共查询到20条相似文献,搜索用时 31 毫秒
1.
气相爆轰波在周期性非均匀介质中的起爆, 稳态传播和失效机制都极为复杂, 很多物理机制尚不明确, 是当前爆轰物理领域研究的热点和难点. 本文使用反应欧拉方程和两步化学反应模型对爆轰波在非均匀介质中的传播机理进行了数值模拟研究, 非均匀性由横向周期性分布的温度扰动体现, 重点分析不同波长、不同幅度的温度扰动对波阵面波系结构的影响. 计算结果表明, ZND爆轰波在温度扰动下向胞格爆轰波的转变主要受制于两种竞争性因素: 一是爆轰波内在的不稳定性; 二是温度扰动的波长和幅度, 前者是内因, 后者是外因. 温度扰动的存在抑制横波的发展, 延迟了ZND爆轰波向胞格爆轰波的演化, 并且内在不稳定性的增加可以减慢这种延迟现象. 这说明, 温度扰动可以在一定的范围内抑制胞格不稳定性的发展, 但是不能够终止这一过程. 温度的不连续性使得爆轰波阵面更为扭曲, 并在横波附近存在较弱的三波点结构, 即温度扰动可增加爆轰波固有的不稳定性, 改变爆轰波阵面的传播机理. 幅值较大的人工温度扰动可抑制爆轰波的传播和爆轰波自身的不稳定性. 爆轰波阵面胞格结构的形成取决于温度扰动与其自身的不稳定性. 相似文献
2.
The interactions of a spherical flame with an in- cident 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 chemical 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 detonations arise from hot spots in the unburned region which are initiated by the shock-detonation-transition mechanism. 相似文献
3.
Recent work on gaseous detonations 总被引:1,自引:0,他引:1
M.A. Nettleton 《Shock Waves》2002,12(1):3-12
The paper reviews recent progress in the field of gaseous detonations, with sections on shock diffraction and reflection,
the transition to detonation, hybrid, spherically-imploding, and galloping and stuttering fronts, their structure, their transmission
and quenching by additives, the critical energy for initiation and detonation of more unusual fuels. The final section points
out areas where our understanding is still far from being complete and contains some suggestions of ways in which progress
might be made.
Received 9 September 1999 / Accepted 10 May 2001 相似文献
4.
Detonation initiation is investigated in aluminium/oxygen and aluminium/air mixtures. Critical conditions for initiation of
spherical detonations are examined in analogy with the criteria defined for gaseous mixtures, which correlate critical parameters
of detonation initiation to the characteristic size of the cellular structure. However, experimental data on the detonation
cell size in these two-phase mixtures are very scarce, on account of the difficulty to perform large-scale experiments. Therefore,
2D numerical simulations of the detonation cellular structure have been undertaken, with the same combustion model for Al/air
and Al/O2 mixtures. The cell size is found to be λ = 37.5 cm for a rich (r = 1.61) aluminium–air mixture, and λ = 7.5 cm for a stoichiometric aluminium-oxygen mixture, which is in reasonable agreement with available experimental data.
Calculations performed in large-scale configurations (up to 25 m in length and 1.5 m in lateral direction) suggest that the
critical initiation energy and predetonation radius for direct initiation of the unconfined detonation in the aluminium–air
mixture are, respectively, 10 kg of TNT and 8 m. Moreover, numerical simulations reveal that the structure of the detonation
wave behind the leading front is even more complicated than in pure gaseous mixtures, due to two-phase flow effects.
This paper is based on work that was presented at the 21st International Colloquium on the Dynamics of Explosions and Reactive
Systems, Poitiers, France, July 23–27, 2007. 相似文献
5.
