The Experts below are selected from a list of 17892 Experts worldwide ranked by ideXlab platform
Zoran Stokic - One of the best experts on this subject based on the ideXlab platform.
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optimization of gravity flow discharge chutes under the speed dependent resisting forces maximizing Exit Velocity
Powder Technology, 2015Co-Authors: Slavisa Salinic, Aleksandar Obradovic, Srdjan Rusov, Zoran Mitrovic, Zoran StokicAbstract:Using the optimal control theory, the problem of finding profiles of gravity flow discharge chutes required to achieve maximum Exit Velocity of granular material under the speed dependent resisting forces is solved. A model of a particle moving down a curve which is treated as a unilateral constraint is used. The fast flow condition and the condition that the particle does not leave the curve are introduced as the additional inequality constraints. The influence of the initial particle speed and the power of the speed in the expression for the resisting force on the optimal chute profile are analyzed.
Christophe Bogey - One of the best experts on this subject based on the ideXlab platform.
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Effects of nozzle-Exit boundary-layer profile on the initial shear-layer instability, flow field and noise of subsonic jets
Journal of Fluid Mechanics, 2019Co-Authors: Christophe Bogey, Roberto SabatiniAbstract:The influence of the nozzle-Exit boundary-layer profile on high-subsonic jets is investigated by performing compressible large-eddy simulations (LES) for three isothermal jets at a Mach number of 0.9 and a diameter-based Reynolds number of $5\times 10^{4}$ , and by conducting linear stability analyses from the mean-flow fields. At the Exit section of a pipe nozzle, the jets exhibit boundary layers of momentum thickness of approximately 2.8 % of the nozzle radius and a peak value of turbulence intensity of 6 %. The boundary-layer shape factors, however, vary and are equal to 2.29, 1.96 and 1.71. The LES flow and sound fields differ significantly between the first jet with a laminar mean Exit Velocity profile and the two others with transitional profiles. They are close to each other in these two cases, suggesting that similar results would also be obtained for a jet with a turbulent profile. For the two jets with non-laminar profiles, the instability waves in the near-nozzle region emerge at higher frequencies, the mixing layers spread more slowly and contain weaker low-frequency Velocity fluctuations and the noise levels in the acoustic field are lower by 2–3 dB compared to the laminar case. These trends can be explained by the linear stability analyses. For the laminar boundary-layer profile, the initial shear-layer instability waves are most strongly amplified at a momentum-thickness-based Strouhal number $St_{\unicode[STIX]{x1D703}}=0.018$ , which is very similar to the value obtained downstream in the mixing-layer Velocity profiles. For the transitional profiles, on the contrary, they predominantly grow at higher Strouhal numbers, around $St_{\unicode[STIX]{x1D703}}=0.026$ and 0.032, respectively. As a consequence, the instability waves rapidly vanish during the boundary-layer/shear-layer transition in the latter cases, but continue to grow over a large distance from the nozzle in the former case, leading to persistent large-scale coherent structures in the mixing layers for the jet with a laminar Exit Velocity profile.
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on the spectra of nozzle Exit Velocity disturbances in initially nominally turbulent transitional jets
Physics of Fluids, 2011Co-Authors: Christophe Bogey, Olivier Marsden, Christophe BaillyAbstract:In a recent paper by C. Bogey, O. Marsden, and C. Bailly [“Large-eddy simulation of the flow and acoustic fields of a Reynolds number 105 subsonic jet with tripped Exit boundary layers,” Phys. Fluids 23(3), 035104 (2011)], simulation results were presented for round jets with tripped boundary layers, displaying nozzle-Exit conditions typical of initially nominally turbulent, transitional jets, namely laminar mean Velocity profiles and high fluctuation intensities. The Velocity spectra evaluated just downstream of the nozzle Exit are re-examined here with respect to literature data. They agree qualitatively very well with spectra obtained in a fully turbulent pipe flow using direct numerical simulation. The wave numbers dominating in the azimuthal direction are also consistent with measurements of spanwise energy distribution in fully turbulent boundary layers. The initial turbulent structures in the jets, therefore, appear to be organized similarly to those in fully developed wall-bounded flows.
Slavisa Salinic - One of the best experts on this subject based on the ideXlab platform.
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optimization of gravity flow discharge chutes under the speed dependent resisting forces maximizing Exit Velocity
Powder Technology, 2015Co-Authors: Slavisa Salinic, Aleksandar Obradovic, Srdjan Rusov, Zoran Mitrovic, Zoran StokicAbstract:Using the optimal control theory, the problem of finding profiles of gravity flow discharge chutes required to achieve maximum Exit Velocity of granular material under the speed dependent resisting forces is solved. A model of a particle moving down a curve which is treated as a unilateral constraint is used. The fast flow condition and the condition that the particle does not leave the curve are introduced as the additional inequality constraints. The influence of the initial particle speed and the power of the speed in the expression for the resisting force on the optimal chute profile are analyzed.
