唐山1 000吨级船主推进系统集成优化设计

针对唐山1 000吨级船主推进系统的差异性需求,对主推进冷却系统、艉轴艉管润滑、轴功率平衡等进行了集成优化设计。目前该船主推进系统使用情况良好,表明:该船主推进系统的集成优化设计合理;并可为类似船舶主推进系统的设计提供参考。     

三沙1号交通补给船主推进动力系统集成研究

从主推进动力系统方案设计、技术设计、施工设计、试验验证等方面介绍了三沙1号交通补给船主推进动力系统集成。该船主推进动力系统集成的成功应用表明:船舶动力系统集成的优势巨大,尤其对于系统复杂、技术难度高、质量要求高的高附加值船舶。     

Influence of Surface Radius Curvature on Laser Plasma Propulsion with Ablation Water Propellant

The surface shape of liquid water is well controlled during nanosecond pulse laser ablation plasma propulsion. In this study, we measured the effect of the shape on the coupling coefficient and the specific impulse. We found that the coupling coefficient and specific impulse could be optimized by varying the surface convexity. Based on the analysis of the surface radius curvature, we demonstrate that the convex surface changes the laser focal positions to achieve high efficiency.     

空气螺旋桨地面电驱动在线测试系统设计

为提高飞行器螺旋桨性能的测试精度和效率,设计了空气螺旋桨地面电驱动在线测试系统.通过从螺旋桨电驱动、转速控制与调节以及转矩与功率测量等方面分析螺旋桨电驱动测试的关键技术,实现了以高功率密度异步电动机为动力的螺旋桨电驱动测试地面测试系统,并通过实验进行了验证.与传统测试方法和系统相比,该测试系统能够节省人力,简化测试操作,提高测量精度,提高测试效率.     

Combustion of fine aluminum and magnesium powders in water

Micron-sized metal powders carried by a nitrogen flow were fed along the axis of a cylindrical hydrogen/oxygen diffusion flame. The particles ignited and burned in the water vapor at approximately 2500 K. Experiments were performed at atmospheric pressure. The environment in which particles burned was characterized in detail using computational fluid dynamics. The computations confirmed that the metal powders burned in water while the effect of oxygen and other oxidizing species could be neglected. Combustion was characterized experimentally for micron-sized powders of both aluminum and magnesium. Particle size distributions were measured using low-angle laser light scattering. Optical emission of the burning particles was recorded using filtered photomultiplier tubes. Measured durations of individual particle emission pulses were assumed to represent their burn times; these data were classified into logarithmically spaced time bins. The distribution of the particle burn times was correlated with their size distributions assuming that larger size particles burned longer. It was observed that correlation between the burn times, t, and particle diameters, D, can be approximately described as t ∼ D^0.64 and t ∼ D^0.68 for aluminum and magnesium powders, respectively. The results were compared to previous reports and possible reasons for discrepancies between the present and earlier results were discussed.     

Measurement of ion acceleration characteristics of a laser-electrostatic hybrid microthruster for space propulsion applications

For space propulsion applications, a fundamental study of a laser-electrostatic hybrid thruster was conducted. A new type of thruster, in which a laser-produced plasma was accelerated by an additional electrostatic field, was tested to optimize the ion acceleration process. A time-of-flight measurement by a Faraday cup showed that the average speed of ions was about 15 km/s when only 0.04 mJ of laser impulse was introduced to a copper target. When an accelerator electrode with a 6-mm-diameter hole was placed in front of the laser target, it was observed that the average speed of ions increased. The maximum velocity was 23 km/s, which corresponded to the case where the accelerator grid was biased to +100 V for the target-to-electrode gap of 2 mm. It was found that the positively biased electrode was more effective than the negatively biased electrode for ion acceleration in the thruster.     

Effect of spanwise flexibility on propulsion performance of a flapping hydrofoil at low Reynolds number

Spanwise flexibility is a key factor influencing propulsion performance of pectoral foils.Performances of bionic fish with oscillating pectoral foils can be enhanced by properly selecting the spanwise flexibility.The influence law of spanwise flexibility on thrust generation and propulsion efficiency of a rectangular hydro-foil is discussed.Series foils constructed by the two-component silicon rubber are developed.NACA0015 shape of chordwise cross-section is employed.The foils are strengthened by fin rays of different rigidity to realize variant spanwise rigidity and almost the same chordwise flexibility.Experiments on a towing platform developed are carried out at low Reynolds numbers of 10 000,15 000,and 20 000 and Strouhal numbers from 0.1 to 1.The following experimental results are achieved: (1) The average forward thrust increases with the St number increased;(2) Certain degree of spanwise flexibility is beneficial to the forward thrust generation,but the thrust gap is not large for the fins of different spanwise rigidity;(3) The fin of the maximal spanwise flexibility owns the highest propulsion efficiency;(4) Effect of the Reynolds number on the propulsion efficiency is significant.The experimental results can be utilized as a reference in deciding the spanwise flexibility of bionic pectoral fins in designing of robotic fish prototype propelled by flapping-wing.     

舷外机喷水推进研究

喷水推进是较螺旋桨更为先进的一种推进技术,将其应用于舷外机可进一步提升舷外机的性能。围绕将喷水推进技术应用于舷外机这一课题展开研究,阐述了舷外机喷水推进的工作原理,设计了其总体方案并分析了实现舷外机喷水推进的技术要点。     

脉冲数目和重复频率对纳秒激光推进的影响

以抛物形点聚焦激光推进器模型为研究对象,数值模拟了脉冲重复频率在2~50Hz范围内吸气式多脉冲纳秒激光推进的流场演变过程,分析了脉冲数目和重复频率对推进性能的影响。结果表明:随着脉冲数目的增加,喷管内气体密度减小、温度升高,导致平均冲量耦合系数下降,但纳秒脉冲激光作用获得的平均冲量耦合系数明显高于微秒脉冲激光;相同脉冲数目条件下,随着脉冲重复频率的增大,流场恢复时间缩短,使得流场状态不能及时恢复,导致平均冲量耦合系数下降,其中脉冲重复频率f10 Hz时的下降趋势明显大于f10 Hz。     

Influence of jet-to-crossflow pressure ratio on nonreacting and reacting processes in a scramjet combustor with backward-facing steps

The jet-to-crossflow pressure ratio has a large impact on the combustion mode transition in the scramjet engine, and this information needs to be explored comprehensively. The effect of the jet-to-crossflow pressure ratio on the mixing and combustion processes in a backward-facing step combustor has been investigated numerically, and two similar cases have been utilized to validate the numerical approaches employed. The obtained results show that the wall pressure distribution for the nonreacting flow field has been predicted well, and the peak pressures are all a bit underestimated. However, the predicted wall pressure distribution for the reacting flow field does not match well with the experimental data, and it is overestimated. When the hydrogen is injected only from the bottom wall of the combustor, the mixing efficiency decreases with the increase of the jet-to-crossflow pressure ratio irrespective of the nonreacting or reacting flow field. When the hydrogen is injected simultaneously from the top and bottom walls, the separation shock wave is pushed forward to the entrance of the combustor, and it varies from an oblique one to a normal one. This means that the jet-to-crossflow pressure ratio has a great impact on the combustion mode transition for the scramjet engine, and the stable ramjet/scramjet mode transition can be obtained by controlling the fuel injection scheme.