共查询到20条相似文献,搜索用时 109 毫秒
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对具有轴向初始速度即竖直下抛液体燃料的爆炸抛撒云雾形成过程进行了数值研究。近场的数据来自丁珏等的工作,以此数据作为远场初始参数。远场是燃料液滴与空气、燃料蒸汽、不同尺寸的液滴颗粒组成的多相体系之间的相互作用的过程。液滴的直径比较小,把液滴看成连续介质,且相互作用只考虑液滴的蒸发、破碎、碰撞聚合。轴向初速为0(静爆)时计算结果与实验结果相吻合。这说明本模型可以模拟爆炸抛撒云雾的形成过程,进而可以预估高速运动下云雾的形成过程。用以上模型计算了竖直下抛初速为100m/s、装填5kgPO的FAE装置的爆炸抛撒过程。所得的结果表明,100m/s的初速将影响云雾的最终形状及云雾内部的浓度分布。 相似文献
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利用LS-DYNA三维动力有限元程序对三点起爆的翻转型EFP形成过程及三个尾翼进行了数值模拟,结果表明:数值计算结果和实验结果吻合得较好,可为弹丸设计的改进和优化提供重要的参考依据。分别选择Johnson-Cook和Steinberg两种本构模型对药型罩材料进行了数值模拟对比,结果表明:药型罩材料的本构模型选取对形成的尾翼效果有一定的影响,Steinberg本构模型与试验结果符合得更好。 相似文献
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为研究内弹道初始阶段中心点火管燃气在膛内药床中的流动特性和传播规律,设计了可视化点传火实验平台,并进行了膛内假药床的点传火实验。基于加权本质无震荡(weighted essentially non-oscillatory, WENO)格式,构造了膛内轴对称二维内弹道两相流模型,对膛内燃气在假药床中的流动过程进行数值模拟。计算结果与可视化实验结果符合较好,全局压力平均误差为5.35%。表明数值计算准确地描述了燃气流动特性,完整地呈现了点火管燃气在假药床中的发展过程。在点火初始阶段,膛内压力径向效应明显,气相沿径向传播较快,药床药粒基本不会发生运动;随着燃气逐渐在膛内传播,膛内压力呈现径向一致、轴向梯度分布的特征,在压力梯度作用下,气相轴向速度开始占据主导,径向速度在膛底和中部区域减小为零,而固相速度随气相速度变化而变化;气相在到达弹底前,由于固相颗粒的壅塞,会提前出现速度反向波动现象。 相似文献
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The two-phase flow process in an ejector was numerically and experimentally studied using R141b as a working fluid. A modified one-dimensional gas–liquid ejector model was proposed to remedy the defect in the traditional one. Gas–liquid boundary layer regions were discussed and used to close the model. Mac Cormack method is used to discrete controlling equations of gas–liquid two-phase flow in the ejector. The radial distribution of velocity and temperature, the variation of void fraction, the axial velocity variation and the influence of primary steam pressure on the mixing process were predicted with the numerical model. An experimental rig was set up to validate the model by comparing the experimental pressure distribution in the ejector with the calculating one. 相似文献
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本文对动失速型非定常分离涡结构的控制方法,在低速风洞中应用相平均测压技术进行了实验研究。在二元平板模型中部安装一作俯仰振荡的扰流板产生动失速型分离涡,在其上游安装另一用作控制的小扰流板。实验结果表明,应用前置的振荡小扰流板可影响并改变动失速分离涡的强度和对流特性。在最有利的控制相位下,涡吸力峰可降低48%,涡对流时间可以推迟0.19周期。对于间歇式振荡扰流板,采用相位提前控制方式比相位滞后控制方式更有效。 相似文献
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The purpose of a supersonic ejector consists in the mixing of two fluids with different stagnation pressures in order to obtain a fluid at an intermediate stagnation pressure at the discharge. Depending on the geometry of the ejector and on the operating conditions, the entrained secondary stream may reach sonic/supersonic velocities within the ejector, leading to the capping of the entrained mass flow rate for fixed reservoir conditions. Although the associated limitation of the entrainment ratio (due to choking) is a well known phenomenon, there is still a lack of understanding of the complex flow phenomena at play within supersonic ejectors, and further detailed knowledge and modeling of the choking process is necessary. This paper presents a detailed analysis of the choking phenomenon through advanced post-processing of CFD calculations which are validated with experimental results both at the global and the local scales. This in-depth investigation of the choking phenomenon within the ejector is proposed both qualitatively and quantitatively for given reservoir conditions. The complex flow signature highlighted by means of the numerical results is then investigated and corroborated through experimental shadowgraphy. Studies combining experimental results (including visualizations) with numerical simulations are rather scarce in the open literature and to the knowledge of the authors, this study is the first one that proposes such a detailed analysis. For the present ejector geometry and operating conditions, the choking phenomenology of the secondary stream is found to closely correspond to the model of the Fabri-choking early postulated in Fabri and Siestrunck (1958). 相似文献
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The use of a non-steady ejector based on wave rotor technology is modeled for pulse detonation engine performance improvement
and for compatibility with turbomachinery components in hybrid propulsion systems. The rotary wave ejector device integrates
a pulse detonation process with an efficient momentum transfer process in specially shaped channels of a single wave-rotor
component. In this paper, a quasi-one-dimensional numerical model is developed to help design the basic geometry and operating
parameters of the device. The unsteady combustion and flow processes are simulated and compared with a baseline PDE without
ejector enhancement. A preliminary performance assessment is presented for the wave ejector configuration, considering the
effect of key geometric parameters, which are selected for high specific impulse. It is shown that the rotary wave ejector
concept has significant potential for thrust augmentation relative to a basic pulse detonation engine. 相似文献
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The impact of 12 spoiler–tab configurations, of different heights and widths, on the tip vortex generated by an oscillating
NACA 0015 wing was investigated experimentally. For an oscillating wing equipped with a spoiler, the peak tangential velocity
and core and total circulation were greatly reduced compared to a tab, regardless of its width, while the core radius remained
largely unaffected with its center displaced vertically above the baseline wing. The most noticeable impact of a spoiler with
a reduced height was its potential in alleviating the blade–vortex interaction (BVI) strength. Meanwhile, the largest favorable
impact on the critical vortex flow parameters was achieved via a 25%-span spoiler–tab combination with a height of 5 and 2.5%
chord, respectively. A contrary effect on the BVI suppression, especially during pitch-up, was, however, observed. The impact
