热声起振机理的研究进展

主要总结了近年来国内外热声起振机理的研究进展,重点介绍了热声起振机理的理论研究、数值模拟以及实验研究;同时指出了当前所开展研究的不足。最后讨论了热声起振机理研究亟需解决的问题以及深入研究的方向。     

热声发动机起振行为实验研究

研究了热声发动机起振过程,对Benavides构建的动力学模型的计算方法进行了优化,计算了控制压力、回热器参数和系统频率对热声发动机起振温度的影响。并进行了实验,计算结果与实验结果一致,证明了优化效果。     

热声起振现象的模拟研究

热声现象中广泛存在非线性效应,其中最典型的就是热声自激起振.本文建立了一个四分之三波长的Rijke管计算模型,基于并行计算,采用数值模拟对其起振现象进行了模拟.研究了不同初场对起振行为的影响,得出起振后的气体振荡频率,并对管内的流动与换热规律进行了详尽分析.模拟结果与文献结果相吻合.本文工作有助于更多地了解热声起振现象,同时也为我们开展热声问题的介观模拟提供了有力的参考.     

热声发动机起振、消振过程的动态行为

针对热声发动机中复杂的起振、消振行为,在自行研制的"驻波型热声发动机试验平台"上,开展了工质类型、加热功率、充气压力等参数对热声发动机起振、消振行为的影响规律研究.试验结果表明:当采用纯氦气和90%氦气+10%氩气的混合气体时,系统存在一最佳的充气压力值,使起振温度和消振温度达到最低;而其余工质,其起振温度与消振温度均随着充气压力增加而逐渐提高;与此同时,由于加热功率对板叠热端温度影响较小,故采用板叠热端温度作为行为特性参数更为合理.     

热自然对流对热声起振行为的研究

主要研究热自然对流对热声发动机系统的影响。通过一系列的实验 ,发现热声发动机空间位置的变化对行波型热声机的起振温度、回热器的温度分布等重要参数有着相当大的影响。作者通过分析 ,对该现象进行了定性的解释。     

容腔调相的单级行波热声发动机起振特性

将容腔结构引入单级环路行波热声发动机系统中进行相位调节,分析了不同容腔位置、容腔内径和容腔长度时系统的起振特性。基于线性热声理论,采用网格传输矩阵数值方法求解系统的起振频率和起振温差;此外,将计算结果与实验结果进行了对比,验证了计算方法的合理性。结果表明:容腔结构可以明显改善系统的起振特性,系统起振温差大幅下降;不同容腔位置处,热机起振特性差异明显;存在最优的容腔内径和容腔长度组合,使得起振温差最低,而容腔尺寸对热机起振频率的影响较小。     

行波型热声发动机起振温差的研究

热声机械作为一种新型的能量转化装置 ,讨论其起振温差对于利用低品位能源具有非常重要的意义。文中讨论了行波型热声发动机起振温差的计算方法 ,得到了回热器结构、工作介质、丝网、频率等对起振温差的影响规律     

热声发动机起消振过程中压比演化规律研究

实验研究了热声发动机起振过程中典型的非线性现象,即双阈起消振现象。实验结果表明,充气压力以及加热功率对于双阈起振现象有着明显的影响,而双阈消振现象则主要由充气压力和消振时刻系统压力振幅决定。该研究有助于增进对热声振荡现象的进一步理解与认识。     

热声发动机起振过程系统温度时序特性

针对热声发动机起振过程中复杂的温度变化,在自行研制的"驻波型热声发动机试验平台"上,开展了在不同的工质类型、充气压力等试验工况下,热声发动机起振过程的轴向温度分布规律和变化特征的试验研究,试验结果表明:对于氮气、氩气而言,其系统温度动态特性规律基本一致,且热声核温度梯度和热声板叠温度梯度存在较明显的差别;而对于氦气,其系统温度动态特性不同于前两类气体,且热声核的温度梯度和热声板叠温度梯度的差别十分微弱,可见,不同的工质类型将直接影响到发动机起振过程系统温度的动态变化特性.     

热声热机起振过程中回热器内气体的温度分布

文中研究了驻波型热声发动机回热器内的气体,研究时段为从加热到起振前的过程,对气体在此时段内建立数学模型并加以分析。通过求解该模型,得出了回热器内不同时间和位置点的温度变化,其计算结果与实验数据相吻合。最后对模型简化导致的误差进行了分析修正。     

An experimental investigation of the propagation mechanism of critical deflagration waves that lead to the onset of detonation

