共查询到18条相似文献,搜索用时 68 毫秒
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激光等离子体堵口效应的理论模拟 总被引:1,自引:0,他引:1
采用较为简化的理论模型,根据离子运动方程的自相似解,模拟了激光辐照腔靶时产生的妨碍能量继续注入的堵口效应,获得了注入腔靶的能量份额随小孔初始半径及激光参数的变化曲线。理论与实验结果相符。 相似文献
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辐射加热腔诊断孔堵口特性实验研究 总被引:1,自引:1,他引:0
研究辐射加热腔诊断孔堵口现象。实验采用波长为1.053μm、能量为300-400J、脉宽为-800ps的高斯型激光脉冲,双束对打具有双源区的腔靶。在激光入射口及内腔口服两台亚千电子伏特X射线能谱仪监测源区与内爆区发射的X光谱。定性分析和讨论了堵口现象。 相似文献
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一、开展中能重离子反应研究的意义对轰击能量较低的重离子反应已经进行了广泛的研究。此时质心系轰击能E_(cm)超过库仑位垒V_B 约3~5MeV/核子,在核接触时的相对速度V_(Rel)(?)3cm/ns,反应时间τ大于3×10~(-22)s/fm。核中核子的费米速度约为8cm/ns,相当于τ_F为10~(-22)s/fm,因此时τ(?)τ_F。大量实验表明此时主要发生二体反应,过程是绝热的。通过相互作用,能量、角动量、N/Z 自由度及质量逐步发生弛豫。 相似文献
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“多靶串接”饱和增益软X光激光实验研究 总被引:4,自引:2,他引:2
采用“多靶串接”设计,利用强度为0.8×10~(13)~1.0×10~(13)W/cm~2,波长为1.05μm,脉宽约1ns的两路钕玻璃激光线聚焦辐照四块串接的平面厚锗靶,观察到波长为23.2和23.6nm的接近饱和的类Ne锗软X光激光输出。当总靶长为5.6cm时,这两种波长的软X光激光输出的GL值都达到16左右,沿靶法线和靶平面方向的发散角都只有3~4mrad。 相似文献
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The timing and location of autoignition can be highly sensitive to turbulent fluctuations of composition. Second-order Conditional Moment Closure (CMC) provides transport equations for conditional (co)variances in turbulent reacting flows. CMC equations accounting for compressibility and differential diffusion are analyzed using data from direct numerical simulation of an autoignitive lifted turbulent hydrogen jet flame [C.S. Yoo, R. Sankaran, J.H. Chen, Three-dimensional direct numerical simulation of turbulent lifted hydrogen/air jet flame in a heated coflow. Part 1. J. Fluid. Mech., (2008)]. At the flame base, second-order moments were required to accurately model the conditional reaction rates. However, over 80% of the second-order reaction rate component was obtainable with a small subset (16%) of the species-temperature covariances. The balance of the second-order CMC equation showed that turbulent transport across spatial composition gradients initiates generation of conditional variances. 相似文献
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Turbulent piloted Bunsen flames of stoichiometric methane–air mixtures are computed using the large eddy simulation (LES) paradigm involving an algebraic closure for the filtered reaction rate. This closure involves the filtered scalar dissipation rate of a reaction progress variable. The model for this dissipation rate involves a parameter βc representing the flame front curvature effects induced by turbulence, chemical reactions, molecular dissipation, and their interactions at the sub-grid level, suggesting that this parameter may vary with filter width or be a scale-dependent. Thus, it would be ideal to evaluate this parameter dynamically by LES. A procedure for this evaluation is discussed and assessed using direct numerical simulation (DNS) data and LES calculations. The probability density functions of βc obtained from the DNS and LES calculations are very similar when the turbulent Reynolds number is sufficiently large and when the filter width normalised by the laminar flame thermal thickness is larger than unity. Results obtained using a constant (static) value for this parameter are also used for comparative evaluation. Detailed discussion presented in this paper suggests that the dynamic procedure works well and physical insights and reasonings are provided to explain the observed behaviour. 相似文献
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Simulations of turbulent lifted jet flames with two-dimensional conditional moment closure 总被引:1,自引:0,他引:1
Simulations of H2 air lifted jet flames are presented, obtained in terms of two-dimensional, first-order conditional moment closure (CMC). The unsteady CMC equation with detailed chemistry is solved without the need for operator splitting, while the accompanying flow field is determined using commercial CFD software employing a k − ε turbulence model. Computed lift-off heights and Favre-averaged species mole fractions are found to be very close to values obtained experimentally for a wide range of jet velocities and fuel–air mixtures. Simulations for which the initial condition is an attached flame and the jet velocity gradually increased do not result in lift-off, a result fully consistent with experimental observation and capturing the hysteresis behaviour of lifted flames. The stabilisation mechanism is explored by quantifying the balance of terms comprising the CMC in the lift-off region. In line with experimental data, it is found that the scalar dissipation rate at the stabilisation height is well below the extinction value, and that axial transport and molecular diffusion play a major role. The radial components of spatial convection and diffusion are always small, fully justifying the alternative approach of employing a cross-stream averaged CMC. 相似文献
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Giulio Borghesi Epaminondas Mastorakos Cécile B. Devaud Robert W. Bilger 《Combustion Theory and Modelling》2013,17(5):725-752
Simulations of an n-heptane spray autoigniting under conditions relevant to a diesel engine are performed using two-dimensional, first-order conditional moment closure (CMC) with full treatment of spray terms in the mixture fraction variance and CMC equations. The conditional evaporation term in the CMC equations is closed assuming interphase exchange to occur at the droplet saturation mixture fraction values only. Modeling of the unclosed terms in the mixture fraction variance equation is done accordingly. Comparison with experimental data for a range of ambient oxygen concentrations shows that the ignition delay is overpredicted. The trend of increasing ignition delay with decreasing oxygen concentration, however, is correctly captured. Good agreement is found between the computed and measured flame lift-off height for all conditions investigated. Analysis of source terms in the CMC temperature equation reveals that a convective–reactive balance sets in at the flame base, with spatial diffusion terms being important, but not as important as in lifted jet flames in cold air. Inclusion of droplet terms in the governing equations is found to affect the mixture fraction variance field in the region where evaporation is the strongest, and to slightly increase the ignition delay time due to the cooling associated with the evaporation. Both flame propagation and stabilization mechanisms, however, remain unaffected. 相似文献
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Numerical simulation of the flow within and over an intersection model with Reynolds-averaged Navier--Stokes method 总被引:2,自引:0,他引:2 下载免费PDF全文
In this study, the Reynolds-averaged Navier--Stokes (RANS) method is
employed to simulate the flow within and
over an intersection model with three kinds of $k$--$\varepsilon$ turbulence closure schemes,
namely, standard model, renormalization group (RNG) model and realizable $k$--$\varepsilon$model. The comparison
between the simulated and observed flow fields shows that the RANS simulation
with all the three turbulence models cannot completely and accurately reproduce
the observed flow field in all details. A detailed comparison between the
predicted profiles of wind velocities and the measured data shows that the
realizable $k$--$\varepsilon$ model is the best one among the three turbulence closure models
in general. However, the extent to which the improvement is achieved by
the realizable $k$--$\varepsilon$ model is still not enough to completely and
accurately describe the turbulent flow in a relatively complex
environment. 相似文献