Experimental study of a hydrogen-air rotating detonation engine with variable air-inlet slot

Rotating detonation engines have attracted considerable attentions in recent years. In this study, the experiments of initiating rotating detonation waves were performed on a H₂/air rotating detonation wave with the variable air-inlet slot. The results showed that the stability of detonation-wave pressure and velocity both initially increased and then decreased with the increase of slot width, and it could improve the stability of detonation-wave velocity via increasing the equivalence ratio. The intensity of reflected wave was strong for the tests of d = 0.5 mm, which leaded to the advance ignition of fresh mixture and a velocity deficit reaching up to 20%. The strong interaction between air plenum and combustor and bad mixing effect may be the reasons of forming unstable detonation wave for the tests of large-scale slots. The air-inlet slot of d = 1 mm, which got a best experiment results relative to other tests, had a wide equivalence-ratio scope to produce stable detonation wave.     

Effects of a turbine guide vane on hydrogen-air rotating detonation wave propagation characteristics

The rotating detonation engine is a new machine that can generate thrust via continuous rotating detonation waves (RDWs). In this study, experiments were performed on a structure combining a rotating detonation combustor (RDC) and a turbine guide vane to investigate the propagation characteristic of hydrogen-air RDW. The results showed that the velocity of detonation wave initially increased and then decreased with the increase of equivalence ratio, and it got a velocity of 84% Chapman-Jouguet value. The velocity of detonation wave generally rose by 4.31% comparing with the no guide vane tests, while the scope of steady-operation state became narrow. The oscillation pressure was reduced by 64% after passing through the guide vane, and the magnitude of pressure was only 0.4 bar at the guide vane exit. Meanwhile, part of the shock wave was reflected back to combustor resulting in some small pressure disturbances, and the propagation mode of reflected wave was related to the propagation direction of RDW.     

Numerical investigation of the effect of inlet mass flow rates on H2/air non-premixed rotating detonation wave

In this paper, a three dimensional numerical investigation was carried out to study the formation and propagation characteristics of non-premixed rotating detonation wave using H₂/air as reactive mixtures. At a constant global equivalence ratio, the effects of inlet mass flow rates of H₂ and air on various performance parameters of rotating detonation wave and based on it combustor were analyzed in detail. On this basis, the mode switching process of rotating detonation wave caused by transiently changing the inlet mass flow rates was also discussed. The numerical results showed that inlet mass flow rates of H₂ and air played a very critical role in the formation, propagation and mode switching of rotating detonation wave. With the increase of inlet mass flow rates, rotating detonation wave could be switched from single wave to double waves. The propagation direction of double waves depended on the changing process of inlet mass flow rates. Meanwhile, compared to the single wave, double waves or its based combustor had the obvious advantages in formation time, stability and thrust, but had disadvantage in pressure ratio. In addition, both fill characteristics and mixing quality of fresh reactive mixtures are the underlying important mechanisms to explain the effects of inlet mass flow rates on rotating detonation waves.     

Numerical investigation of two-wave collision and wave structure evolution of rotating detonation engine with hollow combustor

A three-dimensional numerical simulation of rotating detonation engine (RDE) with hollow combustor is performed to analyze wave structure evolution systematically. Wave structure evolution is classified into four categories, namely two-wave collision (counter-rotating waves), abscission of detonation tail, and shock wave to detonation transition. Two-wave collision consists of symmetric detonation collision, asymmetric detonation collision, and detonation/shock collision. Two symmetric detonation waves turn into shock waves after collision. Collision of asymmetric detonation waves creates single detonation wave. The detonation/shock collision decreases the detonation wave intensity. Abscission of detonation tail and shock to detonation transition can both create single detonation wave or two opposite-direction detonation waves, depending on the wave hitting angle and the amount of fresh gas. All phenomena mentioned above affect the number of detonation waves in the combustion chamber.     

