Detonation initiation resulting from the Richtmyer-Meshkov instability is investigated numerically in the configuration of the shock/spark-induced-deflagration interaction in a combustive gas mixture.Two-dimensional m...Detonation initiation resulting from the Richtmyer-Meshkov instability is investigated numerically in the configuration of the shock/spark-induced-deflagration interaction in a combustive gas mixture.Two-dimensional multi-species Navier-Stokes equations implemented with the detailed chemical reaction model are solved with the dispersion-controlled dissipative scheme.Numerical results show that the spark can create a blast wave and ignite deflagrations.Then,the deflagration waves are enhanced due to the Richtmyer-Meshkov instability,which provides detonation initiations with local environment conditions.By examining the deflagration fronts,two kinds of the initiation mechanisms are identified.One is referred to as the deflagration front acceleration with the help of the weak shock wave,occurring on the convex surfaces,and the other is the hot spot explosion deriving from the deflagration front focusing,occurring on the concave surfaces.展开更多
The interactions of a spherical flame with an incident shock wave and its reflected shock wave in a confined space were investigated using the three-dimensional reactive Navier-Stokes equations, with emphasis placed o...The interactions of a spherical flame with an incident shock wave and its reflected shock wave in a confined space were investigated using the three-dimensional reactive Navier-Stokes equations, with emphasis placed on the effect of chemical reactivity of mixture on the flame distortion and detonation initiation after the passage of the reflected shock wave. It is shown that the spatio-temporal characteristics of detonation initiation depend highly on the chemi- cal reactivity of the mixture. When the chemical reactivity enhances, the flame can be severely distorted to form a reactive shock bifurcation structure with detonations initiating at different three-dimensional spatial locations. Moreover, the detonation initiation would occur earlier in a mixture of more enhanced reactivity. The results reveal that the detona- tions arise from hot spots in the unburned region which are initiated by the shock-detonation-transition mechanism.展开更多
The geometric structure, mechanism of detonation initiation and stability of transition metal carbohydrazide （CHZ） nitrates are investigated via density functional theory. The obtained results show that the Heyd-Scu...The geometric structure, mechanism of detonation initiation and stability of transition metal carbohydrazide （CHZ） nitrates are investigated via density functional theory. The obtained results show that the Heyd-Scuseria-Ernzerhof （HSE） functional yields the most accurate geometry. The initiating reaction of detonation in [Mn（CHZ）3]（NO3）2 and [Zn（CHZ）3]（NO3）2 is the formation of NO3 radicals. The calculated heat of formation and energy gap predict that the Mn and Zn complexes, which have the half-filled （3d5） and full-filled （3d10） electron configurations for the transition metal ions, respectively are more stable than the Co, Ni and Cu complexes. This indicates that the electron configuration of transition metal ion plays an important role in the stabilities of these energetic complexes.展开更多
Aiming at studying the influence of actuating frequency on plasma assisted detonation initiation by alternating current dielectric barrier discharge, a loosely coupled method is used to simulate the detonation initiat...Aiming at studying the influence of actuating frequency on plasma assisted detonation initiation by alternating current dielectric barrier discharge, a loosely coupled method is used to simulate the detonation initiation process of a hydrogenoxygen mixture in a detonation tube at different actuating frequencies. Both the discharge products and the detonation forming process which is assisted by the plasma are analyzed. It is found that the patterns of the temporal and spatial distributions of discharge products in one cycle are not changed by the actuating frequency. However, the concentration of every species decreases as the actuating frequency rises, and atom O is the most sensitive to this variation, which is related to the decrease of discharge power. With respect to the reaction flow of the detonation tube, the deflagration-todetonation transition（DDT） time and distance both increase as the actuating frequency rises, but the degree of effect on DDT development during flow field evolution is erratic. Generally, the actuating frequency affects none of the amplitude value of the pressure, temperature, species concentration of the flow field, and the combustion degree within the reaction zone.展开更多
The direct initiation of detonations in one-dimensional （1D） and two-dimensional （2D） cylindrical geometries is investigated through numerical simulations. In comparison of 1D and 2D simulations, it is found that ...The direct initiation of detonations in one-dimensional （1D） and two-dimensional （2D） cylindrical geometries is investigated through numerical simulations. In comparison of 1D and 2D simulations, it is found that cellular instability has a negative effect on the 2D initiation and makes it more difficult to initiate a sustaining 2D cylindrical detonation. This effect associates closely with the activation energy. For the lower activation energy, the 2D initiation of cylindrical detonations can be achieved through a subcritical initiation way. With increasing the activation energy, the 2D cylindrical detonation has increased difficulty in its initiation due to the presence of unreacted pockets behind the detonation front and usually requires rather larger source energy.展开更多
