Zhijun Wei

Theoretical Modeling and Numerical Study for Thrust- Oscillation Characteristics in Solid Rocket Motors

Todiscover thrust-oscillation characteristics in solid rocketmotors, analyticalmodeling andnumerical simulation are carried out by an experimentalmotor in the vonKarman Institute for FluidDynamics. The numericalmethod by means of amesh sensitivity analysis is proposed for validation. Velocity profiles, oscillation frequencies, and pressure amplitudes were obtained by numerical simulations and then compared with the experimental data. Various cases with different inlet temperatures are proposed to investigate the influences of parameters on the oscillation characteristics. The results indicate that it is not a necessary condition for vortex-shedding frequency to approach a certain acoustic frequency when periodic oscillations are generated. Oscillations are more severe if the vortexsheddingphenomenon coupleswithhigh-order acousticmodes.Velocitymagnitude in the combustion chamber is the main factor that influences the vortex-shedding frequency; meanwhile, the pressure amplitude is mostly determined by themeanMach number. Theoretical modeling in conjunction with numerical calculations proves that the ratio of dimensionless thrust amplitude to pressure amplitude is predominantly determined by the throat-to-port-area ratio J, and it varies inversely as J. An integrated formula is presented to describe the relationship between thrust amplitude and pressure amplitude.

Numerical Investigation on Internal Regressing Shapes of Solid-Fuel Scramjet Combustor

The purpose of this paper is to investigate the combustion process and its change with time due to solid-fuel regression in a solid-fuel scramjet combustor. The combustion process is simplified in the sequence changing of three regression shapes. The solid fuel uses hydroxyl-terminated polybutadiene with a global one-step reaction mechanism. Numerical simulations based on the shear stress transport k-ω model are confirmed by experiments. The simulation data generally agree with the experimental data published in the literature. For simplification, three typical instants during the combustion process, implying three different internal shapes due to fuel regression, are considered. With the sequence of three regression shapes, the fuel diffusion from a solid-fuel surface becomes more extensive and, furthermore, enhances the global combustion efficiency, which is nearly up to 45% at the outlet of the combustor. The simulation results also reveal that the cavity in the combustor provides a fuel enrichment zon...

Experimental and Numerical Studies on Methane/Air Combustion in a Micro Swiss-Roll Combustor

To understand effects of an air groove on working characteristics of micro Swiss-roll combustors, combustion of premixed CH4/air is conducted in 2 micro Swiss-roll combustors, one with an air groove and the other without. Experimental results show that stable combustion of premixed CH4/air in 2 combustors can be achieved and the flame is kept in combustors center. An air groove can extend flammable limit of the combustor and make it work at a larger excess air coefficient and a lower methane flow rate. Furthermore, it increases the radial surface temperature gradient on outer wall of the combustor. Additionally, the combustor with an air groove is numerically simulated. Numerical results indicate that hot combustion products play a strong role in heating incoming mixtures. On one hand, it makes premixed flame surface inclined across inlet channel; on the other hand, it makes flame position vary with flow velocity, excess air coefficient and heat loss to the environment.

Study on infrared signature of solid rocket motor afterburning exhaust plume

To study the infrared signature of afterburning exhaust plume of solid rocket motor, the coupling calculation model for infrared radiation transfer in the afterburning plume was built. The radiation source term was induced to energy equation, thus the plume flow field and radiation transfer was calculated in a coupling way. Finite rate chemistry reaction model was used to simulate the 10 species afterburning exhaust plume; finite volume method and discrete ordinates method was separately used to solve the plume flow field and the radiation transfer equation. The spectral radiation intensity from 1 m � to 15 m � and radiation intensity contour were obtained, and both of them accord well with the experimental data from reference. The results show that the radiation characteristics in the near plume field can be captured varying with the physical characteristics of flow field, which shows that the coupling solution can increase the calculation resolution of radiation transfer.

Numerical Investigation of Self-Ignition Characteristics of Solid-Fuel Scramjet Combustor

The self-ignition characteristics of a solid fuel under supersonic flow have been investigated theoretically and numerically. Time-dependent two-dimensional axisymmetric compressible Navier–Stokes equations and species transport equations are solved numerically. Turbulence closure is achieved using the shear stress transport k-ω model. Polymethylmethacrylate fuel and a global one-step reaction mechanism are used in this study. The reaction rate is determined by finite-rate chemical kinetics with the turbulence–chemistry interaction modeled by an eddy-dissipation model. The numerical results generally agree with the experimental data in the published literature. The flame spread and pressurization during the self-ignition of polymethylmethacrylate in the combustor have been studied. The effect of inlet flow conditions and the geometry of the combustor on self-ignition behavior have been analyzed. Three stages of flame spread (namely, heat accumulation, secondary recirculation zone self-ignition, and orderl...

Numerical Investigation on Self-ignition and Flammability Characteristics in Solid Fuel Scramjet Combustor

The characteristics of self-ignition and self-sustained combustion of a solid fuel under supersonic cross flow have been investigated theoretically and numerically. A time dependent two-dimensional, axisymmetric compressible Navier-Stokes equations and species transport equations are solved numerically. Turbulence model is using the Shear Stress Transport k  model. The PMMA fuel and a global one step reaction mechanism are used in this study. The reaction rate is determined by finite-rate chemical kinetics with the turbulence-chemistry interaction modeled using eddy-dissipation model. The numerical model is validated by comparing the numerical results with experimental data. The flame spread and pressurization during self-ignition of PMMA in combustor have been studied. The behaviors of both sustained and un-sustained combustion in SFSCRJ combustor have been analyzed. The simulation results reveal that three stages of flame spread are identified during the self-ignition transient, which consists of heat accumulation, self-ignition in the secondary recirculation zone, and whole combustor self-ignition orderly. The pressure suddenly rises in combustor during the third stage. The difference of combustor shape affects the self-ignition. There have always been high temperature zone and high mass fraction of reaction products in combustor during sustained combustion. Once the recirculation zone area and residual time provided by cavity are unable to meet the time needed for chemical reaction of reactants and the ignition of fresh mixture, flame is blew out by supersonic cross flow.