Behavior of detonation waves at low pressures 总被引:1,自引:0,他引:1
With respect to stability of gaseous detonations, unsteady behavior of galloping detonations and re-initiation process of
hydrogen-oxygen mixtures are studied using a detonation tube of 14 m in length and 45 mm i.d. The arrival of the shock wave
and the reaction front is detected individually by a double probe combining of a pressure and an ion probe. The experimental
results show that there are two different types of the re-initiation mechanism. One is essentially the same as that of deflagration
to detonation transition in the sense that a shock wave generated by flame acceleration causes a local explosion. From calculated
values of ignition delay behind the shock wave decoupled from the reaction front, the other is found to be closely related
with spontaneous ignition. In this case, the fundamental propagation mode shows a spinning detonation.
Received 10 March 1997 / Accepted 8 June 1997 相似文献
6.
An analysis of theoretical models and experimental investigations of the detonability of unconfined detonation in uniform
gaseous mixtures shows a disparity in results. The present study is limited to propane, acetylene and methane diluted with
oxygen or air in variable proportions and initial pressures at ambient temperature conditions. Because of the disparity in
results, a simple and general formulation of critical initiation energy for gaseous detonations has been investigated. The
problem has been formulated using the conservation equation of total energy enclosed by the shock. From this, a simple form
for the critical energy has been deduced. This approach leads to a good simulation in uniform mixtures, regardless of initiation
conditions. Some applications are presented in this paper.
A new experimental study on the detonability of methane/oxygen mixtures diluted with propane and/or nitrogen is reported.
The gaseous mixtures are confined in a cylindrical vessel. The initial conditions are various equivalence ratio and pressure
under room temperature. In the case of methane/oxygen mixtures, the predetonation radius varies directly with the cell width.
The constant ratio is in the order of 18, slightly different from the classical relation R
c= 20λ. For propane the slope variation of the critical energy versus initial pressure depends on the dilution.
We have compared the critical energy obtained by several authors with the theoretical values. Fuel ratio and initial pressure
are the chosen parameters. These comparisons show that the formulation allows for the prediction of the critical energy of
detonation of uniform mixtures with a good estimation range. The correlation between the different geometries has been deduced
and a test has been conducted as well in the case of stoichiometric methane/oxygen and acetylene/oxygen mixtures versus initial
pressure for a cylindrical detonation.
Received 9 January 1996 / Accepted 24 January 1997 相似文献
7.
An experimental investigation has been undertaken to improve understanding of the role of the obturator and detonations in
the subdetonative ram accelerator starting process. Ram accelerator start experiments were conducted with various obturator
geometries to determine the obturator dynamics and assess its effect on the outcome of a start attempt. The obturator rapidly
decelerates upon entrance and then moves backwards. Reversal of direction occurs more rapidly after propellant ignition, for
less massive obturators, and solid geometries. Perforated geometries and decreasing obturator mass are less conducive to igniting
a given propellant, as evidenced by the flowfield and start attempt outcome data presented. Wave unstarts were observed to
occur with and without detonations, indicating more than one mechanism responsible for this type of start failure. Piston-initiated
detonation experiments were conducted by firing the obturators without the ram accelerator projectile. The piston experiments
identified the detonation limits for a wide range of propellants, but were found to not always be indicative of the upper
Mach number at which a ram accelerator can be successfully started. In some instances a successful start or wave fall-off
would occur at Mach numbers above which a piston alone detonated the propellant. Thus, the projectile can play a mitigating
role in detonation initiation and use of piston detonation limits to quantitatively define a detonation wave unstart limit
was not realized.
Received 6 April 1998 / Accepted 15 January 1999 相似文献
8.
