Makoto Asahara

Three-Dimensional Simulation of Deflagration-to-Detonation Transition with a Detailed Chemical Reaction Model

A three-dimensional simulation of the deflagration-to-detonation transition (DDT) in a H2/O2 mixture in a rectangular tube is performed under adiabatic and isothermal wall boundary conditions. In the isothermal wall boundary case, a local explosion triggering the onset of detonation occurs near the center of the tube behind the incident shock wave, which agrees qualitatively with the two-dimensional simulation in our earlier study. In contrast, in the adiabatic case, auto-ignition is observed near the corner of the tube before the local explosion occurs on each wall behind the flame, which is accelerated by the high-temperature condition (preheated zone) caused by the generation of compression waves. The flame overtakes the incident shock and propagates toward the upper and lower walls. In some experimental studies, the local explosion occurred near the wall. Therefore, the present adiabatic case received special attention. Moreover, these phenomena are discussed in detail in terms of the flame acceleration, preheated zone, and x–t diagram.

Implementation of a Robust Weighted Compact Nonlinear Scheme for Modeling of Hydrogen/Air Detonation

In order to simulate detonation, a high-order shock-capturing scheme that models chemical reactions is implemented, and its resolution is examined by testing it on several numerical problems. A robust weighted compact nonlinear scheme (RWCNS) is adopted to take advantage of its robustness and ability to handle different flux types. This study shows the high resolution of the RWCNS compared with the conventional scheme. The results show that the RWCNS predicts the detailed vortex structure behind the detonation wavefront.

Two-Dimensional Simulation on Propagation Mechanism of H2/O2 Cylindrical Detonation with a Detailed Reaction Model: Influence of Initial Energy and Propagation Mechanism

The authors studied cylindrical detonation (CD) induced by a direct initiation in the hydrogen/oxygen gas mixture using the 2-dimensional compressible Euler equations with a detailed chemical reaction model. As the result, a cellular structure of cylindrical detonation is obtained in the maximum pressure histories such as an open-shutter photograph and a smoked-foil record in the experimental results. The influence of the initiation energy on the propagation of cylindrical detonation is studied to obtain the subcritical and supercritical regimes: The generation of new transverse wave is observed and small cells during their propagation appear just after the detonation initiation. Furthermore, the number of transverse waves increases nonlinearly near the detonation front in each condition. The generation rate of the transverse wave under the high initiation energy becomes slow because the overdriven state which produces a strong shock wave is maintained longer than that under the low initiation energy.

Coupling Problem Between Solid Tube and Shock Wave/Detonation Wave

A detonation is a combustion wave that propagates in an inflammable medium at supersonic speeds. This phenomenon is important in the fields of supersonic propulsion and combustion safety. A shock wave or explosion wave shows complicated behavior when it interacts with a structure. Studying the behavior of a pressure wave loaded by a shock wave or detonation wave in a confined tube and its interaction with the tube wall is important. This type of coupling problem has gained even more importance after the Fukushima nuclear reactor accident in 2011 and has become the topic of many studies. One difficulty with the coupling problem is how a gas or liquid couples with a solid. A numerical solution to this problem has not yet been found. In the present study, we numerically examined the one-way coupling between a shock wave/a detonation wave and a tube. We used the open-source code Elmer to calculate the solid phase and our in-house code to calculate the shock wave. We compared our numerical results for the shock wave problem with experimental results from another research group for validation and simulated the detonation to observe the physics of the solid tube behavior. The results revealed an interesting behavior in the solid tube response.

Generation and Dynamics of Sub-Transverse Wave of Cylindrical Detonation

This article shows a numerical simulation of the transverse cell in a H2/O2 diverging cylindrical detonation. An advection upstream splitting method with a diminishing variation scheme (AUSMDV scheme) and a detailed chemical kinetic model of H2/O2 by Petersen and Hanson were used to improve the numerical resolutions for fluid dynamics and for chemical kinetics, respectively. In the numerical results, the irregular cellular pattern and transverse cells were obtained by direct initiation. The numerical results indicated the detailed transverse detonation structure formed the complex Mach configuration, and sub-transverse waves on the transverse detonation were observed. These discussions suggest that the sub-transverse wave on thetransverse detonation destabilizes the cylindrical detonation front due to sub-transverse wave propagation toward the detonation front. This unstable factor from the sub-transverse wave develops the new transverse wave, which traces the fine cell, resulting in the appearance of cell bifurcation.

Numerical Analysis of Spinning Detonation Dependency on Initial Pressure Using AUSMDV Scheme

In order to investigate the fundamental characteristics of spinning detonation propagating tubes, this present study shows a numerical simulation using AUSMDV scheme which is more capable to capture detonation phenomenon clearly than TVD scheme and a detailed chemical kinetic model of H2/O2 by Petersen and Hanson. By analyzing the lower limit of spinning detonation propagation, disclosing the detonation propagation limit and the feature is the present purpose. In the numerical results, the lower limit of spinning detonation propagating in a rectangular tube has partially analyzed. The numerical results indicated the differences of the propagation limit of spinning detonation propagating in between a circular tube and a rectangular tube. Because of the number of transverse wave, spinning detonation propagating in rectangular tube is able to maintain more than circular tube’s one.

Effects of detailed chemical reaction model on detonation simulations

Unsteady two-dimensional simulations were performed for hydrogen/air mixtures in order to evaluate the effects of the detailed chemical reaction model on detonations. The reaction models in the present study are Petersen and Hanson model, and Koshi model. The pressure, specific heat release, and OH mass fraction are not affected by the reaction models, however, HO2 and H2 O2 mass fractions are dependent on them. These features also appear in the results of the zero-dimensional ignition simulation for the high pressure gas mixture. Therefore the chemical kinetic models for the high pressure affects the results of detonation simulations because the chemical properties in high pressure are significant different between them.