Pressure profiles in detonation cells with rectangular and diagonal structures

Experimental results presented in this work enable us to classify the three-dimensional structure of the detonation into two fundamental types: a rectangular structure and a diagonal structure. The rectangular structure is well documented in the literature and consists of orthogonal waves travelling independently from each another. The soot record in this case shows the classical diamond detonation cell exhibiting ‘slapping waves’. The experiments indicate that the diagonal structure is a structure with the triple point intersections moving along the diagonal line of the tube cross section. The axes of the transverse waves are canted at 45 degrees to the wall, accounting for the lack of slapping waves. It is possible to reproduce these diagonal structures by appropriately controlling the experimental ignition procedure. The characteristics of the diagonal structure show some similarities with detonation structure in round tube. Pressure measurements recorded along the central axis of the cellular structure show a series of pressure peaks, depending on the type of structure and the position inside the detonation cell. Pressure profiles measured for the whole length of the two types of detonation cells show that the intensity of the shock front is higher and the length of the detonation cell is shorter for the diagonal structures. Received 17 May 2000 / Accepted 29 November 2000     

直管内胞格爆轰的基元反应数值研究

基于基元反应和二维欧拉方程，对直管内胞格爆轰进行了数值模拟。采用5阶WENO(weighted essentially nonoscillatory scheme)求解对流项，采用2阶附加半隐的龙格-库塔法处理化学反应源相引起的刚性。获得了密度、压力、温度和典型组元质量分数流场及数值胞格结构等。结果表明:网格精度的差异明显影响胞格的规则性和爆轰的平衡模数，随着网格尺度的减小，胞格由不规则变为规则。预混气组成、初压、初温及管道宽度给定，三波点数收敛为确定值。足够强度的初始扰动可再现胞格爆轰，最终形成的自持胞格爆轰模数与初始扰动的形状、大小、位置均无关。沿胞格中心线，爆轰波速度变化范围为0.88DCJ~1.5DCJ，爆轰波平均速度与CJ爆轰速度仅偏差0.88％。峰值压力与初压之比为14~50。计算爆轰波平均速度、胞格宽长比与实验值基本一致，但计算胞格宽度比实验值略小。数值模拟加深了对横波的产生和发展、未反应气囊、爆轰胞格的二次起爆等胞格爆轰特性的认识。     

可燃气体中激波与障碍物作用在下游形成爆轰波的数值研究

对平面激波和单个矩形障碍物作用的过程进行了数值模拟,研究了反射产生的上行爆轰波在下游可燃气体中形成爆轰波的过程。数值结果表明,下游爆轰波形成过程主要有2种模式:爆轰波直接绕射和绕射波在上壁面反射,这和已有的实验结果是一致的。通过研究下游爆轰波的形成过程受入射激波马赫数、混合气体的压力和管道尺度的影响,分析了上游爆轰波向下游传播的波动力学过程,讨论了2种形成过程的作用规律和控制因素,阐明了下游爆轰波的形成规律。     

Numerical simulation of spinning detonation in square tube

A single spinning detonation wave propagating in a square tube is simulated three-dimensionally with the detailed chemical reaction mechanism for hydrogen/air mixture proposed by Petersen and Hanson. The spinning detonation is composed of a transverse detonation rotating around the wall normal to the tube axis, triple lines propagating partially out of phase, and a short pressure trail. The formation of an unburned gas pocket behind the detonation front was not observed in the present simulations because the rotating transverse detonation completely consumed the unburned gas. The calculated profiles of instantaneous OH mass fraction have a keystone shape behind the detonation front. The numerical results for the pitch and track angle on the tube wall agree well with the experimental results. This paper is based on work that was presented at the 20th International Colloquium on the Dynamics of Explosions and Reactive Systems at Montreal, Canada, from July 31 to August 5, 2005.     

孔板扰动对爆轰波胞格结构特性影响的实验研究

实验采用稳定预混气2H₂+O₂+3Ar及不稳定预混气C₂H₂+5N₂O和CH₄+2O₂,在圆形爆轰管内通过烟膜手段记录了爆轰波的胞格结构,得到了胞格尺寸与初始压力之间的关系式;研究了胞格结构在扰动上下游的变化过程,分析了胞格不稳定性对胞格结构特征的影响,获得了爆轰波经过扰动后重新恢复至平衡状态的特征尺度。结果表明:爆轰波经过扰动后,对于稳定预混气,在扰动下游主胞格结构变得不规则,没有出现次生胞格;对于不稳定预混气,扰动下游伊始爆轰波的次生模态被抑制,由于爆轰波自身的不稳定性,随后出现了局部爆炸点及精细胞格结构;爆轰波在扰动下游传播了一段距离后恢复至平衡状态,该长度在8～15倍之间的胞格尺寸范围内变化,并且随初始压力的变化趋势并不明显。研究结果反映出爆轰波经过孔板扰动后恢复至平衡态所需的长度与爆轰波流体动力学厚度相当。     

