Investigations of three-dimensional flow characteristics in a liquid ramjet combustor using the PIV method

Three-dimensional flow characteristics in a liquid fuel ramjet combustor were investigated using the PIV method. The combustor had two rectangular inlets that form a 90-degree angle with each other, with intake angles of 30 degrees. Three guide vanes were installed in each rectangular inlet to improve flow stability. The experiments were performed in a water tunnel test with the same Reynolds number as Mach 0.3 at the inlet. PIV software was developed to measure the characteristics of the flow field in the combustor. Accuracy of the developed PIV program was verified with a rotating disk experiment and standard data. The experimental results showed that the two main streams from the rectangular intakes collided near the plane of symmetry and generated two large longitudinal vortices, which was in agreement with three dimensional computational results. A large and complex threedimensional recirculating flow was measured behind the intakes.     

Combustion characteristics in a supersonic combustor with hydrogen injection upstream of cavity flameholder

Combustion characteristics in a supersonic combustor with hydrogen injection upstream of a cavity flameholder were investigated both experimentally and numerically. The combustion was observed to be stabilized in the cavity mode around the shear layer via a dynamic balance and then spread into the main stream in the region around the jet centerplane where the flow was decelerated and turned to the main stream, supplying a favorable condition for the combustion to spread. The combustion spreading from the cavity shear layer to the main stream seemed to be dominated not only by the traditional diffusion process but also by the convection process associated with the extended recirculation flows resulting from the heat release and the interaction between the jet and the cavity shear layer. Therefore, the cavity-stabilized combustion appeared to be a strongly coupled process of flow and heat release around the cavity flameholder.     

PSP measurement of flow fields in a supersonic combustor with a backward-facing step

The mixing fields within a SCRAM-jet combustion chamber are visualized using pressuresensitive paint (PSP) as an oxygen sensor. The experiments are performed in a small supersonic wind tunnel at the National Aerospace Laboratory — Kakuda Research Center (NAL-KRC). The main stream Mach number is 2.4, and the dynamic pressure ratios between the injected gas and the main flow are 0.3, 0.7, 1.1 and 1.5. Three fuel injection nozzles are used; oxygen is injected from the central nozzle and air from the two nozzles at either side. The spread of the injected gas is measured to observe the effects of placing the nozzles in different positions. The results show that the jet has its own independent flow structure, and that little mixing of gases occurs between the flow structures created by each nozzle. When the injection dynamic pressure ratio is increased, the oxygen fraction rises in the recirculation zone and falls in the separation zone downstream of the injection.     

Simulation of a round supersonic combustor using wall-modeled large eddy simulation and partially-stirred reactor models

Simulations are presented for a generic, round supersonic combustor. Turbulence is modeled in the combustor using a wall-modeled large eddy simulation approach. Combustion is modeled using a small quasi-global mechanism and a more detailed skeletal mechanism. Both mechanisms are used in conjunction with two variations of the partially-stirred reactor model for sub-grid turbulence chemistry interactions. Sensitivity of the solutions to grid resolution is investigated. It is found that in order to achieve reasonable grid convergence in the mean wall pressure, the model constant that appears in the partially-stirred reactor model must be a function of both the chemistry mechanism and the grid resolution. Most of the combinations of mechanism and turbulent combustion model tested can be tuned in order to predict the location of the pre-combustion shock train and the peak mean pressure in the combustor. It is found that while the different models are able to reproduce the mean wall pressure, there are significant differences in the mean temperature and heat release rate fields. The sensitivity of the different combinations of mechanisms and partially-stirred reactor formulation is quantified and some combinations are found to be more prone to blowout. Two of the tuned models were tested across several fuel equivalence ratios with a single value of the partially-stirred reactor model constant. One model produced reasonable predictions of shock location and peak mean pressure for each equivalence ratio. The second model captured the global trends in the mean wall pressure, but was unable to quantitatively predict the shock location and peak mean pressure for all equivalence ratios tested.     

超音速等离子体点火过程的三维数值模拟

为了研究等离子体点燃超音速混合气流的过程,设计并验证了超音速燃烧室的三维计算模型,计算出了燃烧室等离子体点火时的流场参数和化学反应规律,分析了等离子体点火对燃烧室内燃烧的影响。计算结果表明:高温等离子体射流的滞止作用通过增加混合气在燃烧室内的停留时间提高了点火效率; 等离子体点火时燃烧区域的压力扩散比较充分,内部为压力相对平衡的低速流动; 高温等离子体射流高速射向混合气流时产生的速度矢量偏移扩大了点火面积,从而使点火效率得到提高; 氢气、空气燃烧的燃烧产物主要是水,燃烧区域局部温度主要受局部放热反应的影响。     

Visualization of flameholding mechanisms in a supersonic combustor using PLIF

Laser-induced fluorescence of OH and CH₂O was imaged to investigate the flame stabilization mechanism in a flameholder with a Mach 2.4 free stream. Ethylene was burned in a rectangular cavity with two points of injection: the aft wall and the cavity floor. When injected from the aft wall, the fuel came into immediate contact with hot combustion products from the reaction zone under the shear layer. Primary combustion occurred under the shear layer and in the aft region of the cavity volume. In contrast, when fuel was injected from the floor, a jet-driven recirculation zone of hot products near the upstream wall of the cavity served as a flameholder. The reaction then occurred on the underside of the shear layer. In conditions near lean blowout, significant changes in the flameholding mechanisms were observed. Improved CH₂O fluorescence signal was obtained by taking advantage of the long fluorescence lifetime at low pressures and delaying the camera gate to reduce the background signal.     

