Honghui Teng

Numerical study of oblique detonation wave initiation in a stoichiometric hydrogen-air mixture

Two-dimensional, oblique detonations induced by a wedge are simulated using the reactive Euler equations with a detailed chemical reaction model. The focus of this study is on the oblique shock-to-detonation transition in a stoichiometric hydrogen-air mixture. A combustible, gas mixture at low pressure and high temperature, corresponding to the realistic, inflow conditions applied in oblique detonation wave engines, is presented in this study. At practical flight conditions, the present numerical results illustrate that oblique detonation initiation is achieved through a smooth transition from a curved shock, which differs from the abrupt transition depicted in the previous studies. The formation mechanism of this smooth transition is discussed and a quantitative analysis is carried out by defining a characteristic length for the initiation process. The dependence of the initiation length on different parameters including the wedge angle, flight Mach number, and inflow Mach number is discussed. Despite the hypothetical nature of the simulation configuration, the present numerical study uses parameters we deem relevant to practical conditions and provides important observations for which future investigations can benefit from in reaching toward a rigorous theory of the formation and self-sustenance of oblique detonation waves.

Initiation structure of oblique detonation waves behind conical shocks

The understanding of oblique detonation dynamics has both inherent basic research value for high-speed compressible reacting flow and propulsion application in hypersonic aerospace systems. In this study, the oblique detonation structures formed by semi-infinite cones are investigated numerically by solving the unsteady, two-dimensional axisymmetric Euler equations with a one-step irreversible Arrhenius reaction model. The present simulation results show that a novel wave structure, featured by two distinct points where there is close-coupling between the shock and combustion front, is depicted when either the cone angle or incident Mach number is reduced. This structure is analyzed by examining the variation of the reaction length scale and comparing the flow field with that of planar, wedge-induced oblique detonations. Further simulations are performed to study the effects of chemical length scale and activation energy, which are both found to influence the formation of this novel structure. The initiat...

Investigations of Three-Dimensional Shock/Shock Interactions over Symmetrical Intersecting Wedges

This study explored inviscid supersonic corner flows induced by three-dimensional symmetrical intersecting compression wedges by introducing the spatial dimension reduction theoretical approach to transform the three-dimensional steady shock/shock interaction problem into a two-dimensional pseudosteady problem; this method allows not only wave configurations, which include regular reflection and Mach reflection, to be determined accurately, but also flowfield characteristics, which include density, temperature, pressure, and total pressure recovery coefficient near the regular reflection point (or in the vicinity of the Mach reflection triple point), as well as the location and the strength of the Mach stem. Theoretical results were compared to numerical simulation (performed by solving three-dimensional inviscid Euler equations with an non-oscillatory and non-free-parameters dissipative finite difference scheme) and analyzed thoroughly. The effects of inflow Mach number, sweep angle, and wedge angle on flowfield parameters and wave configurations were also considered. The influence of sweep angle is negligible, but the effects of Mach number and wedge angle are significant.

