运行过程中载荷突变时可倾瓦推力轴承瞬态热效应的实验研究

研究了可倾瓦推力轴承在名义转速分别为2000r/min和4000r/min下,当载荷突然变化时推力轴在油膜温度和油膜厚度的瞬态变化规律。实验结果表明：当载荷突然增大时,油膜温度以及进油边温度上升,油膜厚度减小;随着载荷变化幅度的增大,温度上升幅度也增大,油膜厚度进一步减小;在载荷变化相同的情况下,相同时间间隔内转速高时油膜温度增大幅度比转速低时要大,而油膜厚度减小幅度比低转速下小。     

海事直升机垂直下降涡环状态实验研究

直升机涡环状态严重影响飞行安全,其气流特性非常复杂,难以准确计算。本文在旋臂机设备上开展了涡环状态的专题实验,首先介绍了旋臂机的组成以及模型子系统、控制子系统和测试及数据采集子系统的工作特点。然后说明实验过程及实验数据处理方法。进行了不同总距、不同下滑角以及不同垂直速度的直升机下降实验,并测量其气流特性。最后以实验数据为基础,分析了在悬停状态、低速下降状态、涡环状态前期、中期及后期扭矩平均值和脉动幅度、拉力平均值和脉动幅度随下降速度的变化关系,确定了涡环状态的一般规律,探讨了涡环状态的改出方法。本文结果可为保证飞行安全提供参考。     

Modelling of thrust generated by oscillation caudal fin of underwater bionic robot

A simplified model of the thrust force is proposed based on a caudal fin oscillation of an underwater bionic robot. The caudal fin oscillation is generalized by central pattern generators (CPGs). In this model, the drag coefficient and lift coefficient are the two critical parameters which are obtained by the digital particle image velocimetry (DPIV) and the force transducer experiment. Numerical simulation and physical experiments have been performed to verify this dynamic model.     

永磁体结构对高温超导推力轴承静态特性的影响

基于商用电磁场有限元软件以及M e issner效应假设,提出了对由块状高温超导体和永磁体组成的高温超导推力轴承静态特性进行分析的方法,分析了永磁体的结构对高温超导推力轴承悬浮力的影响。结果发现:永磁体的结构及磁极排列方式对高温超导推力轴承悬浮力的影响很大,适当地选择永磁体的结构和磁极排列方式可以显著地提高高温超导推力轴承的悬浮力。     

推力轴承瓦面形面对润滑性能影响的研究

以三峡机组推力轴承为研究对象，运用瓦面二次曲面数学模型和三维热弹流润滑性能分析软件，对平面形面、圆柱形面、马鞍形面、横弯形面、球形形面和反横弯形面等6种瓦面形面的推力轴承的最小油膜厚度，最大油膜压力和最高油膜温度等进行了大量的数值计算。在分析和比较上述6种瓦面形面推力轴承优点和缺点的基础上，指出沿周向凸起的瓦面形面及沿径向下凹的瓦面形面均有利于形成收敛的油膜几何形状，从而显著提高轴承润滑性能。     

反拱水垫塘底板块上举力变化规律的试验研究

：反拱水垫塘是一种新型消能防冲结构，拟在我国溪洛渡等300m级高拱坝中采用，其稳定性是其在高水头、大流量作用下能否安全运用的关键技术之一。结合溪洛渡拱坝，试验研究了拱坝坝身泄量达30000m^3／s，反拱圈横缝止水设施破坏，动水压力贯入底板缝隙，基岩锚固力失效的极端情况下，反拱水垫塘底板块上举力，得出底板块上举力分布规律，脉动上举力谱密度特性等，并推算出拱端的极限推力。研究成果对反拱水垫塘设计、运用和稳定研究具有理论和实际意义。     

局部多孔质气体静压轴向轴承静态特性的数值求解

运用数值方法分析局部多孔质节流气体静压轴向轴承的静态性能,分别建立局部多孔质圆柱塞内的压力分布方程和气体薄膜内的压力分布方程,利用坐标变换将局部多孔质圆柱塞的圆柱坐标与气体薄膜的圆柱坐标转换到同一笛卡儿坐标系,为有限元离散奠定基础.经过有限元推导,求得局部多孔质气体静压轴向轴承的承载能力与静态刚度,并对局部多孔质节流进行试验以验证理论模型的正确性.另外,对局部多孔质节流气体静压轴向轴承和小孔节流气体静压轴向轴承进行对比试验.结果表明:局部多孔质节流和小孔节流静压轴承的承载能力随着气膜厚度的减小而增加;静态刚度随着气膜厚度的增加先增加后减小;局部多孔质节流比小孔节流具有较高的承载能力和静态刚度.     