单路脉冲功率真空装置的三维数值模拟研究

研究了单路脉冲功率真空装置中脉冲功率的馈入、汇聚及传输, 在CHIPIC平台上, 采用多台计算机进行分进程并行计算的方法, 突破了单台计算机的内存及运行速度限制, 对单路脉冲功率的馈入、汇聚及传输装置进行建模, 并设置相应的参数, 从而对该大尺度装置进行了整体模拟. 模拟得到的该器件各个部分的阴阳极间电压、阴阳极电流等一些重要的物理参数. 模拟结果表明: 该单路真空脉冲功率器件整体都可以保持磁绝缘状态, 并达到了很好的功率汇聚的作用. 该工作验证了真空状态下脉冲功率产生及传输器件的可行性, 为进一步的实验研究提供了有力保证. 关键词： 单路脉冲功率真空装置 并行计算 数值模拟 磁绝缘     

Three-dimensional numerical simulation of the operation of the rotating-detonation chamber

The aim of this work is to apply three-dimensional numerical simulation to determining the conditions of the stable operation of the rotating-detonation chamber (RDC), the thermal state of the chamber walls, as well as the most important parameters of the flow at the inlet and outlet, keeping in mind the possibility of placing the RDC between a compressor and a turbine in a prospective gas turbine installation. The model is based on a system of three-dimensional unsteady Reynolds-averaged Navier-Stokes, energy, and species conservation equations for a multicomponent reacting gas mixture supplemented by a turbulence model. The system is solved using a combined algorithm based on the finite-volume and particle methods. The capabilities of the computer program are demonstrated by the example of a circular RDC with inner and outer walls 260 and 306 mm in diameter and with axial introduction of a hydrogen-air mixture through an annular gap at the bottom of the chamber (with a relative area of 0.6). The detonation wave spun over the bottom at a frequency of ??126000 rpm. Calculations have shown that such an RDC can operate in a steady mode with one detonation wave.     

微空心阴极放电的3维数值模拟

给出了圆筒形微空心阴极的3维流体方程组及其稳态的差分方程和合理的边界条件,并利用计算机模拟计算,得出了He放电形成的粒子密度、电子能量、 电场及电势分布。讨论了在阴极孔径为240~360 mm,气压6 666.1~13 332.2 Pa的范围内放电参量的变化规律:固定电压和气压时,阴极孔径减小,负辉区重合越多;固定阴极孔径和气压时,气压升高,带电粒子密度随着气压增加而增加。结果表明放电参量强烈依赖阴极孔径和气压。     

微空心阴极放电的3维数值模拟

 给出了圆筒形微空心阴极的3维流体方程组及其稳态的差分方程和合理的边界条件,并利用计算机模拟计算,得出了He放电形成的粒子密度、电子能量、 电场及电势分布。讨论了在阴极孔径为240~360 mm,气压6 666.1~13 332.2 Pa的范围内放电参量的变化规律:固定电压和气压时,阴极孔径减小,负辉区重合越多;固定阴极孔径和气压时,气压升高,带电粒子密度随着气压增加而增加。结果表明放电参量强烈依赖阴极孔径和气压。     

Computer simulation of a combined cycle power plant

This paper presents the simulation procedure developed to predict the performance of a combined cycle power plant from given performance characteristics of its main components. In order that the procedure could be validated, the simulation technique has been applied to a typical combined cycle power plant (having a dual pressure bottoming cycle) manufactured by a prominent company. The characteristics of the standard equipment like the air compressor, steam and gas turbines, various pumps, etc. have been taken from the manufacturer's catalogues and converted into appropriate equations based on theoretical understanding. The performance of various heat exchangers (like economizers, superheaters, evaporators, etc.) has been determined by using the effectiveness concept after evaluating the overall heat transfer coefficient by using appropriate correlations from literature. The strategy of system simulation is obtained by judiciously interlinking the information flow diagrams of various components and thus the task is finally reduced to that of solving nine non-linear equations for nine variables. The predicted performance of the system is seen to be in good agreement with in good agreement with its rated performance.     

Simulation of a combined cycle power plant based on a pressurized circulating fluidized bed combustor

A comprehensive mathematical model for the simulation of a pressurized circulating fluidized bed combustor will be presented. The model consists of a combustor model describing the combustion chamber, the cyclone and the external heat exchanger as well as of a gas turbine model. The results of the simulation for the combustor at full load and different pressures and for the combined cycle power plant at full and part load are presented in form of temperature-, flue gas composition- and heat transfer-profiles in the combustor. Especially, energy fluxes from the combustor to the water-/steam cycle and the output of gas- and steam-turbine will be shown. The validity of the model will be shown by comparative simulation of an existing plant for the special case of atmospheric conditions.     

