Analysis of oil shedding and ligaments formation on bearing rotary elements

For designing efficient lubrication system of an aeroengine bearing chamber, sufficient knowledge on oil/air two-phase flow characteristics is required. When analyzing bearing chamber two-phase flow, the essential prerequisite is quantifying the oil ligaments, which are detached from bearing rotary elements and shed into the bearing chamber. Related investigations are mainly targeted at liquid shedding on the rotating disk as opposed to the bearing rotary elements. Moreover, the research based on bearing rotary elements is conducted by experiment. Due to the limited operating conditions, experimental studies cannot guide engineering applications. To overcome these limitations, a theoretical model is established in this paper, for revealing the mechanism of oil shedding from bearing rotary elements and quantifying the shedding ligaments. The theoretical model is validated against experimental results from classical studies. In addition, the correlation for shedding ligaments number based on aeroengine bearing structural and operational parameters is obtained via theoretical analysis. The analytical results demonstrate that oil shedding and ligaments formation appear at the edge of bearing inner race outer-periphery. The number of shedding ligaments increases with the rise of shaft rotational speed while decreases with the growth of oil viscosity.     

Mixing and combustion characteristics in a scramjet combustor with different distances between cavity and backward-facing step

The mixing and combustion characteristics in a cavity flameholding combustor under inlet Mach number 2.92 are numerically investigated with ethylene injection. Dimensionless distance is defined as the ratio of the actual distance to the height of the combustor entrance. The cavity shear-layer mode, the lifted cavity shear-layer mode, and jet wake mode with upstream separation are observed respectively with dimensionless distance equals to 1.5, 4.5, and 7.5. In both non-reacting and reacting flow...     

Promotional effect of silica on the combustion of nano-sized aluminum powder in carbon dioxide

This paper presents how the combustion performance of nano-sized aluminum(nAl)powder in carbon dioxide are affected by silica. The ignition and combustion performance of nAl powder with silica addition were studied by a high-temperature tube furnace. An s-type thermocouple and a high-speed motion acquisition instrument were performed to evaluate the ignition temperature, maximum combustion temperature, maximum change of rate of temperature, and combustion propagation speed. The combustion effici...     

肋参数对液氧甲烷发动机推力室强化换热的影响

为深入研究带肋推力室强化传热的机理，对带肋液氧/甲烷推力室的燃烧与再生冷却进行了流动与传热耦合分析，并针对不同肋高和肋数目进行了参数化分析。结果表明:引入等效平均热流密度的概念可以准确描述带肋推力室中的实际传热过程;平均热流密度总是随着肋数目的增加而减小，当肋高恒定时，由于总换热面积增大，等效平均热流密度会随着肋数目的增加而增大;而当总表面积恒定时，等效平均热流密度会随肋数目的增加而减小。此外，盲目地增大总换热面积并不一定能改善传热强化，甚至会在某些情况下恶化传热，因此在设计过程中也应该结合其他肋参数进行综合考虑。     

低温液体火箭燃烧室内射流雾化研究进展

从理论、实验和数值计算方面，阐述和总结了低温推进剂射流雾化的研究现状和进展。对射流雾化机理及形态进行了分类，重点从对比常温流体与低温流体射流雾化特征参数不同的角度，梳理了射流雾化方面的数值研究方法，并介绍了低温射流雾化的相关实验研究。结果表明:空气扰动破碎机理仍是最广为接受的理论，而超临界工况下射流雾化形态不符合现有的射流雾化分类；数值计算方法逐渐由流体体积法和水平集法向直接数值模拟转变，对闪蒸现象的建模是研究重难点之一；低温流体射流喷雾实验数据匮乏，需通过丰富测量手段，提高测量精度的途径获得完整、准确的实验数据。      

排气扩压器对高空舱压的影响与控制方法

为研究排气扩压器流动特性对高空舱后舱压力控制的影响,采用ANSYS19.1对排气扩压器进行数学建模和流场数值模拟分析,揭示其内部实际流动的物理过程;在次流质量流量为20kg/s时,数值模拟不同排气扩压器背压和主流流量时后舱压力的变化规律,并通过样条插值得到排气扩压器背压、主流流量和后舱压力三者关系模型;建立高空舱后舱压...     

Numerical study on combustion efficiency of aluminum particles in solid rocket motor

The combustion of aluminum particles in solid rocket motor plays an important role in energy release of propellants. However, due to the limited residence time, aluminum particles may not be burned completely, thus hindering the improvement of specific impulse. This study aims to explore the characteristics of aluminum combustion efficiency and its influencing factors by experiments and numerical simulations, providing a guideline for engine performance improvement. As an input of simulation, the initial agglomerate size was measured by a high pressure system. Meanwhile, the size distribution of the particles in plume was measured by ground firing test to validate the numerical model. Then, a two-phase flow model coupling combustion of micro aluminum particle was developed, by which the detailed effects of particle size, detaching position and nozzle convergent section structure on aluminum combustion efficiency were explored. The results suggest that the average combustion temperature in the chamber drops with increasing initial particle size, while the maximum temperature increases slightly. In the tested motors, the aluminum particle burns completely as its diameter is smaller than 50 μm, and beyond 50 μm the combustion efficiency decreases obviously with the increase of initial size. As the diameter approaches to 75 μm, the combustion efficiency becomes more sensitive to particle size. The combustion efficiency of aluminum particle escaping from end-burning surfaces is significantly higher than that from internal burning surface, where the particle combustion efficiency decreases during approaching the convergent section. Furthermore, the combustion efficiency decreases slightly with increasing nozzle convergent section angle. And theoretically it is feasible to improve combustion efficiency of aluminum particles by designing the convergent profile of nozzle.     

燃料预加热对超声速剪切掺混的增强效果

随着高超声速飞行器不断朝着高马赫、宽速域方向发展，推进系统面临低动压的工作条件，对燃烧室内的流动掺混带来巨大挑战。针对碳氢燃料超燃冲压发动机燃烧室，本文研究了碳氢燃料预加热对超声速剪切掺混特性的影响机制，分析了温度与碳氢燃料热裂解对掺混特性的影响规律。研究发现，当碳氢燃料未发生热裂解反应时，燃料预加热会使射流黏性耗散增强从而掺混效率降低，燃料温度从750 K增加到900 K时，燃烧室掺混效率降低约5%、总压损失约增加20%；但燃料热裂解反应对剪切掺混有双重影响，裂解后的碳氢燃料膨胀性能提升，使喷嘴附近的掺混效率提高约18%；由于剪切层内流体湍动能下降，在远离喷嘴的位置掺混效率降低约6%。