The reflection of a CJ detonation from a perforated plate is used to generate high speed deflagrations downstream in order to investigate the critical conditions that lead to the onset of detonation. Different perforated plates were used to control the turbulence in the downstream deflagration waves. Streak Schlieren photography, ionization probes and pressure transducers are used to monitor the flow field and the transition to detonation. Stoichiometric mixtures of acetylene–oxygen and propane–oxygen were tested at low initial pressures. In some cases, acetylene–oxygen was diluted with 80% argon in order to render the mixture more “stable” (i.e., more regular detonation cell structure). The results show that prior to successful detonation initiation, a deflagration is formed that propagates at about half the CJ detonation velocity of the mixture. This “critical” deflagration (which propagates at a relatively constant velocity for a certain duration prior to the onset of detonation) is comprised of a leading shock wave followed by an extended turbulent reaction zone. The critical deflagration speed is not dependent on the turbulence characteristics of the perforated plate but rather on the energetics of the mixture like a CJ detonation (i.e., the deflagration front is driven by the expansion of the combustion products). Hence, the critical deflagration is identified as a CJ deflagration. The high intensity turbulence that is required to sustain its propagation is maintained via chemical instabilities in the reaction zone due to the coupling of pressure fluctuations with the energy release. Therefore, in “unstable” mixtures, critical deflagrations can be supported for long durations, whereas in “stable” mixtures, deflagrations decay as the initial plate generated turbulence decays. The eventual onset of detonation is postulated to be a result of the amplification of pressure waves (i.e., turbulence) that leads to the formation of local explosion centers via the SWACER mechanism during the pre-detonation period.     

可调频率的热声振荡演示器的研制

基于热声理论,介绍了一种相对于传统热声振荡演示器更为简单、有效、直观的热声振荡演示装置,该装置除可调节声波振幅外,还可以调节声波的频率。该装置有助于更好地理解热声效应,了解影响热声振荡的因素,为进一步的深入研究奠定基础。     

Investigations of the excitation energy transport mechanism in donor-acceptor systems

Measurements of fluorescence quantum yield _D/_oD of Na-fluorescein (donor; D) versus concentration of rhodamine B (acceptor; A) in viscous solutions have been carried out. The donor concentration in these solutions was as follows:C _D=2·10^–2 M (system I), 1.5·10^–2 M (II), 10^–2 M (III), 3·10^–3 M (IV), and 5·10^–5 M (V). The experimental results have been compared with current theories of nonradiative electronic energy transfer (NEET). In the case of very strong migration (systems I, II, and III), a significant influence of correlations (between configurations of D and A molecules in the surroundings of successively excited donors) on quantum yield _D/_oD has been determined. Experimental values have been found to be clearly higher in comparison with those predicted theoretically. The influence of possible factors on the decrease in the effectiveness of excitation energy transport to traps-acceptors in systems of very strong migration has been discussed.Dedicated to Professor A. Kawski on the occasion of his 65th birthday.     

高温超导材料、物理、应用和实验方法研究进展

文章介绍了中国科学院物理研究所超导国家重点实验室在新超导材料探索合成、高质量样品的制备、超导机理和物理性质研究、以及仪器建设方面的研究进展.在超导材料方面,生长出具有国际一流水平的氧化物高温超导单晶;在铁基高温超导材料方面,获得最高的超导转变温度;在超导机理的研究方面,建立了一些行之有效的手段,如低温比热、隧道谱、角分辨光电子谱、红外光电导谱等等,利用这些重要手段获得了一些重要结果,如从比热角度提出欠掺杂氧化物超导体应该具有一个费米弧基态,利用高精度角分辨光电子谱测量第一次观察到115meV和150meV两个新的高能量精细结构.另外,还在介观尺度超导薄膜上面观察到一些有趣的现象,如磁通系统和人工微结构之间的匹配效应.     

Nonlinear charge transport mechanism in periodic and disordered DNA

We study a model for polaron-like charge transport mechanism along DNA molecules with emphasis on the impact of parametrical and structural disorder. Our model Hamiltonian takes into account the coupling of the charge carrier to two different kinds of modes representing fluctuating twist motions of the base pairs and H-bond distortions within the double helix structure of λ-DNA. Localized stationary states are constructed with the help of a nonlinear map approach for a periodic double helix and in the presence of intrinsic static parametrical and/or structural disorder reflecting the impact of ambient solvent coordinates. It is demonstrated that charge transport is mediated by moving polarons and breather compounds carrying not only the charge but also causing local temporal deformations of the helix structure through the traveling torsion and bond breather components illustrating the interplay of structure and function in biomolecules.     

Adaptive synchronization of uncertain chaotic systems via switching mechanism

This paper deals with the problem of synchronization for a class of uncertain chaotic systems.The uncertainties under consideration are assumed to be Lipschitz-like nonlinearity in tracking error,with unknown growth rate.A logic-based switching mechanism is presented for tracking a smooth orbit that can be a limit cycle or a chaotic orbit of another system.Based on the Lyapunov approach,the adaptation law is determined to tune the controller gain vector online according to the possible nonlinearities.To demonstrate the efficiency of the proposed scheme,the well-known chaotic system namely Chua’s circuit is considered as an illustrative example.     

Review of the research on heliotrons

A brief history of the heliotron, one of the promising candidates for a commercial fusion reactor, is given. The heliotron device can be operated in steady state, since it has a stable magnetic field with high rotational transform and high shear and without ohmic current in the plasma. The results of experimental and theoretical studies on heliotron devices are reported, and future prospects are given