Numerical Investigation on Cavity Length for Solid Fuel Scramjet

The g oal of this study is to i nvestigate into the influence of the cavi ty for solid fuel scramjet (SFSCRJ) combustion performance, mainl y on the length-to-depth ratio(L/D) of cavity. Scientific visualizati on of the numerical simulations by the Shear Stress Transport (SST) k-ω model allows a detailed anal ysis of shocks and waves. A second-order-upwi nd computational flui d dynamics is used for simulating the dynamic flow associated with an axisymmetric, cavi ty i nstalled combustor under reacting condi tions. The combustor inlet condi tion airflow is set as Mach number of 1.6, total temperature of 1156 K and average air mass flow rate of 0.184kg/s. The soli d fuel uses the hydroxyl-termi nated-pol ybutadiene (HTPB) wi th a global one step reaction mechanism. Numerical simulations are confirmed by the experiments. The study concerns the combustion enhancement when a cavi ty is installed in the soli d fuel supersonic combustor. The pri mary emphasis is to exami ne the sensiti vity of the primary properties due to variations on the cavity L /D ratio ranging from 3-5. The cavi ty effect is discussed from a viewpoi nt of total pressure loss, combustion efficiency, thrust, specific thrust and s pecific impulse. The combustor with cavity is found to enhance combustion efficiency while de creasing the pressure loss, compared wi th the case without cavity. It is noted that there exists an appropriate length of cavity regarding the combustion efficiency and total pressure loss. The investigation of the cavity L/D ratio woul d provi de some insight into the design considerations of cavity for solid fuel scramjet.

Experimental Study on Flame Stability and Thermal Performance of an n-Heptane-Fueled Microscale Combustor

ABSTRACT In this work, we study the stabilization behavior of micro-diffusion flame of n-heptane formed in a combustor with the inside diameter of 4 mm, in order to elucidate the unique stability mechanism due to miniaturization of diffusion flame downstream porous medium. Effects of incoming Reynolds number and fuel flow rate on overall flame shape, exhaust temperature, and wall temperature are examined experimentally. Furthermore, an energy balance model of the micro combustor is established and optimal working conditions are proposed. Liquid n-heptane is used as fuel and two types of outer tubes are employed in order to examine the role of the heat recirculation. It turns out that the outer tube increases the wall temperature and broadens the flame stability limits. The incoming Reynolds number changes flame position and energy balance in the micro combustors. At low Reynolds number, the outer tube allows the flame to stay close to the porous medium and, accordingly, the porous medium is substantially heated up. Then, the fuel flowing through the porous medium “receives” the heat from the burner (heated by flame) effectively to enhance the reactivity, resulting in improving the stability. At high Reynolds number, the outer tube allows the flame to stay close to the bottom wall of the outer tube and, hence, more radiative heat is transferred through the outer tube, ideal for micro-photovoltaic systems. Additionally, in the case of fixed equivalence ratio, with increasing of the fuel flow rate, combustion releases more heat and the flame is blown toward the bottom of the outer tube. More energy is transferred to the surroundings via the outer tube wall and the maximum value is up to 72.7% of the total combustion heat release.

Quasi-One-Dimensional Numerical Method for Solid Fuel Scramjet Combustor Analysis and Design

AbstractTo research the performance of a solid fuel scramjet combustor, a solid fuel regression rate model was coupled into a quasi-one-dimensional flow equation, and so the flow parameters and fuel regression rate could be calculated together. According to the regression rate and the combustor diameter in the previous moment, the combustor diameter of the next moment could be obtained. The unsteady combustion and flow matter in the combustor was simplified into a steady calculation of every moment by solving the boundary condition at different moments independently. The numerical results were compared to actual experimental data from the literature, and they agreed well with the experiment. Taking the fuel/air ratio and Mach number as the optimization conditions, the initial size of the combustor could be obtained. On the basis of an optimized combustor, the relevant parameters’ variation rules were calculated and analyzed. It was found that during the working process, the combustor flow field could be k...

Numerical Investigation on Influence on the Regression Rate of the Inlet Parameters in Solid Fuel Scramjet Combustor

The influence on the regression rate of the inlet parameters of a solid fuel (PMMA) under supersonic cross flow has been investigated theoretically and numerically. Based on two-dimensional compressible N-S equations and species transport equations, the regression rate values were obtained by adding to the source term in the quality、momentum and energy of the fuel. With different inlet parameters , i.e., stagnation temperature and pressure , the combustion conditions were analyzed at the flame-holding zone and the constant diameter cylindrical section. Comparison between numerical results with test data showed fair agreement, indicating the correctness of the calculation model. The results show that increasing the amount of oxygen or the mixture of the fuel and oxidant can improve the combustion efficiency; the inlet mass flow of air、stagnation temperature and depth of cavity has a great impact on the regression rate, then the impact of the length of cavity was slightly smaller, the impact of the stagnation pressure was minimum.