In this experimental study, the critical tube diameter phenomenon of gaseous detonations is investigated in both stable and unstable mixtures with focus on the failure mechanism. It was previously postulated that in unstable mixtures, where the cellular detonation front is highly irregular, the failure is caused by the suppression of local re-initiation centers linked to the dynamics of instabilities. In stable mixtures, typically with high argon dilution, the detonation structure is very regular and the failure mode is attributed to the excessive curvature of the global front. In order to differentiate between these two failure mechanisms, flow perturbations are introduced by placing an obstacle resulting in a minimal blockage ratio of approximately 8 %. The obstacle is placed at the tube exit, before the detonation diffraction. Results show that the perturbations caused by the obstacle only have an effect on undiluted (i.e., unstable) mixtures, causing a decrease in the minimum initial pressure required for successful detonation transmission. This thus demonstrates that local hydrodynamic instabilities play an important role for the critical tube diameter phenomenon in undiluted, unstable mixtures. In contrast, the results for the stable, argon-diluted mixture exhibit little variation in critical initial pressure between the perturbed and unperturbed cases. This can be attributed to the minimal effect of the perturbations on global curvature for the emergent detonation wave. The geometry of the perturbation is also tested, while holding the blockage area constant, by varying the number and position of the obstacle(s). The results demonstrate that the transmission of a detonation is independent of the blockage geometry and is only a function of its imposed blockage area. Consequently, the change in required minimum pressure for transmission shows an identical behavior in unstable mixtures for different perturbation geometries while the transmission characteristics of the stable mixture remain unaffected. 相似文献
9.
气相爆轰物理的若干研究进展 总被引:1,自引:0,他引:1
爆轰现象的研究已经有一百多年的历史了,爆轰物理的研究取得了许多重要进展.本文从爆轰波的经典理论、胞格爆轰波的多波结构、气相爆轰波形成机理、气相爆轰波传播机制等方面综述了相关的若干研究进展,评述了这些进展的科学性与局限性,并探讨了将来可能的研究方向.这些研究进展主要包括:CJ(Chapman-Jouguet)理论和ZND(Zel'dovich,von Neumann,D?ring)模型、爆轰波多波结构、爆轰胞格特征、直接起爆和爆燃转爆轰过程、热点起爆机制、爆轰波稳定性、扰动爆轰波的传播等.爆轰波是以超声速传播的自持燃烧现象,涉及了激波相互作用、燃烧化学反应、湍流扩散和流动不稳定性等复杂的气动物理过程,相关研究具有重要的学科理论意义.另外,爆轰燃烧具有高效的热化学能释放特点,在先进的热力推进技术方面有着重要的应用背景,因此相关研究也具有重要的工程应用价值. 相似文献
10.
This paper summarizes the studies of DDT and stable detonation waves in dust-air mixtures at the Stosswellenlabor of RWTH
Aachen. The DDT process and propagation mechanism for stable heterogeneous dust detonations in air are essentially the same
as in the oxygen environment studied previously. The dust DDT process in tubes is composed of a reaction compression stage
followed by a reaction shock stage as the pre-detonation process. The transverse waves that couple the shock wave and the
chemical energy release are responsible for the propagation of a stable dust-air detonation. However, the transverse wave
spacing of dust-air mixtures is much larger. Therefore, DDT and propagation of a stable detonation in most industrial and
agricultural, combustible dust-air mixtures require a tube that has a large diameter between 0.1 m and 1 m and a sufficient
length-diameter ratio beyond 100, when an appropriately strong initiation energy is used. Two dust detonation tubes, 0.14
m and 0.3 m in diameter, were used for observation of the above-mentioned results in cornstarch, anthraquinone and aluminum
dust suspended in air. Smoked-foil technique was also used to measure the cellular structure of dust detonations in the 0.3
m detonation tube.
Received 11 February 2000 / Accepted 1 August 2000 相似文献
11.
Spinning detonations are characteristic of detonation limit phenomena in round tubes. In this work we study experimentally
the structure of the transverse wave of single-headed spinning detonations. The flow field is experimentally analysed and
an original approach enables us to calculate the overall shock structure. The calculations and experimental results indicate
that the actual structure of the spinning detonation tries to match closely to the condition where the state parameters (pressure
and temperature) reach their maximum values. This condition corresponds to a spinning head where the Mach stem is normal to
the incoming flow and could be readily used as boundary condition by further investigators to determine the structure of spinning
detonations.
Received 1 August 1997/ Accepted 13 July 1998 相似文献
12.