Numerical simulation on the operating characteristics of rotating detonation ramjet engines at high flight mach number

For high-Mach-number incoming flow circumstances, a rotating detonation ramjet engine configuration is proposed in this research. By installing supporting blocks at the rear of the combustor, this configuration achieves continuous rotating detonation operation. Based on the Comparison of the flow structures obtained from the engine configuration with and without the supporting block before and after detonation ignition respectively, we obtain the intrinsic mechanism of detonation wave's propagation and re-initiation under the action of the supporting block. The supporting block creates a deflagration wave that is almost stationary before detonation ignition. In the detonation-ignited state, the deflagration wave is continually formed and traveling upstream under the influence of the supporting block, which is analogous to the periodical before detonation ignition of a transverse wave structure. The dynamic deflagration wave will cause the incomplete reactants behind the detonation wave to burn as the intensity of the detonation wave decreases. As a result, the incident shock wave is transformed into a Mach stem to achieve the re-initiation of the detonation wave.     

等离子体点火对燃烧转爆轰影响的数值计算

采用CE/SE方法对耦合的流体力学方程与麦克斯韦方程求解,对等离子体点火和气液两相爆轰过程进行数值模拟.讨论了3种不同点火位置对燃烧转爆轰(DDT)的影响.结果表明,等离子体点火可以在短时间内点燃爆轰管内汽油/空气混合物,经过一系列复杂的波系与波系、波系与管壁之间的相互作用最终形成稳定的爆轰波.壁面点火比中心点火具有优...     

热管蓄冰过程的数值模拟研究．

通过建立热管的简化热阻模型,采用数值计算的方法模拟了热管的动态蓄冰。模拟结果与实验结果吻合。同时,对热管冷凝段和蒸发段的长度比为1：2和1：4两种形式进行了数值模拟比较。结果表明,1：4的布置形式更优。     

The evolution and cellular structure of a detonation subsequent to a head-on interaction with a shock wave

This paper analyzes the results of a head-on collision between a detonation and a planar shock wave. The evolution of the detonation cellular structure subsequent to the frontal collision was examined through smoked foil experiments. It is shown that a large reduction in cell size is observed following the frontal collision, and that the detonation cell widths are correlated well with the chemical kinetic calculations from the ZND model. From chemical kinetic calculations, the density increase caused by shock compression appears to be the main factor leading to the significant reduction in cell size. It was found that depending on the initial conditions, the transition to the final cellular pattern can be either smooth or spotty. This phenomenon appears to be equivalent to Oppenheim's strong and mild reflected shock ignition experiments. The difference between these two transitions is, however, more related to the stability of the incident detonation and the strength of the perturbation generated by the incident shock.     

Numerical study of interaction of propagated shock with boundary layer behind contact surface in ducts

The interactions of the shock with the boundary layer of the cold gas behind the contact in many different conditions, i.e. three kinds of test gases and three kinds of sound speed ratios across the contact, were explored by numerical study. The trajectories of the transmitted shock in cold gas flow and the development of shock bifurcation in the process of interaction with boundary layer are illustrated by many kinds of figures (e.g. the time-distance diagrams of the acoustic impedance contours on the axis, the pressure and density contours and the static pressure distributions on the axis).     

Numerical simulation of snow melting on pavement surface with heat dissipation pipe embedded

Programmed software was developed in order to numerically simulate time variation of the temperature field and snow depth around a pipe‐in‐pile snow‐melting system, using meteorological data. The system utilized underground piles as the heat exchanger between underground soil and water flowing inside the pipes. The water was pumped into heat dissipation pipes embedded beneath the pavement surface, on which snow melted. The unsteady three‐dimensional heat conduction inside the pavement and the underground soil was numerically solved. On the surface, the heat balance of conduction, convection, and radiation was considered. Snow fall depth was estimated by rainfall weather data, ratio of snowfall to rainfall, and dry density of snowfall. For simulating the snow layer, an unsteady one‐dimensional heat conduction was solved while incorporating partial absorption of solar radiation. Experiments for measuring time variation of the temperature field and snow depth around the system were conducted for verification of the software. The obtained simulation results showed good agreements with experimental data, demonstrating the utility and validity of the software. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20226     

添加物对石蜡相变螺旋盘管蓄热器蓄热和放热性能的影响

对以石蜡为相变材料的螺旋盘管蓄热器的蓄热和放热性能进行了实验研究,探讨了在石蜡中添加铜粉、硅粉和不锈钢丝带对石蜡螺旋盘管蓄热器蓄热和放热性能的影响。结果表明：在蓄热过程中,随着加热时间的增加,蓄热器内的温度分布不均匀性逐渐增大;纯石蜡蓄热器内温度分布不均匀性最为严重;插入不锈钢丝带的蓄热器内温度分布最均匀。在放热过程中,纯石蜡蓄热器的出口水温下降最快;而石蜡加不锈钢丝带的蓄热器出口水温最高。     

