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Pineau Pierre - One of the best experts on this subject based on the ideXlab platform.
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Temperature Effects on Convection Speed and Steepened Waves of Temporally Developing Supersonic Jets
'American Institute of Aeronautics and Astronautics (AIAA)', 2020Co-Authors: Pineau Pierre, Bogey ChristopheAbstract:International audienceTemperature effects on the convection speed of large-scale structures in supersonic temporally-1 developing jets and on the steepened aspect of the acoustic waves generated by these structures 2 are investigated. For that, one isothermal jet at Mach 2 and four others at static temperatures 3 equal to 2 or 4 times that of the ambient medium are simulated at either the same exit velocity 4 or Mach Number as the isothermal jet. For all temporally-developing jets, steepened acoustic 5 waves are emitted in the near field, leading to significant values of the pressure skewness and 6 kurtosis factors. Using conditional averages, their formation is directly linked to the supersonic 7 motion of large-scale structures at a convection speed whose ratio with the jet velocity is shown 8 to decrease with temperature. At a higher temperature, this leads to the generation of less 9 skewed acoustic waves for a Constant jet velocity. For a Constant Mach Number, however, this 10 decrease is compensated by the rise of the jet speed, leading to steeper acoustic waves at a 11 higher temperature. Therefore, the modification of the steepened aspect of near-field acoustic 12 waves appears to be related to the change in the convection speed in both cases. 13 Nomenclature 14 T = temperature p = pressure ρ = density u = velocity a = speed of sound M = Mach Number F = Net thrust m = Mass flow rate µ = dynamic viscosity ν = kinematic viscosity * PhD, post-doctoral fellow at CNES, pierre.pineau@doctorant.ec-lyon.fr † CNRS Research Scientist, AIAA senior member r s = specific ideal gas Constant γ = ratio of specific heats r = radial coordinate θ = azimuthal coordinate z = axial coordinate t = time ∆r = radial mesh spacing ∆θ = azimuthal resolution ∆z = axial mesh spacing D = jet diameter r 0 = jet radius Re D = diameter-based Reynolds Number δ θ = shear-layer momentum thickness δ θ = momentum thickness growth rate δ θ,inc = momentum thickness growth rate for an incompressible mixing layer δ 05 = jet half-width α = Mach wave radiation angle Subscripts ∞ = ambient quantity j = initial value of the jet parameters c = potential core closure axis = centerline quantity cond = conditionally averaged trig = conditional averages trigge
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Temperature effects on the generation of steepened waves by supersonic temporal round jets
'American Institute of Aeronautics and Astronautics (AIAA)', 2019Co-Authors: Pineau Pierre, Bogey ChristopheAbstract:International audienceNumerical simulations of temporally-developing round jets at a diameter-based Reynolds Number of 12,500 are carried out with the aim of investigating temperature effects on the formation of the steepened acoustic waves usually associated with crackle noise. One isothermal and four hot jets at a static temperature equal to 2 or 4 times that of the ambient medium are considered. The isothermal jet has a Mach Number of 2 while the hot jets have either the same Mach Number or the same jet speed as the isothermal jet. At a Constant Mach Number, the pressure levels and skewness factors are higher at a higher temperature, indicating a more pronounced steepened aspect of the acoustic waves. This increase is due to the rise of the jet speed from 2 to 4 times the ambient sound speed in that case. When the jet velocity is Constant, lower pressure levels are obtained at a higher temperature, and a slight reduction of the skewness factor is observed. This reduction is explained by the decrease of the ratio between the convection speed and the jet velocity with temperature. The present study thus allows us to isolate the effects of temperature on the generation of steepened waves near high-speed free shear flows
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Etude numérique de la production et de la propagation d'ondes non linéaires dans les jets supersoniques