Direct numerical simulation of shock/turbulent boundary layer interaction in a supersonic compression ramp

A direct numerical simulation of the shock/turbulent boundary layer interaction flow in a supersonic 24-degree compression ramp is conducted with the free stream Mach number 2.9.The blow-and-suction disturbance in the upstream wall boundary is used to trigger the transition.Both the mean wall pressure and the velocity profiles agree with those of the experimental data,which validates the simulation.The turbulent kinetic energy budget in the separation region is analyzed.Results show that the turbulent production term increases fast in the separation region,while the turbulent dissipation term reaches its peak in the near-wall region.The turbulent transport term contributes to the balance of the turbulent conduction and turbulent dissipation.Based on the analysis of instantaneous pressure in the downstream region of the mean shock and that in the separation bubble,the authors suggest that the low frequency oscillation of the shock is not caused by the upstream turbulent disturbance,but rather the instability of separation bubble.     

Planar laser-induced fluorescence imaging of OH in a supersonic combustor fueled with ethylene and methane

A supersonic combustor was experimentally investigated using both conventional instrumentation and laser-based diagnostics. Planar laser-induced fluorescence (PLIF) imaging of OH was used in the main section of the combustor to examine flameholding and flame propagation during a series of evaluations at conditions simulating Mach-5.5 flight. Parameters of interest in this study included the angle of the primary fuel injectors, the distribution of fuel throughout the combustor, and the fuel composition. Changes in fuel-injection angle were expected to influence the mixing and combustion processes, and therefore combustor operation. Fuel-distribution variations were expected to modify the flame propagation between flameholding regions. Finally, ethylene and methane were used to examine the suitability of the flameholder designs over a wide range of fuel reactivity. Results suggest that the combustor provides relatively robust flameholding regardless of the fuel used and good flame propagation as long as the fuel distribution provides favorable conditions in the flameholding regions. In addition, the results show that the primary injectors can be useful in controlling certain aspects of combustor operability.     

Three-dimensional numerical simulation of the operation of a rotating-detonation chamber with separate supply of fuel and oxidizer

A three-dimensional numerical simulation of the operation of an annular rotating-detonation chamber (RDC) with separate supply of combustible mixture components, hydrogen and air, is performed, and the calculation results are compared to available experimental data. The model is based on a system of time-dependent Reynolds-averaged Navier-Stokes equations complemented with a turbulence model and continuity and energy equations for a multicomponent reacting gas mixture. The system is solved using a coupled algorithm based on the finite volume method and particle method. Calculations are for the first time performed with allowance for effects of finite rates of turbulent and molecular mixing of the combustible mixture components with each other and with reaction and detonation products. The calculation results compare favorably with the experimental data obtained at the Lavrentyev Institute of Hydrodynamics of the Siberian Branch of the Russian Academy of Sciences.     

高频腔本征值问题的三维数值模拟

 运用有限积分法软件MAFIA和有限元软件ANSYS对两类高频腔的本征值问题进行数值模拟，将模拟结果与部分实验数据进行验证，得到了比较一致的结果，其平均计算精度在5%以内，证实了两种电磁软件都可用于高频腔本征值问题的数值模拟，在计算精度上为满足工程设计需要做了一些研究。另外将两种模拟软件在计算时间上作了对比。     

Direct numerical simulation of a supersonic turbulent boundary layer on a flat plate and its analysis

In the past three decades, considerable progress has been made in the investigation of incompressible turbulent boundary layer through experiments, DNS and theoretical works, including: (1) the statistics characteristic and structure of turbulence; (2) the co-herent structures in turbulent flows; (3) turbulence modeling and the large eddy simula-tion (LES). In contrast, the progress was very slow for the compressible, in particular, the super-sonic turbulent boundary layer. Recent works on d…     

Thrust characteristics of an airbreathing pulse detonation engine in supersonic flight at various altitudes

The main thrust characteristics, such as thrust force, specific impulse, specific fuel consumption, and specific thrust, of a pulse detonation engine (PDE) with an air intake and nozzle in conditions of flight at a Mach number of 3 and various altitudes (from 8 to 28 km above sea level) are for the first time calculated with consideration given to the physicochemical characteristics of the oxidation and combustion of hydro-carbon fuel (propane), finite time of turbulent flame acceleration, and deflagration-to-detonation transition (DDT). In addition, a parametric analysis of the influence of the operation mode and design parameters of the PDE on its thrust characteristics in flight at a Mach number of 3 and an altitude of 16 km is performed, and the characteristics of engines with direct initiation of detonation and fast deflagration are compared. It is shown that a PDE of this design greatly exceeds an ideal ramjet engine in specific thrust, whereas regarding the specific impulse and specific fuel consumption, it is not inferior to the ideal ramjet.