氢喷射温度对氢氧火箭发动机燃烧稳定性的影响

应用CFD方法对氢氧火箭发动机中高频燃烧不稳定性进行了数值模拟,研究分析了不同工况条件下氢喷射温度对燃烧振荡的影响规律,得出了压力振荡频率变化规律及稳定性极限图。结果表明：在一定的氢喷射温度范围内会发生不稳定燃烧,且随着混合比的增大,发生不稳定燃烧的氢喷射温度上限增大;不稳定燃烧振荡主频呈倍频关系,且在氢喷射温度（70K～110K）内,振荡主频最大。     

Hydrodynamic instabilities and transverse waves in propagation mechanism of gaseous detonations

The present study examines the role of transverse waves and hydrodynamic instabilities mainly, Richtmyer–Meshkov instability (RMI) and Kelvin–Helmholtz instability (KHI) in detonation structure using two-dimensional high-resolution numerical simulations of Euler equations. To compare the numerical results with those of experiments, Navier–Stokes simulations are also performed by utilizing the effect of diffusion in highly irregular detonations. Results for both moderate and low activation energy mixtures reveal that upon collision of two triple points a pair of forward and backward facing jets is formed. As the jets spread, they undergo Richtmyer–Meshkov instability. The drastic growth of the forward jet found to have profound role in re-acceleration of the detonation wave at the end of a detonation cell cycle. For irregular detonations, the transverse waves found to have substantial role in propagation mechanism of such detonations. In regular detonations, the lead shock ignites all the gases passing through it, hence, the transverse waves and hydrodynamic instabilities do not play crucial role in propagation mechanism of such regular detonations. In comparison with previous numerical simulations present simulation using single-step kinetics shows a distinct keystone-shaped region at the end of the detonation cell.     

Heliopause stability revisited: dispersion analysis and numerical simulations

The heliopause, a surface separating the tenuous hot heliosheath flow and the dense, strongly magnetized interstellar flow, is subject to instabilities of the Rayleigh–Taylor and Kelvin–Helmholtz types. The dynamic evolution of this discontinuity is of considerable importance for understanding the neutral atom and cosmic-ray filtration at the interface. Here, we investigate the stability of the upwind heliopause in the presence of charge exchange collisions using both an analytic (dispersion relation) approach and a numerical model that includes the interstellar magnetic field. The linear analysis yields a cubic dispersion relation that admits imaginary solutions for the full range of wavenumbers, implying that the stagnation point on the heliopause is unconditionally Rayleigh–Taylor unstable to small perturbations propagating parallel to the discontinuity surface. We confirm this result by following the nonlinear development of the instability with a time-dependent simulation using a four fluid MHD-neutral numerical code. For the typical solar wind and LISM conditions, we obtain cyclical evolution of the upwind heliopause with a period of the order of 100 years. We also identify two areas of space physics where the instability may have important implications.     

某涡喷发动机压气机气动失稳过程的非线性分析

对某涡喷发动机压气机的气动失稳过程进行了相关积分分析。对节流过程中压气机静压信号进行延时嵌入重构,发现失稳过程中重构相空间的吸引子结构发生了显著变化;应用相关积分值作为压气机内部流动状况变化的评价指标,发现节流过程中压气机第1级端部的流动最先发生不稳定,随后第2级先于第3,4级发生不稳定征兆;1,2级的失速类型为渐进型失速,3,4级为突变型失速;第3级叶根最先发生不稳定,且发展较快,最终导致全叶高失速;低通滤波可以提高相关积分方法检测失速征兆的时效性。分析表明,非线性的相关积分分析方法是进行压气机气动失稳过程研究的有效手段。      

可控肥皂膜气柱界面与激波相互作用的实验研究

基于肥皂膜技术提出了一种生成气柱界面的简单方法。形成的界面不需要支撑网格,因此初始条件可以很好地控制。在水平激波管中结合高速纹影开展了平面激波与二维或三维气柱界面作用的实验。纹影照片显示实验结果杂波更少,演变中的界面也比文献的结果更对称。此外,还特别研究了由极小曲面特征导致的三维效应,发现三维效应使界面的演变和发展变慢了。本研究将有助于更多了解三维性对Richtmyer-Meshkov不稳定性发展的影响。     