HAL CCSD, 2018Co-Authors: Pineau PierreAbstract:Numerical simulations are carried out with the aim of investigating the formation of nonlinear steepened waves at the origin of crackle in the near acoustic field of supersonic jets. In these simulations, the compressible Navier-Stokes equations are solved in cylindrical coordinates using high-order low-dissipative and low-dispersive finite difference schemes.Four temporally-developing isothermal round jets are first simulated at Mach Numbers of~2 and~3 and at Reynolds Numbers ranging from 3,125 to 50,000. Strong acoustic waves containing sharp pressure variations are observed in the vicinity of the jets. Their formation process is described by the computation of conditional averages which are triggered by the detection of strong pressure peaks in the near field. Such steepened waves are then shown to be produced by the supersonic motion of coherent structures inside the jet shear layers.Temperature effects are then investigated by considering five temporal round jets at temperature ratios of 1, 2 and~4 and at acoustic Mach Numbers of 2, 2.8 and 4. For a given jet speed, the sound levels produced by the hot jets are lower than those of the isothermal one. However, the properties of the steepened waves they generate are not significantly affected by a rise of temperature. On the contrary, when the Mach Number is held Constant, pressure levels are higher at high temperature. The skewness and kurtosis factors of pressure fluctuations are also increased, which indicates a strengthening of the asymmetry and the intermittency of the pressure fluctuations. It is likely that the influence of temperature on these waves results from the variations of the convection speed, which is found to significantly increase with temperature at Constant Mach Number, but to slightly decrease at Constant jet speed.Finally, three simulations of spatially-developing axisymmetric, isothermal and hot jets at a Mach Number of~2 and at Reynolds Numbers of 12500 and 50000 are performed. Strong Mach waves possessing the distinctive features of crackle are visible in the near vicinity of the jets. As observed for temporal simulations, their formations are associated with the supersonic motion of large-scale coherent structures inside the jet shear layers. The far acoustic field is determined using linear as well as nonlinear extrapolation methods. When nonlinear propagation effects are taken into account, a further steepening of the wavefronts is observed with increasing propagation distance.Dans ce travail de thèse, les mécanismes à l'origine de la formation des chocs associés à la perception de crackle proche de jets supersoniques axisymétriques sont étudiés à l'aide de simulations numériques. Dans ces simulations, les équations de Navier-Stokes instationnaires et compressibles sont résolues en coordonnées cylindriques à l'aide de différences finies d'ordre élevé peu dissipatives et peu dispersives. Quatre jets temporels à des nombres de Mach de 2 et~3 et à des nombres de Reynolds compris entre 3125 et 50000 sont simulés dans un premier temps. Des ondes acoustiques de forte amplitude présentant d'importants gradients de pression sont mises en évidence à proximité des jets. Elles se forment par un mécanisme de raidissement à la source qui est étudié par le calcul de moyennes conditionnelles synchronisées autour des pics de pression en champ proche. Ces moyennes montrent un lien direct entre ces ondes non linéaires et la convection de structures cohérentes à desvitesses supersoniques dans les couches de~mélange. L'influence de la température sur la formation de ces ondes est examinée dans un second temps par le calcul de cinq jets temporels à des rapports de température de 1, 2 et 4, et à des nombres de Mach acoustique compris entre 2 et 4. À vitesse d'éjection Constante, les niveaux de bruit produits par les jets chauds sont moins élevés que ceux du jet isotherme, mais les ondes non linéaires qu'ils rayonnent sont peu affectées par une hausse de température. À nombre de Mach Constant, les niveaux augmentent avec la température, de même que l'asymétrie des fluctuations de pression, traduisant un renforcement du caractère non linéaire des ondes rayonnées. Ces variations pourraient être dues à celles de la vitesse de convection des structures cohérentes, qui augmente de façon significative avec la température lorsque le nombre de Mach est Constant, mais diminue légèrement à vitesse~Constante. Finalement, trois simulations de jets spatiaux isothermes et chauds à un nombre de Mach acoustique de 2 et à des nombres de Reynolds de 12500 et 50000 sont mises en \oe uvre. Des ondes de Mach présentant d'importants gradients de pression sont visibles au voisinage direct des jets. La formation de ces ondes est liée, comme dans le cas des jets temporels, à la convection supersonique de structures cohérentes dans les couches de mélange. Le champ lointain acoustique est enfin déterminé par des méthodes d'extrapolation linéaire et non linéaire. Lorsque la propagation est non linéaire, un raidissement additionnel des fronts d'onde est constaté en champ lointain
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Numerical study of the generation and propagation of nonlinear acoustic waves in supersonic jets