Numerical modeling of the propagation of shock and detonation waves is carried out in a duct with an abrupt expansion for
a heterogeneous mixture of fine particles of aluminum and oxygen. A considerable difference from corresponding flows in pure
gas is found. The influence of the size and mass loading of particles on the flow and shock wave structure behind the backward-facing
step is determined. As in gaseous detonations, three types of scenarios of detonation development are obtained. Specific features
of the flow structure are revealed such as deformation of the combustion front due to interaction between the relaxation zone
and the vortex structure. The influence of particle size and channel width on detonation propagation is analyzed.
This paper is based on work that was presented at the 21th International Colloquium on the Dynamics of Explosions and Reactive
Systems, Poitiers, France, July 23–27, 2007. 相似文献
13.
《Comptes Rendus de l'Académie des Sciences》2001,329(7):489-496
A weakly nonlinear analysis of cellular detonations at onset of the instability against transverse disturbances is carried out in the Newtonian limit at strong overdrive. A nonlinear integral-differential equation describing the formation of cusps representative of Mach-stems on the detonation front is obtained as an asymptotic solution of the reactive Euler equations. A numerical study of this equation exhibits patterns that are similar to the cellular structures observed experimentally in gaseous detonation waves. 相似文献
14.
Measurement of effective blast energy for direct initiation of spherical gaseous detonations from high-voltage spark discharge 总被引:1,自引:0,他引:1
In this study, effective energy from spark discharge for direct blast initiation of spherical gaseous detonations is investigated.
In the experiment, direct initiation of detonation is achieved via a spark discharge from a high-voltage and low-inductance
capacitor bank and the spark energy is estimated from the analysis of the current output. To determine the blast wave energy
from the powerful spark, the time-of-arrival of the blast wave in air is measured at different radii using a piezoelectric
pressure transducer. Good agreement is found in the scaled blast trajectories, i.e., scaled time c
o·t/R
o where c
o is the ambient sound speed, as a function of blast radius R
s/R
o between the numerical simulation of a spherical blast wave from a point energy source and the experimental results where
the explosion length scale R
o is computed using the equivalent spark energy from the first 1/4 current discharge cycle. Alternatively, by fitting the experimental
trajectories data, the blast energy estimated from the numerical simulation appears also in good agreement with that obtained
experimentally using the 1/4 cycle criterion. Using the 1/4 cycle of spark discharge for the effective energy, direct initiation
experiments of spherical gaseous detonations are carried out to determine the critical initiation energy in C2H2–2.5O2 mixtures with 70 and 0% argon dilution. The experimental results obtained from the 1/4 cycle of spark discharge agree well
with the prediction from two initiation models, namely, the Lee’s surface energy model and a simplified work done model. The
main source of discrepancy in the comparison can be explained by the uncertainty of cell size measurement which is needed
for both the semi-empirical models. 相似文献
15.
This paper summarizes the studies on dust detonations at the Stosswellenlabor of RWTH Aachen since 1987. The onset and propagation mechanism of heterogeneous dust detonations are similar to those of marginal gas phase detonations. A self-sustained dust detonation has transverse wave structures that provide the coupling between shock and reaction. Large transition distances and transverse wave spacings require large sized tubes for the propagation of self-sustained dust detonations. The Hugoniot analysis of the Chapman-Jouguet detonation predicts equilibrium detonation states being in reasonable agreement with the self-sustained dust detonations observed. Shock matching calculations at the triple point adequately determine the wave structures of those stable dust detonations.This article was processed using Springer-Verlag TEX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society. 相似文献
16.
17.
In this study, detonation limits in very small diameter tubes are investigated to further the understanding of the near-limit
detonation phenomenon. Three small diameter circular tubes of 1.8, 6.3, and 9.5 mm inner diameters, of 3 m length, were used
to permit the near-limit detonations to be observed over long distances of 300 to 1500 tube diameters. Mixtures with high
argon dilution (stable) and without dilution (unstable) are used for the experiments. For stable mixtures highly diluted with
argon for which instabilities are not important and where failure is due to losses only, the limit obtained experimentally
appears well to be in good agreement in comparison to that computed by the quasi-steady ZND theory with flow divergence or
curvature term modeling the boundary layer effects. For unstable detonations it is suggested that suppression of the instabilities
of the cellular detonation due to boundary conditions is responsible for the failure of the detonation wave. Different near-limit
propagation regimes are also observed, including the spinning and galloping mode. Based on the present experimental results,
an attempt is made to study an operational criterion for the propagation limits of stable and unstable detonations. 相似文献
18.
