IMECH-IR  > 高温气体动力学国家重点实验室
氩气和空气混合气高温电离特性激波管研究
张勇勇
导师王苏
2018-05-22
学位授予单位中国科学院大学
学位授予地点北京
学位类别硕士
学位专业流体力学
关键词激波管 等离子体 Langmuir 静电探针 微波透射技术
摘要

在中科院力学所Φ800mm高温低密度激波管上开展与“黑障”现象相关的电磁波在等离子体中传输机理研究时,低密度和强激波条件下,由于气体解离和电离等非平衡过程,激波前后压缩比增加使得激波后2区宽度显著减小;同时由于边界层效应,造成激波衰减,接触面加速,也使得激波后2区宽度减小。这两个效应导致激波管2区实验观测时间减小,2区气体处于非平衡状态,增加了观察数据的不稳定性和数据分析的难度。

本论文提出在Φ800mm高温低密度激波管低压段充入95%Ar+5%Air和90%Ar+10%Air两种混合气替代空气作为激波管实验介质气体,利用Ar不解离和难电离的特性,减小激波前后压缩比,从而增加激波后2区气体宽度和2区实验时间。论文主要研究内容及结论概括如下:

(1)对Φ800mm激波管理想流动中2区实验时间进行了理论计算,分析了影响激波管实验时间的因素,利用萨哈方程计算了激波后Ar+Air混合气的平衡电子密度。在激波Mach数7~11,激波后Ar+Air混合气平衡电子密度随实验Mach数增加先增加后减小,激波后平衡电子密度随初始压力和混合气中空气比例的增加而增加。

(2)在Φ800mm高温低密度激波管中,采用Langmuir 静电探针技术和微波透射诊断技术,对Ar+Air混合气激波后电子密度进行了测量。在激波Mach数7~11,激波后电子密度随Mach数增加而增加,2区电子密度达到1012~1013cm-3量级。初始压力P1=0.4torr和P1=0.8torr条件下,微波和探针两种测量方法的电子密度结果一致性较好;初始压力P1=0.2torr时,微波测量结果大于静电探针测量结果。

(3)在Φ800mm高温低密度激波管中,采用Langmuir静电探针对激波后2区实验时间进行了测量。 Ar+Air混合气激波后2区实验时间约为300~800μs,2区气体宽度1m左右,同时探针信号显示2区气体达到电离平衡状态。在相同电子密度和碰撞频率条件下,Ar+Air混合气激波后2区实验时间约为Air的5倍。

(4)采用95%Ar+5%Air和90%Ar+10%Air混合气作为Φ800mm高温低密度激波管实验介质气体进行电磁波传输实验,可以获得为纯空气5倍的2区实验时间和平衡的实验气体。在低碰撞频率条件下,Ar+Air混合气能够获得与纯Air相同电子密度和碰撞频率;在高碰撞频率条件下, Ar+Air混合气能够获得与纯Air相同的电子密度,但碰撞频率值小于纯Air。

英文摘要

In the study of the transmission mechanism of electromagnetic wave in plasma related to the "blackout" phenomenonin Φ800mm high temperature and low density shock tube in the Institute of Mechanics, CAS, under  conditions of low density and strong shock, the experimental time at region 2 behind shock is significantly reduced due to the non-equilibrium processes such as gas dissociation and ionization. At the same time, the boundary layer effect leads to both the attenuation of the shock wave and the acceleration of the contact surface towards the shock front. Therefore, the experimental time at region 2 will further be reduced. These two effects lead to the reduction of the experimental observation time and the non-equilibrium state of test gas at region 2, resulting in the instability of data observation and the difficulty of data analysis.

In this dissertation, instead of air,two kinds of Ar+Air mixtures (95%Ar+5%Air and 90%Ar+10%Air) were used as the experimental test gas in the driven section in the Φ800mm high temperature and low density shock tube. Since Argon does not dissociate and is difficult to ionize, the density ratio across shock is reduced, thereby increasing the length of region 2 and the experimental time at region 2. The main research contents and conclusions in this dissertation are summarized as follows:

(1) The experimental time at region 2 of ideal flow in the Φ800mm shock tube was calculated and the factors that influence experimental times in the shock tube were analyzed. The Saha equation was used to calculate the equilibrium electron density behind the shock wave of Ar+Air mixtures. At the experimental Mach number range of 7-11,the equilibrium electron density increases first and then decreases with the increasing Mach number. Meanwhile, the equilibrium electron density increases with the initial pressure and the ratio of air to Argon.

(2) In the Φ800mm high temperature and low density shock tube, the electron density behind the shock wave of Ar+Air mixtures was measured with both the Langmuir electrostatic probe method and the microwave transmission attenuation method. The electron density behind the shock wave increases with the increasing Mach number, and reaches the order of 1012~1013cm-3. The electron densities obtained with the two measurement methods are consistent at the initial pressures of 0.4torr and 0.8torr. The electron densities measured with the microwave transmission attenuation method are higher than those with the electrostatic probe at the initial pressure of 0.2torr.

(3) In the Φ800mm high temperature and low density shock tube, the experimental times at region 2 were measured with the Langmuir electrostatic probe. The experimental times at region 2 of Ar and Air mixtures are about 300~800μs, and the lengths of region 2 are about 1 meter. At the same time, the probe signal showed that the gases at 2 region reached ionization equilibrium. Under the conditions of the same electron density and collision frequency, the experimental times at region 2 of Ar and Air mixtures are about 5 times than the pure air.

(4) When the 95%Ar+5%Air and 90%Ar+10%Air mixtures are used as the test gas in the Φ800mm high temperature and low density shock tube for electromagnetic wave transmission experiments, the experimental times at region 2 are about 5 times than the pure air and the equilibrium state of test gases at region 2 are reached.  Under the condition of low collision frequency, the same electron density and collision frequency as the pure air can be obtained by using Ar+Air mixtures. Under the condition of high collision frequency, however, the same electron density as the pure air can be obtained by using Ar+Air mixtures, but the collision frequency value is less than the pure air.

语种中文
文献类型学位论文
条目标识符http://dspace.imech.ac.cn/handle/311007/77094
专题高温气体动力学国家重点实验室
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张勇勇. 氩气和空气混合气高温电离特性激波管研究[D]. 北京. 中国科学院大学,2018.
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