2018Co-Authors: Pineau PierreAbstract:Dans ce travail de thèse, les mécanismes à l'origine de la formation des chocs associés à la perception de crackle proche de jets supersoniques axisymétriques sont étudiés à l'aide de simulations numériques. Dans ces simulations, les équations de Navier-Stokes instationnaires et compressibles sont résolues en coordonnées cylindriques à l'aide de différences finies d'ordre élevé peu dissipatives et peu dispersives. Quatre jets temporels à des nombres de Mach de 2 et~3 et à des nombres de Reynolds compris entre 3125 et 50000 sont simulés dans un premier temps. Des ondes acoustiques de forte amplitude présentant d'importants gradients de pression sont mises en évidence à proximité des jets. Elles se forment par un mécanisme de raidissement à la source qui est étudié par le calcul de moyennes conditionnelles synchronisées autour des pics de pression en champ proche. Ces moyennes montrent un lien direct entre ces ondes non linéaires et la convection de structures cohérentes à desvitesses supersoniques dans les couches de~mélange. L'influence de la température sur la formation de ces ondes est examinée dans un second temps par le calcul de cinq jets temporels à des rapports de température de 1, 2 et 4, et à des nombres de Mach acoustique compris entre 2 et 4. À vitesse d'éjection Constante, les niveaux de bruit produits par les jets chauds sont moins élevés que ceux du jet isotherme, mais les ondes non linéaires qu'ils rayonnent sont peu affectées par une hausse de température. À nombre de Mach Constant, les niveaux augmentent avec la température, de même que l'asymétrie des fluctuations de pression, traduisant un renforcement du caractère non linéaire des ondes rayonnées. Ces variations pourraient être dues à celles de la vitesse de convection des structures cohérentes, qui augmente de façon significative avec la température lorsque le nombre de Mach est Constant, mais diminue légèrement à vitesse~Constante. Finalement, trois simulations de jets spatiaux isothermes et chauds à un nombre de Mach acoustique de 2 et à des nombres de Reynolds de 12500 et 50000 sont mises en \oe uvre. Des ondes de Mach présentant d'importants gradients de pression sont visibles au voisinage direct des jets. La formation de ces ondes est liée, comme dans le cas des jets temporels, à la convection supersonique de structures cohérentes dans les couches de mélange. Le champ lointain acoustique est enfin déterminé par des méthodes d'extrapolation linéaire et non linéaire. Lorsque la propagation est non linéaire, un raidissement additionnel des fronts d'onde est constaté en champ lointain.Numerical simulations are carried out with the aim of investigating the formation of nonlinear steepened waves at the origin of crackle in the near acoustic field of supersonic jets. In these simulations, the compressible Navier-Stokes equations are solved in cylindrical coordinates using high-order low-dissipative and low-dispersive finite difference schemes.Four temporally-developing isothermal round jets are first simulated at Mach Numbers of~2 and~3 and at Reynolds Numbers ranging from 3,125 to 50,000. Strong acoustic waves containing sharp pressure variations are observed in the vicinity of the jets. Their formation process is described by the computation of conditional averages which are triggered by the detection of strong pressure peaks in the near field. Such steepened waves are then shown to be produced by the supersonic motion of coherent structures inside the jet shear layers.Temperature effects are then investigated by considering five temporal round jets at temperature ratios of 1, 2 and~4 and at acoustic Mach Numbers of 2, 2.8 and 4. For a given jet speed, the sound levels produced by the hot jets are lower than those of the isothermal one. However, the properties of the steepened waves they generate are not significantly affected by a rise of temperature. On the contrary, when the Mach Number is held Constant, pressure levels are higher at high temperature. The skewness and kurtosis factors of pressure fluctuations are also increased, which indicates a strengthening of the asymmetry and the intermittency of the pressure fluctuations. It is likely that the influence of temperature on these waves results from the variations of the convection speed, which is found to significantly increase with temperature at Constant Mach Number, but to slightly decrease at Constant jet speed.Finally, three simulations of spatially-developing axisymmetric, isothermal and hot jets at a Mach Number of~2 and at Reynolds Numbers of 12500 and 50000 are performed. Strong Mach waves possessing the distinctive features of crackle are visible in the near vicinity of the jets. As observed for temporal simulations, their formations are associated with the supersonic motion of large-scale coherent structures inside the jet shear layers. The far acoustic field is determined using linear as well as nonlinear extrapolation methods. When nonlinear propagation effects are taken into account, a further steepening of the wavefronts is observed with increasing propagation distance
