation of a turbulent jet of nitrogen into nitrog... more ABSTRACT This paper presents the numerical computation of a turbulent jet of nitrogen into nitrogen under supercritical pressure. The large-eddy simulation framework for turbulence modeling is used and real-gas effects are accounted for through a cubic equation of state and appropriate viscosity and conductivity coefficients. The purpose of this paper is to evaluate how low-pressure large-eddy simulation equations coupled with real-gas thermodynamics and transport compare with experiments. Although this approach does not take into account the impact of high density gradients and nonlinear thermodynamics on turbulence modeling, the results show reasonable agreement with available experimental data and reveal the importance of numerics for such computations. The simulations indicate a limited influence of the density ratio and the thermodynamic conditions on the jets spreading rate and pseudosimilarity behavior.