The three-dimensional premixed H2-O2 detonation propagation in rectangular ducts is simulated using an in-house parallel detonation code based on the second-order space-time conservation element and solution element（...The three-dimensional premixed H2-O2 detonation propagation in rectangular ducts is simulated using an in-house parallel detonation code based on the second-order space-time conservation element and solution element（CE/SE） scheme.The simulation reproduces three typical cellular structures by setting appropriate cross-sectional size and initial perturbation in square tubes.As the cross-sectional size decreases,critical cellular structures transforming the rectangular or diagonal mode into the spinning mode are obtained and discussed in the perspective of phase variation as well as decreasing of triple point lines.Furthermore,multiple cellular structures are observed through examples with typical aspect ratios.Utilizing the visualization of detailed three-dimensional structures,their formation mechanism is further analyzed.展开更多
Structural damage is significantly influenced by the various parameters of a close-in explosion.To establish a close-in blast loading model for cylindrical charges according to these parameters,a series of field exper...Structural damage is significantly influenced by the various parameters of a close-in explosion.To establish a close-in blast loading model for cylindrical charges according to these parameters,a series of field experiments and a systematic numerical analysis were conducted.A high-fidelity finite element model developed using AUTODYN was first validated using blast data collected from field tests conducted in this and previous studies.A quantitative analysis was then performed to determine the influence of the charge shape,aspect ratio(length to diameter),orientation,and detonation configuration on the characteristics and distributions of the blast loading(incident peak overpressure and impulse)according to scaled distance.The results revealed that the secondary peak overpressure generated by a cylindrical charge was mainly distributed along the axial direction and was smaller than the overpressure generated by an equivalent spherical charge.The effects of charge shape on the blast loading at 45°and 67.5°in the axial plane could be neglected at scaled distances greater than 2 m/kg^(1/3);the effect of aspect ratios greater than 2 on the peak overpressure in the 90°(radial)direction could be neglected at all scaled distances;and double-end detonation increased the radial blast loading by up to 60%compared to singleend detonation.Finally,an empirical cylindrical charge blast loading model was developed considering the influences of charge aspect ratio,orientation,and detonation configuration.The results obtained in this study can serve as a reference for the design of blast tests using cylindrical charges and aid engineers in the design of blast-resistant structures.展开更多
Aluminum（Al） powders are used in composite explosives as a typical reducing agent for improving explosion performance. To understand energy release of aluminum in aluminized RDX-based explosives, a series of thermal...Aluminum（Al） powders are used in composite explosives as a typical reducing agent for improving explosion performance. To understand energy release of aluminum in aluminized RDX-based explosives, a series of thermal measurements and underwater explosion（UNDEX） experiments were conducted. Lithium fluoride（LiF） was added in RDX-based explosives, as a replacement of aluminum, and used in constant temperature calorimeter experiments and UNDEXs. The influence of aluminum powder on explosion heat（Qv） was measured. A rich supply of data about aluminum energy release rate was gained. There are other oxides（CO2, CO, and H2O） in detonation products besides alumina when the content of RDX is maintained at the same levels. Aluminum cannot fully combine with oxygen in the detonation products. To study the relationship between the explosive formulation and energy release, pressure and impulse signals in underwater experiments were recorded and analyzed after charges were initiated underwater. The shock wave energy（Esk）, bubble energy（Eb）, and total energy（Et） monotony increase with the Al/O ratio, while the growth rates of the shock wave energy,bubble energy, and total energy become slow.展开更多
基金The project supported by the National Natural Science Foundation of China(90205027 and 10632090)
文摘Detonation initiation resulting from the Richtmyer-Meshkov instability is investigated numerically in the configuration of the shock/spark-induced-deflagration interaction in a combustive gas mixture.Two-dimensional multi-species Navier-Stokes equations implemented with the detailed chemical reaction model are solved with the dispersion-controlled dissipative scheme.Numerical results show that the spark can create a blast wave and ignite deflagrations.Then,the deflagration waves are enhanced due to the Richtmyer-Meshkov instability,which provides detonation initiations with local environment conditions.By examining the deflagration fronts,two kinds of the initiation mechanisms are identified.One is referred to as the deflagration front acceleration with the help of the weak shock wave,occurring on the convex surfaces,and the other is the hot spot explosion deriving from the deflagration front focusing,occurring on the concave surfaces.