Numerical study of oblique detonation initiations with chain-branching kinetics

Supersonic combustion in the hydrogen fueled DLR model scramjet combustor was computationally investigated by using Large Eddy Simulation (LES) combined with the latest detailed reaction mechanism for hydrogen combustion. Two computational models were employed including a two-dimensional reduced model and a three-dimensional model with periodicity in the spanwise direction. The two-dimensional model was fully validated against the three-dimensional model and the experimental data for the wall pressure measurements and the axial velocity under non-reacting flow condition. For reacting flow, the present model shows good agreement with the experimental axial velocity and static temperature measurements. Furthermore, radical evolution and heat release analysis were conducted both qualitatively and quantitatively to reveal the flame stabilization mechanism in the DLR combustor. The results show that the combustion is characterized by a three-stage combustion mode, namely induction, radical transportation and intense turbulent combustion stages. 漏 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.To aim at improving the aerodynamic performance of hypersonic air-breathers, a family of novel waverider-based configurations which integrating two dorsal mounted engines are proposed. The key feature of this type of configurations is that the lower surface of the vehicle could fully preserve the characteristics of waveriders, thus it is conducive to enhance the lift-to-drag ratio effectively. Basic waveriders of configurations are obtained by using a method that generating waverider as two parts which are defined by the leading edge and the trailing edge respectively. The forebody of the vehicle is designed by rotating and assembling two waverider-based-surfaces, which are the front part of basic waveriders. A group of conceptual configurations with different aspect ratio is presented. Computational Fluid Dynamics is employed to evaluate the aerodynamic performance. The results demonstrate that the maximum lift-to-drag ratio of configurations is greater than 5 in viscous condition, meanwhile, the forebody could produce a good quality flowfield for the propulsion system. 漏 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.To improve the large eddy simulation鈥檚 ability of simulating complex flow fields in the scramjet, a low-dissipation solver has been developed based on the original compressible solver rhoCentralFoam within the free open source computational fluid dynamics software OpenFOAM platforms. In rhoCentralFoam, the central-upwind scheme of Kurganov and Tadmor (Kurganov-Tadmor scheme) is applied to capture the flow discontinuity, whose dissipation is too strong to resolve turbulence under finite resolution. The low-dissipation solver adopts a new hybrid scheme, which combines the dissipative Kurganov-Tadmor scheme with the nondissipative central scheme through the shock sensor, where the dissipative scheme is used to capture the flow discontinuity near shock wave and the central scheme is used to resolve the turbulence structure in the smooth flow area. In the framework of unstructured mesh algorithm, the central scheme is extended from linear order to forth order, which greatly reduces the dispersion error and weakens the oscillations near flow discontinuity. To keep the numerical stability of the central scheme, we adopt the skew-symmetric form of the convective term, which could be able to preserve the local kinetic energy and help keep the self-stability of central scheme without adding an explicit dissipative term. In addition, a low-storage TVD Runge-Kutta method for third order temporal discretization is newly implemented in the low-dissipation solver to make the time marching in order to meet the requirement of large eddy simulation. A series of benchmark problems, such as Sod shock tube test, Shu-Osher problem, Green-Taylor vortex evolution, and wall-bounded turbulence generation based on synthetic eddy method, are computed and compared to examine the low-dissipation solver鈥檚 ability of capturing flow discontinuity as well as resolving turbulence structure. The accuracy and stability of the low-dissipation solver are further validated against experimental data when the supersonic airstream flows past the flame holder structure in the scramjet model. 漏 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.A novel design method that is based on a local shape deformation technique is presented in this paper to extend the design space of waveriders. Moreover, an inviscid analysis based optimization study was carried out to research the effect of compression surface deformation on aerodynamic performances of waveriders by integrating the increment-based parameterization method, the computational fluid dynamic analysis, and the differential evolution algorithm. Afterwards, six selected waverider configurations were polished to blunt leading edges, and then their aerodynamic performances were evaluated by solving the Navier-Stokes equations. The results show that both the L/D and the relative pressure center coefficient of the waverider produce significant changes with the variation of compression surface shape. 漏 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The current work is an experimental investigation of the dependence of film-cooling effectiveness on the injection angle, mass flux and injection temperature in supersonic combustors. The mainstream Mach number is 2.5, and the coolant was injected with sonic speed. The total temperature of the mainstream is 1500K, and for the injection it ranges from 300K to 1060K. Three injection angle is respectively 00, 430, 1370. The coolant mass flux ranges from 1% to 6% of the mainstream mass flux, and the mainstream mass flux is 2.5kg/s. The results show that a smaller injection angle has a better performance in film cooling effectiveness and indicate that an increase in film-cooling effectiveness with the increase of the coolant mass flux. The influence of coolant temperature is more complex. The rising of coolant temperature reduces the film-cooling effectiveness without kerosene combustion, while has not significant difference with kerosene combustion. 