Rotation effects on hybrid air journal bearings

Rotation effects of hybrid air journal bearings with multi-arrays of orifice feedings are investigated numerically. Porous air bearings are also solved for comparison. The results show that bearing load capacity W increases faster with eccentricity ratio than with rotation speed, i.e. bearing number Be. There are optimum orifice diameters, i.e. optimum feeding parameters λ_o, which give maximum load capacity W for orifice feeding; but for porous feeding, load capacity W increases with feeding parameters λ_p. It was found that the load capacity increases with feeding arrays of orifices and five rows of orifice feedings can approximate the operations of porous bearings very well. It was also found that load capacity W does not increase further when air supply pressure exceeds 5 atm because there is a critical pressure ratio through orifice (e.g. (P_o/P_s)<0.53).     

Discharge coefficients of orifice-type restrictor for aerostatic bearings

The paper describes an experimental study conducted in order to determine the supply hole discharge coefficients of externally pressurized gas bearings. Tests were carried out on annular orifices and simple orifices with feed pocket. Air consumption and pressure distributions were measured as a function of supply pressure and air gap height for several different orifice and pocket sizes. Discharge coefficients were approximated by an experimental formula based on the Reynolds number and feeding systems geometry.     

环形多孔气体静压止推轴承静态性能研究

为提升气体静压止推轴承的静态性能,设计一种新型环形多孔气体静压止推轴承。依据气体润滑原理、采用有限体积法对环形多孔气体静压止推轴承的三维物理模型进行数值模拟,研究节流器上节流孔数量、直径、分布方式和供气压力对气体静压止推轴承静态性能的影响。结果表明：节流孔数量对环形气体静压止推轴承的承载力影响显著,但孔数增加到一定程度后承载力增速放缓;节流孔直径对承载刚度影响较大,随着节流孔直径逐渐减小最佳刚度逐渐增大;节流孔排布方式和供气压力对气体静压止推轴承的静态性能均有明显影响。     

遗传小波神经网络在飞机加油管路设计中的应用

基于给出的飞机地面压力加油管路模型 ,分析并找到了解决大容量、多吨位、多功能加油系统常用吨位加油和最大吨位加油所需时间之间矛盾的方法。针对传统遗传算法易陷入早熟收敛的缺点 ,将遗传算法全局优化搜索和小波分析的时 -频局部性相结合 ,使用一种基于遗传算法学习的小波神经网络—遗传小波神经网络 (GAWNN)得到了各管路优化的节流孔尺寸。试验结果证明 ,该算法大大提高了飞机地面压力加油管路设计的效率     

基于节流-分流耦合的高压高速节流口空化抑制方法

开展高压高速节流口的空化抑制方法研究是提升阀的寿命和可靠性的关键环节。针对高压高速节流口空化破坏严重的问题,提出了一种基于节流-分流耦合的空化抑制方法。该方法采用多级节流的方式,实现阀口压降的多级承担,有效减小阀口压力梯度并降低流速;通过在阀出口采取多排孔分流的方式,改善流线布局,减少流体冲击。以电磁卸荷阀为例,分析卸荷阀动态性能,获得高压高速节流口实际工况,开展高压高速工况下节流口流体仿真。仿真结果显示,相较多级节流方式和多孔分流方式,所提出的方法可显著改善流场的压力和流速分布,实现了阀口空化现象的有效抑制。     

An experimental investigation on the pressure characteristics of high speed self-resonating pulsed waterjets influenced by feeding pipe diameter

The destructive power of a continuous waterjet issuing from a nozzle can be greatly enhanced by generating self-resonance in the nozzle assembly to produce a Self-resonating pulsed waterjet (SRPW). To further improve the performance of SRPW, effects of feeding pipe diameter on the pressure characteristics were experimentally investigated by measuring and analyzing the axial pressure oscillation peaks and amplitudes. Four organ-pipe nozzles of different chamber lengths and three feeding pipes of different diameters were employed. Results show that feeding pipe diameter cannot change the feature of SRPW of having an optimum standoff distance, but it slightly changes the oscillating frequency of the jet. It is also found that feeding pipe diameter significantly affects the magnitudes of pressure oscillation peak and amplitude, largely depending on the pump pressure and standoff distance. The enhancement or attenuation of the pressure oscillation peak and amplitude can be differently affected by the same feeding pipe diameter.