A L Winfrey - One of the best experts on this subject based on the ideXlab platform.
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optimization of capillary source geometry for maximum pellet Exit Velocity in electrothermal plasma launchers
International Conference on Plasma Science, 2014Co-Authors: M J Esmond, Sanaz Mostaghim, T E Gebhart, A L WinfreyAbstract:Deep fueling for large-scale tokamak fusion reactors requires the use of high-Velocity fuel pellet injectors. The fuel pellets consist of deuterium or deuterium-tritium ice. Electrothermal plasma guns can be used to launch fuel pellets into the fusion plasma at a range of velocities. The plasma guns can be used to launch pellets at the velocities required for fusion reactor deep fueling or for the control of edge localized modes.
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optimization of capillary source geometry for maximum pellet Exit Velocity in electrothermal plasma launchers
IEEE Symposium on Fusion Engineering, 2013Co-Authors: M J Esmond, A L WinfreyAbstract:Deep fueling for large-scale tokamak fusion reactors requires the use of high-Velocity pellet injectors. The fuel pellets consist of frozen deuterium or deuterium-tritium ice. A fuel pellet must be launched into the fusion plasma at a high enough Velocity to reach the core of the plasma before too much of the pellet melts, ablates and disintegrates. For tokamak fusion reactors, the fusion plasma is predicted to operate at temperatures of up to 15×107 °C at its core. At these extreme temperatures, the fuel pellets need to be launched at large velocities to prevent excessive melting and vaporization before reaching the core of the plasma. Obtaining this Exit Velocity is possible through the use of electrothermal (ET) plasma guns. Electrothermal plasma guns use a capillary tube where plasma is sparked inside the source and is allowed to continue travelling in an extension acceleration barrel. The plasma is sparked inside the source via the discharge of a capacitor bank that is charged up to 10 kV or higher. A liner material inside the source is ablated and forms plasma that draws discharge current (several kA) over 100 microseconds and can propel a pellet to velocities exceeding 3 km/s. Using a 1-D time-dependent computer code, a variety of computational predictions can be made on the plasma, as well as the pellet, as it moves through the barrel until it leaves towards the fusion core. Characteristics of different geometric configurations of the plasma gun can be simulated using the code to predict the optimal geometric configuration that will maximize the pellet's Exit Velocity. Previous research studies have been conducted by varying the length of the acceleration barrel and computing the effect on the pellet's Exit Velocity. In the present research, to complement the prior studies, the one dimensional computer code, ETFLOW, was used to simulate the effect of varying the source geometry, i.e. length, radius, and aspect ratio, on the pellet's Exit Velocity. For optimal geometries, pellet Exit velocities of up to 3.9 km/s were computed. This is an increase of nearly 12% from previous computational studies. Computed pellet velocities are correlated to source geometry and plasma parameters.
Roberto Sabatini - One of the best experts on this subject based on the ideXlab platform.
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Effects of nozzle-Exit boundary-layer profile on the initial shear-layer instability, flow field and noise of subsonic jets
Journal of Fluid Mechanics, 2019Co-Authors: Christophe Bogey, Roberto SabatiniAbstract:The influence of the nozzle-Exit boundary-layer profile on high-subsonic jets is investigated by performing compressible large-eddy simulations (LES) for three isothermal jets at a Mach number of 0.9 and a diameter-based Reynolds number of $5\times 10^{4}$ , and by conducting linear stability analyses from the mean-flow fields. At the Exit section of a pipe nozzle, the jets exhibit boundary layers of momentum thickness of approximately 2.8 % of the nozzle radius and a peak value of turbulence intensity of 6 %. The boundary-layer shape factors, however, vary and are equal to 2.29, 1.96 and 1.71. The LES flow and sound fields differ significantly between the first jet with a laminar mean Exit Velocity profile and the two others with transitional profiles. They are close to each other in these two cases, suggesting that similar results would also be obtained for a jet with a turbulent profile. For the two jets with non-laminar profiles, the instability waves in the near-nozzle region emerge at higher frequencies, the mixing layers spread more slowly and contain weaker low-frequency Velocity fluctuations and the noise levels in the acoustic field are lower by 2–3 dB compared to the laminar case. These trends can be explained by the linear stability analyses. For the laminar boundary-layer profile, the initial shear-layer instability waves are most strongly amplified at a momentum-thickness-based Strouhal number $St_{\unicode[STIX]{x1D703}}=0.018$ , which is very similar to the value obtained downstream in the mixing-layer Velocity profiles. For the transitional profiles, on the contrary, they predominantly grow at higher Strouhal numbers, around $St_{\unicode[STIX]{x1D703}}=0.026$ and 0.032, respectively. As a consequence, the instability waves rapidly vanish during the boundary-layer/shear-layer transition in the latter cases, but continue to grow over a large distance from the nozzle in the former case, leading to persistent large-scale coherent structures in the mixing layers for the jet with a laminar Exit Velocity profile.