Numerical Simulation of Gaseous Detonation of H_2-O_2 Mixture with Detailed Chemical Reaction Model

采用高精度的ENO格式和基于基元化学反应的真实化学反应模型求解氢氧混合气体一维爆轰波的精细结构。采用直接起爆方法得到稳定传播的爆轰波,计算的爆轰波阵面参数和实验相当符合。对爆轰波反应区化学反应的研究表明,参与反应的不同组分具有不同类型的变化特征。网格尺寸影响的研究表明,计算结果的精度随着网格尺寸的增加而增加,并能保持较好的收敛性。移动网格研究结果表明,网格运动速度和爆轰速度接近时,两者的相互作用对计算结果产生一定影响。

爆轰波在楔面上反射数值分析

应用基元反应模型和频散可控耗散格式(DCD)对氢氧爆轰波在楔面反射进行了数值模拟.计算中氢氧混合物的化学反应采用了8种组分20个反应方程式.在处理化学反应引起的刚性问题时采用了时间算子分裂的方法.模拟了爆轰波在楔面反射由马赫反射向规则反射转变的过程,得到了反射转变临界角,同时考虑了初始压力和组分的影响,并和实验及理论分析结果进行了比较,结果是令人满意的.

The cellular structure of a two-dimensional H2/O2/Ar detonation wave

In this paper, the cellular structure of a two-dimensional detonation wave in a low pressure H2/O2/Ar mixture calculated with a detailed chemical reaction model, high order scheme and high resolution grids is investigated. The regular cellular structure is produced about 1 ms after introducing perturbations in the reaction zone of a steady one-dimensional detonation wave. It is found from the present resolution study that the discrepancies concerning the structure type arising from the coarser grid employed can be resolved using a sufficiently fine grid size of 0.05 mm and below and shows a double-Mach-like strong-type configuration. During the structure evolution process, the structure configuration does not change much in the periods before and after the triple point collision. Through the triple point collision, three regular collision processes are observed and are followed by a quick change to the double-Mach-like configuration. The simulated structure tracks show that there are three different tracks associated with different triple points or the kink on the transverse wave. Comparisons with previous work and experiments indicate the presence of a strong structure for an ordinary detonation.

The Structure and Evolution of a Two-Dimensional H2/O2/Ar Cellular Detonation

This paper reports on two-dimensional numerical simulation of cellular detonation wave in a / / mixture with low initial pressure using a detailed chemical reaction model and high order WENO scheme. Before the final equilibrium structure is produced, a fairly regular but still non-equilibrium mode is observed during the early stage of structure formation process. The numerically tracked detonation cells show that the cell size always adapts to the channel height such that the cell ratio is fairly independent of the grid sizes and initial and boundary conditions. During the structural evolution in a detonation cell, even as the simulated detonation wave characteristics suggest the presence of an ordinary detonation, the evolving instantaneous detonation state indicates a mainly underdriven state. As a considerable region of the gas mixture in a cell is observed to be ignited by the incident wave and transverse wave, it is further suggested that these two said waves play an essential role in the detonation propagation.

Forward-Running Detonation Drivers for High-Enthalpy Shock Tunnels

To improve the quality of driving flows generated with detonation-driven shock tunnels operated in the forward-running mode, various detonation drivers with specially designed sections were examined. Four configurations of the specially designed section, three with different converging angles and one with a cavity ring, were simulated by solving the Euler equations implemented with a pseudo kinetic reaction model. From the first three cases, it is observed that the reflection of detonation fronts at the converging wall results in an upstream-traveling shock wave that can increase the flow pressure that has decreased due to expansion waves, which leads to improvement of the driving flow. The configuration with a cavity ring is found to be more promising because the upstream-traveling shock wave appears stronger and the detonation front is less overdriven. Although pressure fluctuations due to shock wave focusing and shock wave reflection are observable in these detonation-drivers, they attenuate very rapidly to an acceptable level as the detonation wave propagates downstream. Based on the numerical observations, a new detonation-driven shock tunnel with a cavity ring is designed and installed for experimental investigation. Experimental results confirm the conclusion drawn from numerical simulations. The generated driving flow in this shock tunnel could maintain uniformity for as long as 4 ms. Feasibility of the proposed detonation driver for high-enthalpy shock tunnels is well demonstrated.