on the BVI can be improved by reducing the height of the spoiler at the expense of unfavorable change in the vortex strength
and displacement. 相似文献
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Peng ChangxinFan Wei Zhang QunYuan Cheng Chen WenjuanYan Chuanjun 《Experimental Thermal and Fluid Science》2011,35(6):971-977
Experimental studies were performed in order to improve the understanding of the performance of ejector driven by an air-breathing pulse detonation engine (PDE) with a convergent nozzle. This research utilized a gasoline-air PDE at four different operating frequencies of 8 Hz, 10 Hz, 12 Hz and 15 Hz. The performance of PDE-ejector was quantified by thrust measurements. The effects of single ejector length and axial location on thrust augmentation were investigated. It was found that the single ejector with L/D of 2 showed the best performance and the maximum thrust augmentation occurred at a downstream placement of +1 tube diameter. The performances of two-stage and three-stage ejectors were also investigated. The results indicated that both the overlap ratio and the flow area between two stages should not be too large. The performance of the two-stage ejector was not as sensitive as single-stage ejector to axial position in current conditions. The three-stage ejector behaved better than the two-stage ejector but worse than the single-stage ejector in this work. A maximum thrust augmentation of 1.8 was obtained with an L/D of 2 at a downstream placement of +1 position and 15 Hz operating frequency. 相似文献
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Conventional compression-refrigeration systems not only consume a large amount of electric power, but also cause serious environmental pollution. Among the various possible approaches in overcoming these two problems, a steam-ejector refrigeration system is believed to be most effective. This paper experimentally investigates the controlling parameters of a steam ejector, including operating conditions and the exit Mach number of the primary nozzle. Operation maps useful to the practical design are constructed from experimental results, and the empirical equations are correspondingly derived. Excessively increasing the exit Mach number of primary nozzle is unnecessary, and 4.35 should be a moderate value. With regard to the performance characteristics of the ejector itself, a steam ejector is better than an R114 ejector and is comparable to an R113 ejector. Moreover, with the use of a two-stage ejector, the required pressure to drive a steam ejector is reduced, and the low-grade heat source can be efficiently used. The results of primitive observation of the flow field are also discussed in this work. 相似文献
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Peter Vorobieff C. Randall Truman Adam M. Ragheb Gregory S. Elliott Julia K. Laystrom-Woodard Darren M. King David L. Carroll Wayne C. Solomon 《Experiments in fluids》2011,51(3):711-722
We present quantitative analysis of image sequences of multi-stream injection nozzle flows with several different injection
geometries in an experiment simulating mixing in a chemical oxygen-iodine laser. To visualize mixing, image sequences were
acquired with planar laser-induced fluorescence (PLIF) in iodine that was injected into the main flow. The injection nozzle
consisted of a slot, ejector, and injector block, with rows of ejector and injector holes along the slot length. The ejector
flow exits in an underexpanded state so that upon expanding it forces the slot and injector flows together to enhance mixing.
For this study, the diameter and geometry of ejector holes were varied to assess their effect on mixing. Two configurations
of ejector holes were used, each with two different diameters for a total of four cases with data collected at downstream
stations. We carry out a quantitative mixing analysis for these configurations, using two methods to quantify the mixing.
The first method considers the statistics of the PLIF image intensity histograms, which are bimodal for poorly-mixed flows
and have a single peak in well-mixed flows. The second method quantifies the properties of the mixing interface. Our analysis
shows that two injection schemes significantly enhance mixing by stretching the mixing interface. 相似文献
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Notched spoilers have been observed to be more effective than uniform spoilers to suppress the flow-induced cavity resonance
of vehicles with open sunroofs. In this study, a few mechanisms possibly involved in buffeting suppression from notched spoilers
were investigated experimentally and numerically. One objective was to investigate the spatial coherence and phase of the
wall pressure fluctuations downstream of notched spoilers in comparison with the same quantities for uniform spoilers. Another
objective was to gather detailed measured data to allow the verification of computer simulations of the flow over the notched
spoiler. Experiments were performed to measure the velocity and wall pressure fields downstream of spoilers mounted on the
rigid floor of a closed test section wind tunnel. Efforts were made to reproduce the spoiler and wind tunnel geometry and
boundary conditions of the experimental setup in the numerical simulations. The numerical investigation used the Lattice Boltzmann
Method (LBM), with the so-called Very Large Eddy Simulation (VLES) viscosity turbulence model. The results of the numerical
investigation were in satisfactory agreement with measured data at low frequencies, where buffeting is expected to occur.
The results suggested that the notches break down the homogeneity of the leading edge cross-stream vortices predominantly
responsible for the cavity excitation. This decreased the cross-stream coherence of the surface pressure field, thereby reducing
the magnitude of the net equivalent excitation force acting over the surface downstream. 相似文献