The instabilities of a three-dimensional sinusoidally premixed flame induced by an incident shock wave with Mach = 1.7 and its reshock waves were studied by using the Navier-Stokes (NS) equations with a single-step ch...The instabilities of a three-dimensional sinusoidally premixed flame induced by an incident shock wave with Mach = 1.7 and its reshock waves were studied by using the Navier-Stokes (NS) equations with a single-step chemical reaction and a high resolution, 9th-order weighted essentially non-oscillatory scheme. The computational results were validated by the grid independence test and the experimental results in the literature. The computational results show that after the passage of incident shock wave the flame interface develops in symmetric structure accompanied by large-scale transverse vortex structures. After the interactions by successive reshock waves, the flame interface is gradually destabilized and broken up, and the large-scale vortex structures are gradually transformed into small-scale vortex structures. The small-scale vortices tend to be isotropic later. The results also reveal that the evolution of the flame interface is affected by both mixing process and chemical reaction. In order to identify the relationship between the mixing and the chemical reaction, a dimensionless parameter, , that is defined as the ratio of mixing time scale to chemical reaction time scale, is introduced. It is found that at each interaction stage the effect of chemical reaction is enhanced with time. The enhanced effect of chemical reaction at the interaction stage by incident shock wave is greater than that at the interaction stages by reshock waves. The result suggests that the parameter can reasonably character the features of flame interface development induced by the multiple shock waves.展开更多
An experiment on deformation of flame under the effect of focusing shock wave reflection is performed with the help of multiple-spark camera to understand the flame instability of the deformation process. Methane and ...An experiment on deformation of flame under the effect of focusing shock wave reflection is performed with the help of multiple-spark camera to understand the flame instability of the deformation process. Methane and oxygen are mixed stoichiometrically to be used in the experiment. Based on Navier-Strokes equations,two-dimensional axisymmetric elementary reactions are numerically simulated. And the simulation results are solved by optical calculation. Shaded pictures by simulation fit well with experimental photos. Focusing reflecton shock waves can affect the flame,which accelerates the deformation of flame and renders violent burning in high-energy flammable gases behind waves. Therefore anticlockwise whirlpool appears. It clusters around the external surface of flame and has a tendency to develop toward the right. Finally,the whirlpool focuses on the right side of the flame,which involves the fresh unfired gases into the whirlpool circle,and consequently the head of mushroom cloud is formed. Meanwhile,when shock wave passes through the flame,the intensity of the shock waves on the axis is strengthened.展开更多
High-speed turbulent critical deflagration waves before detonation onset in H2–air mixture propagated into a square cross section channel, which was assembled of optional rigid rough, rigid smooth, or flexible walls....High-speed turbulent critical deflagration waves before detonation onset in H2–air mixture propagated into a square cross section channel, which was assembled of optional rigid rough, rigid smooth, or flexible walls. The corresponding propagation characteristic and the influence of the wall boundaries on the propagation were investigated via high-speed shadowgraph and a high-frequency pressure sampling system. As a comprehensive supplement to the different walls effect investigation, the effect of porous absorbing walls on the detonation propagation was also investigated via smoke foils and the high-frequency pressure sampling system. Results are as follows. In the critical deflagration stage, the leading shock and the closely following turbulent flame front travel at a speed of nearly half the CJ detonation velocity. In the preheated zone, a zonary flame arises from the overlapping part of the boundary layer and the pressure waves, and then merges into the mainstream flame. Among these wall boundary conditions, the rigid rough wall plays a most positive role in the formation of the zonary flame and thus accelerates the transition of the deflagration to detonation（DDT）, which is due to the boost of the boundary layer growth and the pressure wave reflection. Even though the flexible wall is not conducive to the pressure wave reflection, it brings out a faster boundary layer growth, which plays a more significant role in the zonary flame formation. Additionally, the porous absorbing wall absorbs the transverse wave and yields detonation decay and velocity deficit. After the absorbing wall, below some low initial pressure conditions, no re-initiation occurs and the deflagration propagates in critical deflagration for a relatively long distance.展开更多
