进口润滑条件对活塞环-缸套摩擦副润滑性能的影响

目前内燃机活塞环-缸套摩擦副润滑分析中,活塞环与缸套之间的润滑状态一般假设为充分润滑或固定状况的贫油润滑,不是通过对实际润滑油膜形成情况的分析确定.本文中以一多缸四行程内燃机为研究对象,基于润滑油流量以及控制体体积变化方程,建立活塞环-缸套间润滑油的流动模型,进行了不同进口处润滑油膜供给量对活塞环-缸套摩擦副润滑特性的影响分析.结果表明:活塞环进口处的润滑条件对活塞环-缸套摩擦副的润滑性能有显著影响;进口处润滑油供给量增加,活塞环-缸套摩擦副的最小油膜厚度增加,最大油膜压力、微凸体作用力、摩擦力和功耗均相应减小;进口处供给油膜厚度较小的情况下,增加油膜供给厚度可以明显改善活塞环-缸套摩擦副的润滑性能.     

Cracks with interfacial bonds in the hub of a friction pair

The contact deformation of the hub of a plunger pair is considered. It is assumed that, during the repeated reciprocating motion of the plunger, fracture of the materials of the elements of the contact pair occurs. The friction surface of the bushing contains rectilinear cracks with the end zones characterized by the presence of interaction between the cracks faces. The boundary-value problem of equilibrium of the hub of a friction pair with a crack reduced to solving system of nonlinear singular integro-differential equations with a Cauchy type kernel.     

Effect of velocity ratio on the streamwise vortex structures in the wake of a stack

The time-averaged velocity and streamwise vorticity fields within the wake of a stack were investigated in a low-speed wind tunnel using a seven-hole pressure probe. The experiments were conducted at a Reynolds number, based on the stack external diameter, of Re_D=2.3×10⁴. The stack, of aspect ratio AR=9, was mounted normal to a ground plane and was partially immersed in a flat-plate turbulent boundary layer, where the ratio of the boundary layer thickness to the stack height was δ/H≈0.5. The jet-to-cross-flow velocity ratio was varied from R=0 to 3, which covered the downwash, crosswind-dominated and jet-dominated flow regimes. In the downwash and crosswind-dominated flow regimes, two pairs of counter-rotating streamwise vortex structures were identified within the stack wake. The tip vortex pair located close to the free end of the stack, and the base vortex pair located close to the ground plane within the flat-plate boundary layer, were similar to those found in the wake of a finite circular cylinder, and were associated with the upwash and downwash flow fields within the stack wake, respectively. In the jet-dominated flow regime, a third pair of streamwise vortex structures was observed, referred to as the jet-wake vortex pair, which occurred within the jet-wake region above the free end of the stack. The jet-wake vortex pair had the same orientation as the base vortex pair and was associated with the jet rise. The peak vorticity and strength of the streamwise vortex structures were functions of the jet-to-cross-flow velocity ratio. For the tip vortex structures, their peak vorticity and strength reduced as the jet-to-cross-flow velocity ratio increased.     

On the stable posture of a pair of parallel cylinders in a uniform flow *

The stable posture of a pair of parallel circular cylinders in a uniform flow was experimentally studied when it was free to rotate about an axis at the middle of the two cylinders. The cylinder pair comes to rest facing the oncoming flow side by side, the line connecting the centers of the two cylinders being perpendicular to the flow, when s/d = 0.5, where s is the distance between the center of rotation and the central axis of each cylinder and d is the diameter of the cylinder. When s/d = 1.0 or 1.5, the cylinder pair is stable both in tandem, with one cylinder behind the other, and in side-by-side arrangements to the oncoming flow. When s/d 2.0, the cylinder pair is stable only in tandem arrangements.     

Stereoscopic imaging and reconstruction of the 3D geometry of flame surfaces

Stereoscopic imaging and reconstruction of turbulent impinging diffusion flames have been demonstrated. The 3D geometry of the flame surface is reconstructed from any pair of stereo images through digital image processing and computer vision. Only one camera is required to capture the pair of stereo images due to the use of a stereo adapter. As a result the pair of flame images is captured on a single CCD chip. They are then post-processed to produce a 3D geometry of the flame. The 3D results and surface area calculations demonstrate the potential of stereo visualisation, data extraction and the validity of the proposed methodology.     

On the viscosity of a concentrated suspension of solid spheres

Explanations of the very high viscosities of concentrated suspensions of spheres based on the dissipation in squeezing flow between particles pairs are shown to be in error. The dissipation in pair interactions is always of the order of that generated by shearing motions, and this dissipation is of too low an order in concentration for single pair interactions to explain the observed viscosities.     