高浓度氩气稀释气体爆轰波临界管径和临界间距关系

建立圆管及环形管道系统研究临近极限下爆轰波在管道内传播失效机理。选用C₂H₂+2.5O₂+70%Ar气体,采用光纤探针测量爆轰波在管道内传播速度,用烟迹法记录管道内爆轰波胞格结构。结果表明:初始压力远大于爆轰极限压力时,爆轰波在管道内以稳定速度传播;随着初始压力的减小,爆轰波速度逐渐降低;当初始压力一定时,爆轰波速度随着管道尺寸的减小而逐渐减小;当初始压力达到临界压力时,爆轰波在进入到管道内后其速度会逐渐衰减直至爆轰波完全失效。对于不同几何尺寸的圆管与环管,通过引入无量纲参数d/λ及w /λ(d为圆管管径,w为环管间距,λ为爆轰胞格尺寸)得出,爆轰波在管道内传播的临界圆管直径为环形间距的2倍,与理论模型结果相吻合,验证了稳态气体基于爆轰波波面曲率的失效机理。     

Three-dimensional numerical simulation of detonations in coaxial tubes

Three-dimensional numerical simulation of detonations in both a circular tube and a coaxial tube are simulated to reveal characteristics of single spinning and two-headed detonations. The numerical results show a feature of a single spinning detonation which was discovered in 1926. Transverse detonations are observed in both tubes, however, the single spinning mode maintains the complex Mach reflection whereas the two-headed mode develops periodically from the single Mach reflection to the complex one. The calculated cell aspect ratio for the two-headed mode changes from 1.09 to 1.34 as the radius of axial insert increases from r ₁/R = 0.1 to 0.9. The calculated cell aspect ratio for r ₁/R = 0.1 is close to the experimental results without an axial insert. The formation of an unreacted gas pocket behind the detonation front was not observed in the single spinning mode; however, the two-headed mode has unreacted gas pocket behind the front near the axial insert.      

Self-similar magnetogasdynamic flows accompanied by detonation and combustion waves

Magnetogasdynamic (MGD) flows with detonation waves and combustion fronts have attracted more and more attention in recent years. Intensive heat supply assures such a significant increase in the temperature and pressure behind the heat liberation fronts that the gaseous combustion products become conductive so that the flow map in the electric and magnetic fields can vary substantially as compared with ordinary gasdynamics. In the case of finite gas conductivity, when the magnetic Reynolds numbers R_m are low, the asymptotic laws of detonation wave propagation which either go over into the Chapman-Jouguet (CJ) mode (in a number of cases at a finite distance from the initiation source) or remain overcompressed, have been studied [1]. Stationary flow modes behind detonation waves have been investigated in [2] and the problem of the detonation wave originating at the closed end of the tube emerging in the stationary mode in crossed homogeneous magnetic and electric fields has been examined. Results are presented in this paper of an investigation of one-dimensional self-similar flows caused by piston motion in a hot gas mixture in which a detonation wave or combustion front is propagated. The motion is realized in external electric and magnetic fields which exert a substantial effect on the flow of the conductive combustion products. Domains of application of the governing parameters in which the various flow modes are realized are found by using a qualitative and numerical analysis. The results obtained are used to solve problems about the hypersonic gas flow around a thin wedge in an axial magnetic field.     

Experimental investigation into the detonation characteristics of hybrid RDX–ethylene–air mixtures

An experimental study is conducted to determine the detonation characteristics of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) particles dispersed in a gaseous fuel air mixture in a vertical detonation tube with an inner diameter of 200 mm and a height of 5400 mm. Experiments are performed in both ethylene–air mixtures and RDX–ethylene–air hybrid mixtures. The detonation front pressure and velocity are measured with six pressure transducers along the detonation tube. The results show that the addition of RDX assists 4.0 vol.% ethylene–air mixtures in achieving detonation. The detonation front pressure increases noticeably with dust concentration up to \(474\hbox { g/m}^{3}\) in the RDX–ethylene–air hybrid mixtures, but the velocity only increases slightly. The cellular structures of RDX–ethylene–air hybrid mixtures and ethylene–air mixtures were obtained with the use of smoked foils and exhibit irregular structures. It is found that the measured cell size has a U-shaped curve with respect to RDX concentration.     

