This paper presents the propulsive performance evaluation for the H2/Air Pulse Detonation Engine (PDE) with a converging-diverging exhaust nozzle by the system-level modeling and multi-cycle numerical simulations. This study deals with the two-dimensional and axisymmetric compressible Euler equations with a detail chemical reaction model. First, single-shot propulsive performance of simplified-PDE, which is without exhaust nozzle, is evaluated to show the validity of the numerical and performance evaluation method. The influences of the initial conditions, ignition energy, grid resolution, and scale effects on the propulsive performance are studied with the multi-cycle simulations. The present results are compared with the results calculated by Ma et al. and Harris et al. and the difference between their results and the present simulations are approximately 2-3% because their chemical reactions use one-step model with one-γ model. The effects of the specific heat ratio should be estimated for various nozzle configurations and flight conditions.
Evaluation of ground effect is important for acoustic measurement in static-firing tests on rocket motors. The effectiveness of existing acoustic impedance models is examined by comparing with some experimental results. Through the comparison and evaluation of effect of meteorological condition, it is confirmed that the existing impedance models are unsatisfactory for the evaluation of long distance propagation over a hard surface, which corresponds to the far field condition in the present static-firing tests of rocket motors. In this study, a new acoustic impedance model is proposed. From the comparison with the existing acoustic measurement data, it is shown that the new model is effective for both of near and far field propagation. The proposed model is applied to acoustic data measured in the static-firing tests of solid rocket motors, assuming distributed acoustic sources along the exhaust jet axis.
Subsonic jets at Mach number Mj = 0.9 are computed using compressible Large Eddy Simulation and Kirchhoff method in order to investigate the effects of the inflow forcing on the flow and sound field. Four parameters are varied in the jet inflow: the use of the first modes in the ring vortex excitation involving several azimuthal modes, the forcing amplitude, the thickness of disturbances, and the existence of the inflow forcing. It is confirmed that there are significant differences whether the disturbances are added or not. The inflow forcing parameter that has the most influence on the flow and sound field is the azimuthal modes. It is shown that the inflow forcing takes an important role to destroy the coherence of velocity disturbances on the shear layer and prevents high amplitude velocity and pressure fluctuations that are caused due to axisymmetric vortices. When first modes in several azimuthal modes are removed, the flow field and far field sound pressure levels are relatively consistent with experimental data.
Effect of kinds of one-component n-alkane liquid fuels on combustion characteristics was investigated experimentally using a model combustor of scramjet engine. The inlet condition of a model combustor is 2.0 of Mach number, up to 2400K of total temperature, and 0.38MPa of total pressure. Five kinds of n-alkane are tested, of which carbon numbers are 7, 8, 10, 13, and 16. They are more chemically active and less volatile with an increase of alkane carbon number. Fuels are injected to the combustor in the upstream of cavity with barbotage nitrogen gas and self-ignition performance was investigated. The result shows that self-ignition occurs with less equivalence ratio when alkane carbon number is smaller. This indicates that physical characteristic of fuel, namely volatile of fuel, is dominant for self-ignition behavior. Effect on flame-holding performance is also examined with adding pilot hydrogen and combustion is kept after cutting off pilot hydrogen with the least equivalence ratio where alkane carbon number is from 8 to 10. These points are discussed qualitatively from the conflict effect of chemical and physical properties on alkane carbon number.