Nobuyuki Tsuboi

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.

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.

Performance on a Pulse Detonation Engine Under Subsonic and Supersonic Flight Conditions

In a Pulse Detonation Engine (PDE), an exit nozzle enhances thrust generation, maintains operating pressure and also controls operating frequency. The performance of a PDE, under subsonic and supersonic flight conditions, was assessed using two parametric studies. The first of these parametric studies employs a 2D CFD model and quantifies the relative impact of four different but separate exit nozzle shapes namely a Converging and Diverging (CD) nozzle, a diverging nozzle, a straight nozzle and a converging nozzle where as a second parametric model uses a quasi-1D model for predicting the effect of a CD nozzle geometry parameters on the systems-level performance of a PDE. The 2D CFD performance model predictions for the subsonic flight (Mach number (Minf) = 0.8 and altitude (hinf) = 20 kft), using single pulse simulations of the detonation and the blowdown processes, show that the fuel-specific impulse Ispf, is higher for the case of a diverging nozzle when compared to all other nozzles. These results are in agreement with the results reported earlier [14,20] in the literature. The 2D CFD performance model predictions of a PDE under supersonic flight conditions (Minf = 3.0 and hinf = 30 kft), obtained using single pulse simulations of the detonation and the blowdown processes, show that the Ispf, total impulse and thrust generated are higher for the case of the diverging nozzle and the CD nozzle, when compared to the performance metrics of the straight nozzle or the diverging nozzle. A second parametric study employs the Q1D limit cycle model, and the exit CD nozzle contraction ratio (Rnc) is varied from 1.6 to 6.4. For the subsonic flight conditions, Ispf increases with increasing values of the exit nozzle contraction ratio and attains a constant value of 1600 for an exit nozzle contraction ratio of 3.0. For the supersonic flight conditions, Ispf increases with increasing values of the exit nozzle contraction ratio and attains a constant value of 1950 for Rnc > 5.0. The design choice of the optimum value for Rnc is predicted to be a compromise between optimizing the performance metric Ispf and generating the required thrust.

Fundamental Study on Pressure Oscillation in a Liquid Rocket Engine Combustion Chamber

An oscillation of the combustion field is numerically studied inside a model combustor with two-dimensional configuration. It is found that the pressure oscillation consists of transverse and longitudinal modes and the amplitude of the pressure fluctuation is less than 0.5% of the chamber pressure. The periods of each oscillation mode is estimated and visualized by the numerical results. In addition, for deep understanding of the cause of the combustion instability, we estimate a fluctuation energy of the flow field based on the numerical results and discuss its ability to explain the numerical results.

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.

Numerical Study and Performance Evaluation for Pulse Detonation Engine with an Aerospike Nozzle

The propulsive performance was estimated for the H2/Air PDE with an aerospike exhaust nozzle using multi-cycle two-dimensional limit cycle simulations with the detailed chemical reaction model. The present simulation also compared with the results for a convergingdiverging nozzle. The present results show that Ispf and F for the aerospike nozzle is 14% and 15% lower than those for the CD nozzle at M=2.1 and H=9.3 km. Most of the thrust for the CD nozzle is produced by the momentum thrust, however, the pressure thrust for the aerospike nozzle is approximately 30-50% of the momentum thrust.

Numerical and Experimental Study of Detonation Propagation in a Rectangular Tube with Obstacles

When detonation propagates in tubes with obstacles or with variable section, it is fundamentally an important issue to elucidate how detonation fails or re-initiates in such tubes. In the present study experiments and numerical simulation are performed to investigate mechanisms of failure and re-initiation of detonation propagation in obstacled tubes. First of all, numerical simulation is validated by comparing data with experiments to analyze propagation mechanism of detonation in obstacled tubes. Two different obstacle configurations, staggered and symmetrical array, are used to see detonation failure and re-initiations. It is found that detonation failure occurs when it collides with obstacles to become expansion waves and re-initiations behind combustion wave fronts for both staggered and symmetrical cases. Jet ignition promotes fast deflagration to detonation in the symmetrical obstacle configurations.