|Alternative Title||Research on the Key Technology of Total Pressure Increase in Long Test Duration Detonation Driven Wind Tunnels|
|Thesis Advisor||俞鸿儒 ; 李进平|
|Place of Conferral||北京|
|Keyword||爆轰驱动 激波风洞 总压 直接起爆 点火管|
由于高超声速流动本身的复杂性，相关研究很大程度上需要依赖地面实验，因此风洞的实验能力对高超声速技术的发展具有重要影响。在各种高超声速风洞中，爆轰驱动激波风洞具有结构和运行简单、实验成本低的优势，是一种颇具潜力的高超声速风洞。 激波风洞属于脉冲类风洞，试验时间很短。为了延长试验时间，通常要求驱动气体和试验气体的声速相互匹配。模拟来流总温越高，所需的驱动气体声速也越高。“爆轰驱动”是以气相爆轰产物作为驱动气体的驱动方式，爆轰产物的声速通常较高，故爆轰驱动技术适于模拟高总温的来流，在模拟较低总温工况时困难很大。为了获得低总温工况的模拟能力，JF-12大型高超声速激波风洞采用了一种特殊的驱动方法——“小驱大”，即以细的驱动段来驱动粗的被驱动段。由于驱动气体在进入被驱动段前先经过了等熵膨胀，气体声速显著降低，所以能够模拟总温较低的来流。但是，等熵膨胀过程中驱动气体的压力下降严重，导致风洞的来流总压模拟能力显著降低。 总压和总温对于流动模拟都非常重要。为了保留宽总温模拟范围的同时提高总压模拟能力，本文研究了调整驱动气体组份来获得低声速驱动气体的方式。调整组份（主要是氮气稀释度提高）会导致严重的爆轰起始困难，现有的点火方法均无法实现起爆。因此，调整驱动组份的核心问题在于解决驱动气体的起爆困难。 提高点火方法的起爆能力有助于解决起爆困难。为了增强起爆能力，本文提出了一种封闭式点火管设计。这种设计没有延用点火管与驱动段连通的传统结构，而是以膜片将点火管隔离为独立腔体。点火管的封闭性带来了提升起爆能力的新途径——提高点火管初始压力和填充当量比可燃气体。实验表明，封闭式点火管的起爆能力比传统点火管显著增加，大幅拓宽了直接起爆的稀释度范围，能够起爆所需的驱动气体。 提高点火管初始压力虽然能够有效提高起爆能力，但点火管初始压力过高会导致操作安全问题。为了优化点火管设计，以降低起爆所需的初始压力，本文就以下几种因素对起爆能力的影响进行了实验研究：点火管出口直径、单/双点火管、点火气体爆轰敏感性。研究表明对点火管的数量、内型面和点火气体爆轰敏感性进行特定组合时可以获得较高的起爆能力：采用单根点火管时，宜使用缩颈内型面，点火气体应选择爆轰敏感性低的混气，如CO/O2。采用双点火管时，为了保证点火同步性，宜选择爆轰敏感性强的点火气体，如含微量H2的CO/O2，或C2H2/O2，同时点火管应采用等径内型面。此外，提高点火管出口直径也能大幅提高起爆能力。 采用封闭式点火管进行风洞缝合运行实验时发现，虽然点火管成功实现了高稀释度驱动气体的直接起爆，但封闭式点火管严重干扰了风洞的缝合运行状态。通过理论分析、数值模拟和实验验证，确定了干扰原因是点火气体声速与驱动气体相差过大，不满足与试验气体声速匹配的要求。据此，得到了封闭式点火管的“声速匹配”原则，即根据试验气体和工况选择点火气体的组份（和声速）。实验表明，基于“声速匹配”原则可以显著改善缝合程度，能够获得满足实用要求的平稳驻室状态。 利用封闭式点火管相关技术，无需变截面驱动即可满足宽范围总温模拟的要求，避免了变截面驱动导致的总压损失等问题。利用该方法可以在总温相同的条件下，获得比“小驱大”方式高出一倍的驻室压强。
Due to the complexity of hypersonic flow, related research largely relies on ground experiments. Therefore, the experimental ability of wind tunnels has an important impact on the development of hypersonic technology. Among various hypersonic wind tunnels, the detonation-driven shock wave tunnel has the advantages of simple structure, simple operation and low experimental cost, hence is a promising hypersonic wind tunnel. The shock tunnel belongs to the blow-down wind tunnel and its test duration is extremely short. In order to extend the test time, the sound speed of the driving gas and the test gas should match with each other. When this matching condition is satisfied, the sound velocity of the driving gas is positively correlated with the total temperature of the wind tunnel. This means that the higher the total temperature of the incoming flow to be simulated, the higher the required sound velocity of the driving gas. "Detonation driver" is a driving method in which the gas phase detonation products are used as the driving gas. Since the speed of sound of the detonation product is usually relatively high, the detonation driving technique is more suitable for simulating the inflow of high total temperature compared to the simulation of low total temperature conditions. In order to expand the simulation capability on low total temperature conditions, the JF-12 large hypersonic shock tunnel uses a special driving method, by which a thick driven tube and a thin driving tube are used. Since the driving gas undergoes isentropic expansion before entering the driven section, the sound velocity of the driving gas is remarkably lowered, so that the inflow of the low total temperature can be simulated. However, the pressure drop of the driving gas during the isentropic expansion is severe, resulting in a significant decrease in the total flow simulation ability of the wind tunnel. Both the total pressure and the total temperature are very important for flow simulation. In order to improve the total pressure simulation capability while preserving the wide simulation range of total temperature, this paper studies the way to obtain low sound velocity driving gas by changing the driving gas composition. Adjusting the components (mainly due to the