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基于现有的文氏咀流量供给管道,提取出轴对称2维计算模型,计算了不同背压下文氏咀及下游管道的流场特性。计算结果显示,随着背压的升高,激波在管道内经历了3种状态,在直管道内为斜激波,到转接段时为拟正激波,进入文氏咀后则为正激波。在进行文氏咀流量计的设计时,应尽量将正激波控制在文氏咀喉道或向下游延伸的一小段距离内,此时是文氏咀的最佳工作状态。另外,采用壁面开孔法在文氏咀下游选取测压点时,为了准确测量截面上的静压,应将测压点选取在距离直管道入口数倍管径处,一般不低于8倍管径。 相似文献
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一维周期性增益介质的临界长度 总被引:1,自引:1,他引:0
用传输矩阵方法研究了一维周期性增益介质的透射频谱随系统层数的变化规律.研究发现:对层数一定的介质,透射率在某些频率上有很大的峰值;增加层数,尖峰在频谱图上出现的位置会发生移动,且对不同的频段,其位置随介质层数的变化规律是不同的.考察了这种系统中每个频率的光所对应的临界长度,解释了不同频段激光出现位置随层数变化的规律.比较了周期系统和随机系统中临界长度与频率关系的异同,用群速度理论和能带理论对此做了解释. 相似文献
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当喷射器应用于天然气开采和海水淡化领域时,由于工作流体或引射流体常携带少量水,喷射器常处于气液两相运行状态。本文对含水喷射器装置性能进行了实验研究,获得了不同工作压力和背压下,喷射器性能的变化规律。研究发现,当喷射器临界运行时,加水对喷射器性能影响很小,引射比变化在2.7%之内;而喷射器非临界运行时,气液两相运行时引射比性能变差,与单相运行时相比,引射比最大减小了17%。 相似文献
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本文实验研究了蒸馏水经内径0.226 mm、长度16.5 mm薄壁不锈钢直管向真空环境排放时形成的液体闪蒸射流现象.实验观察到3种射流形态。在液体初始温度低于背压所对应的饱和温度时,液体不会发生闪蒸,液体射流喷出后保持完整;反之,液体表面蒸发会导致液体射流核周围出现不规则蒸发波,射流破碎散落;进一步降低背压,会使得射流一出喷口即快速破碎形成扩张角大于90°的雾状射流。射流流量在背压低于某个临界数值时出现壅塞现象,即流量不再随背压降低而增加,表现出强烈的可压缩流动特征。 相似文献
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为了研究入射激波变化的隔离段内激波串的运动特性,设计并搭建了直连式变Mach数实验系统,捕捉了相同来流Mach数变化速率、不同背压变化速率下激波串的运动行为,揭示了入射激波与背压同时变化对激波串运动的影响机理。入射激波与背压同时变化时,共有3个方面的因素会影响激波串整体的上下游运动趋势,其一,Mach数变化,Mach数增大导致激波串向下游运动,该影响随Mach数增大逐渐减弱;其二,背景波系移动,背景激波反射点靠近激波串前缘时,可能引起激波串的突跳;其三,背压压比变化,背压压比增大时激波串向上游运动,该影响随背压压比增大逐渐增强。三方面因素共同作用下激波串表现出复杂的运动。 相似文献
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Yu. P. Sukhorukov A. V. Telegin N. G. Bebenin A. A. Buchkevich A. P. Nosov V. D. Bessonov 《JETP Letters》2018,107(1):48-54
An analytical approach that makes it possible to reconstruct the current–phase relation (CPR) in Josephson structures included in one of the arms of a two-junction superconducting quantum interference device (SQUID), where the second junction has a significantly higher critical current and a known (sinusoidal) CPR, has been developed. The developed methods of analytical and numerical studies of current–flow transformations in two-junction SQUIDs make it possible to reconstruct the CPR of a junction with a low critical current taking into account both the existence of the self-inductance of the interferometer contour and a possible asymmetry in the supply current system. The efficiency of this approach has been confirmed by the experimental study of niobium–aluminum/aluminum oxide–niobium test structures with the known CPR. 相似文献
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Hydrogenated amorphous silicon (a-Si:H) films with high and same order of magnitude photosensitivity (-10^5) but different stability were prepared by using microwave electron cyclotron resonance chemical vapour deposition system under the different deposition conditions. It was proposed that there was no direct correlation between the photosensitivity and the hydrogen content (CH) as well as H-Si bonding configurations, but for the stability, they were the critical factors. The experimental results indicated that higher substrate temperature, hydrogen dilution ratio and lower deposition rate played an important role in improving the microstructure of a-Si:H films. We used hydrogen elimination model to explain our experimental results. 相似文献
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本文由速率方程出发分析了带调谐光纤F-P腔的光纤环形腔半导体激光器的频偏特性,结果表明在低频时的频偏功率比自由运转激光器低,而在高频时则趋于一致。改变调制频率和F-P腔的腔长可以改变激光器的频偏功率比,选择适当的调制频率和F-P腔参数就能获得不同的频偏特性。 相似文献