A. N. Kucherov - One of the best experts on this subject based on the ideXlab platform.
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Acceleration of the Flow and Increase in the Enthalpy in an Ionized Gas Source by an Electric Field in the Constant Mach Number Regime
Technical Physics, 2018Co-Authors: A. N. KucherovAbstract:The possibility of passing from some characteristic physical parameters (stagnation enthalpy, temperature, pressure, density, etc.) to other preset parameters is investigated within the problem of control over a radial source (vortex) in the regime of the Mach Number maintained Constant by energy input and an external force (radial electric field in the given case). The variations of the total enthalpy upon the variation of the energy- and force-similarity parameters are demonstrated in the case when the force per unit mass and per unit volume is specified for identical convection current and conduction current, as well as for a conducting current prevailing over the convection current, and vice versa. In the limit of a negligibly small convection current or a conduction current, a transition to analytic solutions is demonstrated for the case of a purely energy action and a purely force action. Analytic dependences of the velocity increment (kinetic energy), temperature, and total enthalpy on the intensities of the external force and energy input, on the Mach Number, and on the length of the zone of action are obtained.
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combined energy power action on a source in the Constant Mach Number regime with the given external force
Technical Physics, 2017Co-Authors: A. N. KucherovAbstract:Combined action on a source that flows into a submerged area or vacuum in the Constant Mach Number regime has been studied. The action by an external force has been defined with a Constant distribution function (the force is given per unit volume) and with a distribution function proportional to the gas density (the force is given per unit mass). The investigations have been carried out for cylindrical and spherical sources. Similarity and differences, advantages and drawbacks of the above-mentioned cases and variants have been analyzed. It has been shown that the enthalpy increases significantly in subsonic flow (for the Mach Number smaller than unity) by several times in the cylindrical source and by more than an order of magnitude in the spherical source. The total enthalpy increment increases with the length of the action zone or with the coordinate of the closing section.
Yuan Liu - One of the best experts on this subject based on the ideXlab platform.
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numerical investigation of hypersonic curved shock two dimensional inlet designed on the wall Constant Mach Number gradient
48th AIAA ASME SAE ASEE Joint Propulsion Conference & Exhibit, 2012Co-Authors: Lin Zhang, Kunyuan Zhang, Lei Wang, Yuan LiuAbstract:A new hypersonic curved shock two-dimensional inlet has been designed on the compression wall Constant Mach Number gradient, which is compared with the normal three wedges compression two-dimensional inlet designed under the identical conditions. Numerical results show that the curved compression system can be designed through method of characteristic according to the given wall Constant Mach Number gradient and pressure ratio. Compared with the normal three wedges compression inlet, the external compression of curved shock inlet has more stable boundary layer and shorter length to some extent. The performance parameters of new inlet are not very sensitive to the change of inflow Mach Number. In particular, the new inlet has an excellent performance at off-design conditions. More detailed investigation should be made on the new curved shock compression inlet.
Bogey Christophe - One of the best experts on this subject based on the ideXlab platform.