漏 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.To alleviate the huge computational cost in supersonic combustor modeling and to improve the accuracy of traditional unsteady flamelet model, a zone flamelet is proposed. The main idea of zone flamelet is to divide the whole turbulent combustion field into a finite number of control zones and the chemical status in each zone is represented by a single flamelet. With proper zone division, the local flow conditions can be assumed to be homogeneous, where the scattering of variables over the mixture fraction space is in controllable small, thus the representative flamelet approaches the real scalar distribution. The flamelets exchange information through flux-conserved convection when across the zone boundary, thus the flamelet variables can be transport from upstream to downstream in a flow manner. Although one additional mixture fraction is resolved, great computational cost is still saved because the zone division in physical space is much coarser than the flow simulation mesh. A simple historical statistics approach is proposed to estimate the representative temperature, in order to further alleviate the computational cost in solving the flamelet temperature equation usually with numerous sub-models for non-adiabatic terms, e.g. radiation and wall heat loss. The zone flamelet model is then applied to model a scramjet combustor operated at a flight Mach number of 6.5 and a fuel equivalence ratio of 0.8. The performance of zone flamelet model in highly non-equilibrium supersonic combustion is compared with the traditional PaSR model. 漏 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The high-pressure capturing wing (HCW) is a novel device that can improve the aerodynamic performance for large volume high-speed aircrafts. In hypersonic flows, the sharp leading edge of HCW must be blunted because of the severe aerothermal load. The oblique shock induced by body intersects to the bow shock induced by HCW. This paper proposes three cases based on the shock interaction location and studies the corresponding aerodynamic and aerothermal performance by numerical simulation under Mach 6 and zero angle of attack. The results show that the maximal heat flux and drag coefficient of HCW is determined by the interaction location. When the shock impinges on the inside of HCW, the shock boundary layer interaction occurs which lead to the increase of local heat flux on the lower surface of HCW. However, the maximal heat flux is almost the same with the freestream stagnation-point heat flux. The local extreme heat flux in the lower surface of HCW is about 20 percentage of the freestream stagnation-point heat flux. The drag coefficient is almost the same with freestream drag coefficient. When the shock impinges on the HCW leading edge, the type IV interference appears which could cause high pressure and heat flux on the surface. The non-dimensional maximal heat flux is about 3.5 and the maximal drag coefficient is about 1.8 in this case. When the oblique shock impinges on the outside of HCW, the non-dimensional maximal heat flux is about 1.5 and the drag coefficient is about 2.7. 漏 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Oblique detonations induced by semi-infinite wedge are simulated by solving Euler equations with chain branching kinetics. Numerical results show the initiation can be triggered by either the abrupt transition or smooth transition, dependent on incident Ma Minand wedge angle 胃, and then their effects on the oblique detonation angle 尾 and initiation length Liniare analyzed. When 胃 increases, Linidecreases monotonically but 尾 has a minimum value, corresponding to 胃 = 29掳 in this study. When Min decreases, both Liniand 尾 increases monotonically until Mindecreases below certain critical value, Min= 9.2 in this study. Then low inflow Ma effects generate the maximum Lini, with the complex of ODW (oblique detonation wave), SODW (secondary oblique detonation wave) and SIDW (self-ignition deflagration wave). The transient process is observed, demonstrating the structure can self-adjust to find a proper position. The wave structure suggests two wave/heat release process determining the detonation initiation. In the cases with high Minfeatured by SIDW, the oblique-shock induced self-ignition dominates, and Liniincreases when Mindecreases. In the cases with low Minfeatured by SODW, the interaction of ODW and SODW dominates, and Linidecreases when Min decreases. 漏 2017 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.A combined near-infrared and mid-infrared laser-based absorption sensor is developed for simultaneous measurements of N2O, CO, NO and gas temperature for a 1-Newton ADN monopropellant thruster. ADN monopropellant represents a new generation of green propellant for spacecraft propulsion and goes with developing ADN based thruster. An optimization design for an ADN based thruster with catalytic bed length of 14mm is studied in this paper. Both steady-state firing and pulse-mode firing for the ADN based thruster operation are conducted over feed-pressure range of 5-12 bar at ignition temperature of 200掳C. Scanned-wavelength direct absorption is utilized to measure the multispecies concentration and gas temperature under the firing conditions. Measurements employing the developed laser-based absorption sensor provide an access to characterize the combustion process inside the ADN based thruster. Additional measurements for the combustion pressure are made by using a high-temperature resistant and high frequency pressure sensor. 漏 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

New Accurate and Efficient Method for Stiff Detonation Capturing

An alternative approach to prevent spurious behavior caused by conventional shock-capturing schemes when solving stiff detonation wave problems is introduced. In engineering research of detonation ...

GPU-based simulation of the two-dimensional unstable structure of gaseous oblique detonations

In this paper, the two-dimensional structure of unstable oblique detonations induced by the wedge from a supersonic combustible gas flow is simulated using the reactive Euler equations with a one-step Arrhenius chemistry model. A wide range of activation energy of the combustible mixture is considered. Computations are performed on the Graphical Processing Unit (GPU) to reduce the simulation runtimes. A large computational domain covered by a uniform mesh with high grid resolution is used to properly capture the development of instabilities and the formation of different transverse wave structures. After the initiation point, where the oblique shock transits into a detonation, an instability begins to manifest and in all cases, the left-running transverse waves first appear, followed by the subsequent emergence of right-running transverse waves forming the dual-head triple point structure. This study shows that for low activation energies, a long computational length must be carefully considered to reveal the unstable surface due to the slow growth rate of the instability. For high activation energies, the flow behind the unstable oblique detonation features the formation of unburnt gas pockets and strong vortex-pressure wave interaction resulting in a chaotic-like vortical structure.