圆形可倾瓦推力轴承入油边界条件的确定

采用有限元法对Reynolds方程、能量方程及弹性方程进行了联立求解,通过计算瓦边法向平均速度,较精确地确定了瓦的入油边界条件,从而更精确地计算出圆形瓦的压力分布及温度分布,通过轴承试验台试验发现,计算结果和实验结果较吻合。     

Interfacial flow computations using adaptive Eulerian–Lagrangian method for spacecraft applications

Understanding the interfacial dynamics and fluid physics associated with the operation of spacecraft is important for scientific as well as engineering purposes. To help address the issues associated with moving boundaries, interfacial dynamics, and spatial‐temporal variations in time and length scales, a 3‐D adaptive Eulerian–Lagrangian method is extended and further developed. The stationary (Eulerian) Cartesian grid is adopted to resolve the fluid flow, and the marker‐based triangulated moving (Lagrangian) surface meshes are utilized to treat the phase boundary. The key concepts and numerical procedures, along with the selected interfacial flow problems are presented. Specifically, the liquid fuel draining dynamics in different flow regimes, and the liquid surface stability under vertically oscillating gravitational acceleration are investigated. Direct assessment of experimental measurement and scaling analysis is made to highlight the computational performance of the present approach as well as the key fluid physics influenced by the given flow parameters. Copyright © 2010 John Wiley & Sons, Ltd.     

Numerical modelling and flow analysis of a centrifugal pump running as a turbine: Unsteady flow structures and its effects on the global performance

The purpose of this paper is to investigate the flow patterns in a centrifugal pump when it works as a centripetal turbine, with special interest in the unsteady behavior in order to explain the shape of the performance curves. Also, we focus on the determination of the radial thrust and other mechanical loads over a pump‐designed machine. The pump studied is commercial, with single axial suction and a vaneless spiral volute casing. A numerical study has been carried out in order to obtain more information about the flow into the volute and the impeller. A numerical three‐dimensional unsteady simulation has been developed using a commercial code that solves the URANS set of equations with a standard k–ε turbulence model. The results show the non‐axisymmetric flow developed in the volute, responsible for a significant radial thrust; the interaction between the tongue and the impeller, generating force fluctuations; the velocity and pressure distributions inside the impeller; and the exit flow, characterized with post‐rotation and low‐pressure. These flow results allow us to understand the behavior of the machine by comparing it with the pump mode. Complementarily, an experimental study was conducted to validate the numerical model and characterize the pump‐turbine performance curves at constant head. Fast‐response pressure taps and a three‐hole pneumatic pressure probe were employed to obtain a complete data set of non‐stationary and stationary measurements throughout the centrifugal machine. As a result, loss of efficiency or susceptibility to cavitation, detected numerically, was confirmed experimentally. The study demonstrates that the numerical methodology presented here has shown its reliability and possibilities to predict the unsteady flow and time‐mean characteristics of centrifugal pumps working as turbines. In particular, it is shown that the commercial design of the pump allows a reasonable use of the impeller as a turbine runner, due to the suitable adaptation of the inflow distributions to the volute casing. Moreover, the efficiency for the inverse mode is shown to be as high as achieved for the pumping operational mode. In addition, it is concluded that both axial and radial thrusts are controlled, though important unsteady fluctuations—up to 25%—clocked with the blade passing frequency appear beyond the nominal conditions. In that case, a moderate use of the pump as a turbine is recommended in order to minimize risks of fatigue failure of the bearings. Copyright © 2009 John Wiley & Sons, Ltd.