凹凸前缘叶片气动性能与绕流流场数值研究

以NACA0018翼型为原始模型进行前缘结构设计,采用计算流体动力学(CFD)方法分析凹凸前缘结构参数对叶片绕流流动及气动性能的影响。结果表明:在0°～10°攻角范围内,凹凸前缘叶片气动性能与原始叶片基本一致,但在15°～25°攻角范围内,正弦波形凹凸前缘叶片升力系数最大提升20.2%;叠加波形凹凸前缘叶片在15°～25°攻角内,气动性能均有不同程度的下降,波峰处推迟分离,而在波谷分离提前,在吸力面每个波谷顺流方向叶片及展向形成反向涡对,相互卷吸并与主流掺混增加能量交换向尾缘处移动,改变了叶片原始流场反馈回路,阻碍了叶片展向涡及流向涡的发展。     

Numerical investigation on the characteristics of mass transport and performance of PEMFC with baffle plates installed in the flow channel

A 3D numerical model of proton exchange membrane fuel cell (PEMFC) with the installation of baffle plates is developed. The majority of the conservation equations and physical parameters are implemented through the user defined functions (UDFs) in the FLUENT software. The characteristics of mass transport and performance of PEMFC are investigated. The results reveal that the baffle plate can enhance the mass transport efficiency and the performance of PEMFC. The baffle plate installed in the PEMFC flow channel increases the local gas velocity, which can promote the reactant gas transport and the liquid water removal in the porous electrode. As a result, the reactant gas concentration is larger in the porous electrode, which enhances the fuel cell performance for decreasing the over-potential of concentration. The fuel cell output power increases with the blockage ratio of the baffle plate. Considering the extra pumping power resulted from pressure loss caused by the baffle plate, the fuel cell with the blockage ratio of 0.8 is found to perform best in terms of the fuel cell net power generation. The fuel cell performance increases first with the baffle plate number, due to the better reactant distribution and water management, but decreases when the baffle plate number is too large, due to the excessive blockage for the reactant gas transport to the channel downstream. The PEMFC investigated with 5 baffle plates in the channel is found to be optimal. A channel design to achieve gradually increasing blockage ratios is also proposed, which exhibits better cell performance than the design with even blockage ratios.     

Numerical Methods for Inverse Problem of Heat Conduction with Unknown Boundary Based on Variational Principles with Variable Domain

In this article a variable-domain variational approach to the entitled problem is presented.A pair of comple-mentary variational principles with a variable domain in terms of temperature and heat-streamfunction are firstestablished.Based on them,two methods of solution—generalized Ritz method and variable-domain FEM—both capable of handling problems with unknown boundaries,are suggested.Then,three sample numericalexamples have been tested.The computational process is quite stable,and the results are encouraging.Thisvariational approach can be extended straightforwardly to 3-D inverse problems as well as to other problems inmathematical physics.     

Numerical analysis for a falling liquid film with interfacial waves on an inclined plate. Part 2: Effects of interfacial waves on flow dynamics and heat transfer

Flow and temperature fields in falling liquid films with interfacial waves have been obtained by means of a numerical simulation in which the algorithm is based on the HSMAC method and interfacial boundary conditions are treated with newly proposed methods. Small‐amplitude disturbance waves at a low frequency develop into isolated solitary waves which are composed of a roll wave and capillary waves. Waves disturbed at a high frequency interfere with each other and develop into disordered waves. Circulation flow is observed in the roll wave, while there is no circulation flow in the disordered waves. Temperature fields in the wavy film are distorted by convection effects and differ greatly from those in the laminar film. The circulation in the roll wave has an especially strong effect on the temperature fields. The interfacial waves enhance the heat transfer by two kinds of effects: the variation of film thickness and convection in the film. The dominating effect depends on the Prandtl number. © 2000 Scripta Technica, Heat Trans Asian Res, 29(3): 233–248, 2000