爆轰波在弯管内传播过程数值分析

应用基元反应模型和频散可控耗散格式(DCD)对氢氧爆轰波在弯管内的传播过程进行了数值模拟.计算中氢氧混合物化学反应采用了8种组分20个反应方程式.在处理化学反应引起的刚性问题时采用了时间算子分裂的方法.计算结果表明,在弯管小曲率半径壁面附近,由于膨胀稀疏作用,爆轰波强度减弱,在局部出现前导激波与放热反应区的解藕以及二次起爆现象;在弯管大曲率半径壁面上爆轰波在马赫反射和正规反射之间相互转变,使爆轰波加强.弯管内的爆轰现象与弯管曲率半径有关.

Wave Dynamic Processes in Cellular Detonation Reflection from Wedges

When the cell width of the incident detonation wave (IDW) is comparable to or larger than the Mach stem height, self-similarity will fail during IDW reflection from a wedge surface. In this paper, the detonation reflection from wedges is investigated for the wave dynamic processes occurring in the wave front, including transverse shock motion and detonation cell variations behind the Mach stem. A detailed reaction model is implemented to simulate two-dimensional cellular detonations in stoichiometric mixtures of H (2)/O (2) diluted by Argon. The numerical results show that the transverse waves, which cross the triple point trajectory of Mach reflection, travel along the Mach stem and reflect back from the wedge surface, control the size of the cells in the region swept by the Mach stem. It is the energy carried by these transverse waves that sustains the triple-wave-collision with a higher frequency within the over-driven Mach stem. In some cases, local wave dynamic processes and wave structures play a dominant role in determining the pattern of cellular record, leading to the fact that the cellular patterns after the Mach stem exhibit some peculiar modes.

气相爆轰波基元反应模型数值模拟

应用频散可控格式和基元反应模型计算了氢气-氧气和氢气-空气混合物的爆轰波一维结构，并对爆轰波在二维轴对称突扩截面管内的传播过程进行了数值模拟。采用算子分裂的方法来处理化学反应的刚性问题。计算结果表明，频散可控格式可以精确捕捉爆轰波及其反射过程。爆轰波在突扩截面处绕射，由于稀疏波的作用而引起局部熄爆现象。数值结果还反应出，在一定条件下，熄爆区域可以二次起爆，而且二次起爆过程与可燃混合气体的敏感度有关，对于敏感度高的可燃气体，由于爆轰波具有较强的自持能力，其波阵面在绕射过程中所产生的局部熄爆区后会自动再次起爆

气相爆轰基元反应模型数值模拟

采用基元反应模型和高精度的ENO格式对气相爆轰进行数值研究，对H2／O2／Ar混合气体起爆和爆轰波传播过程的数值模拟结果表明，计算的爆轰波阵面参数和实验相当符合。数值研究的结果还表明，爆轰波反应区中参与反应的不同组分具有不同类型的变化特征。计算结果的精度随着网格尺寸增加而增加，并能保持较好的收敛性。

Numerical Investigation On Detonation Cell Evolution In A Channel With Area-Changing Cross Section

The two-dimensional cellular detonation propagating in a channel with area-changing cross section was numerically simulated with the dispersion-controlled dissipative scheme and a detailed chemical reaction model. Effects of the flow expansion and compression on the cellular detonation cell were investigated to illustrate the mechanism of the transverse wave development and the cellular detonation cell evolution. By examining gas composition variations behind the leading shock, the chemical reaction rate, the reaction zone length, and thermodynamic parameters, two kinds of the abnormal detonation waves were identified. To explore their development mechanism, chemical reactions, reflected shocks and rarefaction waves were discussed, which interact with each other and affect the cellular detonation in different ways.

