A. Koichi Hayashi

Three-dimensional numerical simulation for hydrogen/air detonation: Rectangular and diagonal structures

Unsteady three-dimensional simulations of hydrogen/air detonations in a rectangular tube have been performed using a detailed chemical kinetics model to reveal its structure. The simulations clearly show detailed three-dimensional detonation modes, namely a rectangular mode and a diagonal mode. The rectangular modes that were obtained are of two types: in phase and partially out of phase. These rectangular modes consist of two two-dimensional waves, and the cell length for these modes is approximately the same as in two-dimensional simulations. The diagonal mode is shown to result from three-dimensional diagonal motion of the triple-point lines. The cell length of the diagonal mode is about three-quarters of those obtained in the two-dimensional and other three-dimensional simulations. The detonation front for both rectangular and diagonal modes adopts a complicated three-dimensional time-dependent pattern, and the results agree well with experimental observations reported by many researchers. Furthermore, formation of unreacted pockets behind the detonation is observed in the results for rectangular mode in phase. The computational results clearly capture the resulting complicated shape patterns.

Experiments and numerical simulation on methane flame quenching by water mist

Abstract The study of extinguishment using water mist has been motivated due to the phase-out of the use of halens and the search for alternative means that preserve all of the benefits of a clean total flooding agent without adverse environmental impact. With the numerical simulation, we analyzed a gas–liquid two-phase problem including water (liquid), air and methane (gas) using Eulerian equations for the liquid phase and the full Navier–Stokes equations for the gas phase. Gaseous mass, momentum and energy equations are integrated simultaneously by a Harten–Yee explicit non-MUSCL modified-flux type TVD scheme for the convective terms and a central difference scheme for the viscous terms. Liquid phase conservation equations are solved with an application of a flux-vector-splitting scheme. In the experiments in an open room (500×500×500 mm) we observed an interaction of the diffusion flame with the water mists. The results show remarkable flame quenching and a good agreement between the numerical and experimental results.

Sensitivity Analysis of Rotating Detonation Engine with a Detailed Reaction Model

D compressible Euler equations are used for hydrogen/oxygen rotating detonation engine (RDE) to perform a sensitivity analysis for rotating detonation conditions. First of all the used program was compared with the experimental data obtained by Kindracki and Wolanski. The computational average pressure just after the injection of mixture is similar to that of experimental one; about 0.2 to 0.4 MPa. Sensitivity analyses show that the inlet pressure, Mach number, and temperature have a significant effect on rotating detonation device performance. The results show a narrow window of the inlet conditions for the stable operation while achieving high performance of rotating detonation engine.

Detonation Limit Thresholds in H2/O2 Rotating Detonation Engine

The rotating detonation engine (RDE) is a new engine system using detonation, which may provide a higher performance and smaller and simpler design in comparison with the pulse detonation engine (PDE) and other traditional engines. However the research on RDE stands just at the first step now. The authors perform a numerical analysis to understand about RDE in terms of features of rotating detonation and its propagation limit. The lower threshold pressure of detonation limit was 2.6 MPa and the upper threshold pressure of detonation limit was 7.1 MPa. The engine performance analysis shows that the maximum mixture based specific impulse (I spm ) was about 440 s, which is comparable with that of the present typical rocket engine.

Aluminum dust ignition behind reflected shock wave: two-dimensional simulations

In this paper results of parallel computer simulations on aluminum dust ignition behind a reflected shock wave are presented. Computations show the time-evolution of a complicated flow field created due to a shock wave collision with a pile of dust, shock reflection from a wall, and its interaction with vortices. Particles, blown away by the incident shock, are heated mainly behind the reflected shock wave. The estimated ignition delay time is of the order of 80–100 μs and is a strong function of the incident shock wave strength. The simulations show that it may be very difficult to ignite aluminum particles when the incident shock wave Mach number is smaller than about Ms ≈ 3, while for stronger shocks the estimated ignition delay time quickly decreases.