基金supported by the National Natural Science Foundation of China (10972107)Open Fund of State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology (KFJJ12-4Y)Jiangsu Innovation Program for Graduate Education (CXLX11 0271)
文摘The interactions of a spherical flame with an incident shock wave and its reflected shock wave in a confined space were investigated using the three-dimensional reactive Navier-Stokes equations, with emphasis placed on the effect of chemical reactivity of mixture on the flame distortion and detonation initiation after the passage of the reflected shock wave. It is shown that the spatio-temporal characteristics of detonation initiation depend highly on the chemi- cal reactivity of the mixture. When the chemical reactivity enhances, the flame can be severely distorted to form a reactive shock bifurcation structure with detonations initiating at different three-dimensional spatial locations. Moreover, the detonation initiation would occur earlier in a mixture of more enhanced reactivity. The results reveal that the detona- tions arise from hot spots in the unburned region which are initiated by the shock-detonation-transition mechanism.
基金supported by the National Natural Science Foundation of China(No.20471008)the Natural Science Foundation of Chongqing(No.cstc2011jjA50013)the Chongqing Municipal Commission of Education(No.KJ111310)
文摘The geometric structure, mechanism of detonation initiation and stability of transition metal carbohydrazide （CHZ） nitrates are investigated via density functional theory. The obtained results show that the Heyd-Scuseria-Ernzerhof （HSE） functional yields the most accurate geometry. The initiating reaction of detonation in [Mn（CHZ）3]（NO3）2 and [Zn（CHZ）3]（NO3）2 is the formation of NO3 radicals. The calculated heat of formation and energy gap predict that the Mn and Zn complexes, which have the half-filled （3d5） and full-filled （3d10） electron configurations for the transition metal ions, respectively are more stable than the Co, Ni and Cu complexes. This indicates that the electron configuration of transition metal ion plays an important role in the stabilities of these energetic complexes.
基金Project supported by the Open Project of Science and Technology on Scramjet Laboratory,China(Grant No.CG-2014-05-118)the National Natural Science Foundation of China(Grant No.91441123)
文摘Aiming at studying the influence of actuating frequency on plasma assisted detonation initiation by alternating current dielectric barrier discharge, a loosely coupled method is used to simulate the detonation initiation process of a hydrogenoxygen mixture in a detonation tube at different actuating frequencies. Both the discharge products and the detonation forming process which is assisted by the plasma are analyzed. It is found that the patterns of the temporal and spatial distributions of discharge products in one cycle are not changed by the actuating frequency. However, the concentration of every species decreases as the actuating frequency rises, and atom O is the most sensitive to this variation, which is related to the decrease of discharge power. With respect to the reaction flow of the detonation tube, the deflagration-todetonation transition（DDT） time and distance both increase as the actuating frequency rises, but the degree of effect on DDT development during flow field evolution is erratic. Generally, the actuating frequency affects none of the amplitude value of the pressure, temperature, species concentration of the flow field, and the combustion degree within the reaction zone.
