面向爆轰发动机的射流模式对激励爆轰起爆的湍流机制研究

How to develop effective technology to enhance turbulence, to form stable detonation within the shortest distance, and to reduce engine weight to the greatest degree, but can improve the efficiency of detonation propulsion, is one of the key problems for the application of detonation combustion in the engines. Aiming at to solve the aforementioned problem properly, this project intends to carry out systematic work to investigate the turbulence mechanism of fluidic jet on the facilitating of detonation initiation. First of all, by measuring the flow fluid evolution for the turbulent flame passing through fixed obstacles and jet flow obstacles, to investigate the field structure and turbulence intensity under those two conditions, respectively. Through a quantitative research on the flow field parameters affect the performance of detonation initiation, to develop an effective method to facilitate the detonation initiation. Second, a detailed investigation is performed on the relationship between the physical parameters of the jet flow and its properties with the detonation initiation mechanism, to establish the connection between the characteristics of the jet flow with the initiation mechanism of detonation, the purpose is to further improve the detonation initiation and propulsion performance in engines. Third, a deep analysis is performed on the facilitating mechanism of detonation by turbulence enhancing, revealing the generating mechanism of turbulent flow, and a theory of turbulence enhancing to the facilitating mechanism of detonation initiation is eventually established. The results can provide theoretical support for the development of efficiency propulsion technology in detonation engine, meanwhile can deepen the understanding of efficient combustion organization and its properties at high supersonic mode, which provides basis for the further development of detonation engine and detonation physics.

爆轰燃烧在发动机上应用的关键问题之一是：如何采取有效技术强化湍流，在尽可能短的距离内形成稳定爆轰，最大程度降低发动机重量，但同时又能提高爆轰推进效率。射流喷射技术可有效解决上述难题，本项目着重研究射流模式对激励爆轰起爆的湍流机制。首先，通过测量湍流火焰经过固定障碍物和射流障碍物的流场演变，分别考察两种工况下流场结构和湍流强度，通过定量研究流场参数对爆轰起爆性能的影响，从而建立射流激励爆轰起爆的方法；其次，考察射流物理参数和化学属性对爆轰起爆的影响规律，建立射流特性与爆轰起爆机制的联系，通过对射流理化特性的调控达到提高爆轰起爆及推进性能目的；再次，对射流模式激励爆轰起爆的机制进行深入剖析，揭示湍流的生成机制以及建立湍流强化对爆轰起爆激励机制的理论。研究成果可为提升爆轰发动机推进效率提供理论支撑，同时能加深对超高音速模态下高效燃烧组织和性能的理解，为进一步发展爆轰发动机和研究爆轰物理提供依据。

本项目开展了面向爆轰发动机的射流模式对激励爆轰起爆的湍流机制研究，主要取得的成果有：1）通过开展固定障碍物对爆轰波传播的影响机制研究，发现障碍物产生的衍射波对于非规则爆轰波影响较小，表明障碍物的扰动会加剧爆轰不稳定性，从而降低了衍射波对其影响；2）开展了湍流强度对爆轰起爆机制影响的分析研究，研究中改变射流与测试气体的压差比值，用于产生不同强度的湍流强度。研究发现随着射流压力的增加，湍流强度以及射流导致的稀释作用逐渐增强，两者对于DDT的发展存在反向竞争关系，并获得了湍流强度对DDT的定量影响关系；3）开展了射流属性对提升爆轰起爆性能的研究，研究采用了三种不同射流，即He、N2和CO2。发现引入射流，可加速一次激波和二次激波的耦合，形成较强的前导冲击波，定量比较了三种不同射流在甲烷氧气混合气体中对爆轰激励的影响。由于CO2射流密度较大，引发的湍流效应更强，其产生的扰动更显著，因此有利于一次激波的形成和加速；但同时也由于CO2比重大的特性，易堆积产生局部阻燃区，使得火焰在后期通过时会受到抑制；4）开展了射流与爆燃波相互作用及其对爆轰起爆激励机制的可视化研究。实验发现射流在短时间内喷射进入可燃气体之后，由于射流不可燃，可将其类视为流体障碍物。引入射流后，会在射流位置上游形成高压区，而在下游形成低压区。上游的压力梯度会使的爆燃波和火焰锋面前气体绕过射流向下游传播，而下游存在的逆压梯度和流动分离则形成了回流区。射流加速了湍流火焰的演化，造成更大的流动不稳定性，湍流扰动增加了火焰表面积，增强了湍流输运，这一过程导致燃烧消耗速率和热量的释放速度加快，从而增加气体的膨胀，进一步导致火焰加速。上述研究成果可为提升爆轰发动机推进效率提供理论支撑，同时能加深对超高音速模态下高效燃烧组织和性能的理解，为进一步发展爆轰发动机和研究爆轰物理提供依据。