Numerical study of reacting flow characteristics of a 2D twin cavity trapped vortex combustor

In the present work, reacting flow characteristics of a 2D trapped vortex combustor (TVC) have been investigated numerically. Turbulent flow prevailing in the combustor is modelled using the two equation shear stress transport (SST) k-ω model and the turbulence–chemistry interactions are modelled using the eddy dissipation concept (EDC) model. Validation study reveals that the data generated by numerical model for reacting flow cases matches reasonably well with the experimental data. Simulation results indicate that for a particular operating condition, the flow structure within the cavity for reacting flow cases is significantly different from non-reacting flow cases. Besides this, under reacting flow condition, the vortex core location shifts with variation in operating condition. This study also reveals significant differences in the velocity gradient at the shear layer between reacting and non-reacting flow conditions. Furthermore, the turbulent kinetic energy at the cavity zone increases for the reacting flow condition, which is attributed to the volume expansion associated with the combustion processes. Also, temperature contours at locations downstream of the trailing edge indicate that both cavity flames are merged together for higher primary air velocity cases, and this is essential for efficient performance of TVC.     

量子点场效应单光子探测器二维电子气载流子浓度研究

设计了一种基于场效应晶体管的量子点场效应单光子探测器(quantum dot field effect transistor,QDFET),建立了二维电子气(two-dimensional electron gas,2DEG)的薛定谔方程和泊松方程,通过对薛定谔方程和泊松方程的自洽求解,对2DEG的载流子浓度进行了模拟。模拟结果显示,AlGaAs的Al组分、δ掺杂层的掺杂浓度以及隔离层的厚度对于2DEG的载流子浓度均有影响。为了使2DEG具有较高的载流子浓度,AlGaAs的Al组分应为0.2~0.4,δ掺杂浓度应为6~8×10~(13)/cm~2,隔离层厚度应在50nm以下。通过对2DEG的载流子浓度进行研究,可以掌握2DEG载流子浓度的影响因素,从而通过优化QDFET结构,可提高2DEG的载流子浓度。这对于高灵敏度QDFET的制备具有重要的意义和应用价值。     

石英增强光声光谱技术研究进展

石英增强光声光谱（QEPAS）技术是一种新颖的气体探测技术,具有体积小、灵敏度高等优点,是痕量气体检测技术的研究热点。本文对QEPAS技术的基本原理、发展历史及发展现状进行了综述,并对多种不同结构的QEPAS系统发展情况进行了介绍,最后对该技术的发展前景进行了展望。     

气体体积粘性对二维环形激波聚焦的影响

基于体积粘性系数ζ的分子运动论和连续介质理论,对二维环形激波聚焦（马赫数Ma=2.0）的体积粘性效应进行数值研究,结果表明：对于热完全气体,体积粘性使得激波汇聚中心点处的压力减小、温度增加、密度减小,聚焦点物理参数的改变量分别可达20%、10%、30%,体积粘性效应对环形激波聚焦的影响是不可忽略的;与转动模态相比,在振动模态下环形激波聚焦的体积粘性效应更为明显,因为激波聚焦点附近的体积粘性应力ζ▽·V与热力学压力p达到同一数量级,从而显著改变了流动参数.     

The two-dimensional Coulomb gas on a sphere: Exact results

At the special value of the reduced inverse temperature=2, the equilibrium statistical mechanics of a two-dimensional Coulomb gas confined to the surface of a sphere is an exactly solvable problem, just as it was for the Coulomb gas in a plane. The thermodynamic quantities and all the correlation functions can be calculated. Use is made of an isomorphism between the classical Coulomb gas and the free Fermi field theory associated with the Dirac operator on the sphere.Laboratory associated with the Centre National de la Recherche Scientifique.     

Biased lattice gases with correlated equilibrium states

The approach to and structure of the equilibrium state is studied for a 7-bit lattice gas with biased forward and backward transition rates by means of mean field theory and computer simulations. If the rate constants obey the factorizability and the detailed balance conditions, the occupations of different velocity directions are uncorrelated, anH-theorem is valid, and a nonuniversal equilibrium state exists that depends explicitly on the transition rates. In case the above conditions are not satisfied, theH-theorem is no longer valid, and mean field theory also predicts nontrivial velocity correlations in postcollision states. The simulations are mainly concentrated on the time dependence of pre- and postcollision velocity correlations on a single node, and on slowly increasing fluctuations that might indicate metastable behavior.     

Enhanced emission of the laser generated plume in Ar gas

We report an effect of enhanced emission of laser generated plume in gas ambi-ent.Nonreactive argon gas was used in the experiment of UV laser ablation of copper plate.The emission of Cu atoms from the plume was increased more than the times.The emission in-tensity is sensitive to the gas pressure,but in a certain region of gas pressure,the enhanced ef-fect can be controlled stably.For the emission lines from other element,Zn,in the plume,the intensities are subjected to the same factor of increasement.     

二级轻气炮超高速弹丸发射技术的研究

 本文研究了提高二级轻气炮弹丸速度的发射技术途径。通过数值计算对各种装填参量的影响进行了详细讨论。认为减小弹丸质量、活塞质量以及注气压力，可使二级轻气炮在较少的装药量条件下提供较高的弹丸速度。目前已经做到在5 kg装药时，使30 g的弹丸达到7.2 km/s速度；60 g弹丸达到5.7 km/s速度；26 g弹丸达到7.4 km/s速度。装填3.5 kg药量时，使10.3 g弹丸达到了8.1 km/s速度。     

The effective ionization coefficients and electron drift velocities in gas mixtures of CF3I with N2 and CO2 obtained from Boltzmann equation analysis

The electron swarm parameters including the density-normalized effective ionization coefficients(α-η)/N and the electron drift velocities V e are calculated for a gas mixture of CF3I with N2 and CO2 by solving the Boltzmann equation in the condition of a steady-state Townsend(SST) experiment.The overall density-reduced electric field strength is from 100 Td to 1000 Td(1 Td = 10-17V·cm2),while the CF3I content k in the gas mixture can be varied over the range from 0% to 100%.From the variation of(αη)/N with the CF3I mixture ratio k,the limiting field strength(E/N) lim for each CF3I concentration is derived.It is found that for the mixtures with 70% CF3I,the values of(E/N) lim are essentially the same as that for pure SF 6.Additionally,the global warming potential(GWP) and the liquefaction temperature of the gas mixtures are also taken into account to evaluate the possibility of application in the gas insulation of power equipment.     

超声空化引起界面湍动促进的传质机理

本文分析了超声空化引起界面湍动对传质过程的影响,提出了相界面上超声空化气泡析出增强边界层液体湍动并促进传质的机理,在传质理论和流体动力学原理的基础上,建立了超声空化引起界面湍动促进的传质机理模型,获得了超声空化引起界面湍动促进的传质系数表达式。实验结果验证了模型的合理性。该模型既证实了超声对传质有强化效应,又对传质过程有很好的预测功能,为工业化提供了理论依据。