加氢装置是炼化企业典型的高危装置,涉及氢气等易燃易爆介质,安全风险较高。为研究加氢装置在开敞空间条件下氢气泄漏爆炸事故火焰及冲击波时空演化过程,基于FLACS三维模拟软件对某企业加氢装置建立了等比例模型,并对其进行氢气爆炸模...加氢装置是炼化企业典型的高危装置,涉及氢气等易燃易爆介质,安全风险较高。为研究加氢装置在开敞空间条件下氢气泄漏爆炸事故火焰及冲击波时空演化过程,基于FLACS三维模拟软件对某企业加氢装置建立了等比例模型,并对其进行氢气爆炸模拟研究,探究了不同当量比(ER)对氢气云燃爆超压值及温度的影响。研究结果表明,当量比(ER)在0.8~1.4范围内时,氢气爆炸的温度、超压峰值P max均随ER的增大呈先增大后减小的趋势,ER为1.05时,爆炸温度峰值及超压峰值最大,高温火焰传播范围半径约35 m,影响面积达到3800 m 2。此外,模拟结果为类似场景建筑物抗爆工程改造提供了理论指导。展开更多
基金supported by the National Natural Science Foundation of China (Grant 11372140)
文摘The instabilities of a three-dimensional sinusoidally premixed flame induced by an incident shock wave with Mach = 1.7 and its reshock waves were studied by using the Navier-Stokes (NS) equations with a single-step chemical reaction and a high resolution, 9th-order weighted essentially non-oscillatory scheme. The computational results were validated by the grid independence test and the experimental results in the literature. The computational results show that after the passage of incident shock wave the flame interface develops in symmetric structure accompanied by large-scale transverse vortex structures. After the interactions by successive reshock waves, the flame interface is gradually destabilized and broken up, and the large-scale vortex structures are gradually transformed into small-scale vortex structures. The small-scale vortices tend to be isotropic later. The results also reveal that the evolution of the flame interface is affected by both mixing process and chemical reaction. In order to identify the relationship between the mixing and the chemical reaction, a dimensionless parameter, , that is defined as the ratio of mixing time scale to chemical reaction time scale, is introduced. It is found that at each interaction stage the effect of chemical reaction is enhanced with time. The enhanced effect of chemical reaction at the interaction stage by incident shock wave is greater than that at the interaction stages by reshock waves. The result suggests that the parameter can reasonably character the features of flame interface development induced by the multiple shock waves.
文摘An experiment on deformation of flame under the effect of focusing shock wave reflection is performed with the help of multiple-spark camera to understand the flame instability of the deformation process. Methane and oxygen are mixed stoichiometrically to be used in the experiment. Based on Navier-Strokes equations,two-dimensional axisymmetric elementary reactions are numerically simulated. And the simulation results are solved by optical calculation. Shaded pictures by simulation fit well with experimental photos. Focusing reflecton shock waves can affect the flame,which accelerates the deformation of flame and renders violent burning in high-energy flammable gases behind waves. Therefore anticlockwise whirlpool appears. It clusters around the external surface of flame and has a tendency to develop toward the right. Finally,the whirlpool focuses on the right side of the flame,which involves the fresh unfired gases into the whirlpool circle,and consequently the head of mushroom cloud is formed. Meanwhile,when shock wave passes through the flame,the intensity of the shock waves on the axis is strengthened.
基金Project supported by the National Natural Science Foundation of China(Grant No.51206182)
文摘High-speed turbulent critical deflagration waves before detonation onset in H2–air mixture propagated into a square cross section channel, which was assembled of optional rigid rough, rigid smooth, or flexible walls. The corresponding propagation characteristic and the influence of the wall boundaries on the propagation were investigated via high-speed shadowgraph and a high-frequency pressure sampling system. As a comprehensive supplement to the different walls effect investigation, the effect of porous absorbing walls on the detonation propagation was also investigated via smoke foils and the high-frequency pressure sampling system. Results are as follows. In the critical deflagration stage, the leading shock and the closely following turbulent flame front travel at a speed of nearly half the CJ detonation velocity. In the preheated zone, a zonary flame arises from the overlapping part of the boundary layer and the pressure waves, and then merges into the mainstream flame. Among these wall boundary conditions, the rigid rough wall plays a most positive role in the formation of the zonary flame and thus accelerates the transition of the deflagration to detonation（DDT）, which is due to the boost of the boundary layer growth and the pressure wave reflection. Even though the flexible wall is not conducive to the pressure wave reflection, it brings out a faster boundary layer growth, which plays a more significant role in the zonary flame formation. Additionally, the porous absorbing wall absorbs the transverse wave and yields detonation decay and velocity deficit. After the absorbing wall, below some low initial pressure conditions, no re-initiation occurs and the deflagration propagates in critical deflagration for a relatively long distance.
文摘加氢装置是炼化企业典型的高危装置,涉及氢气等易燃易爆介质,安全风险较高。为研究加氢装置在开敞空间条件下氢气泄漏爆炸事故火焰及冲击波时空演化过程,基于FLACS三维模拟软件对某企业加氢装置建立了等比例模型,并对其进行氢气爆炸模拟研究,探究了不同当量比(ER)对氢气云燃爆超压值及温度的影响。研究结果表明,当量比(ER)在0.8~1.4范围内时,氢气爆炸的温度、超压峰值P max均随ER的增大呈先增大后减小的趋势,ER为1.05时,爆炸温度峰值及超压峰值最大,高温火焰传播范围半径约35 m,影响面积达到3800 m 2。此外,模拟结果为类似场景建筑物抗爆工程改造提供了理论指导。