一维爆轰传播的理论完备、计算准确, 二维斜爆轰传播由于壁面与黏性效应, 大尺度、高精度预测还有一定难度. 利用Euler方程和H2-Air基元反应模型, 对二维有限长楔面诱导的斜爆轰和活塞驱动一维非定常正爆轰进行计算比较研究, 从时空两个维度方面, 分析了两者在起爆过程、稀疏波传播、爆轰波面演化中的关联特性. 研究结果表明: 在过驱动度相同的条件下, 经过时空变换的活塞驱动一维爆轰传播与二维驻定斜爆轰在起爆区波系结构、波面演化特征和主要参数分布规律方面无论定性或者定量对比均符合较好, 所以, 一维非定常爆轰和二维驻定斜爆轰具有时空相关性. 两者的差异主要体现在过驱动斜爆轰受稀疏波影响过渡到近Chapman-Jouguet (C-J)爆轰状态所需的弛豫时间不同, 原因可能是起源于活塞和壁面稀疏波强度的差异. 本文提出的一维与二维爆轰传播的时空关联方法不仅有助于认知斜爆轰起爆、过驱爆轰产生、胞格爆轰演化的三阶段规律, 还可以对比揭示壁面、边界层和黏性效应的影响, 应用在斜爆轰发动机燃烧室设计中能够有效节约计算时间和成本, 并降低复杂度. 相似文献
19.
为了研究退役单基药的冲击起爆特性,参照GJB772A-97中卡片式隔板法实验方法,分别开展了退役单基药的连续爆速实验、冲击波感度实验及锰铜压力计实验,观测了其冲击起爆的爆轰建立过程,得到了临界隔板值以及临界起爆压力。在连续爆速实验中,隔板厚度为50 mm时,观察到了退役单基药反应冲击波不断增长的过程,并在90mm处转变为爆轰; 在冲击波感度以及锰铜压力计实验中,测得其临界隔板厚度为50~52 mm,临界起爆压力为1.35~1.49 GPa。对退役单基药的冲击起爆过程进行了数值模拟,结合三种实验的实验结果,标定了其点火增长模型反应速率方程参数。
相似文献20.
Three-dimensional (3-D) detonation structure transformations from rectangular and diagonal modes into spinning modes in a narrow square tube are investigated by high-resolution simulation. Numerical simulations are performed with a Riemann solver of the HLLC-type, new cell-based structured adaptive mesh refinement data structure, high-order, parallel adaptive mesh refinement reactive flow code. A simplified one-step kinetic reaction model is used to reveal the 3-D detonation structure. The four different types of initial disturbances applied in the ZND profiles lead to the structures of rectangular in phase, rectangular out of phase, rectangular partial out of phase and diagonal, respectively, during the initial stages of detonation propagation. Eventually, all these detonation structures evolve into the self-sustained spinning detonations. The asymmetric disturbance leads to a stable spinning detonation much faster than the rest. The important features in the formation of spinning detonation are revealed using a 3-D visualization, and a remarkable qualitative agreement with experimental and numerical results is obtained with respect to the transverse wave dynamics and detonation front structures. The transverse wave collisions produce the unburnt gas pockets and the energy to sustain the detonation front propagation and distortion. The periodic pressure oscillation of front plays a complex role as it shifts the reaction zone structure with an accompanying change in the driving energy of transition and the detonation parameters which result in the more distorted front and the unstable detonation. Eventually, the unstable distorted detonation evolves into a spinning detonation. 相似文献