     

局部多孔质气浮止推轴承的设计研究

建立了局部多孔质气浮轴承的理论模型,该模型考虑了轴承气膜交界面处的切向速度滑移。利用有限元方法对所建立的模型进行了理论仿真,轴承静态特性的仿真与试验结果取得了较好的一致性,说明经过修改后的雷诺方程可以用来作为局部多孔质气浮轴承研究的理论模型。利用该模型成功计算出不同渗透系数、不同厚度及不同直径的局部多孔质气浮轴承的流量、承载及刚度特性,并给出了相应的变化曲线。根据仿真结论,提出了局部多孔质气浮止推轴承的设计准则。另外,从理论上将该类轴承与全多孔质类型气浮轴的承特性进行了对比,表明局部多孔质气浮轴承有着优良的特性,有很好的应用前景。     

液压阻尼孔的宽温度范围流动特性试验研究

研制一种适合对各种液压孔口或缝隙进行高低温流体力学试验的新型试验装置,运用该装置对具有不同几何参数的液压阻尼孔进行在-50~80℃宽温度范围内的流动特性试验,研究以普通抗磨液压油HM46和低温抗凝减振器油TITAN SAF 5045为工质及其温度变化时对液压阻尼孔流量-压力特性曲线、幂指数和流量系数的影响,研究表明,在低温条件下,液压阻尼孔的流量系数均因油液黏度增大、流动性变差而呈线性下降的趋势,从宏观上看,HM46通过液压阻尼孔时的流动稳定性较差,其对应流量系数的下降幅度明显大于TITAN SAF 5045对应的下降幅度,厚壁小孔流量系数的下降幅度明显大于薄壁小孔对应的下降幅度。研究所获得的新型试验装置、试验数据分析方法和具体理论公式为深入研究和优化现代液压元件在宽温度范围内的动态性能提供新型试验平台与理论基础。     

Metal woven wire cloth feeding system for gas bearings

The paper presents an experimental investigation of pneumatic resistances constructed using woven wire cloth. Tests were carried out on commercial Touraille stainless steel wire cloth featuring different mesh sizes.Two types of experiments were performed: (a) Mass flow rate through single resistances was measured with different upstream and downstream pressures and wire mesh sizes. (b) Pressure distribution and mass flow rate were measured on a pneumatic pad with a fine wire mesh feeding system. Two approaches of identification of the single resistances are discussed.Test results can be used as the basis for developing woven wire cloth pneumatic resistances whose conductance is equivalent to that of certain of the calibrated orifices normally used in gas bearings.     

The Self-Regulated Hydrostatic Opposed-Pad Bearing in a Constant Pressure System

It is shown that a self-regulated hydrostatic opposed-pad bearing which allows for the continuous and automatic distribution of the total flow into two half-flows in the two recesses is highly efficient in a constant pressure system.

Its performance is comparable to that of a conventional hydrostatic opposed-pad bearing compensated with flow control valves, and is superior to that of a conventional bearing compensated with orifices or capillary tubes.

Its performance may be further improved if the self-regulated bearing itself is compensated with an orifice or a capillary tube.     

Best steady state performance of a thrust supporting system

An optimization method to reach the best steady state performance of a double-recess circular thrust bearing with variable area orifices in its compensation circuit is discussed. Guidelines for the range for each design variable are established. Pocket size should be maximized for maximum bearing load carrying capacity, but minimized for maximum static film stiffness. Annular groove width recommendations are recess-pressure dependent. Variable area orifices in the supply circuit for bearings having either single or double recess can give improved static performance. A discussion of the practical applications of the supporting system proposed is included.     

气体静压小孔节流与多孔质节流性能的比较

本文给出了传统的小孔节流和多孔质节流轴承的理论分析，分析了外部供压气体轴承的进气形式对轴承性能的影响，对于不同类型的小孔节流和多孔质节流的轴承，本文给出了实验结果，并对轴承的性能参数即承载能力，刚度等进行了比较，作者分析了小孔节流和多孔节流止推轴承的承载能力和刚度，结果表明多孔质止推轴承同小孔节流轴承相比，具有高的承载能力。     

油气润滑滚动轴承最佳供油量试验研究

在自行研制的油气润滑滚动轴承的试验装置上,研究了在不同载荷下供油量变化对油气润滑滚动轴承外圈温度的影响过程。结果表明,发现随着载荷的升高,最佳供油量的数值不断增大,表明油气润滑在不同的工况条件下要采用不同的最佳供油量进行工作,才能实现最佳的油气润滑效果。     

Evaluation of grinding wheel performance

Experiments were carried out on a horizontal surface grinding machine under dry plunge-cut conditions to evaluate grinding wheel performance in the grinding of steels of various hardnesses. It was found that an optimum wheel grade exists which gives the highest grinding ratio and this optimum grade is different for different materials. There is also an optimum grain size for a particular work material. However, this optimum grain size did not vary for the three materials tested. In all cases grain size 46 gave the best performance.     