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AA Yan LI Kai CAO ZhongHua & HU WenRui Key Laboratory of Microgravity 《中国科学:物理学 力学 天文学(英文版)》2011,(2)
The dependency of the critical Marangoni number on the geometrical aspect ratio of the floating half zone is essential to predict the onset of oscillatory thermocapillary convection.The experimental studies in the microgravity conditions on floating half zones of several centimeters in diameter have predicted that the critical Marangoni number increases with the increasing aspect ratio,and the terrestrial experimental studies have predicted the contradictory conclusion for floating half zones of several mil... 相似文献
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采用热力学方法和Benedict-Webb-Rubin(BWR)方程及相应的参数,计 算了临界温度附近H2气体的绝对焓和熵值,同时拟合了一组高准确度的定压比热容与温度 关联式参数.通过计算值与实验值的比较发现:在临界温度以上,计算值与实验值符合良好 ,对低于临界温度的未饱和H2气体也能计算出较好了结果.但对临界点和温度低于临界温 度、压强高于临界压强的过饱和H2气体的计算误差比较大,说明此时的H2气体的热力学性质特别,应当专门处理. 相似文献
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Acoustic emissions were characterized for fourteen, 8 × 8 arrays of axisymmetric supersonic jets experimentally. The nozzle diameters ranged from 3.2 mm (1/8 in.) to 6.4 mm (1/4 in.) and the hole-to-hole spacing (S) over hole diameter (d), or the S/d ratios ranged from 1.44 to 3. The arrays were tested at several net pressure ratios ranging from 2 to 24. It was found that up to a critical net pressure ratio, the arrays radiated ultrasonic frequencies. Beyond this critical net pressure ratio the characteristic frequency decreased to lie within the audible range. Frequency response plots of the sound pressure indicate a broadband frequency peak generated by the turbulent mixing noise of the jet. At lower net pressure ratio (NPR) values, this broadband peak is similar to a single jet within the jet array. However, as the NPR continues to increase this frequency peak shifts to lower values which are similar to a single jet with an equivalent exit area of the entire array. Dimensional analysis revealed that at a critical net pressure ratio a dramatic reduction in the characteristic Strouhal number occurred. A small increase in the characteristic acoustic pressure was also observed at net pressure ratios below the critical net pressure ratio and a larger increase was observed at higher net pressure ratios. The critical net pressure ratio appeared to be a linear function of S/d for the nozzle arrays. A linear curve fit was applied to the measured critical net pressure ratio and this was compared to a theoretical model prediction. The experimental results revealed that the critical net pressure ratio is well predicted by the models. 相似文献
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采用二带Ginziburg-Landau(G-L)理论模型计算了各向异性超导体的上临界磁场,发现上临界磁场Hc2的解析式中包含序参量的各向异性和有效质量的各向异性;上临界磁场ab-面内分量Hc|2|ab、c-轴方向分量Hc|2|ab与实验数据符合;上临界磁场比率在实验许可范围之内。 相似文献
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HT-7 Tokamak拥有离子回旋波(ICRF)和低杂波(LHW)两套加热系统.ICRF主要对加热离子有比较好的加热效果,LHW则主要是通过电子Landau阻尼加热电子.除此之外,在ICRF和LHW协同加热的条件下,可以对等离子体产生更有效的加热效果,增加等离子体的聚变反应截面,增加聚变中子产额.本文报道了LHW对改善ICRF和等离子体耦合的重要作用,ICRF和LHW加热等离子体中电子温度随时间的演化过程,计算了放电过程中电子逃逸的阈值能量,分析了逃逸电子的产生过程,以及放电过程中的中子产额.研究结果发 相似文献
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为实现一束激光在90°锥形范围内的扫描,利用液晶空间光调制器在光束偏转控制时精度高、无机械惯性等优点,研究并建立了基于液晶空间光调制器的光束偏转和角放大光路系统。提出了空间光调制器的可编程相位调制算法和角放大光路结构,推导了空间光调制器光束偏转角度与相位灰度驱动图的关系,设计了角度放大倍率高于22倍的角放大光路系统。在此基础上,建立了光束扫描控制实验系统,对该装置角度出射范围进行了测量,将实际的角放大倍率与设计值进行对比。实验结果表明:研制系统的出射视场角可达91.22°,并可通过畸变校正实现出射视场角范围内的规则形状扫描。该研究在光束敏捷控制、无线激光通信、目标搜索与追踪等领域具有重要的研究价值和应用前景。 相似文献