The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
V L Varsegov - One of the best experts on this subject based on the ideXlab platform.
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the Recirculation Zone characteristics of the circular transverse jet in crossflow
Energies, 2020Co-Authors: Ziwan Li, Yixiang Yuan, V L VarsegovAbstract:Transverse jets in crossflow are widely used in energy systems, especially as dilution air jets, fuel/air mixers, and combustion equipment, and have received extensive attention and plenty of research. However, the studies of the circular transverse jet issued from a circular gap at the circumferential direction of a tube in crossflow are very limited. This paper studies a relatively new jet: the circular transverse jet. Firstly, numerical calculations are conducted under different turbulence models but with the same boundary conditions. By comparing the numerical results of different turbulence models with the existing experimental data, the turbulence model which is most suitable for the numerical calculation of the circular transverse jet is selected. Then, this turbulence model is used to calculate and analyze the flow field structure and its characteristics. It is found that due to the aerodynamic barrier effect of the high-velocity jet, a negative pressure Zone is formed behind the jet trajectory; the existence of the negative pressure Zone causes the formation of a vortex structure and a Recirculation Zone downstream the circular transverse jet; and the length/width ratio of the Recirculation Zone does not change with the changes of the crossflow and the jet parameters. It means that the Recirculation Zone is a fixed shape for a definite device. This would be fundamental references for the studying of fuel/air mixing characteristics and combustion efficiency when the circular transverse jet is used as a fuel/air mixer and stable combustion system.
Xingang Liang - One of the best experts on this subject based on the ideXlab platform.
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thermal effect on the Recirculation Zone in sudden expansion gas flows
International Journal of Heat and Mass Transfer, 1996Co-Authors: Deyu Li, Xingang LiangAbstract:A systematic study has been carried out numerically and compared with some experimental data to examine the heating effect on the corner Recirculation Zone (CRZ) in sudden-expansion gas flows. The heat addition to such flows will lead to the reduction of the CRZ length, and the CRZ can even disappear if the heating intensity is sufficiently large. The concept of thermal drag (heating induced pressure drop in duct flows) has been used to clarify the underlying mechanism of the heating effect on CRZ. The heating induced reduction of the adverse pressure gradient in sudden-expansion flows should be largely responsible for the shrinkage of the CRZ due to heating. Computational results also show that heating the CRZ and the upstream part of expansion flow are more efficient for changes of the CRZ.
Hideaki Kobayashi - One of the best experts on this subject based on the ideXlab platform.
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effect of the incident shock wave interacting with transversal jet flow on the mixing and combustion
Proceedings of the Combustion Institute, 2011Co-Authors: Yoshimune Sakimitsu, Hisashi Nakamura, Yasuhiro Ogami, Taku Kudo, Hideaki KobayashiAbstract:Abstract The interaction between an incident shock wave and a transverse jet flow for mixing and combustion in a supersonic airstream was investigated experimentally and numerically. NO planar laser induced fluorescence (NO-PLIF) and particle imaging velocimetry (PIV) for non-reactive flows and three-dimensional reactive/non-reactive numerical simulations were conducted to examine the effect of the incident shock wave on the three-dimensional flow structure and mixing mechanism between the airstream and the injected gas downstream of the injection slot. Results of NO-PLIF measurement and numerical simulation showed that, in the case without the incident shock wave, injected gas is seldom seen in the Recirculation Zone just downstream of the injection slot, while the injected gas with higher concentration is almost uniformly distributed in the Recirculation Zone when the incident shock wave is introduced downstream of the injection slot. Moreover, it was shown by the numerical simulations that the profiles of the local equivalence ratio is in the combustible range due to the enhanced entrainment of the airstream when the incident shock wave is introduced downstream of the injection slot. A large-scale Recirculation in the direction parallel to the wall is generated by the three-dimensional flow effects, which enhances the mixing and extends the residence time in the Recirculation Zone in the case with incident shock wave downstream of the injection slot, the Recirculation flow being confirmed successfully by PIV measurements as well. The results of three-dimensional reactive numerical simulations were in good agreement with the experimental flame-holding characteristics at a lower total temperature, which showed that flame-holding can be attained only when the incident shock wave was introduced downstream of the injection slot, confirming that the formation of three-dimensional and large-scale Recirculation flow downstream of the injection slot enlarges the Recirculation Zone and enhances the mixing to produce the conditions for robust flame-holding.