基金Supported by the National Natural Science Foundation of China under Grant Nos 91541206 and 91441131
文摘The direct initiation of detonations in one-dimensional （1D） and two-dimensional （2D） cylindrical geometries is investigated through numerical simulations. In comparison of 1D and 2D simulations, it is found that cellular instability has a negative effect on the 2D initiation and makes it more difficult to initiate a sustaining 2D cylindrical detonation. This effect associates closely with the activation energy. For the lower activation energy, the 2D initiation of cylindrical detonations can be achieved through a subcritical initiation way. With increasing the activation energy, the 2D cylindrical detonation has increased difficulty in its initiation due to the presence of unreacted pockets behind the detonation front and usually requires rather larger source energy.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.10732010 and 10972010)
文摘The three-dimensional premixed H2-O2 detonation propagation in rectangular ducts is simulated using an in-house parallel detonation code based on the second-order space-time conservation element and solution element（CE/SE） scheme.The simulation reproduces three typical cellular structures by setting appropriate cross-sectional size and initial perturbation in square tubes.As the cross-sectional size decreases,critical cellular structures transforming the rectangular or diagonal mode into the spinning mode are obtained and discussed in the perspective of phase variation as well as decreasing of triple point lines.Furthermore,multiple cellular structures are observed through examples with typical aspect ratios.Utilizing the visualization of detailed three-dimensional structures,their formation mechanism is further analyzed.
基金supported by the National Natural Science Foundation of China[No.51978166]。
文摘Structural damage is significantly influenced by the various parameters of a close-in explosion.To establish a close-in blast loading model for cylindrical charges according to these parameters,a series of field experiments and a systematic numerical analysis were conducted.A high-fidelity finite element model developed using AUTODYN was first validated using blast data collected from field tests conducted in this and previous studies.A quantitative analysis was then performed to determine the influence of the charge shape,aspect ratio(length to diameter),orientation,and detonation configuration on the characteristics and distributions of the blast loading(incident peak overpressure and impulse)according to scaled distance.The results revealed that the secondary peak overpressure generated by a cylindrical charge was mainly distributed along the axial direction and was smaller than the overpressure generated by an equivalent spherical charge.The effects of charge shape on the blast loading at 45°and 67.5°in the axial plane could be neglected at scaled distances greater than 2 m/kg^(1/3);the effect of aspect ratios greater than 2 on the peak overpressure in the 90°(radial)direction could be neglected at all scaled distances;and double-end detonation increased the radial blast loading by up to 60%compared to singleend detonation.Finally,an empirical cylindrical charge blast loading model was developed considering the influences of charge aspect ratio,orientation,and detonation configuration.The results obtained in this study can serve as a reference for the design of blast tests using cylindrical charges and aid engineers in the design of blast-resistant structures.
文摘Aluminum（Al） powders are used in composite explosives as a typical reducing agent for improving explosion performance. To understand energy release of aluminum in aluminized RDX-based explosives, a series of thermal measurements and underwater explosion（UNDEX） experiments were conducted. Lithium fluoride（LiF） was added in RDX-based explosives, as a replacement of aluminum, and used in constant temperature calorimeter experiments and UNDEXs. The influence of aluminum powder on explosion heat（Qv） was measured. A rich supply of data about aluminum energy release rate was gained. There are other oxides（CO2, CO, and H2O） in detonation products besides alumina when the content of RDX is maintained at the same levels. Aluminum cannot fully combine with oxygen in the detonation products. To study the relationship between the explosive formulation and energy release, pressure and impulse signals in underwater experiments were recorded and analyzed after charges were initiated underwater. The shock wave energy（Esk）, bubble energy（Eb）, and total energy（Et） monotony increase with the Al/O ratio, while the growth rates of the shock wave energy,bubble energy, and total energy become slow.