increased dilution of nitrogen) can lead to severe detonation initiation difficulty, and the existing ignition methods are unable to achieve direct detonation. Therefore, the core problem in this method is to solve the difficulty in initiating the driving gas. Increasing the detonation capability of the ignition method helps to solve the difficulty of ingnition. In order to enhance the detonation initiation ability, this paper proposes a closed ignition tube design. This design does not extend the conventional structure in which the igniter is interconnected with the driver, but instead isolates the ignition tube into a closed chamber with a diaphragm. The closure of the igniter brings new ways to increase the initiation ability which are increasing the initial pressure of the ignition tube and using combustible gas in chemical equivalent ratio as the igniter gas. Experiments have shown that the ignition capability of the closed igniter is significantly higher than that of the conventional igniters. By this way, the dilution range of the driving gas that can be ignited directly is greatly broadened and the required driving gas can be successfully initiated instantaneously. Increasing the initial pressure of the ignition tube can effectively improve the initiation capability, but the initial pressure of the igniter needed is too high, which may cause operational safety problems. In order to reduce the initial pressure, the ignition tube should be optimized. In this paper, the following factors are studied experimentally on their impacts of ignition capability: ignition tube outlet diameter, single/double igniters and detonation sensitivity of ignition gas. Studies have shown that a certain combination of the number of ignition tubes, internal profile and ignition gas detonation sensitivity can achieve a higher detonation capability: when using a single ignition tube, the necking profile should be used, and the ignition gas should be less-sensitive to detonate, such as CO/O2. When using double igniters, in order to ensure ignition synchronization, it is preferable to select an ignition gas with strong detonation sensitivity, such as CO/O2 containing a small amount of H2, or C2H2/O2, and the ignition tube should adopt an equal diameter inner surface. In addition, increasing the diameter of the outlet of the ignition tube can also greatly increase the ability to detonate. When the closed-type ignition tube was used for the wind tunnel experiments, it was found that the closed ignition tube seriously interfered with the tailored operation state of the wind tunnel, although the ignition tube successfully initiated the high dilution driving gas. Based on theoretical analysis, numerical simulation and experimental verification, it is determined that the cause of the interference is that the difference in sound speed between the driving gas and the ignition gas is too large. It means that tailoring conditions are not meet. Accordingly, the principle that the sound speed of the ignition gas should be as close to that of the driving gas as possible is obtained. Experiments show that if the principle is followed in selecting ignition gas, the flow field quality of the chamber can be significantly improved, and a stable stagnation pressure state that meets practical requirements can be obtained. With the related technology of closed ignition tube, a wide simulation range of total temperature can be obtained without using thin driver structure, hence the problem of total pressure loss caused by thin driver is avoided. By this method, it is possible to obtain a stagnation pressure that is twice as high as that of the above method under the conditions of the same total temperature.
|陆星宇. 长试验时间爆轰驱动激波风洞总压提升技术[D]. 北京. 中国科学院大学,2018.|
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