Vigor Yang

Numerical Investigation of Combustion/Shock-train Interactions in a Dual-Mode Scramjet Engine

A high-resolution numerical study is carried out to investigate the transient process of the combustion and the shock-train developments in an ethylene-fueled directconnect dual-mode scramjet combustor. The transient simulation begins with the supersonic air flow development followed by fuel injection. Air-throttling is then applied at the expansion part of the combustor to provide mass addition to block the flow to subsonic speed. The ignition occurs several milliseconds later when the fuel and air are mixed sufficiently. The pressure build up by the combustion leads to the shock train formation in the isolator section that advances to the exit of the intake nozzle. Then, the air-throttling is deactivated and the exhaust process begins and the situation before the air-throttling is restored. Present simulation shows the detailed processes in the dual-mode scramjet combustor for better understanding of the operation regimes and characteristics.

High Resolution Numerical Study on the Supersonic Turbulent Flame Structures and Dynamics in Dual Combustion Ramjet

Numerical study is carried out to investigate the characteristics of supersonic turbulent combustion in Dual Combustion Ramjet(DCR) engine using a multi-dimensional 5-order high resolution scheme. Two series of numerical experiment are carried out for the DCR combustors with various divergence angles and the length of the constant area combustor section. Operating conditions are selected by considering the flight conditions. Two different combustion modes are found by the investigation of the results depending on the formation of Mach reflection. It is analyzed that the relation between the turbulent combustion and the formation of the Mach reflection by the variation of scalar dissipation rate. Dynamic characteristics the turbulent supersonic combustion were investigated by the variation of wall pressure compared with other properties. Critical conditions for the combustion stabilization are reasoned from the characteristics of the turbulent combustion. The detailed mechanism of coupling between the compressibility effects and the turbulent combustion is understood as they are supporting with each other, similarly in detonation phenomena.

DES Study of H 2 +CO Turbulent Combustion with Supersonic Coflow Air at Elevated Enthalpy Condition

High-resolution numerical study is carried out to investigate the flame stability of the turbulent supersonic combustion in a Dual-Combustion Ramjet (DCR). The auto-ignition in a shear layer between hydrogen/carbon-monoxide syngas and air was studied at elevated enthalpy condition. Comparison of a constant area combustor and a combustor with a small divergence angle shows that the supersonic combustion has a characteristics of the lifted flame and its stability is influenced significantly by the compressibility.

Detonation Wave Simulation of Thermally Cracked JP-7 Fuel/Oxygen Mixture using Induction Parameter Modeling

The detonation wave characteristics of JP-7 and oxygen mixture is investigated by one-step induction parameter model (IPM) obtained from a detailed chemistry mechanism. A general procedure of obtaining reliable one-step kinetics IPM for hydrocarbon mixture from the fully detailed chemistry is described in this study. The IPM is obtained by the reconstruction of the induction time database obtained from a detailed kinetics library. The IPM was confirmed by the comparison of the induction time calculations with that from detailed kinetics. The IPM is later implemented to a fluid dynamics code and applied for the numerical simulation of detonation wave propagation. The numerical results show the detailed characteristics of the detonation wave propagation in JP-7 and oxygen mixture at affordable computing time, which is not be possible by the direct application of the detailed chemical kinetics mechanism of hydrocarbon fuel combustion.

Capturing Unstable Wrinkled Oblique Detonation Wave Front by Hi-Fi Numerical Simulation

Numerical studies were carried out to investigate the cell-like unsteady structure of oblique detonation wave (ODW) with the systematical examination of the effect of grid resolutions. To focus on the effect of activation energy, computations were carried out for a fixed flow condition of Mach number 7 flow over wedge of 30 o turning angle with dimensionless heat addition of 10.0. The ODW front remains stable for low activation energy cases regardless of grid resolution, but becomes unstable for high activation energies resulting cell-like wave front structure. Similarly to ordinary normal detonation wave (NDW), intermediate activation energy results in regular oscillation, but higher one results in irregular oscillation. However, the wave structure of unstable ODW was quite different from NDW. Triple points and transverse waves propagate downstream only for the present flow conditions, and numerically simulated smoked foil record exhibits several traces of triple points those rarely intersects with each other. Several sources of the instability were conjectured from the highly refined results. Since the reaction wave behind a shock wave becomes unstable easily by any disturbances, ODW front becomes unstable and results in cell-like front structures by vorticity generated pressure waves and/or the reflected shock wave originating from the triple point. The combined effects of the different sources of instabilities exhibit highly unstable and very complex flow field behind the unstable ODW.

Numerical Analysis of Turbulent Combustion Flow in HyShot Scramjet Engine

This paper describes numerical efforts to investigate combustion characteristics of HyShot scramjet combustor, where gaseous hydrogen is transversely injected into a supersonic cross flow. The corresponding altitude, angle of attack, and equivalence ratio are 35-23km, 0°, and 0.426 respectively. H2 and OH mass fraction show that the upstream recirculation region generated by the fuel injection has flame-holding effects. Twodimensional simulation reasonably predicts combustor inner pressure distribution and reveals periodic combustion characteristics of HyShot scramjet combustor. Altitude effects are also investigated and the strength of instability and subsonic boundary layer thickness affect the combustion efficiency according to altitudes.

Numerical Study of Detonation Wave Propagation in CWI System

A numerical study is carried out on the detonation wave propagation through a T-shaped flame tube, which represents a crucial part of the combustion wave ignition (CWI) system aimed for simultaneous ignition of multiple combustion chambers by delivering detonation waves. The formulation includes the Euler equations and an induction-parameter model. The reaction rate is treated based on a chemical kinetics database obtained from a detailed chemistry mechanism. A second-order implicit time integration and a thirdorder TVD algorithm are implemented to solve the theoretical model numerically. A total of more than two-million grid points are used to provide direct insight into the dynamics of the detonation wave. Several important phenomena including detonation wave propagation, degeneration, and re-initiation are carefully examined. Information obtained can be effectively used to facilitate the design and optimization of the flame tubes of CWI systems.