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Temperature Effects on Convection Speed and Steepened Waves of Temporally Developing Supersonic Jets
'American Institute of Aeronautics and Astronautics (AIAA)', 2020Co-Authors: Pineau Pierre, Bogey ChristopheAbstract:International audienceTemperature effects on the convection speed of large-scale structures in supersonic temporally-1 developing jets and on the steepened aspect of the acoustic waves generated by these structures 2 are investigated. For that, one isothermal jet at Mach 2 and four others at static temperatures 3 equal to 2 or 4 times that of the ambient medium are simulated at either the same exit velocity 4 or Mach Number as the isothermal jet. For all temporally-developing jets, steepened acoustic 5 waves are emitted in the near field, leading to significant values of the pressure skewness and 6 kurtosis factors. Using conditional averages, their formation is directly linked to the supersonic 7 motion of large-scale structures at a convection speed whose ratio with the jet velocity is shown 8 to decrease with temperature. At a higher temperature, this leads to the generation of less 9 skewed acoustic waves for a Constant jet velocity. For a Constant Mach Number, however, this 10 decrease is compensated by the rise of the jet speed, leading to steeper acoustic waves at a 11 higher temperature. Therefore, the modification of the steepened aspect of near-field acoustic 12 waves appears to be related to the change in the convection speed in both cases. 13 Nomenclature 14 T = temperature p = pressure ρ = density u = velocity a = speed of sound M = Mach Number F = Net thrust m = Mass flow rate µ = dynamic viscosity ν = kinematic viscosity * PhD, post-doctoral fellow at CNES, pierre.pineau@doctorant.ec-lyon.fr † CNRS Research Scientist, AIAA senior member r s = specific ideal gas Constant γ = ratio of specific heats r = radial coordinate θ = azimuthal coordinate z = axial coordinate t = time ∆r = radial mesh spacing ∆θ = azimuthal resolution ∆z = axial mesh spacing D = jet diameter r 0 = jet radius Re D = diameter-based Reynolds Number δ θ = shear-layer momentum thickness δ θ = momentum thickness growth rate δ θ,inc = momentum thickness growth rate for an incompressible mixing layer δ 05 = jet half-width α = Mach wave radiation angle Subscripts ∞ = ambient quantity j = initial value of the jet parameters c = potential core closure axis = centerline quantity cond = conditionally averaged trig = conditional averages trigge
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Temperature effects on the generation of steepened waves by supersonic temporal round jets
'American Institute of Aeronautics and Astronautics (AIAA)', 2019Co-Authors: Pineau Pierre, Bogey ChristopheAbstract:International audienceNumerical simulations of temporally-developing round jets at a diameter-based Reynolds Number of 12,500 are carried out with the aim of investigating temperature effects on the formation of the steepened acoustic waves usually associated with crackle noise. One isothermal and four hot jets at a static temperature equal to 2 or 4 times that of the ambient medium are considered. The isothermal jet has a Mach Number of 2 while the hot jets have either the same Mach Number or the same jet speed as the isothermal jet. At a Constant Mach Number, the pressure levels and skewness factors are higher at a higher temperature, indicating a more pronounced steepened aspect of the acoustic waves. This increase is due to the rise of the jet speed from 2 to 4 times the ambient sound speed in that case. When the jet velocity is Constant, lower pressure levels are obtained at a higher temperature, and a slight reduction of the skewness factor is observed. This reduction is explained by the decrease of the ratio between the convection speed and the jet velocity with temperature. The present study thus allows us to isolate the effects of temperature on the generation of steepened waves near high-speed free shear flows
M. El Haj Assad - One of the best experts on this subject based on the ideXlab platform.
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Thermodynamic performance of an irreversible MHD power cycle running at Constant Mach Number
International Journal of Ambient Energy, 2008Co-Authors: M. El Haj AssadAbstract:SYNOPSIS In this work an analysis is carried out of a magnetohydrodynamic (MHD) power plant with an MHD generator operating at Constant Mach Number. The model takes into account the internal irreversibilities of the compressor and MHD generator. General expressions for power output and power density are obtained and compared with the maximum power output and maximum power density, respectively. The thermal efficiency at maximum power output and maximum power density are also obtained. The results show that the use of power density criteria improves effectively the MHD power plant efficiency. It is shown that operating the MHD generator at lower Mach Number improves the maximum thermal efficiency and the thermal efficiency at the maximum power output and maximum power density.