Ziwan Li - One of the best experts on this subject based on the ideXlab platform.
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the Recirculation Zone characteristics of the circular transverse jet in crossflow
Energies, 2020Co-Authors: Ziwan Li, Yixiang Yuan, V L VarsegovAbstract:Transverse jets in crossflow are widely used in energy systems, especially as dilution air jets, fuel/air mixers, and combustion equipment, and have received extensive attention and plenty of research. However, the studies of the circular transverse jet issued from a circular gap at the circumferential direction of a tube in crossflow are very limited. This paper studies a relatively new jet: the circular transverse jet. Firstly, numerical calculations are conducted under different turbulence models but with the same boundary conditions. By comparing the numerical results of different turbulence models with the existing experimental data, the turbulence model which is most suitable for the numerical calculation of the circular transverse jet is selected. Then, this turbulence model is used to calculate and analyze the flow field structure and its characteristics. It is found that due to the aerodynamic barrier effect of the high-velocity jet, a negative pressure Zone is formed behind the jet trajectory; the existence of the negative pressure Zone causes the formation of a vortex structure and a Recirculation Zone downstream the circular transverse jet; and the length/width ratio of the Recirculation Zone does not change with the changes of the crossflow and the jet parameters. It means that the Recirculation Zone is a fixed shape for a definite device. This would be fundamental references for the studying of fuel/air mixing characteristics and combustion efficiency when the circular transverse jet is used as a fuel/air mixer and stable combustion system.
Wenqiang Lu - One of the best experts on this subject based on the ideXlab platform.
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theoretical analysis of Recirculation Zone and buffer Zone in the ads windowless spallation target
Annals of Nuclear Energy, 2015Co-Authors: Jianfei Tong, Wenqiang LuAbstract:The thermo-hydraulic analysis including reduction of the height of Recirculation Zone and stability of the free surface is very important in the design and optimization of ADS windowless spallation targets. In the present study, the Bernoulli equation is used to analyze the entire flow process in the target. Formulae for the height of the Recirculation Zone and the buffer Zone are both obtained explicitly. Furthermore, numerical simulation for the heavy metal lead bismuth eutectic liquid and vapor with cavitation phase change is also performed, and a novel method to calculate the height of the Recirculation Zone is put forward. By comparison of the theoretical formulae and numerical results, it is clearly shown that they agree with each other very well, and the heights predicted by the two methods are both determined by their own upstream flow parameters. (C) 2014 Elsevier Ltd. All rights reserved.
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effect of adding a swirl on flow pattern and Recirculation Zone in ads windowless spallation target
Nuclear Engineering and Design, 2014Co-Authors: Lei Yang, Wenqiang LuAbstract:Abstract Aiming the key issues in the accelerator driven system (ADS), windowless spallation target focus on the minimization of the Recirculation Zone and on the stability of the free surface, an innovation has been made by numerically adding swirl to the fluid at the inlet. At first, two phase flow pattern in the simulation is compared with the experiments and numerical method is employed correctly. The results reveal that the Recirculation Zone and the flow pattern are greatly influenced when the swirl strength is changed from 1.0 rad/s to 2.5 rad/s. The height of the Recirculation Zone decreases with increase in swirl strength and completely disappears when the swirl strength reaches 2.0 rad/s. In addition, larger swirl strength leads to different flow pattern and a new cavitation Zone is generated under the Recirculation Zone. The Bernoulli's equation and angular momentum conservation are applied to make it clear that this phenomena is due to the decrease of the axial pressure caused by the radial velocity. Moreover, the new cavitation Zone totally links to the vapor area above the Recirculation Zone when the swirl strength is 2.5 rad/s. The results are very helpful to the design and optimization of the ADS windowless spallation target.