A pressure probe for the detection of the flow direction close to walls. Case study: flow through a bend

We report on the development of a new pressure probe that detects the flow direction in wall-bound flow. Two pressure differences are measured and combined in a pressure coefficient which is proportional to the flow direction in a ±20° range. The probe is applied to the secondary flow vortex pair generated in a 90° pipe bend, with excellent results. The vortex pair, and its downstream decay, are identified. Furthermore, the stability of the vortex pair is found to depend sensitively on the upstream conditions. When these are fixed, the vortices stay put; in other words they are spatially stabilized. The consequences for installation effects on flow metering are discussed.     

基于有限元法的面接触摩擦热流分配系数反推研究

本文基于有限元基础,利用红外测温-温度场有限元模拟-热电偶验证相结合的方法,反推得出摩擦副热流分配系数,分析了不同摩擦副材料、表面接触状况、散热条件对摩擦副热流分配系数的影响.分析表明:反推热流法为热流分配系数的计算提供了1个可行的方案;当摩擦副材料具有较好的减摩、抗黏着特性时,摩擦副运行稳定,摩擦副动态热流分配系数随时间变化平缓;摩擦副表面接触状况和散热条件对热流分配系数有明显的影响,利用本文提出的修正系数,可对理论公式进行修正.     

On the synthesis of spatial cycloidal gears

The subject of this paper is the synthesis of spatial cycloidal gears, based on Disteli’s work, which was published at the turn of the 20th century. In particular, the properties of the Plücker conoid or the cylindroid for the relative motion between a pair of skew gears are analyzed in order to extend Camus’ Theorem from the planar and spherical cases to the spatial case with the aim of synthesizing a pair of conjugate cycloidal teeth.     

不同表面粗糙度的摩擦副润滑状态的 Stribeck曲线研究

利用Stribeck润滑曲线理论分析和薄膜润滑试验考察了不同表面粗糙度的钢球与圆盘点接触及钢滑块与圆盘面接触摩擦副的润滑状态，通过改变圆盘转速获得了包含薄膜润滑状态的Stribeck曲线．结果表明：在Stribeck曲线上可以划分出薄膜润滑状态，其位于摩擦系数谷底附近；薄膜润滑的产生及其区间大小同圆盘表面粗糙度密切相关；圆盘表面粗糙度较小时更易形成薄膜润滑状态，而圆盘表面粗糙度较大时薄膜润滑状态不明显；光滑表面对应的Stribeck曲线谷底较宽，相应的薄膜润滑区间亦较宽．     

A numerical evaluation on the effect of sister holes on film cooling effectiveness and the surrounding flow field

A numerical study was performed to evaluate the effectiveness of the novel sister hole film cooling technique. Two secondary coolant holes bound the primary coolant hole slightly downstream of its midpoint, intended to minimize the primary vortex pair and improve cooling performance. An unstructured hexahedral mesh was generated and the realizable k–ε turbulence model with near-wall modeling was used in these simulations. Blowing ratios of 0.2, 0.5, 1.0, and 1.5 were simulated to evaluate the applicability of sister holes in practical applications. It was found that sister holes significantly improved cooling performance over the entire computational domain, particularly at high blowing ratios. These results arose by countering the primary vortex pair with a secondary pair from these sister holes, ultimately maintaining flow adhesion where the coolant stream would have otherwise separated.     

Theory of the influence of changes in salt concentration on the configuration of intrinsically curved, impenetrable, rod-like structures modeling DNA minicircles

DNA molecules in the familiar double helical B form are treated here as though they have rod-like structures obtained by stacking the nearly planar base pairs comprising them one on top of another with each rotated by approximately one-tenth of a full turn with respect to its immediate predecessor in the stack. As each base in a base pair is attached to the sugar-phosphate backbone chain of one of the two DNA strands that have come together to form the Watson-Crick structure, and each phosphate group in a backbone chain bears one electronic charge, two such charges are associated with each base pair. Thus, each base pair is subject to not only the elastic forces and moments exerted on it by its neighboring base pairs but also to electrostatic forces, of sequentially remote origin, that, because they are only partially screened out by positively charged counter ions, can render the molecule's equilibrium configurations sensitive to changes in the concentration of salt in the medium. As there are cases in which, even though the intramolecular electrostatic forces of repulsion are strong, the distance of closest approach has value equal to that of the impenetrable diameter of the molecule, the theory presented here takes into account self-contact. Examples are given of cases in which the theory predicts that the radius of gyration of the minimum energy configuration of a small (549 base pair) circularized DNA molecule (called a “DNA minicircle”) has a remarkably strong dependence on the salt concentration.     