Numerical study of three-dimensional detonation structure transformations in a narrow square tube: from rectangular and diagonal modes into spinning modes

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.     

Response of critical tube diameter phenomenon to small perturbations for gaseous detonations

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.     

不同角度分叉管道内氢气-空气爆轰传播特性

在3种角度分叉管道内开展化学计量比氢气-空气爆轰实验,采用自制的火焰传感器和烟迹法分别获得了爆轰波传播速度和胞格结构,探究了不同角度管道分叉对爆轰传播的影响。结果表明:氢气-空气爆轰在经过分叉三通时受分叉口稀疏波影响导致爆轰波衰减解耦,但随着入射激波与下游管道壁面碰撞,逐渐由规则反射向马赫反射转变,最终完成重起爆过程。其中,直通支管内爆轰衰减主要受支管入口面积的影响,随着分叉角度增大,入口面积减小,爆轰衰减程度和重起爆距离也随之减小;而分叉支管内,爆轰衰减受支管入口面积与入口渐扩程度共同影响,但随着分叉角度的增大,入口面积变为主要影响因素。不同角度分叉管内的实验结果均表明,初始压力升高能显著提高爆轰稳定性,从而削弱分叉几何结构的影响。     

Investigation of the detonation regimes in gaseous mixtures with suspended starch particles

The existence of a secondary discontinuity at the rear of a detonation front shown in experiments by Peraldi and Veyssiere (1986) in stoichiometric hydrogen-oxygen mixtures with suspended 20-m starch particles has not been explained satisfactorily. Recently Veyssiere et al. (1997) analyzed these results using a one-dimensional (1-D) numerical model, and concluded that the heat release rate provided by the burning of starch particles in gaseous detonation products is too weak to support a double-front detonation (DFD), in contrast to the case of hybrid mixtures of hydrogen-air with suspended aluminium particles in which a double-front detonation structure was observed by Veyssiere (1986). A two-dimensional (2-D) numerical model was used in the present work to investigate abovementioned experimental results for hybrid mixtures with starch particles. The formation and propagation of the detonation has been examined in the geometry similar to the experimental tube of Peraldi and Veyssiere (1986), which has an area change after 2 m of propagation from the ignition point from a 69 mm dia. section to a 53 mm 53 mm square cross section corresponding to a 33% area contraction. It is shown that the detonation propagation regime in these experiments has a different nature from the double-front detonation observed in hybrid mixtures with aluminium particles. The detonation propagates as a pseudo-gas detonation (PGD) because starch particles release their heat downstream of the CJ plane giving rise to a non-stationary compression wave. The discontinuity wave at the rear of the detonation front is due to the interaction of the leading detonation front with the tube contraction, and is detected at the farthest pressure gauge location because the tube length is insufficient for the perturbation generated by the tube contraction to decay. Thus, numerical simulations explain experimental observations made by Peraldi and Veyssiere (1986). Received 5 July 1997 / Accepted 13 July 1998     

氢燃料缓燃向爆震转捩过程中波与火焰的匹配特性

为了解氢燃料爆震过程中压力波与火焰之间相互匹配的特性,在60mm60mm2000mm 方 爆震管内,用氢气和空气混合物进行了单爆震性能研究。在爆震转捩区内布置压力传感器与离子探针,用来 监控压力波和火焰的信号,同时利用高速摄影仪集中拍摄转捩区域。根据压力波和火焰面在爆震管不同时刻 的强度特性、速度特性及位置特性来分析爆震过程中波与火焰匹配的规律。结果表明:压力波和火焰的强度 呈现为相互正反馈匹配性质;缓燃向爆震转捩(DDT)过程中,压力波和火焰的速度表现为相互交替的变化过 程,且缓燃阶段中火焰速度的增幅大于压力波速度的增幅;当火焰面追赶上激波时,产生过爆,火焰面会临时 位于激波前面;在过爆衰减为正常爆震波的过程中,激波在火焰前面。     

Two-cell detonation: losses effects on cellular structure and propagation in rich H2–NO2/N2O4–Ar mixtures

Detonation experiments in H₂–NO₂/N₂O₄–Ar mixtures (Equivalence ratio 1.2 and initial pressure lower than 0.1 MPa) confined in a tube of internal diameter 52 mm reveal two propagation regimes depending on initial pressure: (1) a quasi-CJ regime is observed along with a double cellular structure at high pressures; (2) at lower pressures, a low velocity detonation regime is observed with a single structure. Transition between this two regimes happens when the spinning detonation of the larger cell vanishes. Each detonation regime is characterized by velocity and pressure measurements and cellular structure records. Coherence between all experimental data for each experiment leads in assumption that losses are responsible for the transition between one regime to another. In a second part, we study such behaviour for a two-step mixture through numerical simulations using a global two-step chemical kinetics and a simple losses model. Numerical simulations qualitatively agree with experiments. Both detonation regimes with their own cellular structures are reproduced.     