低中等雷诺数超声速轴对称射流气动声场

采用线性抛物化稳定性方程(LPSE)方法对低、中等雷诺数条件下的超声速轴对称射流进行了研究。结果表明:射流中不稳定波的增长特性决定了声辐射的特性。在低雷诺数条件下,不稳定波的频率范围较窄,且由于不稳定波的增长区间较长,因此声辐射的范围较宽,声源不集中,声辐射的方向角不明确。在中雷诺数条件下,不稳定波的频率范围较宽,且由于不稳定波的增长区间较短,因此声辐射的范围较窄,声源集中,声辐射的方向角较明确;且随着斯特劳哈尔数增加,声辐射的方向角增加。在低雷诺数条件下,射流基本流的法向速度对射流气动声场的影响较弱,而在中等雷诺数条件下,其对射流的气动声场影响较强。      

A high-order model of rotating stall in axial compressors with inlet distortion

In this paper,a high-order distortion model is proposed for analyzing the rotating stall inception process induced by inlet distortion in axial compressors.A distortion-generating screen in the compressor inlet is considered.By assuming a quadratic function for the local flow total pressure-drop,the existing Mansoux model is extended to include the effects of static inlet distor tion,and a new high-order distortion model is derived.To illustrate the effectiveness of the distortion model,numerical simulations are performed on an eighteenth-order model.It is demonstrated that long length-scale disturbances emerge out of the distorted background flow,and further induce the onset of rotating stall in advance.In addition,the circumferential non-uniform distribution and time evolution of the axial flow are also shown to be consistent with the existing features.It is thus shown that the high-order distortion model is capable of describing the transient behavior of stall inception and will contribute further to stall detection under inlet distortion.     

跨声速压气机转子旋转失速现象的非定常模拟

为研究跨声速压气机转子失速机理,全周非定常数值模拟了某跨声速压气机单转子的失稳过程。结果表明:该转子由叶尖Spike扰动诱发旋转失速。在小流量稳定工作状态,压气机转子叶尖区域存在"旋转不稳定"(Rotating Instability,RI)流动现象。压气机节流过程中,转子进出口的流量降低,叶尖区流场非定常波动幅值增大。近失速状态时,RI扰动团的典型流场结构"径向涡"在叶尖区域形成堵塞,导致相邻叶片前缘间歇性地出现溢流现象。随着压气机进一步节流,转子叶尖的负荷达到极值,叶片通道尾缘逆压力梯度过大,出现倒流。尾缘倒流的出现又进一步增加通道内的堵塞,最终形成Spike扰动。失速先兆对应的流场结构是沿叶片前缘额线向相邻叶片压力面周向运动的"径向涡"结构。     

Effect of baffle injectors on the first-order tangential acoustic mode in a cylindrical combustor

Combustion instability is a very important issue in the development of the propulsion systems used in aerospace. It is very important to associate the high frequency combustion instabilities with the acoustic characteristics of the combustion chamber. In this paper, the effects of various baffle injectors which were installed on the injector faceplate on the first-order tangential acoustic mode were investigated theoretically and experimentally. The effects of the gap between adjacent injectors on the first-order tangential acoustic mode in a cylindrical chamber were considered. The acoustic admittance of the injectors was derived. The results showed that the amplitude and frequency of the first-order tangential acoustic mode increase with the increase in the gap between adjacent injectors, but decrease with the increase in the number and height of the baffles. The baffle injectors have a greater influence on the amplitude and frequency of the first-order tangential acoustic mode than the baffle blades.     

大功率高频无线电波对赤道E区双流不稳定性的影响——PIC静电粒子模拟研究

地面入射的大功率高频无线电波（泵波）和电离层等离子体之间的参数相互作用,能够引起静电波的激发,在一定条件下,产生不稳定性.本文用PIC静电粒子模拟方法,研究泵波与赤道电离层E区等离子体的相互作用.研究结果表明,泵波能够控制双流不稳定性的发生,在不同条件下,泵波对双流不稳定性起着稳定与不稳作用,模拟结果定性地与理论研究结果相符合,这为我们对不规则体产生的地面人工控制提供了依据.