Numerical Analysis of Threshold of Limit Detonation in Rotating Detonation Engine

Rotating Detonation Engine (RDE) is a new kind of detonation engine, which may provide a high performance with a smaller and simpler system than the traditional ones. In order to optimize RDE system, the threshold of detonation limit must be studied for its best design and its best run. In this paper, the following four aspects are discussed: (1) what will be happen to the rotating detonation li mit when the computational area is doubled; (2) what will be happen to rotating detonation when the ignition energy is increased; (3) what will be happen to specific impulse (Isp) when the ignition energy is increased. The results show that the lower detonation limit gets the computational area effct, but the upper one does not. The max specific impulse of Ispf is about 4000 s and that of Ispm is about 450 s.

Deployment and Flight Test of Inflatable Membrane Aeroshell using Large Scientific Balloon

A flexible aeroshell for atmospheric entry vehicles has attracted attention as an innovative space transportation system because the aerodynamic heating during an atmospheric entry can be reduced dramatically due to its low ballistic coefficient. We have researched and developed a capsule-type vehicle with a flare-type membrane aeroshell sustained by an inflatable torus frame. One of the key technologies is to develop a large and low-mass aeroshell including inflatable structures. As a part of the development, a miniature experimental vehicle was developed and a balloon drop test was carried out in order to acquire the vehicle with inflatable structures in a high altitude and a free flight condition. The diameter, the total mass, and the ballistic coefficient of the experimental vehicle are 1.264m, 3.375kg, and 2.69kg/m 2 , respectively and its aeroshell consists of a thin membrane flare made of nylon and a torus which can be inflated by gas pressure. The inflatable aeroshell was deployed and the experimental vehicle was separated from the balloon at an altitude of 25km. After the separation, the vehicle flied 30 minutes until a splashdown. This balloon test is very successful and fruitful and following results were achieved. 1) Remote deployment system of the inflatable aeroshell by sending a command from a ground station

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.

A New Ignition System for Pulse Detonation Engine

A new ignition system is applied to pulse detonation engine (PDE), which is flame jet ignition (FJI) system, to enhance a deflagration to detonation transition (DDT) time and length. The idea of FJI is not new, but its use to PDE has not been seen ever. The present study is to show the feasibility of FJI to PDE by comparing with a conventional spark ignition (CSI) system. FJI system has a small sub-chamber of 0.5-12.8 cm 3 in volume with a spark plug to produce a lot of ions and radicals in the PDE main chamber. Three subjects are studied: 1) to optimize the best configuration of FJI sub-chamber to obtain its basic design, 2) to evaluate FJI performance on multi-cycle operation using the best FJI configuration, 3) to visualize the ignition mechanism by FJI system in the PDE chamber. All experiments are also compared with those operated by the CSI system. As for results, the best size and design for FJI system is obtained using a non-dimensional value. The FJI system is shown to be a most effective ignition system to shorten DDT time by a factor of 3.9 comparing with the CSI system. A visualization of injection system by Schlieren movies reveals the essence of faster flame ignition and propagation by FJI system.

Front Cellular Structure and Thrust Performance on Hydrogen–Oxygen Rotating Detonation Engine

Numerical simulations of three-dimensional rotating detonation engines for a hydrogen–oxygen mixture are performed using the detailed chemistry model. The grid-resolution study indicates that the cellular structure of the detonation appears near the inner wall as the circumferential grid resolution increases. However, the effects of the grid resolution are small on Isp. The grid resolution for the high-mass-flow cases should be carefully considered because the rotating detonation velocity increases to produce higher thrust under the low grid resolution. As the annular width increases, a complicated shock structure such as a Mach stem appears, and the cycle time decreases. The effects of the annular width are small on Isp. As the number of the rotating detonations increases, the asymmetric detonation heads rotate along the circumferential direction with the same cycle time after 30 cycles. Isp for the two-waved rotating detonation engine decreases approximately 10% less than Isp for the one-waved rotating ...