Numerical Simulation for the 16 August 1999 EUV Brightenings

The 16 August 1999 EUV brightenings are numerically simulated by a third-order upwind compact scheme, basing on the TRACE observation. The present simulation can give a possible explanation to its formation and evolution. The numerical results show that the initial reconnection jets at around X-point are responsible for the occurrence of EUV brightening. The strong and superposed ejections caused by the first and second coalescence of magnetic islands are possibly related to the lifted material which initially appeared as absorption features and Later EUV-emitting structures respectively. The bi-directional reconnection jets may correspond to the lifted material that either continued to move upward along the apparently open field lines or fell down to the surface.      

后缘喷流对三角翼前缘涡的影响

本实验应用染色液流动显示技术和激光测速技术 (LDV)研究了 6 0°后掠三角翼在后缘差动喷流、对称喷流情况下前缘涡破裂位置、涡核的空间分布、涡核的速度分布以及三角翼背风面流动结构随迎角的演化等。实验结果表明 ,喷流增大了三角翼前缘涡涡核保持高速度的区域 ,推迟了涡核减速的位置 ,在大迎角情况下 ,对称喷流有助于消除由前缘涡振荡引起的“摇滚”现象。     

旋转对冲击射流流动及换热影响的数值研究

为了探究旋转对动叶前缘冲击射流流动及换热的影响机制,采用数值模拟的方法对比分析了静止条件和三种不同旋转转速下的流场结构与换热情况.结果表明:冲击靶面的平均努塞尔数随转速的增大而减小,最高转速下,靶面平均努塞尔数下降约16％.另一方面,压力面和吸力面侧对旋转的敏感性不同.高转速下,换热的削弱主要集中在吸力面和压力面无量纲...     

Numerical investigation on flow field characteristics of dual synthetic cold/hot jets using POD and DMD methods

In order to improve the control ability of synthetic jets in compressible boundary layer, a novel control method based on dual synthetic cold/hot jets coupled control of velocity profile and temperature profile was proposed. As fundamental investigations on the effects of synthetic jet temperature on the jet behavior and flow field characteristics were essentially necessary, preliminary numerical simulations were conducted to study the influence of temperature (200 K and 400 K) on the flow field characteristics of synthetic jets using Large Eddy Simulations (LES) model. Time-averaged flow fields showed that different temperatures led to variable behavior of two strands of jets. For dual synthetic cold jets, a potential-core arose apparently with its height ranging from 0.01 to 0.03 m, while for dual synthetic hot jets, two strands of jets emerged downstream. The modal decomposition of instantaneous flow fields had been done using both Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD). Various modes showed different characteristics of the flow fields. As the POD method focuses on the energy of flow while the DMD method focuses on the frequency, the first two modes had many similarities, but the third and fourth modes demonstrated completely different vortex structures. The current researches play a role of preliminary investigations for further and comprehensive exploration of novel flow control measures in global velocity field.     

The Coma of Comet 9P/Tempel 1

As comet 9P/Tempel 1 approaches the Sun in 2004–2005, a temporary atmosphere, or “coma,” will form, composed of molecules and dust expelled from the nucleus as its component icy volatiles sublimate. Driven mainly by water ice sublimation at surface temperatures T > 200 K, this coma is a gravitationally unbound atmosphere in free adiabatic expansion. Near the nucleus (≤ 10² km), it is in collisional equilibrium, at larger distances (≥10⁴ km) it is in free molecular flow. Ultimately the coma components are swept into the comet’s plasma and dust tails or simply dissipate into interplanetary space. Clues to the nature of the cometary nucleus are contained in the chemistry and physics of the coma, as well as with its variability with time, orbital position, and heliocentric distance. The DI instrument payload includes CCD cameras with broadband filters covering the optical spectrum, allowing for sensitive measurement of dust in the comet’s coma, and a number of narrowband filters for studying the spatial distribution of several gas species. DI also carries the first near-infrared spectrometer to a comet flyby since the VEGA mission to Halley in 1986. This spectrograph will allow detection of gas emission lines from the coma in unprecedented detail. Here we discuss the current state of understanding of the 9P/Tempel 1 coma, our expectations for the measurements DI will obtain, and the predicted hazards that the coma presents for the spacecraft. An erratum to this article is available at .     