Stability of a rigid rotor in turbulent hybrid porous journal bearings

Stability characteristics of hybrid porous journal bearings with a turbulent fluid film have been investigated theoretically following Constantinescu's turbulent lubrication theory. The stability curves have been drawn for different Re, eccentricity ratios, slenderness ratios and bearing speed parameters. In the absence of any experimental data, laminar flow results obtained by this analysis have been compared and found to be in excellent agreement with the previous results. It is observed that turbulence deteriorates the stability of the rotor and for better performance the value of the bearing feeding parameter, β, should be kept small.     

The optimum profile for a porous slider bearing

The load capacity of a porous slider bearing was investigated. The optimum profile was found to be a step form with the riser location and step height ratio depending on the porosity. Porosity decreases the load capacity of a slider bearing. A porous slider bearing of optimum profile supports more load than a porous inclined slider bearing     

A preliminary investigation of the design parameters of an air induction nozzle

In the present study, an experimental study on design parameters of an air induction nozzle was performed. These nozzles are capable of producing large size droplets, including microbubbles, which in turn results in high drift reduction. A magnified 2D version of an air induction nozzle was designed and manufactured. The manufactured geometries have the ability to be disassembled easily, thus several geometrical parameters are replaced sequentially. The effects of a venturi throat, air orifices and discharge orifice diameters along with the length of the mixing chamber are analyzed. Analysis of the parameters revealed their strength of prediction on the air liquid ratio and the nozzle performance.     

Porous inclined stepped composite bearings with micropolar fluid

Abstract

This paper describes the theoretical analysis of the effect of micropolar fluid on the lubrication characteristics of porous inclined stepped composite bearing. The lubricant with additives in the film region and also in the porous region is modelled as Eringen's micropolar fluid, which is characterised by the presence of suspended rigid particles with microstructures. The generalised Reynolds type equation is derived for the most general porous bearing configuration (porous composite bearings) lubricated with micropolar fluid. The closed form expressions are obtained for the fluid film pressure, load carrying capacity, frictional force and coefficient of friction. These expressions can be utilised to obtain the performance characteristics of four different bearing systems, namely, porous plane inclined slider, porous composite tapered land bearing, porous stepped bearing and composite porous tapered concave bearing. It is observed that the micropolar fluid lubricants provide an increased load carrying capacity and decreased coefficient of friction as compared to the corresponding Newtonian case.     

含铅量对Fe-Pb-3Cu系含油轴承性能的影响

在含油轴承试验机上，通过对Fe-Pb-3Cu系列含油轴承运转时的摩擦系数和温升等性能参数的试验测试对比，讨论了含铅量对Fe-Pb-3Cu系列含油轴承性能的影响。试验结果表明，在不同含铅量的四种Fe-Pb-3Cu系含油轴承中，Fe-20Pb-3Cu含油轴承的摩擦性能为最好。这就说明在Fe-Pb-3Cu系含油轴承中，含铅量太大和太小都对含油轴承的性能不利，只有当含铅量达到一个恰当的值时，含油轴承的摩擦性能才能达到最佳。     

EXPERIMENTAL INVESTIGATIONS OF CAVITATION EFFECTS ON FLOW CHARACTERISTICS OF SMALL ORIFICES AND VALVES IN WATER HYDRAULICS

The flow characteristics and cavitation effects of water passing through small sharp-edged cylindrical orificesand valves of different shapes in water hydraulics are investigated. The test results using orifices with different aspect ratios and different diameters show that the flow coefficients in the case of non-cavitating flow are larger than that of flow inthe case of cavitation occurrence. The flow coefficients of flow with cavitation initially decrease as Reynolds number increases and ultimately tend to be of constant values close to contraction coefficient. Large aspect ratio has an effect ofsuppressing cavitation. The experimental results about disc valves illustrate that the valves with sharp edge at large opening are less affected by cavitation than that at small opening. Throttle with triangle notch has better anti-cavitation abilitythan that with square notch. The flowrate of the throttle with square notch is significantly affected by the flow direction orthe flow passage shape.