小口径轴对称收缩喷嘴射流冲击大平板噪声特性的实验研究

为研究小口径喷嘴冲击射流的噪声特性，测定了3mm口径的轴对称收缩喷嘴在各种压比情况下产生的亚音速和超音速射流冲击坚固大平板产生的噪声。发现噪声在空间呈近似四瓣分布，当喷嘴与平板距离减小时，噪声指向壁射流下游的瓣到增强，反之，噪声指向喷嘴上游的瓣得到增强。噪声随喷嘴距平板距离的增加呈增强的趋势，在距平板一定距离内有锯齿现象。噪声随喷嘴压比的增加而增强，相应于各种工况，存在一不同的压比值，此压比之前，噪声随压比的增大而迅速提高，但有起伏现象，在此压比之后，噪声平缓地随压比的增大而增强。     

喷嘴结构对液氧煤油火箭发动机高频燃烧不稳定性的影响

为了筛选高压补燃循环液氧煤油火箭发动机的喷嘴,在喷注单元低压高频燃烧不稳定性模拟实验系统上开展实验,研究了喷嘴结构对燃烧稳定性边界的影响。实验使用气态空气与氧气的混合物作为氧化剂,加热的煤油蒸汽作为燃料;喷嘴为全尺寸气液同轴直流离心式喷嘴,模拟燃烧室与真实燃烧室的固有声学频率相等。根据测量模拟燃烧室内的脉动压力区分大幅振荡、小幅振荡和稳定工作。研究结果表明,喷嘴长度、缩进室长度和入口节流嘴直径对高频燃烧不稳定性裕量有很大影响,并存在相对最佳值。     

The effect of nozzle layout on droplet ejection of a piezo-electrically actuated micro-atomizer

We study here effects of nozzle layout on the droplet ejection of a micro atomizer, which was fabricated with the arrayed nozzles by the MEMS technology and actuated by a piezoelectric disc. A theoretical model was first built for this piezoelectric-liquid-structure coupling system to characterize the acoustic wave propagation in the liquid chamber, which determined the droplet formation out of nozzles. The modal analysis was carried out numerically to predict resonant frequencies and simulate the corresponding pressure wave field. By comparing the amplitude contours of pressure wave on the liquid-solid interface at nozzle inlets with the designed nozzle layout, behaviors of the device under different vibration modes can be predicted. Experimentally, an impedance analyzer was used to measure the resonant frequencies of the system. Three types of atomizers with different nozzle layouts were fabricated for measuring the effect of nozzle distribution on the ejection performance. The visualization experiment of droplet generation was carried out and volume flow rates of these devices were measured. The good agreement between the experiment and the prediction proved that only the increase of nozzles may not enhance the droplet generation and a design of nozzle distribution from a viewpoint of frequency is necessary for a resonant related atomizer. The project supported by the National Natural Science Foundation of China (50405001).     

高膨胀比有机工质向心透平气动优化研究

本文采用NURBS曲线参数化表达和控制几何型线,结合CFD数值实验,对膨胀比为8的有机工质向心透平进行气动优化研究。跨声速喷嘴叶型型线经气动优化后,喷嘴内处于顺压梯度的加速流动状态,喉部跨声速膨胀流动得到改善,流场最大Ma降低,全工况下的叶栅总压损失系数显著减小,跨声速工况下的级组效率明显提高。叶轮子午流道型线经优化后,流道宽度变化更均匀平滑,原动叶轮吸力面分离被消除,透平级组效率也有提高。     

自激脉冲喷嘴发生机理数值模拟

本文揭示了自激脉冲喷嘴产生自激振荡的根本原因。由于腔内产生了低于汽化压力的负压,引起低压区液体的汽化,加上射流不稳定剪切层的作用,最终形成大小周期性变化的轴对称空化气囊;对脉冲喷嘴腔内流场进行了二维非定常数值模拟,通过对腔内压力和流场的分析,验证了上述结论;试验研究通过对腔内压力的数据采集及对脉冲现象的同步观察,进一步说明了本文结论的正确性。     

结构参数变化对内混式喷嘴雾化性能的影响作用

通过对比6种结构参数不同的环形内混式喷嘴的雾化平均直径的变化规律,研究了喷嘴结构变化对雾化性能的 影响规律。结果表明,混合腔宽度、内喷嘴缩进长度、出口流程均对喷嘴雾化性能造成明显影响,而不同的混合腔长度、 气体及液体的喷入方式则基本上不影响雾化性能。     

126Ce的EC/β+衰变

利用187 MeV的40Ca离子轰击同位素靶92Mo, 由熔合蒸发反应生成目标核126Ce。 藉助氦喷嘴快速带传输系统和X-X-t与X-γ-t符合测量, 首次建立了126Ce的EC/β+衰变纲图。 建议了可能属于126Ce一个高自旋同核异能态的衰变, 其β衰变后布居在与126La的高自旋同核异能态相关的低位能级区, 测定的半衰期是57(9) s。 也建议了可能属于126Ce基态的衰变, 其β衰变后布居在与126La的低自旋同核异能态相关的低位能级区,它的半衰期被测定为12(4) s。 但偶偶核126Ce存在高自旋同核异能态的物理原因还有待进一步探究。 Ce was produced by bombarding an enriched target of 92Mo with 187 MeV 40Ca beam and studiedby using a helium jet fast tape transport system in combination with X-γ and γ-γ coincidencemeasurements. An EC/β+ decay scheme of 126Ce was proposed for the first time. A group of low lying states associated with the low spin isomer in 126La feeding by β decay was possibly from the ground state EC/β+ decay of 126Ce with the measured half-life 12(4) s. Another group of low lying states associated with the high spin isomer in 126La feeding by β decay was possibly from a high spin isomer EC/β+ decay of 126Ce with the measured half-life 57(9) s. However, the physical reason for the existence of a high spin isomer in even-even nucleus 126Ce is still an open problem.