高压环境下剪切稀化非牛顿撞击射流直接数值模拟

高压环境下的撞击射流是液体火箭推进系统中广泛采用的一种燃料雾化方法,其雾化效果将直接决定最终燃烧效率。采用直接数值模拟（DNS）工具,对10 MPa高压环境下剪切稀化非牛顿直角撞击射流的三维非定常雾化特征、机理及非牛顿特性进行了研究。结果表明：高压环境下该撞击射流的雾化流场呈圆形辐射状分布并形成Mushroom头部和Ω状的局部凸起,气体中的涡量分布表现为有序贴附区和无序爆炸区两类,液膜向液丝的破碎主要受平均气体力和平均黏性力作用影响,而液丝向液滴的破碎则主要受局部流场参数影响,撞击雾化过程中液体无量纲表面积不断增长并可分为5个阶段。此外,撞击射流头部在局部强剪切力作用下其无量纲黏性系数最低降至仅0.7。     

活塞驱动合成喷流动和传热特性

为了揭示合成喷冲击冷却的内在机制和作用效果,采用数值计算和实验方法分别对活塞驱动合成喷的流动特征和冲击靶板的对流换热特征进行了研究。结果表明,在活塞低频往复驱动条件下,活塞往复频率和活塞振幅的加大导致合成喷的穿透距离增大。与常规连续射流冲击冷却相比,合成喷冲击作用下的靶面对流换热系数同样具有随着冲击间距增大而先逐渐增大、后逐渐衰减的变化趋势,但最佳冲击间距值却明显高于常规射流,而且合成喷对冲击靶板的作用范围有所扩大,表明合成喷具有强的夹带能力和穿透能力。     

高压涡轮导向器叶片冲击冷却数值研究

针对高压涡轮导向器叶片表面温度过高的情况,采用在叶片内安装导流片并布置射流孔的方式对高温叶片进行冲击冷却,运用带转捩的Transition k-kl-ω模型完成了气动和传热的三维耦合计算分析,研究了改善冲击冷却效果的方法和途径,实现在保持冷却气体流量不变条件下,提高冷却效果、降低材料的性能要求。计算结果表明:在一定孔径范围内,射流孔数和孔径满足(4n-1)D=h的关系式时,沿叶高方向能满足冷却要求;选择在压力面开3列、吸力面开4列射流孔,能满足叶片中弦区域冷却要求,采用劈缝排气方式可以消除尾缘高温现象;导流片与叶片间距zn/D在1.71～2.57变化时,对叶片内外表面平均温度影响不大,而随间距变小,叶片内外表面最高温度降低,最低温度则会升高;随冷却气体温度降低或流量增加,冷却效果会更好。     

直接力与气动力复合控制前向拦截导引律综述

直接力与气动力复合控制前向追击在拦截高空高速目标方面具有独特的优势。分别综述了前向拦截导引律和直接力气动力复合控制设计方法的研究进展,其中,直气复合控制分别从点火逻辑设计、控制分配方法、气动舵控制和直接力控制分别设计、俯仰和偏航通道同时设计、复合控制导弹的制导律设计等几方面进行分类分析,并介绍了复合控制前向拦截导引律进展。最后,指出了值得进一步研究的几个关键问题,可为今后的研究提供参考。     

双微射流作动器定向控制主流数值模拟

采用改进的Beam-Warming近似因式分解法求解二维、粘性、非定常、可压全N-S方程,对双微射流作动器定向控制主流的合成流场进行数值模拟。计算结果揭示了主流在双微射流作用下会比在单微射流作用下产生更大的偏转,并探讨了其产生偏转的原因。分析了主流的偏转程度与相邻作动器相位差之间的关系,即相邻作动器之间的相位差必须在一定的范围内,主流才能发生更大的偏转。