可爆性气体爆炸极限和爆燃转变成爆轰的研究

我们成功地研制了长为6.6m、内径为100mm的柱形爆炸激波管。利用此激波管我们研究了氢气和氧气混合物的爆炸特性。研究表明:氢气和氧气混合物的可爆性极限为25％H2至84％H2（体积比）;混合物起爆的临界初始压力P0c近似与混合物的浓度无关。我们还用石英传感器技术测量了混合物从爆燃转变为爆轰的过程（DDT）,确定了爆炸速度、爆炸压力与混合物初始压力P0的关系。爆燃波速度D和压力P快速增加,并且DG0（声速）时,爆燃波能转变成爆轰。爆燃波速度D和压力P衰减时,爆燃波将熄灭。氢氧混合物浓度接近上限时,爆燃向爆轰转变时的爆轰呈过激励状态,然后逐渐趋于正常爆轰。C-J理论可近似预估气体爆轰参数。     

Reignition of detonations by reflected shocks

Numerical simulations are used to study the diffraction, decay, and reignition that occurs when a detonation propagates past an increase in cross-sectional area in a rectangular tube. The computations solve the time-dependent two-dimensional equations describing a reactive flow in an argon-diluted stoichiometric hydrogen-oxygen mixture at atmospheric pressure. Previous studies have shown that soon after transmission to a larger area, the reaction front decouples from the leading shock and forms a decaying blast wave (“bubble”) in the larger tube. Then, depending on the initial conditions, the detonation either continues to decay or is reignited as the bubble reflects off confining surfaces. For a strongly overdriven initiating detonation, reignition occurs through an interaction between the bubble and the original contact surface. For a more weakly driven system, reignition can occur in two ways: either in the slip line and Mach stem of the Mach reflection formed when the bubble reflects off the bottom surface of the tube, or by multiple shock interactions that occur when the reflected bubble overtakes the initial detonation front. The computations show the evolution and development of the cellular structure of the steady detonation front. Submitted to the 14th International Colloquium on the Dynamics of Energetic and Reactive Systems, Coimbra, Portugal, August, 1993     

爆轰波在阻尼管道中声吸收的实验研究

实验旨在研究气相爆轰波在阻尼管道 (管壁上衬有吸收材料 )中传播时的衰减现象。先是在光滑管壁的管道中产生稳定的具有胞格结构的爆轰波 ,然后使其通过专门设计的管壁上衬有吸收材料 (金属丝网或不锈钢纤维 )的阻尼段。利用高速摄影、压力传感器和烟迹技术等手段 ,记录和测试了阻尼段对几种混合气体爆轰波的传播速度、爆压及胞格结构产生的影响。实验分别在方管和圆管中进行。发现在某些条件下爆轰波可以被衰减成强爆燃。     

氢气/丙烷/空气预混气体爆轰性能的实验研究

通过采用压力传感器和烟灰板两种测试设备,开展了常温常压下氢气/丙烷和空气混合气体爆轰性能的实验研究。实验过程中观察到自持爆轰波,爆轰速度比值在0.99~1之间,爆轰压力比值在0.8~1.2之间。爆轰胞格尺寸在10~50 mm范围内,建立了爆轰胞格尺寸和化学诱导长度的关系式。随着丙烷不断添加,爆轰速度减小,而爆轰压力和胞格尺寸增加。这种变化趋势起初较快,而后变缓。因为起初氢气摩尔分数较大,混合气体趋向于氢气/空气的爆轰性能;而后因丙烷摩尔质量较大,丙烷逐渐起主要作用,混合气体表现出丙烷/空气的爆轰性能。     

H_2—O_2爆轰时Ar浓度对产生胞格结构的影响

作者在方形爆轰管中进行了H_2—O_2—Ar系统的实验研究。在由Ar稀释的H_2—O_2混合物的爆轰实验中得到了规则的胞格结构图案。也得到了胞格形成的临界曲线,并与爆炸极限曲线进行了对照,两者的趋势是一致的。另外,测量了从点火处到胞格形成处之间的距离及胞格区的长度。最后分析了氩Ar浓度对H_2—O_2爆轰的抑制作用。