Numerical Investigation On Evolution Of Cylindrical Cellular Detonation

Cylindrical cellular detonation is numerically investigated by solving two-dimensional reactive Euler equations with a finite volume method on a two-dimensional self-adaptive unstructured mesh. The one-step reversible chemical reaction model is applied to simplify the control parameters of chemical reaction. Numerical results demonstrate the evolution of cellular cell splitting of cylindrical cellular detonation explored in experimentas. Split of cellular structures shows different features in the near-field and far-field from the initiation zone. Variation of the local curvature is a key factor in the behavior of cell split of cylindrical cellular detonation in propagation. Numerical results show that split of cellular structures comes from the self-organization of transverse waves corresponding to the development of small disturbances along the detonation front related to detonation instability.

氢氧混合气体爆轰波的真实化学反应模型数值模拟

采用高精度的ENO格式和基于基元化学反应的真实化学反应模型求解氢氧混合气体一维爆轰波的精细结构。采用直接起爆方法得到稳定传播的爆轰波，计算的爆轰波阵面参数和实验相当符合。对爆轰波反应区化学反应的研究表明，参与反应的不同组分具有不同类型的变化特征。网格尺寸影响的研究表明，计算结果的精度随着网格尺寸的增加而增加，并能保持较好的收敛性。移动网格研究结果表明，网格运动速度和爆轰速度接近时，两者的相互作用对计算结果产生一定影响。

气相爆轰波马赫反射的实验和数值研究

爆燃和爆轰是自然界中普遍存在的两种自然现象。在一定条件下爆燃完成向爆轰的转变，爆轰形成以后会出现典型的胞格结构，在爆轰波传播过程中遇到障碍物时会发生马赫反射。对这些现象的理论和实验研究在工程和科学上都有着重大的意义。在本文的实验研究中，采用爆轰激波管和烟熏膜技术对可燃气体DDT过程及爆轰波马赫反射问题进行了研究。在不同初压和楔角的情况下进行了系统的实验，得到了清晰的胞格结构图象和三波点轨迹图象。在本文的数值模拟中采用了简化的二阶段化学反应模型，整个化学反应过程被分为两个阶段：诱导反应阶段和放热反应阶段。该模型采用两个无量纲参数α和β来表示化学反应的进程。初始时刻两个参数值都为1，诱导反应开始时α的值由1逐渐减小到0，进入放热反应阶段β的值逐渐减小直到化学反应达到平衡。本文采用了全新的数值方法CE／SE对可燃气体的DDT过程和爆轰波马赫反射问题进行了数值模拟。CE／SE方法是一种在概念和方法上都和以往不同的数值方法。该方法具有构造简单、分辨率高等优点，同时格式保证了在局部和全局均满足时空意义上的守恒律。本文的研究结果表明：爆轰波遇到楔面会发生类似冲击波的正规反射和马赫反射现象。在不同楔角和初压条件下，反射前后爆轰波的胞格尺寸、形状等性质都会有明显的差别。同时三波点迹线与楔面的夹角也会有相应的变化。这些结果对于深入理解可燃气体的DDT过程和爆轰波的马赫反应射机理有重要价值。最后需要提出的是我们把全新的CE／SE方法推广到带有化学反应的流动计算中，计算结果表明这种推广是成功的。

Numerical Study on Critical Wedge Angle of Cellular Detonation Reflections

The critical wedge angle (CWA) for the transition from regular reflection (RR) to Mach reflection (MR) of a cellular detonation wave is studied numerically by an improved space-time conservation element and solution element method together with a two-step chemical reaction model. The accuracy of that numerical way is verified by simulating cellular detonation reflections at a 19.3∘ wedge. The planar and cellular detonation reflections over 45∘–55∘ wedges are also simulated. When the cellular detonation wave is over a 50∘ wedge, numerical results show a new phenomenon that RR and MR occur alternately. The transition process between RR and MR is investigated with the local pressure contours. Numerical analysis shows that the cellular structure is the essential reason for the new phenomenon and the CWA of detonation reflection is not a certain angle but an angle range.