非对称圆环拍的特性研究

建立微小非对称圆环点冲击下拍的理论模型,通过实验验证其有效性。微小非对称圆环是分析大钟拍现象的简化模型,微小非对称圆环的每一对径向振动模态的固有频率非常接近,这对模态互相干涉下出现拍现象。最后利用拍的理论模型绘制沿圆周拍的分布图,详细分析拍的分布特性,为校正钟的拍频声提供理论依据。     

含纳微米硼酸盐和二烷基二硫代磷酸锌液体石蜡润滑下钢—钢体系的摩擦磨损性能研究

在四球试验机上考察了含纳微米硼酸盐及二烷基二硫代磷酸锌（ZDDP）复配添加剂的液体石蜡润滑下钢－钢摩擦副的摩擦学性能。采用X射线光电子能谱仪和扫描电子显微镜分析了复配体系的作用机理。结果表明：纳微米硼酸盐／ZDDP复配添加剂对钢－钢摩擦副的抗磨作用产生对抗效应，在摩擦过程中的某一阶段摩擦系数突然升高，磨损加剧；在试验初期，磨斑表面较为光滑，相应的边界润滑膜为物理和化学吸附膜；随着试验时间的延长，钢球磨斑表面吸附膜表面破裂，磨斑表面变得粗糙并形成微小磨屑碎片，相应的摩擦系数突然升高；随着试验时间的进一步延长，添加剂同钢球磨损表面发生摩擦化学反应，并生成含B、N、S和P等元素的摩擦化学反应膜，从而使摩擦系数波动减小。     

Modeling of the vehicle shimmy system with consideration of clearance of the steering linkage mechanism

The mechanism of vehicle shimmy has been paid much attention in the past decades. In which, the clearance of the steering linkage is usually neglected. Yet the prior research of the authors proved that the clearance can make great effects on the dynamic performance of the linkage. Therefore, based on nonlinear dynamics, a six-DOF dynamic model of vehicle shimmy system with consideration of the clearance was established. In which, the nonlinearity due to clearance of the movement pair in steering mechanism was taken into account. Numerical examples showed that the clearance of the movement pair could make great effects on the dynamic behavior of the vehicle shimmy system, and it is one of the key factors leading to chaos motion of the shimmy system, which provided theoretical basis for vehicle shimmy control.     

A derivation of the Mehrabadi-Cowin equations

An alternative derivation to that given by Mehrabadi and Cowin (1978) is presented here for a pair of kinematic equations governing a certain class of flows in the plastic deformation of dilatant granular materials. This class has been described by Spencer (1981) as double shearing flows. In their derivation Mehrabadi and Cowin (1978), prior to presenting the equations relative to rectangular Cartesian coordinates, obtained an intermediate pair of equations relative to a non-orthogonal network of characteristic coordinates. The essential difference between the original and present derivation is that here, the flow rule, expressed relative to rotating, rectangular Cartesian coordinates, is transformed directly to obtain the kinematic equations relative to fixed rectangular Cartesian coordinate axes, without the need to obtain the characteristic equations.     

Diffraction of antiplane shear waves by two cracks in the presence of a magnetic field

The problem of scattering of horizontal polarized shear waves by the two cracks in a uniform magnetostatic field is considered. The magnetic field is assumed to be parallel to the crack surfaces as well as perpendicular to the crack surfaces. The elastic medium under consideration is a homogeneous, isotropic and infinitely conducting one. The solution of the problem is reduced into a pair of triple integral equations having trigonometrical kernels. Using the finite Hilbert transform technique, solution of the pair of triple integral equations is obtained for the low frequencies. Finally, approximate formulae are derived for the stress intensity factors.     

Characteristics of rogue waves on a periodic background for the Hirota equation

We consider the rogue dn-periodic waves (the rogue wave solutions on the dn-periodic waves background) for the Hirota equation by using Darboux transformation. We take Jacobian elliptic function dn as a seed solution, which is modulationally unstable as regards long wave perturbations. Through nonlinearization of the Lax pair for Hirota equation, the corresponding periodic eigenfunctions are successfully obtained. Based on these periodic eigenfunctions, we further construct the solutions of the Lax pair equations with dn-periodic wave seed solutions. In addition, numerical simulations are presented to reveal the phenomena of these solutions under different parameters choices.     

考虑上游泵送效应的滑靴副动压润滑特性

为了改善轴向柱塞泵滑靴副的润滑性能，利用仿生学原理，在斜盘上构建倾斜椭圆形微坑织构. 通过微坑产生的动压效应和上游泵送效应，以期能够优化滑靴副的摩擦性能并减少泄漏量. 基于CFD方法开展了具有椭圆形微坑织构滑靴副的建模与润滑性能研究，揭示了不同润滑介质黏度和转速下柱塞泵滑靴副的承载能力、泄漏量和摩擦系数随微坑倾斜角度的变化规律. 研究结果表明:通过在斜盘面上建立无倾斜椭圆形微坑，能明显提高滑靴副的承载能力，并降低摩擦系数，但会导致泄漏量增大；而在此基础上，通过将椭圆形微坑相对于其滑动方向旋转一定角度，滑靴副的承载能力和摩擦系数不会明显变化，但可以显著减小润滑介质泄漏量.